JP6294962B2 - Aluminum alloy plate excellent in press formability and shape freezing property and method for producing the same - Google Patents

Description

  The present invention relates to an aluminum alloy plate having press formability and shape freezing property suitable for automobile body sheets, and a method for producing the same.

  Application of Al-Mg-based 5000-based aluminum alloy sheets to automobile body panels and the like as an alternative material for steel sheets has been studied. In order to form a 5000 series aluminum alloy sheet into a desired shape, it is necessary to form it with a press die. For this reason, conventionally, 5000 series aluminum alloy plates excellent in so-called press formability have been developed.

  However, a 5000 series aluminum alloy plate is inferior to press formability compared with a steel plate. For this reason, in the press forming of a 5000 series aluminum alloy plate, it is necessary to devise such as press forming by dividing a part, and there are problems such as an increase in the number of parts and the number of molds. Particularly in press molding with a complicated shape, defects such as cracks often occur in the vicinity of the plane strain region. For this reason, the 5000 series aluminum alloy sheet is required to further improve the so-called plane strain fracture limit.

By the way, as an aluminum alloy plate excellent in formability, for example, in Patent Document 1, when the texture is measured on the thickness surface of the product plate, any one of the Cu orientation, S orientation, and BRASS orientation belonging to the rolling texture Aluminum alloy can lid materials whose components are more than 6 times the random orientation and the number of intermetallic compounds with a maximum length of 5 μm or more measured on the plate thickness surface are 30 or more and 480 or less per 1 mm ^2. ing. According to Patent Document 1, this aluminum alloy can lid material is excellent in rivet formability and score workability. Further, Patent Document 1 focuses on the relationship between the texture of cold-rolled aluminum alloy sheets and press formability, and controls the texture to identify the volume fraction of crystal orientation, thereby providing an aluminum alloy. It describes that the formability of the plate is improved.

  Moreover, as an aluminum alloy plate excellent in formability, for example, Patent Document 2 discloses an Al—Mg alloy plate, in which the ratio of the volume fraction of the CUBE orientation to the volume fraction of the S orientation (S / Cube) is 1. As described above, an Al—Mg alloy plate having a texture with a GOSS orientation of 5% or less and a crystal grain size in the range of 20 to 100 μm is described. According to Patent Document 2, this Al-Mg alloy plate has a large limit drawing ratio (LDR), which is an index of deep drawing formability, and is excellent in deep drawing formability. Patent Document 2 describes that deep drawing formability of a 5000 series aluminum alloy sheet is improved by paying attention to the relationship between the limit drawing ratio (LDR) and texture in deep drawing.

  Furthermore, as an aluminum alloy plate excellent in formability, for example, Patent Document 3 describes an aluminum alloy plate for forming having a recrystallized grain size of 12 μm or less and a limit drawing ratio (LDR) of 2.13 or more. . According to Patent Document 3, this aluminum alloy sheet for forming is excellent in deep drawability and anti-seizure softening property. Patent Document 3 describes that CC material is superior in deep drawability compared to DC material.

  By the way, as a technique for improving the formability of an aluminum alloy plate, a Cube orientation in which the {100} plane of the face-centered cubic is perpendicular to the rolling surface normal direction and the <100> direction is parallel to the rolling direction is used. It is known that it is effective to increase the volume ratio of the crystals. Further, as means for growing the Cube orientation, it is known to perform partial annealing, cold rolling under cold pressure, and annealing. For example, in Non-Patent Document 1, by using EBSP, X-ray diffraction, etc., by examining the nucleation and growth behavior of cube-oriented grains when subjected to partial annealing, cold rolling under low pressure, and intermediate annealing, Attempts have been made to elucidate the mechanism of texture development. In Non-Patent Document 1, the development of a cube texture that is partially annealed and under light pressure does not occur due to the promotion of nucleation of cube-oriented grains, and the growth of cube-oriented grains produced during partial annealing is the other side. It is described that it occurs because it is faster than the grain. In Non-Patent Document 1, it is considered that the main reason why cube-oriented grains are likely to grow is that the increase in residual strain in the cube-oriented grains due to light pressure is less than that of the other grains.

Japanese Patent No. 3904868 Japanese Patent No. 4339869 Japanese Patent No. 5050577

Effect of Partial Annealing and Light Rolling on Formation of Cubic Texture of 3004 Aluminum Alloy (Light Metals Vol. 49 No. 12 (1999), 583-588)

  In view of the above conventional knowledge, in the production of a 5000 series aluminum alloy plate, if the original slab is a thin slab continuous cast material (CC material), the average crystal grain size of recrystallized grains in the metal structure of the final annealed plate is 12 μm. It is considered that an aluminum alloy sheet excellent in deep drawability can be obtained. However, in the production of a 5000 series aluminum alloy plate, if the original slab is simply a thin slab continuous cast material (CC material), the solid solution amount in the matrix of transition elements such as Mn, Fe, Si, etc. becomes high, and the final annealed plate There was a problem that the proof stress of this was increased. In addition, the 5000 series aluminum alloy sheet has good formability under the conditions assuming actual press forming, and secures formability in press forming of complicated shapes for application to body materials. Is desired. However, the 5000 series aluminum alloy sheet produced from the cold rolled material obtained by using the original slab as a thin slab continuous cast material (CC material) has a formability and a complicated shape under the conditions assuming actual press forming. There was a problem that the formability in the press molding was not sufficient.

  Therefore, the inventors of the present application investigated the relationship between the texture and formability of the cold-rolled annealed material based on the thin slab continuous cast material as the original slab, and the volume fraction and plane strain of the Cube orientation in the cold-rolled annealed material. Focusing on the relationship with the fracture limit, the inventors studied the alloy composition and the plate making conditions, and succeeded in obtaining an aluminum alloy plate excellent in press formability and shape freezing property.

  An object of this invention is to provide the aluminum alloy plate excellent in press moldability and shape freezing property, and its manufacturing method.

The aluminum alloy plate according to the first aspect of the present invention contains 4.0 to 5.5% by mass of Mg and 0.005 to 0.10% by mass of Ti, and contains Fe, Mn and Si as impurities. An aluminum alloy plate having a content of less than 0.10% by mass and the balance being Al and inevitable impurities, the average crystal grain size being less than 30 μm, and the volume of the S-oriented crystal relative to the volume fraction of the Cube-oriented crystal Ