WO2022072206A1

WO2022072206A1 - Direct chill cast aluminum ingot with composition gradient for reduced cracking

Info

Publication number: WO2022072206A1
Application number: PCT/US2021/051664
Authority: WO
Inventors: Samuel Robert Wagstaff; Kumar SUNDARAM
Original assignee: Novelis Inc.
Priority date: 2020-10-01
Filing date: 2021-09-23
Publication date: 2022-04-07
Also published as: EP4221914A1; JP2023543872A; US20230256503A1; DE212021000471U1; KR20230044504A; CN116457121A; MX2023003488A; CA3193262A1

Abstract

Described are methods of preparing compositionally gradient aluminum alloy products. The methods may include casting a composite ingot in a mold. The composite ingot may include an inner region comprising a first aluminum alloy, an outer region surrounding the inner region, and a compositionally gradient zone between the inner region and the outer region. The outer region may include a second aluminum alloy different from the first aluminum alloy. At least one alloying element of the first aluminum alloy may have a content that is decreased through the compositionally gradient zone in a direction from the inner region to the outer region. Also described are aluminum alloy composite ingots and rolled aluminum alloy products having a compositionally gradient zone.

Description

DIRECT CHILL CAST ALUMINUM INGOT WITH COMPOSITION GRADIENT FOR REDUCED CRACKING

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of and priority to U.S. Provisional Application No. 63/198,184, filed on October 1, 2020, which is hereby incorporated by reference in its entirety.

FIELD

[0002] The present disclosure relates to metallurgy generally and more specifically to aluminum alloy products and aluminum alloy ingot casting and processing techniques.

BACKGROUND

[0003] Aluminum alloy ingots may be cast using direct chill (DC) casting. However, some metals or alloys may spontaneously rupture due to edge cracking or undergo substantial damage such as cold cracking during or after casting as an ingot. Certain metals or alloys may experience cold cracking during or after casting due to the combination of brittle microstructures, microporosities, and thermal stresses developed during DC casting. High strength alloy products are particularly susceptible to failure resulting from cold cracking stresses forming during casting due to (i) the enriched nature of their composition causing grains to be surrounded by brittle eutectic and/or porous product providing for a ready intergranular fracture mechanism through grain boundaries after crack initiation and (ii) the difference in volumetric contraction of the specific alloying elements during solidification making stresses larger than for more dilute alloys. These susceptibilities to failure may benefit from the use of particular mold profiles to prevent cold cracking. The effects of cold cracking are observable, for example, upon cooling below about 480 °C. Another problem encountered using DC casting techniques includes edge cracking. Edge cracking can be driven by grain boundary melting caused by alkali elements, such as sodium (Na). Edge cracking can also be caused by positive macrosegregation on ingot edges, where positive segregation at short faces of the ingot will be higher as the width of the ingot increases. When there is large macrosegregation, the normal homogenization heat treatment practice can be inadequate, resulting in melting of heavily segregated edges and producing edge cracks during hot rolling. Cold cracking and edge cracking result in recovery and operational time losses, as well as safety concerns including unzipping of the cracks in the ingot or hot tearing. This disclosure addresses the problems of cold cracking and edge cracking by forming a compositional gradient on the outer region of an ingot.

SUMMARY

[0004] The term embodiment and like terms are intended to refer broadly to all of the subject matter of this disclosure and the claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the claims below. Embodiments of the present disclosure covered herein are defined by the claims below, not this summary. This summary is a high-level overview of various aspects of the disclosure and introduces some of the concepts that are further described in the Detailed Description section below. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used in isolation to determine the scope of the claimed subject matter. The subject matter should be understood by reference to appropriate portions of the entire specification of this disclosure, any or all drawings and each claim.

[0005] In an aspect, described are methods of preparing compositionally gradient aluminum alloy products. A method of this aspect may include casting a composite ingot in a mold. The composite ingot may include an inner region comprising a first aluminum alloy; an outer region surrounding the inner region, the outer region comprising a second aluminum alloy different from the first aluminum alloy; and a compositionally gradient zone between the inner region and the outer region. At least one alloying element of the first aluminum alloy may have a content that is decreased through the compositionally gradient zone in a direction from the inner region to the outer region.

[0006] In embodiments, the method may include the first aluminum alloy and the second aluminum alloy being cast concurrently, such as during all or part of the casting process. In some cases, casting of the first aluminum alloy (inner region) can start before casting of the second aluminum alloy (outer region) begins. In some cases, casting of the second aluminum alloy (outer region) can start before casting of the first aluminum alloy (inner region) begins. In embodiments, the method may include the first aluminum alloy being delivered to the mold from a first height and the second aluminum alloy being delivered to the mold from a second height, wherein the second height is different from the first height.

[0007] In embodiments, the method may further include scalping the composite ingot to remove, from a rolling surface, at least a portion of the compositionally gradient zone and the outer region. The scalping may include removing material to generate a monolithic ingot comprising the first aluminum alloy.

[0008] In embodiments, the first aluminum alloy may comprise a 7xxx series aluminum alloy, a 5xxx series aluminum alloy, or a 2xxx series aluminum alloy. The first aluminum alloy may include a 7075 aluminum alloy, a 5182 aluminum alloy, or a 2024 aluminum alloy. In embodiments, the second aluminum alloy may comprise a Ixxx series aluminum alloy. The second aluminum alloy may have a purity of at least 99.7%, for example.

[0009] In embodiments, at least one alloying element of the first aluminum alloy may include Zn, Cu, Mg, or Na. In embodiments, the outer region may be substantially devoid of the at least one alloying element.

[0010] In embodiments, the composite ingot may be substantially devoid of cracking. The cracking may include cold cracking, hot cracking, edge cracking, or butt cracking, for example. Additionally or alternatively, the composite ingot may not undergo alligatoring, for example, during a hot rolling process. In embodiments, the composite ingot may be substantially devoid of porosity. The porosity may include pores as nucleation points from fractures during hot rolling, for example.

[0011] In embodiments, casting the composite ingot may comprise a direct chill casting process in which the inner region and the outer region are co-cast in an arrangement where the outer region is contacted with cooling water.

[0012] In embodiments, the outer region may have a thickness of from 7% to 15% of a total thickness of the composite ingot. In embodiments, the compositionally gradient zone may have a thickness of from 2% to 10% of a total thickness of the composite ingot.

[0013] Methods of this aspect may include additional process steps. For example, a rolled aluminum alloy product may be formed by the methods described herein. In embodiments, a method of this aspect may further include processing the monolithic ingot to form an aluminum alloy shate, plate, or sheet comprising the first aluminum alloy. Methods of this aspect may further include one or more of a homogenization process, a hot rolling process, a cold rolling process, an annealing process, a solution heat treatment process, a quenching process, or a surface treatment process.

[0014] In embodiments, the method may further include directing a magnetic field during casting, the magnetic field configured to suppress turbulence in a direction perpendicular to the compositionally gradient zone. In embodiments, the method may further include directing a magnetic field during casting to suppress turbulence in a direction perpendicular to the compositionally gradient zone. Directing may include, for example, positioning the magnetic field at a height between the first height and the second height. In embodiments, the method may further include directing a magnetic field during casting to suppress turbulence in a direction perpendicular to the compositionally gradient zone. Directing the magnetic field may include, for example, providing a skim dam, the skim dam being positioned within the molten liquids at a height the first height and the second height.

[0015] In an another aspect, described are aluminum alloy composite ingots. In some embodiments, aluminum alloy composite ingots may be prepared by the methods described herein. An aluminum alloy composite ingot may include an inner region comprising a first aluminum alloy, an outer region surrounding the inner region, and a compositionally gradient zone between the inner region and the outer region. The outer region may include a second aluminum alloy different from the first aluminum alloy. At least one alloying element of the first aluminum alloy may have a content that is decreased through the compositionally gradient zone in a direction from the inner region to the outer region.

[0016] In embodiments, the first aluminum alloy may include a 7xxx series aluminum alloy, a 5xxx series aluminum alloy, or a 2xxx series aluminum alloy. The first aluminum alloy may include a 7075 aluminum alloy, a 5182 aluminum alloy, or a 2024 aluminum alloy. In embodiments, the second aluminum alloy may include a Ixxx series aluminum alloy. The second aluminum alloy may have a purity of at least 99.7%, for example. Optionally, the at least one alloying element of the first aluminum alloy may include Zn, Cu, Mg, or Na. In embodiments, the outer region may be substantially devoid of the at least one alloying element.

[0017] In embodiments, the composite ingot may be substantially devoid of cracking, such as devoid of cold cracking, hot cracking, edge cracking, and/or butt cracking, may optionally not undergo alligatoring during rolling. In embodiments, the composite ingot may be substantially devoid of porosity. The porosity may include pores as nucleation points from fractures during hot rolling.

[0018] In embodiments, the outer region may have a thickness of from 7% to 15% of a total thickness of the composite ingot. In embodiments, the compositionally gradient zone may have a thickness of from 2% to 10% of a total thickness of the composite ingot.

[0019] In an another aspect, described are rolled aluminum alloy products. The rolled aluminum alloy products may include an inner region comprising a first aluminum alloy, an outer region surrounding the inner region, and a compositionally gradient zone between the inner region and the outer region. The outer region may include a second aluminum alloy different from the first aluminum alloy. At least one alloying element of the first aluminum alloy may have a content that is decreased through the compositionally gradient zone in a direction from the inner region to the outer region.

[0020] In embodiments, the rolled aluminum alloy product may be made from an ingot described herein, such as an aluminum alloy composite ingot. In embodiments, the first aluminum alloy may include a 7xxx series aluminum alloy, a 5xxx series aluminum alloy, or a 2xxx series aluminum alloy. The first aluminum alloy may include a 7075 aluminum alloy, a 5182 aluminum alloy, or a 2024 aluminum alloy. In embodiments, the second aluminum alloy may include a Ixxx series aluminum alloy. The second aluminum alloy may have a purity of at least 99.7%. In embodiments, the at least one alloying element of the first aluminum alloy may include Zn, Cu, Mg, or Na. In embodiments, the outer region may be substantially devoid of the at least one alloying element.

[0021] Other objects and advantages will be apparent from the following detailed description of non-limiting examples.

BRIEF DESCRIPTION OF THE FIGURES

[0022] The specification makes reference to the following appended figures, in which use of like reference numerals in different figures is intended to illustrate like or analogous components.

[0023] FIG. 1 provides a schematic illustration of direct chill casting a compositionally gradient aluminum alloy product.

[0024] FIG. 2 provides a schematic illustration of direct chill casting the compositionally gradient aluminum alloy product of FIG. 1 as processing continues.

[0025] FIG. 3 provides a schematic illustration of direct chill casting the compositionally gradient aluminum alloy product of FIG. 2 as processing continues.

[0026] FIG. 4 provides a schematic illustration of direct chill casting the compositionally gradient aluminum alloy product of FIG. 3 as processing continues.

[0027] FIG. 5 A provides a cross-sectional illustration of a compositionally gradient aluminum alloy product, for example made according to FIGS. 1-4.

[0028] FIG. 5B provides a schematic illustration of area A of FIG. 5 A in greater detail.

[0029] FIG. 6 provides a perspective view illustration of a compositionally gradient aluminum alloy product, for example made according to FIGS. 1-4.

[0030] FIG. 7A and FIG. 7B provide schematic illustrations of scalping a compositionally gradient aluminum alloy product by methods using a band saw type device and a mill type device, respectively. [0031] FIG. 8A and FIG. 8B provide schematic illustrations of a compositionally gradient aluminum alloy product before scalping (FIG. 8A) and after scalping (FIG. 8B).

[0032] FIG. 9 provides a schematic overview of a compositionally gradient aluminum alloy product, which has been scalped, and processing the monolithic ingot to make an aluminum alloy product.

[0033] FIG. 10A provides a schematic overview of a compositionally gradient aluminum alloy product, which has been partially scalped, e.g., using edge scalping, and processing the ingot to make an aluminum alloy product.

[0034] FIG. 10B provides a schematic overview of a compositionally gradient aluminum alloy product, which has been partially scalped, e.g., using rolling surface scalping, and processing the ingot to make an aluminum alloy product.

[0035] FIG. 11 provides a schematic overview of a compositionally gradient aluminum alloy product, which has not been scalped or sawn, and making and processing the ingot to make an aluminum alloy product.

DETAILED DESCRIPTION

[0036] Described herein are compositionally gradient aluminum alloy products, methods of making and using compositionally gradient aluminum alloy products, and products formed from compositionally gradient aluminum alloy products. The disclosed compositionally gradient aluminum alloy products include aluminum alloys that solve two problems that can occur when using direct chill (DC) casting techniques, namely the problems of edge cracking, such as in the hot mill, and/or cold cracking or brittle fracture events in the as cast ingot (during or after casting). The compositionally gradient aluminum alloys described herein are suitable for direct chill (DC) casting techniques for making alloys, such as aluminum alloys that have high ductile-to-brittle transition temperatures (e.g., greater than or about 200 °C, greater than or about 300 °C, or up to about 400 °C), aluminum alloys that are susceptible to hot-tearing during casting, and aluminum alloys that can undergo brittle fracture events during casting.

[0037] As examples, certain alloys may be difficult to cast as ingots because of internal stresses that develop during casting, due to thermal contraction that occurs during cooling of the ingot by application of cooling fluid directly on a surface of the ingot. In some cases, a brittle aluminum alloy ingot directly cast using a DC casting technique may spontaneously undergo catastrophic fracture and rupture upon a portion of the ingot cooling to or below the ductile-to-brittle transition temperature, resulting in damage, safety hazards, reduced recovery of cast products, and fabrication downtime to allow for cleanup, recovery, and repair of damaged components and materials. Hot-tearing may similarly occur for some aluminum alloys cast directly using DC casting, which may result in similar safety and cleanup issues and low recovery. Techniques described herein provide for ways to reliably obtain aluminum alloy ingots of such aluminum alloys that may be difficult to directly cast using DC casting techniques.

[0038] The disclosed techniques employ a DC casting technique to concurrently cast an aluminum alloy having an inner region including a first aluminum alloy, an outer region surrounding the inner region and including a second aluminum alloy different than the first, and a compositionally gradient zone between the inner and outer regions. The disclosed techniques may also employ a process where the composite ingot may be optionally scalped to remove at least a portion of the compositionally gradient zone and/or the outer region. The disclosed techniques may include scalping the compositionally gradient zone and the outer region completely to generate a monolithic ingot comprising a difficult to cast aluminum alloy, for example. The disclosed techniques may include scalping the compositionally gradient zone and the outer region to generate a composite ingot comprising a difficult to cast aluminum alloy with a gradient zone surrounding the inner region, for example.

[0039] Techniques for dual casting different aluminum alloys to form a composite ingot with inner and outer regions and with a compositionally gradient zone between them may introduce significant complexities, difficulties, and costs as compared to direct chill casting of a monolithic ingot. For example, additional and more complex processing and equipment may be used, including additional furnaces, additional molten aluminum alloy handling equipment, more complex casting equipment, etc.

[0040] The process of scalping an outer region from a composite ingot may also introduce additional complexities, time, and equipment requirements as compared to direct chill casting of a monolithic ingot. For example, scalping machinery may be used, and machinery for moving, turning, or rotating the composite ingot may be used, depending on the scalping configuration. The scalping process may also take a significant amount of time, resulting in reduced production throughput.

[0041] Moreover, scalping an outer region from a composite ingot may also result in considerably higher energy usage and necessary disposal or recycling of scalped materials. For example, the heat requirements of an additional furnace needed to melt the aluminum alloy for the outer region may be significant. Since the aluminum alloy from the outer region may be scalped during the process of forming a monolithic ingot from a composite ingot, the energy required to heat and prepare the outer region may be considered, in some embodiments, as wasted. Increasing energy usage and wasting energy is undesirable in aluminum alloy and alloy ingot casting processes, and may generally make such processes impractical or otherwise undesirable. Scalping may also generate additional excess material to be disposed of or recycled in the form of the scalped outer region, and the process of recycling or disposal may add other complexities and energy usage requirements. In some cases, the scalped material may include a portion of the inner region aluminum alloy, and so recycling of the scalped material may be complicated by having to deal with two different alloy compositions in the scalped material.

[0042] The complexities and additional energy and heat requirements all point to the unfavorability of the disclosed techniques for making a monolithic aluminum alloy ingot by first casting a composite ingot followed by scalping an outer layer or layers. Furthermore, techniques for co-casting of a composite ingot, such as described in U.S. Patent Nos.

7,748,434 and 8,927,113, are focused on how to add material as a clad layer on an outside of an ingot, and so scalping of that additional clad layer of material is directly contrary to the intended purpose of the techniques for co-casting of composite ingots. However, for particular aluminum alloys, the disclosed techniques are unexpectedly advantageous, as they allow creation of monolithic ingots, such as monolithic ingots of brittle aluminum alloys and aluminum alloys subject to hot-tearing and spontaneous rupture, in a way that is safe and reliable and that minimizes or reduces problems associated with directly casting monolithic ingots of brittle aluminum alloys. The recovery of monolithic aluminum alloy ingots in this way can be higher than using other methods (which may be more complex or less complex) for forming aluminum alloy ingots of a difficult to cast aluminum alloy. In some cases, monolithic aluminum alloy ingots formed according to the present disclosure can be significantly larger than those formed using other methods, which again may be more complex or less complex than the presently disclosed methods.

Definitions and Descriptions:

[0043] As used herein, the terms “invention,” “the invention,” “this invention” and “the present invention” are intended to refer broadly to all of the subject matter of this patent application and the claims below. Statements containing these terms should be understood not to limit the subject matter described herein or to limit the meaning or scope of the patent claims below. [0044] In this description, reference is made to alloys identified by AA numbers and other related designations, such as “series” or “7xxx.” For an understanding of the number designation system most commonly used in naming and identifying aluminum and its alloys, see “International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys” or “Registration Record of Aluminum Association Alloy Designations and Chemical Compositions Limits for Aluminum Alloys in the Form of Castings and Ingot,” both published by The Aluminum Association.

[0045] As used herein, a plate generally has a thickness of greater than about 15 mm. For example, a plate may refer to an aluminum product having a thickness of greater than about 15 mm, greater than about 20 mm, greater than about 25 mm, greater than about 30 mm, greater than about 35 mm, greater than about 40 mm, greater than about 45 mm, greater than about 50 mm, or greater than about 100 mm.

[0046] As used herein, a shate (also referred to as a sheet plate) generally has a thickness of from about 4 mm to about 15 mm. For example, a shate may have a thickness of about 4 mm, about 5 mm, about 6 mm, about 7 mm, about 8 mm, about 9 mm, about 10 mm, about 11 mm, about 12 mm, about 13 mm, about 14 mm, or about 15 mm.

[0047] As used herein, a sheet generally refers to an aluminum product having a thickness of less than about 4 mm. For example, a sheet may have a thickness of less than about 4 mm, less than about 3 mm, less than about 2 mm, less than about 1 mm, less than about 0.5 mm, or less than about 0.3 mm (e.g., about 0.2 mm).

[0048] “Ductile-brittle transition temperature” refers to a temperature at which the fracture energy of a metal alloy falls below a predetermined value, such as determined according to an impact test (see, e.g., ASTM A370-19el, Standard Test Methods and Definitions for Mechanical Testing of Steel Products, ASTM International, West Conshohocken, PA, 2019, hereby incorporated by reference). In some embodiments, a ductile-brittle transition temperature refers to a temperature at which a change in ductility of a metal alloy is observed, below which the metal alloy exhibits a more brittle character and above which the metal alloy exhibits a more ductile character. For example, at temperatures below the metal alloy’s ductile-brittle transition temperature, an impact of a particular or standard magnitude may cause the metal alloy to fracture, while at temperatures above the metal alloy’s ductile-brittle transition temperature, an impact of the particular or standard magnitude may instead result in deformation of the metal alloy rather than fracture. In some cases, during casting of a metal alloy ingot, the surface of the ingot may be exposed to cooling fluid (e.g., water) while the center of the ingot may still remain at an elevated temperature. Stresses and strains may occur within the ingot due to the non-uniform temperature profile of the ingot and temperature-dependent thermal expansion/contraction. If the ductile-brittle transition temperature of the metal alloy is too high, the ingot may spontaneously rupture from the stresses and strains that develop during cooling of the ingot. [0049] As used herein, terms such as “cast aluminum alloy product,” “cast product,” “cast aluminum alloy product,” and the like are interchangeable and refer to a product produced by direct chill casting (including direct chill dual or co-casting) or semi-continuous casting, continuous casting (including, for example, by use of a twin belt caster, a twin roll caster, a block caster, or any other continuous caster), electromagnetic casting, hot top casting, or any other casting method. In particular, casting using direct chill casting techniques is described herein.

[0050] All ranges disclosed herein are to be understood to encompass any and all subranges subsumed therein. For example, a stated range of “1 to 10” should be considered to include any and all subranges between (and inclusive of) the minimum value of 1 and the maximum value of 10; that is, all subranges beginning with a minimum value of 1 or more, e.g. 1 to 6.1, and ending with a maximum value of 10 or less, e.g., 5.5 to 10. Unless stated otherwise, the expression “up to” when referring to the compositional amount of an element means that element is optional and includes a zero percent composition of that particular element. Unless stated otherwise, all compositional percentages are in weight percent (wt. %).

[0051] As used herein, the meaning of “a,” “an,” and “the” includes singular and plural references unless the context clearly dictates otherwise.

Methods of Using the Disclosed Aluminum Alloys and Aluminum Alloy Products [0052] The aluminum alloys and aluminum alloy products described herein, such as aluminum alloy ingots, and rolled aluminum alloy products, can be used in automotive applications and other transportation applications, including aircraft and railway applications. For example, disclosed aluminum alloy products can be used to prepare formed aluminum products and automotive structural parts, such as bumpers, side beams, roof beams, cross beams, pillar reinforcements (e.g., A-pillars, B-pillars, and C-pillars), inner panels, outer panels, side panels, inner hoods, outer hoods, or trunk lid panels. The aluminum alloy products and methods described herein can also be used in aircraft or railway vehicle applications, to prepare, for example, external and internal panels. [0053] The aluminum alloy products and methods described herein can also be used in electronics applications. For example, the aluminum alloy products and methods described herein can be used to prepare housings for electronic devices, including mobile phones and tablet computers. In some examples, the aluminum alloy products can be used to prepare housings for the outer casing of mobile phones (e.g., smart phones), tablet bottom chassis, and other portable electronics. The aluminum alloy products and methods described herein can also be used in other applications as desired.

Methods of Producing the Alloys and Alloy Products

[0054] The aluminum alloys and aluminum alloy products described herein can be cast using any suitable casting method known to those of ordinary skill in the art. As a nonlimiting example, the casting process can include a direct chill (DC) casting process.

[0055] An outer region of a first aluminum alloy can surround an inner region of a second aluminum alloy with a compositionally gradient zone between the outer and inner regions as described herein to form compositionally gradient aluminum alloy products. The compositionally gradient zone has at least one alloying element present in the first aluminum alloy from the inner region in a content that is decreasing through the compositionally gradient zone in a direction from the inner region to the outer region, as will be described in detail below. The casting of the first aluminum alloy and the second aluminum alloy may be concurrent or at least partially concurrent. The initial dimensions and final dimensions of the compositionally gradient aluminum alloy products described herein can be determined by the desired properties of the overall final product.

[0056] A cast ingot or other cast product can be processed by any suitable means. Optionally, the processing steps can be used to prepare sheets. Such processing steps include, but are not limited to, homogenization, hot rolling, cold rolling, solution heat treatment, and an optional pre-aging step. Separate rolling steps can optionally be separated by other processing steps, including, for example, annealing steps, cleaning steps, heating steps, cooling steps, and the like.

[0057] FIG. 1 provides a schematic illustration of direct chill casting of a compositionally gradient aluminum alloy product by providing different molten aluminum alloys 105 and 115 to form a composite ingot. Reference to aluminum alloys herein optionally may be substituted with other alloys, such as steel, magnesium alloys, copper alloys, or the like. The direct chill casting technique illustrated in FIG. 1 may be useful for forming a compositionally gradient aluminum alloy product having an inner region surrounded by an outer region, where the inner region and the outer region each include different aluminum alloys. The technique in FIG. 1 is also referred to as a concurrent dual casting technique herein. As illustrated, molten aluminum alloys 105 and 115 are cast in a vertical casting arrangement where they can be allowed to contact one another in a molten and/or partially molten configuration, and the molten aluminum alloys are cooled by cooling water 130. Such a technique may be useful for forming a composite ingot comprising aluminum alloys 110 and 120, which can then undergo further processing. FIG. 1 shows an initial phase of casting wherein molten aluminum alloy 105 is provided in advance of molten aluminum alloy 115. Alternatively, molten aluminum alloy 115 may be provided in advance of molten aluminum alloy 105, or molten aluminum alloy 105 and molten aluminum alloy 115 may be provided concurrently. The molten aluminum alloy 105 is poured into shallow mold 160 on bottom block 170 mounted on a hydraulic table 180 to form a false bottom to the mold to expand the volume of the ingot formed during the casting process. The bottom block 170 may be lowered at a controlled rate as the mold fills to a greater volume and begins to solidify. As molten aluminum is provided to the mold 160, the volume of alloy grows to form the ingot.

[0058] FIG. 2 provides a schematic illustration of direct chill casting the compositionally gradient aluminum alloy product of FIG. 1 as the processing continues. Molten aluminum alloy 105 may continue to be cast concurrently with molten aluminum alloy 115. Molten aluminum alloy 115 forms the inner region aluminum alloy 120, while molten aluminum alloy 105 forms the outer region aluminum alloy 110. Molten aluminum casting may use combo-bags or mesh screens to direct the molten metals. Mesh, mesh screens, and combobags are terms used interchangeably herein. The mesh is used to achieve a limited amount of turbulence such that the flow of molten metal is redirected normal to the casting direction, in other words parallel to the desired interfacial plane. By controlling the flow velocity, turbulence is minimized. The mesh 145 for receiving molten aluminum alloy 105 is at a first height hi. The mesh 155 for receiving molten aluminum alloy 115 is at a second height I12. Heights hi and I12 are relative to mold surface 165 of mold 160. Height hi and height I12 may be the same or different. As shown in FIG. 2, height I12 may be less than height hi, which, without being bound by any theory, may assist in promoting formation of the inner region. [0059] Alternatively, a magnetic field may be used to suppress turbulence in a direction perpendicular to the compositionally gradient zone. A static magnetic field properly oriented can provides selected velocity vectors that can be used to promote the formation of a two- liquid layer and to suppress mixing. One way is to apply the magnetic field during casting at a height between that of the two meshes receiving the liquids such that turbulence and mixing of the two molten aluminum alloys is stopped or at least suppressed. Alternatively, a skim dam may be used to suppress turbulent flow and minimize mixing of the two molten aluminum alloys. The skim dam may be rectangular or other shape suitable to be placed within the molten liquids at a height below that of the meshes. The skim dam may be made of ceramic refractory material.

[0060] FIG. 3 provides a schematic illustration of direct chill casting the compositionally gradient aluminum alloy product of FIG. 2 as processing continues. The inner region aluminum alloy 120 is increasing in volume and the outer region aluminum alloy 110 is being pushed outwardly from the center of the inner region so that the outer region aluminum alloy 110 completely surrounds the inner region aluminum alloy 120. The flow of molten aluminum alloy 105 may optionally be ceased while the flow of molten aluminum alloy 115 continues. Alternatively, the flow of molten aluminum alloy 115 may be optionally ceased while the flow of molten aluminum alloy 105 continues, or the flow of molten aluminum alloys 105 and 115 may optionally be ceased concurrently.

[0061] Molten aluminum alloys 105 and 115 (and consequently outer region aluminum alloy 110 and inner region aluminum alloy 120) can be different aluminum alloys. For example, molten aluminum alloy 115/inner region aluminum alloy 120 may correspond to an alloy that is brittle upon cooling to a temperature greater than or about 200 °C or greater than or about 300 °C.

[0062] In some embodiments, aluminum alloy 115/inner region aluminum alloy 120 may correspond to a high solute alloy, such as exhibiting a solute concentration between about 6% and about 18% by weight. For example, aluminum alloy 115/inner region aluminum alloy 120 may have a solute concentration of about 6%, about 6.5%, about 7%, about 7.5%, about 8%, about 8.5%, about 9%, about 9.5%, about 10%, about 10.5%, about 11%, about 11.5%, about 12%, about 12.5%, about 13%, about 13.5%, about 14%, about 14.5%, about 15%, about 15.5%, about 16%, about 16.5%, about 17%, about 17.5%, or about 18% by weight. Optionally, molten aluminum alloy 115/aluminum alloy 120 may correspond to an aluminum alloy with a high copper composition or a high magnesium composition or a high zinc composition, such as in certain 2xxx series aluminum alloys, certain 5xxx series aluminum alloys, and certain 7xxx series aluminum alloys.

[0063] As discussed, molten aluminum alloy 105/outer region aluminum alloy 110, may correspond to a different alloy than molten aluminum alloy 115/inner region aluminum alloy 120. For example, outer region aluminum alloy 110 may optionally be more ductile than inner region aluminum alloy 120. The interaction of molten aluminum alloy 105 with molten aluminum alloy 115 provides a compositionally gradient zone 125, as shown in FIG. 4, forming between outer region aluminum alloy 110 and inner region aluminum alloy 120. In this way, at least one of molten aluminum alloy 105/outer region aluminum alloy 110 and compositionally gradient zone 125 may function, in embodiments, as a buffer layer between molten aluminum alloy 115/inner region aluminum alloy 120 and cooling water 130 during casting. For example, being more ductile, molten aluminum alloy 105/outer region aluminum alloy 110 may not undergo spontaneous fracture or edge cracking upon exposure to cooling water 130 or may not undergo cold cracking during casting. Molten aluminum alloy 115/inner region aluminum alloy 120, on the other hand, may be subject to spontaneous fracture or edge cracking if directly exposed to cooling water 130 or may be subject to cold cracking during casting, and so compositionally gradient zone 125 and inner region aluminum alloy 120 may act as a protective layer, for example.

[0064] In some embodiments, molten aluminum alloy 105/outer region aluminum alloy 110 may have a heat transfer coefficient between about 100 W/m-K and about 250 W/m-K, such as about 105 W/m-K, about 110 W/m-K, about 115 W/m-K, about 120 W/m-K, about 125 W/m-K, about 130 W/m-K, about 135 W/m-K, about 140 W/m-K, about 145 W/m-K, about 150 W/m-K, about 155 W/m-K, about 160 W/m-K, about 165 W/m-K, about 170 W/m-K, about 175 W/m-K, about 180 W/m-K, about 185 W/m-K, about 190 W/m-K, about 195 W/m-K, about 200 W/m-K, about 205 W/m-K, about 210 W/m-K, about 215 W/m-K, about 220 W/m-K, about 225 W/m-K, about 230 W/m-K, about 235 W/m-K, about 240 W/m-K, about 245 W/m-K, or about 250 W/m-K.

[0065] Referring to FIG. 4, aluminum alloy 110 representing the outer region may have a thickness corresponding to between 5-15% of the total thickness of the ingot. For example, aluminum alloy 110 may have a percent thickness of the total thickness of the ingot of about 5%, about 5.5%, about 6%, about 6.5%, about 7%, about 7.5%, about 8%, about 8.5%, about 9%, about 9.5%, about 10%, about 10.5%, about 11%, about 11.5%, about 12%, about 12.5%, about 13%, about 13.5%, about 14%, about 14.5%, or about 15%.

[0066] Compositionally gradient zone 125 may have a thickness corresponding to between 2-10% of the total thickness of the ingot. For example, compositionally gradient zone 125 may have a percent thickness of the total thickness of the ingot of about 2%, about 2.5%, about 3%, about 3.5%, about 4%, about 4.5%, about 6%, about 6.5%, about 7%, about 7.5%, about 8%, about 8.5%, about 9%, about 9.5%, or about 10%. [0067] Although molten aluminum alloy 105/outer region aluminum alloy 110 are shown as symmetric about molten aluminum alloy 115/inner region aluminum alloy 120 in FIG. 4, the depiction of FIG. 4 is merely exemplary and other dual casting configurations are possible and included within the present disclosure, including where each of molten aluminum alloy 105/aluminum alloy 110 on the left/right of molten aluminum alloy 115/aluminum alloy 120 have different thicknesses and/or have different compositions. In some cases, FIG. 4 may represent a cylindrical ingot or a rectangular or other shaped ingot where outer region aluminum alloy 110 forms a continuous layer around inner region aluminum alloy 120, and with compositionally gradient zone 125 therebetween. Moreover, the schematic depictions in FIGS. 1-4 are not to scale.

[0068] FIG. 4 provides a schematic illustration of direct chill casting the compositionally gradient aluminum alloy product of FIG. 3 as processing continues. As shown in FIG. 4, the inner region aluminum alloy 120 is surrounded by outer region aluminum alloy 110, and a compositionally gradient zone 125 has formed between the inner region aluminum alloy 120 and the outer region aluminum alloy 110. The formation of the compositionally gradient zone 125 occurs gradually during the casting process, in other words, anytime during the process as illustrated in FIGS. 1-4. The compositionally gradient aluminum alloys made according to FIGS. 1-4 can produce a composite ingot that exhibits a limited amount of various types of cracking, such as cold cracking. The compositionally gradient aluminum alloys made according to FIGS. 1-4 can produce a composite ingot that exhibits a limited amount of porosity, which can serve as nucleation points for fractures during hot rolling.

[0069] In some examples, the molten metals for use in the methods described herein include aluminum alloys, for example, a first aluminum alloy for the inner region and a second aluminum alloy for the outer region, where the first aluminum alloy and the second aluminum alloy are different. Each of the first aluminum alloy and the second aluminum alloy may be chosen from Ixxx series aluminum alloys, 2xxx series aluminum alloys, 3xxx series aluminum alloys, 4xxx series aluminum alloys, 5xxx series aluminum alloys, 6xxx series aluminum alloys, 7xxx series aluminum alloys, or 8xxx series aluminum alloys.

[0070] By way of non-limiting example, exemplary Ixxx series aluminum alloys for use in the methods described herein can include AA1100, AA1100A, AA1200, AA1200A, AA1300, AA1110, AA1120, AA1230, AA1230A, AA1235, AA1435, AA1145, AA1345, AA1445, AA1150, AA1350, AA1350A, AA1450, AA1370, AA1275, AA1185, AA1285, AA1385, AA1188, AA1190, AA1290, AA1193, AA1198, or AA1199. Examples may also include a P1020 aluminum alloy or a P0406 aluminum alloy. [0071] Non-limiting exemplary 2xxx series aluminum alloys for use in the methods described herein can include AA2001, A2002, AA2004, AA2005, AA2006, AA2007, AA2007A, AA2007B, AA2008, AA2009, AA2010, AA2011, AA2011A, AA2111, AA2111A, AA2111B, AA2012, AA2013, AA2014, AA2014A, AA2214, AA2015, AA2016, AA2017, AA2017A, AA2117, AA2018, AA2218, AA2618, AA2618A, AA2219, AA2319, AA2419, AA2519, AA2021, AA2022, AA2023, AA2024, AA2024A, AA2124, AA2224, AA2224A, AA2324, AA2424, AA2524, AA2624, AA2724, AA2824, AA2025, AA2026, AA2027, AA2028, AA2028A, AA2028B, AA2028C, AA2029, AA2030, AA2031, AA2032, AA2034, AA2036, AA2037, AA2038, AA2039, AA2139, AA2040, AA2041, AA2044, AA2045, AA2050, AA2055, AA2056, AA2060, AA2065, AA2070, AA2076, AA2090, AA2091, AA2094, AA2095, AA2195, AA2295, AA2196, AA2296, AA2097, AA2197, AA2297, AA2397, AA2098, AA2198, AA2099, or AA2199.

[0072] Non-limiting exemplary 3xxx series aluminum alloys for use in the methods described herein can include AA3002, AA3102, AA3003, AA3103, AA3103A, AA3103B, AA3203, AA3403, AA3004, AA3004A, AA3104, AA3204, AA3304, AA3005, AA3005A, AA3105, AA3105A, AA3105B, AA3007, AA3107, AA3207, AA3207A, AA3307, AA3009, AA3010, AA3110, AA3011, AA3012, AA3012A, AA3013, AA3014, AA3015, AA3016, AA3017, AA3019, AA3020, AA3021, AA3025, AA3026, AA3030, AA3130, or AA3065. [0073] Non-limiting exemplary 4xxx series aluminum alloys for use in the methods described herein can include AA4004, AA4104, AA4006, AA4007, AA4008, AA4009, AA4010, AA4013, AA4014, AA4015, AA4015A, AA4115, AA4016, AA4017, AA4018, AA4019, AA4020, AA4021, AA4026, AA4032, AA4043, AA4043A, AA4143, AA4343, AA4643, AA4943, AA4044, AA4045, AA4145, AA4145A, AA4046, AA4047, AA4047A, or AA4147.

[0074] Non-limiting exemplary 5xxx series aluminum alloys for use in the methods described herein product can include AA5182, AA5183, AA5005, AA5005A, AA5205, AA5305, AA5505, AA5605, AA5006, AA5106, AA5010, AA5110, AA5110A, AA5210, AA5310, AA5016, AA5017, AA5018, AA5018A, AA5019, AA5019A, AA5119, AA5119A, AA5021, AA5022, AA5023, AA5024, AA5026, AA5027, AA5028, AA5040, AA5140, AA5041, AA5042, AA5043, AA5049, AA5149, AA5249, AA5349, AA5449, AA5449A, AA5050, AA5050A, AA5050C, AA5150, AA5051, AA5051A, AA5151, AA5251, AA5251A, AA5351, AA5451, AA5052, AA5252, AA5352, AA5154, AA5154A, AA5154B, AA5154C, AA5254, AA5354, AA5454, AA5554, AA5654, AA5654A, AA5754, AA5854, AA5954, AA5056, AA5356, AA5356A, AA5456, AA5456A, AA5456B, AA5556, AA5556A, AA5556B, AA5556C, AA5257, AA5457, AA5557, AA5657, AA5058, AA5059, AA5070, AA5180, AA5180A, AA5082, AA5182, AA5083, AA5183, AA5183A, AA5283, AA5283A, AA5283B, AA5383, AA5483, AA5086, AA5186, AA5087, AA5187, or AA5088.

[0075] Non-limiting exemplary 6xxx series aluminum alloys for use in the methods described herein can include AA6101, AA6101A, AA6101B, AA6201, AA6201A, AA6401, AA6501, AA6002, AA6003, AA6103, AA6005, AA6005A, AA6005B, AA6005C, AA6105, AA6205, AA6305, AA6006, AA6106, AA6206, AA6306, AA6008, AA6009, AA6010, AA6110, AA6110A, AA6011, AA6111, AA6012, AA6012A, AA6013, AA6113, AA6014, AA6015, AA6016, AA6016A, AA6116, AA6018, AA6019, AA6020, AA6021, AA6022, AA6023, AA6024, AA6025, AA6026, AA6027, AA6028, AA6031, AA6032, AA6033, AA6040, AA6041, AA6042, AA6043, AA6151, AA6351, AA6351A, AA6451, AA6951, AA6053, AA6055, AA6056, AA6156, AA6060, AA6160, AA6260, AA6360, AA6460, AA6460B, AA6560, AA6660, AA6061, AA6061A, AA6261, AA6361, AA6162, AA6262, AA6262A, AA6063, AA6063A, AA6463, AA6463A, AA6763, A6963, AA6064, AA6064A, AA6065, AA6066, AA6068, AA6069, AA6070, AA6081, AA6181, AA6181A, AA6082, AA6082A, AA6182, AA6091, or AA6092.

[0076] Non-limiting exemplary 7xxx series aluminum alloys for use in the methods described herein can include AA7011, AA7019, AA7020, AA7021, AA7039, AA7072, AA7075, AA7085, AA7108, AA7108A, AA7015, AA7017, AA7018, AA7019A, AA7024, AA7025, AA7028, AA7030, AA7031, AA7033, AA7035, AA7035A, AA7046, AA7046A, AA7003, AA7004, AA7005, AA7009, AA7010, AA7011, AA7012, AA7014, AA7016, AA7116, AA7122, AA7023, AA7026, AA7029, AA7129, AA7229, AA7032, AA7033, AA7034, AA7036, AA7136, AA7037, AA7040, AA7140, AA7041, AA7049, AA7049A, AA7149, AA7204, AA7249, AA7349, AA7449, AA7050, AA7050A, AA7150, AA7250, AA7055, AA7155, AA7255, AA7056, AA7060, AA7064, AA7065, AA7068, AA7168, AA7175, AA7475, AA7076, AA7178, AA7278, AA7278A, AA7081, AA7181, AA7185, AA7090, AA7093, AA7095, or AA7099.

[0077] Non-limiting exemplary 8xxx series aluminum alloys for use in the methods described herein can include AA8005, AA8006, AA8007, AA8008, AA8010, AA8011, AA8011A, AA8111, AA8211, AA8112, AA8014, AA8015, AA8016, AA8017, AA8018, AA8019, AA8021, AA8021A, AA8021B, AA8022, AA8023, AA8024, AA8025, AA8026, AA8030, AA8130, AA8040, AA8050, AA8150, AA8076, AA8076A, AA8176, AA8077, AA8177, AA8079, AA8090, AA8091, or AA8093. [0078] In some examples, referring again to FIG. 4, a first aluminum alloy useful for the inner region aluminum alloy 120 includes a 7xxx series aluminum alloy, 5xxx series aluminum alloy, or a 2xxx series aluminum alloy. In some specific examples, the first or inner region aluminum alloy 120 may include a 7075 aluminum alloy, a 5182 aluminum alloy, or a 2024 aluminum alloy. In some examples, a second aluminum alloy useful for the outer region aluminum alloy 110 includes a Ixxx series aluminum alloy. The second or outer region aluminum alloy 110 may optionally include a Ixxx series aluminum alloy of a purity of at least 99.7%. In some specific examples, the second or outer region aluminum alloy 110 may include a Pl 020 aluminum alloy or a P0406 aluminum alloy.

[0079] FIG. 5 A provides a cross-sectional view illustrating a compositionally gradient aluminum alloy product 200 made according to FIGS. 1-4. Outer region 210 surrounds inner region 220, and compositionally gradient zone 225 is disposed between outer region 210 and inner region 220. Area A of FIG. 5A is shown in greater detail in FIG. 5B. At least one alloying element of the first aluminum alloy as in inner region 220 has a content that is decreased through the compositionally gradient zone 225 in a direction D from the inner region 220 to the outer region 210. In other words, the content of an alloying element E is higher in inner region 220 and decreases through the thickness of compositionally gradient zone 225 as shown schematically in FIG. 5B. The outer region 210 may be devoid of or substantially devoid of element E as shown schematically in FIG. 5B. Substantially devoid includes a content of element E less than about 0.1 wt. %. In some embodiments, the at least one alloying element E of the first aluminum alloy, as in the inner region 220 of FIG. 5B, includes Zn, Cu, Mg, or Na.

[0080] FIG. 6 provides a perspective view schematic illustration of a compositionally gradient aluminum alloy product, such as made according to FIGS. 1-4. The ingot may have either flat or full radius ends. The ingot is shown with the head (or top as in FIG. 6) of the ingot cut. The product may be an ingot 600 having an inner region 620 including a first aluminum alloy and an outer region 610 surrounding the inner region 620. The outer region 610 includes a second aluminum alloy, which is different from the first aluminum alloy of inner region 620. Compositionally gradient zone 625 is disposed between the inner region 620 and the outer region 610. In some cases, at least one alloying element of the first aluminum alloy has a content that is decreased through the compositionally gradient zone 625 in a direction from the inner region 620 to the outer region 610. In another embodiment, scalping or other mechanical removal techniques may be optionally used to remove at least a portion of the butt of the ingot (opposite the head or top shown removed as in FIG. 6) after casting. As hard alloy ingots are prone to cracking at the ingot butt end during or after casting, a compositionally gradient aluminum alloy product at the butt end may be utilized to minimize or reduce effects of butt cracking.

[0081] Scalping or other mechanical removal techniques may be optionally used to remove at least a portion of the compositionally gradient zone and the outer region from an ingot. FIG. 7A and FIG. 7B provide schematic illustrations of scalping a compositionally gradient aluminum alloy product, such as a composite ingot 700. Using a scalping apparatus or tool 750 as shown in FIG. 7A, at least one surface 740, which may be a rolling surface as shown, is scalped to remove material. The rolling surface may be the widest surface. As shown, the surface 740 includes compositionally gradient zone 725 and outer region 710. Using another scalping apparatus or tool 750 as shown in FIG. 7B, at least one surface 740 is scalped to remove material. As shown, the surface 740 removed includes compositionally gradient zone 725 and outer region 710. Tool 750 of FIG. 7A is depicted as a band saw type device. In FIG. 7B, tool 750 is depicted as a mill type device, where a rotating cutting tool is used to chip and remove compositionally gradient zone 725 and/or outer region 710, such as using one or more milling operations/passes. In some configurations, multiple machining tools may be used simultaneously and/or sequentially to remove the outer region and/or the compositionally gradient zone, such as when composite ingot 700 is oriented in a configuration where the outer region and/or the compositionally gradient zone layers are vertically arranged, rather than in the horizontal configuration depicted in FIGS. 7 A and 7B. In some embodiments, scalping or other mechanical removal techniques may be optionally used to remove at least a portion of the compositionally gradient zone and the outer region from an ingot on multiple sides (head side, butt side, and edges of ingots) to reduce hot rolling effects such as alligatoring that generally occurs during hot rolling. Effects of hot cracking may also be reduced using the compositionally gradient zone at the outer region on multiple sides. Hot cracking forms due to the long solidification range of alloys and may start at mushy zone of the sump. Typically in the case of DC slabs, cold cracks start and propagate as hot cracks during casting. Hence, having purer alloy material solidified at the outer regions can be useful for reducing hot crack failures.

[0082] Referring to FIG. 8 A, the ingot is shown with the head (or top) of the ingot cut. FIG. 8A and FIG. 8B provide schematic illustrations of a compositionally gradient aluminum alloy product or ingot 800 before and after scalping of the sides to generate a monolithic ingot 850. Aluminum alloy product or ingot 800 of FIG. 8 A, before scalping, includes inner region 820, compositionally gradient zone 825, and outer region 810. To form a monolithic ingot 850, as depicted in FIG. 8B, comprising, consisting of, or consisting essentially of the inner region (e.g., a first aluminum alloy), a process of removing the outer region 810 (or the second aluminum alloy) and the compositionally gradient zone 825 from composite ingot 800 may be used, such as a scalping or other machining process. In the example of FIGS. 8A-8B, aluminum alloy product or ingot 800 is scalped on each longitudinal surface (and ends as needed) to generate a monolithic ingot 850 as in FIG. 8B, wherein the monolithic ingot 850 includes inner region 820 of FIG. 8 A. In some embodiments, the monolithic ingot 850 includes only the first aluminum alloy of inner region 820. In some embodiments, portions of compositionally gradient zone 825 can be retained on an outer surface.

[0083] FIG. 9 provides a schematic overview of a compositionally gradient aluminum alloy product or composite ingot 900, where outer region 910 and compositionally gradient zone 925 are scalped to make a monolithic ingot 920 of the first aluminum alloy, which is then processed further to make an aluminum alloy product by at least one rolling process. Depending on the casting configuration and the thickness, length, width, and composition of the outer region 910 of second aluminum alloy and of the compositionally gradient zone 925 of composite ingot 900, different scalping techniques may be utilized. In FIG. 9, scalping of composite ingot 900 involves a machining process where composite ingot 900 is moved relative to a machining tool 950 to remove outer region 910 including the second aluminum alloy and optionally all or a portion of compositionally gradient zone 925 as an at least partially continuous layer.

[0084] Other components may be useful or required for removing outer region 910 and compositionally gradient zone 925 using the configuration depicted in FIG. 9, such as lubricating/cooling fluids, chip collection mechanisms, etc., but these are not shown in the figures so as not to obscure other details. Other machining techniques and operations beyond those illustrated are also possible. For example, for machining some ingots, such as a cylindrical ingot (not shown), a lathe or other device where the ingot is rotated while the machine tool is held stationary may be used.

[0085] Materials properties may dictate the useful scalping technique, as some aluminum alloys may be more suitably machined using particular techniques than others. Alternatively, the available scalping equipment may be used to dictate which aluminum alloys may be used for the outer region and the compositionally gradient zone.

[0086] In some cases, however, the combination of material properties of the aluminum alloy used for the outer region and the inner region may be evaluated to identify which aluminum alloys are suitable for the outer region. For example, the heat transfer coefficient of the outer region may be a useful characteristic to consider, as it may be desirable to control the rate of heat transfer from the inner region to the outer region and cooling water to prevent fracture and/or damage to the inner region during the casting process. Ductility of the outer region may also play a part in the selection of an appropriate outer region aluminum alloy, as it may be beneficial to select an outer region that has a particular ductility to accommodate stresses that may develop within the inner region to provide a protective effect against fracture, cracking, or other damage to the inner region during the casting process. Thermal expansion characteristics may also play a part in the selection of appropriate alloys for the outer region, as it may be beneficial to use an alloy in the outer region that has the same or different thermal expansion characteristics as the alloy of the inner region to accommodate thermal contraction of the inner region and provide a protective effect against fracturing, cracking, or other damage to the inner region during cooling that takes place while or after casting.

[0087] In some cases, a composite ingot may be stable during casting, but can rupture before or during scalping, due to residual stress within the composite ingot. Optionally, a composite ingot may be subjected to a variety of processing steps after casting and prior to scalping to relieve, limit, or otherwise reduce stress within the composite ingot. For example, the composite ingot may be optionally preheated and/or homogenized after removal from the casting pit and prior to scalping. Example preheating and homogenization temperatures may range from about 325 °C to about 520 °C, such as from about 325 °C to about 450 °C or from about 325 °C to about 400 °C. In some embodiments, the ingot is held at a certain or at a multiple temperatures for hold times of 2 to 24 hours to homogenize, and the ingot is then cooled. Preheating and/or homogenizing a composite ingot to temperature(s) and times within these ranges may be useful for limiting intermetallic precipitation.

[0088] Once prepared, a monolithic ingot, such as the ingot 920 shown in FIG. 9, can be processed by any suitable means. FIG. 9 further provides a schematic overview of subjecting a monolithic ingot 920, prepared according to a composite ingot casting and scalping process 955 with scalping apparatus or tool 950, to additional nonlimiting processing steps including a homogenization step 960, a hot rolling step 965, and a cold rolling step 970. Other example processing steps include, but are not limited to, a solution heat treatment step, a preheating step between the homogenization step 960 and the hot rolling step 965, and a pre-aging step. In some cases, scalping process 955 can optionally be the process described in FIGS. 7A-7B. [0089] In a homogenization step 960, a product, such as monolithic ingot 920, is heated to a temperature ranging from about 400 °C to about 500 °C. For example, the product can be heated to a temperature of about 400 °C, about 410 °C, about 420 °C, about 430 °C, about 440 °C, about 450 °C, about 460 °C, about 470 °C, about 480 °C, about 490 °C, or about 500 °C. The product is then allowed to soak (i.e., held at the indicated temperature) for a period of time to form a homogenized product. In some examples, the total time for the homogenization step 960, including the heating and soaking phases, can be up to 24 hours. For example, the product can be heated from about 400 °C to about 520 °C and soaked, for a total time of up to 24 hours for the homogenization step 960. Optionally, the product can be heated to below 490 °C and soaked, for a total time of greater than 18 hours for the homogenization step 960. In some cases, the homogenization step 960 comprises multiple processes. In some non-limiting examples, the homogenization step 960 includes heating a product to a first temperature for a first period of time followed by heating to a second temperature for a second period of time. In a non-limiting example, a product can be heated to about 465 °C for about 3.5 hours and then heated to about 480 °C for about 6 hours.

[0090] Following a homogenization step 960, a hot rolling step 965 can be performed. Prior to the start of hot rolling, the homogenized product can be allowed to cool to a temperature between 300 °C to 520 °C. For example, the homogenized product can be allowed to cool to a temperature of between 325 °C to 500 °C, or from 350 °C to 450 °C, or from 375 °C to 425 °C. The homogenized product can then be hot rolled at a temperature between 300 °C to 520 °C to form a hot rolled plate, a hot rolled shate or a hot rolled sheet having a gauge between 3 mm and 200 mm (e.g., 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm, 10 mm, 15 mm, 20 mm, 25 mm, 30 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm, 60 mm, 65 mm, 70 mm, 75 mm, 80 mm, 85 mm, 90 mm, 95 mm, 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, 150 mm, 160 mm, 170 mm, 180 mm, 190 mm, 200 mm, or anywhere in between). During hot rolling, temperatures and other operating parameters can be controlled so that the temperature of the hot rolled intermediate product upon exit from the hot rolling mill is no more than 440 °C, no more than 430 °C, no more than 420 °C, no more than 410 °C, or no more than 400 °C.

[0091] As illustrated, the hot-rolled product can be subjected to a cold rolling step 970, using cold rolling mills to process the hot-rolled product into thinner products, such as a cold rolled sheet or shate. The cold rolled product can have a gauge between about 0.5 to 10 mm, e.g., between about 0.7 to 6.5 mm. Optionally, the cold rolled product can have a gauge of 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 7.5 mm, 8.0 mm, 8.5 mm, 9.0 mm, 9.5 mm, or 10.0 mm. The cold rolling can be performed to result in a final gauge thickness that represents a gauge reduction of up to 85 % (e.g., up to 10 %, up to 20 %, up to 30 %, up to 40 %, up to 50 %, up to 60 %, up to 70 %, up to 80 %, or up to 85 % reduction) as compared to a gauge prior to the start of cold rolling.

[0092] Optionally, an interannealing step can be performed during the cold rolling step, such as where a first cold rolling process is performed, followed by an annealing process (interannealing), followed by a second cold rolling process. The interannealing step can be performed at a temperature of from about 300 °C to about 450 °C (e.g., about 310 °C, about 320 °C, about 330 °C, about 340 °C, about 350 °C, about 360 °C, about 370 °C, about 380 °C, about 390 °C, about 400 °C, about 410 °C, about 420 °C, about 430 °C, about 440 °C, or about 450 °C). In some cases, the interannealing step comprises multiple processes. In some non-limiting examples, the interannealing step includes heating the partially cold rolled product to a first temperature for a first period of time followed by heating to a second temperature for a second period of time. For example, the partially cold rolled product can be heated to about 410 °C for about 1 hour and then heated to about 330 °C for about 2 hours. [0093] An unprocessed monolithic aluminum alloy ingot, a homogenized monolithic aluminum alloy ingot, or a rolled monolithic aluminum alloy product can optionally undergo a solution heat treatment step. The solution heat treatment step can be any suitable treatment which results in solutionizing of the soluble particles. The product, for example, can be heated to a peak metal temperature (PMT) of up to 590 °C (e.g., from 400 °C to 590 °C) and soaked for a period of time at the PMT to form a hot product. For example, the cast, homogenized, and/or rolled product can be soaked at 480 °C for a soak time of up to 30 minutes (e.g., 0 seconds, 60 seconds, 75 seconds, 90 seconds, 5 minutes, 10 minutes, 20 minutes, 25 minutes, or 30 minutes). After heating and soaking, the hot product is rapidly cooled at rates greater than 200 °C/s to a temperature between 500 °C and 200 °C to form a heat-treated product. In one example, the hot product is cooled at a quench rate of above 200 °C/second to temperatures between 450 °C and 200 °C. Optionally, the cooling rates can be faster in other cases.

[0094] Optionally, a heat-treated product can undergo a pre-aging treatment by reheating before coiling, for example. The pre-aging treatment can be performed at a temperature of from about 70 °C to about 125 °C for a period of time of up to 6 hours. For example, the preaging treatment can be performed at a temperature of about 70 °C, about 75 °C, about 80 °C, about 85 °C, about 90 °C, about 95 °C, about 100 °C, about 105 °C, about 110 °C, about 115 °C, about 120 °C, or about 125 °C. Optionally, the pre-aging treatment can be performed for about 30 minutes, about 1 hour, about 2 hours, about 3 hours, about 4 hours, about 5 hours, or about 6 hours. The pre-aging treatment can be carried out by passing the heat-treated product through a heating device, such as a device that emits radiant heat, convective heat, induction heat, infrared heat, or the like.

[0095] The monolithic aluminum alloy products described herein can be used to make products in the form of sheets, plates, or other suitable products. For example, plates including the products as described herein can be prepared by processing a monolithic aluminum alloy ingot in a homogenization step followed by a hot rolling step. In the hot rolling step, the monolithic aluminum alloy product can be hot rolled to a 200 mm thick gauge or less (e.g., from about 10 mm to about 200 mm). For example, the monolithic aluminum alloy product can be hot rolled to a plate having a final gauge thickness of about 10 mm to about 175 mm, about 15 mm to about 150 mm, about 20 mm to about 125 mm, about 25 mm to about 100 mm, about 30 mm to about 75 mm, or about 35 mm to about 50 mm. In some cases, plates may be rolled into thinner metal products, such as sheets. In some embodiments, final sheets may be hot stamped and/or hot formed, and optionally anodized. [0096] Referring to FIG. 10A, the ingot is shown with the head and butt of the ingot cut. FIG. 10A and FIG. 10B provide schematic overviews of a compositionally gradient aluminum alloy product, which has been partially scalped, the configuration of FIG. 10A being scalped at first and second edges and the configuration as in FIG. 10B being scalped on upper and lower rolling surfaces. In the embodiment as shown in FIG. 10A having first and second edges (end surfaces) scalped, by having the purer, and hence softer, outer region alloy on the rolling surface, the corrosion resistance and bond durability of the sheet can be improved as compared to a product comprised of the inner region alloy alone. Thus, a sheet demonstrating improved surface properties results without additional treatment and, in some cases, the bending, stamping, streaking, and roping performances is improved. In the embodiment as shown in FIG. 10B having upper and lower rolling surfaces scalped, for an inner region alloy prone to edge crack during hot rolling, the outer region alloy at the ingot ends may provide reduced edge cracking commonly found as a result of hot rolling.

Therefore, after hot rolling, these edges can be trimmed as needed. Additionally, the outer region alloy, being softer (purer), can result in reduced alligatoring effects at the edges. [0097] The as-scalped products 1000 A and 1000B, of FIGS. 10A and 10B respectively, may be processed similarly as described above for ingot 920 of FIG. 9 including, but not limited to, homogenization step 1060, hot rolling step 1065, and cold rolling step 1070. Other example processing steps include, but are not limited to, a solution heat treatment step, a preheating step between the homogenization step 1060 and the hot rolling step 1065, and a pre-aging step.

[0098] FIG. 11 provides a schematic overview of a compositionally gradient aluminum alloy product 1100, which has not been scalped, and making and processing the ingot to make an aluminum alloy product. Alloy product 1100, which is similar to the ingot 600 as shown in FIG. 6, may be processed similarly as described above, such as including, but not limited to, homogenization step 1160, hot rolling step 1165, and cold rolling step 1170. Similarly as with as-scalped products 1000 A and 1000B, of FIGS. 10A and 10B, other example processing steps include, but are not limited to, a solution heat treatment step, a preheating step between the homogenization step 1160 and the hot rolling step 1165, and a pre-aging step.

[0099] The following examples will serve to further illustrate the present invention without, at the same time, however, constituting any limitation thereof. On the contrary, it is to be clearly understood that resort may be had to various embodiments, modifications and equivalents thereof which, after reading the description herein, may suggest themselves to those skilled in the art without departing from the spirit of the invention. During the studies described in the following examples, conventional procedures were followed, unless otherwise stated. Some of the procedures are described below for illustrative purposes.

EXAMPLE 1

[0100] A composite ingot is formed by a concurrent dual casting technique, such as illustrated in FIGS. 1-4. The aluminum alloy used for the inner region is an AA5182 aluminum alloy. The aluminum alloy used for the outer region is an AA1100 aluminum alloy. The AA1100 product is diluted into an AA5182 at the compositionally gradient region. This makes scrap reclamation and recycling straight forward as there is no need for segregation or poisoning of the stream. The gradient liquid layers formed by the molten AA5182 and the molten AA1100 are similar to those found readily in nature in the stratification forms of thermoclines (thermal), haloclines (salinity), or chemoclines (chemical). To maintain the compositionally gradient zone at the interface of the two molten alloys, turbulence is reduced by a method where a structure is used to redirect the pouring velocity vector and thus eliminate mixing. In this example, molten aluminum casting using combo-bags or mesh screens is used to achieve a limited amount of turbulence such that the flow of molten metal is redirected normal to the casting direction. The thickness of the as cast compositionally gradient zone can be about 10.5 mm per side and the outer region about 26 mm per side. During a scalping operation, about 36.5 mm per side, corresponding to the outer region, can be removed from each rolling surface by separate milling operations to form a monolithic AA5182 aluminum ingot. The monolithic ingot is transferred to a rolling mill for subsequent processing. Edge cracking on the short faces of the ingots can be suppressed.

EXAMPLE 2

[0101] Another composite ingot is formed by a concurrent dual casting technique, such as illustrated in FIGS. 1-4, where the two alloys are cast into a single mold. The aluminum alloy used for the inner region is an AA7075 aluminum alloy. The aluminum alloy used for the outer region is an AA1100 aluminum alloy. The AA1100 series product is diluted into the AA7075 at the compositionally gradient region. This makes scrap reclamation and recycling straight forward as there is no need for segregation or poisoning of the stream. The gradient liquid layers formed by the molten AA7075 and the molten AA1100 are similar to those found readily in nature in the stratification forms of thermoclines (thermal), haloclines (salinity), or chemoclines (chemical). To maintain the compositionally gradient zone at the interface of the two molten alloys, turbulence is reduced by a method where a structure is used to redirect the pouring velocity vector and thus eliminate mixing. Combo-bags or mesh screens are used to achieve a limited amount of turbulence such that the flow of molten metal is redirected normal to the casting direction, e.g., parallel to the desired interfacial plane. By controlling the flow velocity, turbulence is minimized. Alternatively, a magnetic field may be used to suppress turbulence in a direction perpendicular to the compositionally gradient zone. The thickness of the as cast compositionally gradient zone is about 10.5 mm per side and the outer region about 26 mm per side. The ingot is transferred to a rolling mill for subsequent processing. Cold cracking during casting the ingots will be suppressed.

ILLUSTRATIVE ASPECTS

[0102] As used below, any reference to a series of aspects (e.g., “Aspects 1-4”) or nonenumerated group of aspects (e.g., “any previous or subsequent aspect”) is to be understood as a reference to each of those aspects disjunctively (e.g., “Aspects 1-4” is to be understood as “Aspects 1, 2, 3, or 4 ”).

[0103] Aspect l is a method of preparing a compositionally gradient aluminum alloy product, comprising: casting a composite ingot in a mold, the composite ingot including: an inner region comprising a first aluminum alloy, an outer region surrounding the inner region, the outer region comprising a second aluminum alloy different from the first aluminum alloy; and a compositionally gradient zone between the inner region and the outer region, wherein at least one alloying element of the first aluminum alloy has a content that is decreased through the compositionally gradient zone in a direction from the inner region to the outer region.

[0104] Aspect 2 is the method of any previous or subsequent aspect, wherein the first aluminum alloy and the second aluminum alloy are cast concurrently.

[0105] Aspect 3 is the method of any previous or subsequent aspect, wherein the first aluminum alloy is delivered to the mold from a first height and the second aluminum alloy is delivered to the mold from a second height, wherein the second height is different from the first height.

[0106] Aspect 4 is the method of any previous or subsequent aspect, further comprising scalping the composite ingot to remove, from a rolling surface, at least a portion of the compositionally gradient zone and the outer region.

[0107] Aspect 5 is the method of any previous or subsequent aspect, wherein scalping includes removing material to generate a monolithic ingot comprising the first aluminum alloy.

[0108] Aspect 6 is the method of any previous or subsequent aspect, wherein the first aluminum alloy comprises a 7xxx series aluminum alloy, a 5xxx series aluminum alloy, or a 2xxx series aluminum alloy.

[0109] Aspect 7 is the method of any previous or subsequent aspect, wherein the first aluminum alloy comprises a 7075 aluminum alloy, a 5182 aluminum alloy, or a 2024 aluminum alloy.

[0110] Aspect 8 is the method of any previous or subsequent aspect, wherein the second aluminum alloy comprises a Ixxx series aluminum alloy.

[0111] Aspect 9 is the method of any previous or subsequent aspect, wherein the second aluminum alloy has a purity of at least 99.7%.

[0112] Aspect 10 is the method of any previous or subsequent aspect, wherein the at least one alloying element of the first aluminum alloy comprises Zn, Cu, Mg, or Na.

[0113] Aspect 11 is the method of any previous or subsequent aspect, wherein the outer region is substantially devoid of the at least one alloying element.

[0114] Aspect 12 is the method of any previous or subsequent aspect, wherein the composite ingot is substantially devoid of cracking.

[0115] Aspect 13 is the method of any previous or subsequent aspect, wherein cracking includes cold cracking, hot cracking, edge cracking, or butt cracking. [0116] Aspect 14 is the method of any previous or subsequent aspect, wherein the composite ingot is substantially devoid of porosity.

[0117] Aspect 15 is the method of any previous or subsequent aspect, wherein porosity includes pores as nucleation points from fractures during hot rolling.

[0118] Aspect 16 is the method of any previous or subsequent aspect, wherein casting the composite ingot comprises a direct chill casting process in which the inner region and the outer region are co-cast in an arrangement where the outer region is contacted with cooling water.

[0119] Aspect 17 is the method of any previous or subsequent aspect, wherein the outer region has a thickness of from 7% to 15% of a total thickness of the composite ingot.

[0120] Aspect 18 is the method of any previous or subsequent aspect, wherein the compositionally gradient zone has a thickness of from 2% to 10% of a total thickness of the composite ingot.

[0121] Aspect 19 is the method of any previous or subsequent aspect, further comprising processing the monolithic ingot or the composite ingot to form an aluminum alloy shate, plate, or sheet comprising the first aluminum alloy.

[0122] Aspect 20 is the method of any previous or subsequent aspect, further comprising one or more of a homogenization process, a hot rolling process, a cold rolling process, an annealing process, a solution heat treatment process, a quenching process, or a surface treatment process.

[0123] Aspect 21 is the method of any previous or subsequent aspect, further comprising directing a magnetic field during casting, the magnetic field configured to suppress turbulence in a direction perpendicular to the compositionally gradient zone.

[0124] Aspect 22 is the method of any previous or subsequent aspect, further comprising directing a magnetic field during casting to suppress turbulence in a direction perpendicular to the compositionally gradient zone, wherein directing includes positioning the magnetic field at a height between the first height and the second height.

[0125] Aspect 23 is the method of any previous or subsequent aspect, further comprising directing a magnetic field during casting to suppress turbulence in a direction perpendicular to the compositionally gradient zone, wherein directing the magnetic field includes providing a skim dam, the skim dam being positioned within the molten liquids at a height the first height and the second height.

[0126] Aspect 24 is an aluminum alloy composite ingot prepared by the method of any one of any previous or subsequent aspect. [0127] Aspect 25 is an aluminum alloy composite ingot, comprising: an inner region comprising a first aluminum alloy, an outer region surrounding the inner region, the outer region comprising a second aluminum alloy different from the first aluminum alloy; and a compositionally gradient zone between the inner region and the outer region, wherein at least one alloying element of the first aluminum alloy has a content that is decreased through the compositionally gradient zone in a direction from the inner region to the outer region.

[0128] Aspect 26 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein the first aluminum alloy comprises a 7xxx series aluminum alloy, a 5xxx series aluminum alloy, or a 2xxx series aluminum alloy.

[0129] Aspect 27 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein the first aluminum alloy comprises a 7075 aluminum alloy, a 5182 aluminum alloy, or a 2024 aluminum alloy.

[0130] Aspect 28 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein the second aluminum alloy comprises a Ixxx series aluminum alloy.

[0131] Aspect 29 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein the second aluminum alloy has a purity of at least 99.7%.

[0132] Aspect 30 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein the at least one alloying element of the first aluminum alloy comprises Zn, Cu, Mg, or Na.

[0133] Aspect 31 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein the outer region is substantially devoid of the at least one alloying element. [0134] Aspect 32 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein the composite ingot is substantially devoid of cracking.

[0135] Aspect 33 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein cracking includes cold cracking, hot cracking, edge cracking, or butt cracking.

[0136] Aspect 34 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein the composite ingot is substantially devoid of porosity.

[0137] Aspect 35 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein porosity includes pores as nucleation points from fractures during hot rolling. [0138] Aspect 36 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein the outer region has a thickness of from 7% to 15% of a total thickness of the composite ingot. [0139] Aspect 37 is the aluminum alloy composite ingot of any previous or subsequent aspect, wherein the compositionally gradient zone has a thickness of from 2% to 10% of a total thickness of the composite ingot.

[0140] Aspect 38 is a rolled aluminum alloy product formed by the method of any one of any previous or subsequent aspect.

[0141] Aspect 39 is a rolled aluminum alloy product, comprising: an inner region comprising a first aluminum alloy, an outer region surrounding the inner region, the outer region comprising a second aluminum alloy different from the first aluminum alloy; and a compositionally gradient zone between the inner region and the outer region, wherein at least one alloying element of the first aluminum alloy has a content that is decreased through the compositionally gradient zone in a direction from the inner region to the outer region.

[0142] Aspect 40 is the rolled aluminum alloy product of any previous or subsequent aspect, made from the ingot of any of any previous or subsequent aspect.

[0143] Aspect 41 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein the first aluminum alloy comprises a 7xxx series aluminum alloy, a 5xxx series aluminum alloy, or a 2xxx series aluminum alloy.

[0144] Aspect 42 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein the first aluminum alloy comprises a 7075 aluminum alloy, a 5182 aluminum alloy, or a 2024 aluminum alloy.

[0145] Aspect 43 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein the second aluminum alloy comprises a Ixxx series aluminum alloy.

[0146] Aspect 44 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein the second aluminum alloy has a purity of at least 99.7%.

[0147] Aspect 45 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein the at least one alloying element of the first aluminum alloy comprises Zn, Cu, Mg, or Na.

[0148] Aspect 46 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein the outer region is substantially devoid of the at least one alloying element. [0149] Aspect 47 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein the composite ingot is substantially devoid of cracking.

[0150] Aspect 48 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein cracking includes cold cracking, hot cracking, edge cracking, or butt cracking. [0151] Aspect 49 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein the composite ingot is substantially devoid of porosity.

[0152] Aspect 50 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein porosity includes pores as nucleation points from fractures during hot rolling. [0153] Aspect 51 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein the outer region has a thickness of from 7% to 15% of a total thickness of the composite ingot.

[0154] Aspect 52 is the rolled aluminum alloy product of any previous or subsequent aspect, wherein the compositionally gradient zone has a thickness of from 2% to 10% of a total thickness of the composite ingot.

[0155] All patents, publications and abstracts cited above are incorporated herein by reference in their entirety. The foregoing description of the embodiments, including illustrated embodiments, has been presented only for the purpose of illustration and description and is not intended to be exhaustive or limiting to the precise forms disclosed. Numerous modifications, adaptations, and uses thereof will be apparent to those skilled in the art.

Claims

WHAT IS CLAIMED IS:

1. A method of preparing a compositionally gradient aluminum alloy product, comprising: casting a composite ingot in a mold, the composite ingot including: an inner region comprising a first aluminum alloy, an outer region surrounding the inner region, the outer region comprising a second aluminum alloy different from the first aluminum alloy; and a compositionally gradient zone between the inner region and the outer region, wherein at least one alloying element of the first aluminum alloy has a content that is decreased through the compositionally gradient zone in a direction from the inner region to the outer region.

2. The method of claim 1, wherein the first aluminum alloy and the second aluminum alloy are cast concurrently.

3. The method of claim 1, further comprising scalping the composite ingot to remove, from a rolling surface, at least a portion of the compositionally gradient zone and the outer region.

4. The method of claim 3, wherein scalping includes removing material to generate a monolithic ingot comprising the first aluminum alloy.

5. The method of claim 1, wherein the first aluminum alloy comprises a 7xxx series aluminum alloy, a 5xxx series aluminum alloy, or a 2xxx series aluminum alloy.

6. The method of claim 5, wherein the first aluminum alloy comprises a 7075 aluminum alloy, a 5182 aluminum alloy, or a 2024 aluminum alloy.

7. The method of claim 1, wherein the second aluminum alloy comprises a Ixxx series aluminum alloy.

8. The method of claim 7, wherein the second aluminum alloy has a purity of at least 99.7%.

9. The method of claim 1, wherein the at least one alloying element of the first aluminum alloy comprises Zn, Cu, Mg, or Na.

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10. The method of claim 1, wherein the outer region is substantially devoid of the at least one alloying element.

11. The method of claim 1, wherein the composite ingot is substantially devoid of cracking.

12. The method of claim 11, wherein cracking includes cold cracking, hot cracking, edge cracking, or butt cracking.

13. The method of claim 1, wherein the composite ingot is substantially devoid of porosity.

14. The method of claim 13, wherein porosity includes pores as nucleation points from fractures during hot rolling.

15. The method of claim 1, wherein casting the composite ingot comprises a direct chill casting process in which the inner region and the outer region are co-cast in an arrangement where the outer region is contacted with cooling water.

16. The method of claim 1, wherein the outer region has a thickness of from 7% to 15% of a total thickness of the composite ingot.

17. The method of claim 16, wherein the compositionally gradient zone has a thickness of from 2% to 10% of a total thickness of the composite ingot.

18. The method of claim 1, further comprising processing the ingot to form an aluminum alloy shate, plate, or sheet comprising the first aluminum alloy.

19. The method of claim 1, further comprising one or more of a homogenization process, a hot rolling process, a cold rolling process, an annealing process, a solution heat treatment process, a quenching process, or a surface treatment process.

20. The method of claim 1, further comprising directing a magnetic field during casting, the magnetic field configured to suppress turbulence in a direction perpendicular to the compositionally gradient zone.

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21. The method of claim 1, wherein the first aluminum alloy is delivered to the mold from a first height and the second aluminum alloy is delivered to the mold from a second height, wherein the second height is different from the first height.

22. The method of claim 21, further comprising directing a magnetic field during casting to suppress turbulence in a direction perpendicular to the compositionally gradient zone, wherein directing includes positioning the magnetic field at a height between the first height and the second height.

23. The method of claim 22, further comprising directing a magnetic field during casting to suppress turbulence in a direction perpendicular to the compositionally gradient zone, wherein directing the magnetic field includes providing a skim dam, the skim dam being positioned within molten liquid at a height between the first height and the second height.

24. An aluminum alloy composite ingot prepared by the method of any one of claims 1-23.

25. An aluminum alloy composite ingot, comprising: an inner region comprising a first aluminum alloy, an outer region surrounding the inner region, the outer region comprising a second aluminum alloy different from the first aluminum alloy; and a compositionally gradient zone between the inner region and the outer region, wherein at least one alloying element of the first aluminum alloy has a content that is decreased through the compositionally gradient zone in a direction from the inner region to the outer region.

26. The aluminum alloy composite ingot of claim 25, wherein the first aluminum alloy comprises a 7xxx series aluminum alloy, a 5xxx series aluminum alloy, or a 2xxx series aluminum alloy.

27. The aluminum alloy composite ingot of claim 26, wherein the first aluminum alloy comprises a 7075 aluminum alloy, a 5182 aluminum alloy, or a 2024 aluminum alloy.

28. The aluminum alloy composite ingot of claim 25, wherein the second aluminum alloy comprises a Ixxx series aluminum alloy.

29. The aluminum alloy composite ingot of claim 28, wherein the second aluminum alloy has a purity of at least 99.7%.

30. The aluminum alloy composite ingot of claim 25, wherein the at least one alloying element of the first aluminum alloy comprises Zn, Cu, Mg, or Na.

31. The aluminum alloy composite ingot of claim 25, wherein the outer region is substantially devoid of the at least one alloying element.

32. The aluminum alloy composite ingot of claim 25, wherein the composite ingot is substantially devoid of cracking.

33. The aluminum alloy composite ingot of claim 32, wherein cracking includes cold cracking, hot cracking, edge cracking, or butt cracking.

34. The aluminum alloy composite ingot of claim 25, wherein the composite ingot is substantially devoid of porosity.

35. The aluminum alloy composite ingot of claim 34, wherein porosity includes pores as nucleation points from fractures during hot rolling.

36. The aluminum alloy composite ingot of claim 25, wherein the outer region has a thickness of from 7% to 15% of a total thickness of the composite ingot.

37. The aluminum alloy composite ingot of claim 36, wherein the compositionally gradient zone has a thickness of from 2% to 10% of a total thickness of the composite ingot.

38. A rolled aluminum alloy product formed by the method of any one of claims 1-23.

39. A rolled aluminum alloy product, comprising: an inner region comprising a first aluminum alloy, an outer region surrounding the inner region, the outer region comprising a second aluminum alloy different from the first aluminum alloy; and a compositionally gradient zone between the inner region and the outer region, wherein at least one alloying element of the first aluminum alloy has a content that is decreased through the compositionally gradient zone in a direction from the inner region to the outer region.

40. The rolled aluminum alloy product of claim 39, made from the aluminum alloy composite ingot of any of claims 24-37.

41. The rolled aluminum alloy product of claim 39, wherein the first aluminum alloy comprises a 7xxx series aluminum alloy, a 5xxx series aluminum alloy, or a 2xxx series aluminum alloy.

42. The rolled aluminum alloy product of claim 41, wherein the first aluminum alloy comprises a 7075 aluminum alloy, a 5182 aluminum alloy, or a 2024 aluminum alloy.

43. The rolled aluminum alloy product of claim 39, wherein the second aluminum alloy comprises a Ixxx series aluminum alloy.

44. The rolled aluminum alloy product of claim 43, wherein the second aluminum alloy has a purity of at least 99.7%.

45. The rolled aluminum alloy product of claim 39, wherein the at least one alloying element of the first aluminum alloy comprises Zn, Cu, Mg, or Na.

46. The rolled aluminum alloy product of claim 39, wherein the outer region is substantially devoid of the at least one alloying element.

47. The rolled aluminum alloy product of claim 40, wherein the composite ingot is substantially devoid of cracking.

48. The rolled aluminum alloy product of claim 47, wherein cracking includes cold cracking, hot cracking, edge cracking, or butt cracking.

49. The rolled aluminum alloy product of claim 40, wherein the composite ingot is substantially devoid of porosity.

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50. The rolled aluminum alloy product of claim 49, wherein porosity includes pores as nucleation points from fractures during hot rolling.

51. The rolled aluminum alloy product of claim 40, wherein the outer region has a thickness of from 7% to 15% of a total thickness of the composite ingot.

52. The rolled aluminum alloy product of claim 51, wherein the compositionally gradient zone has a thickness of from 2% to 10% of a total thickness of the composite ingot.

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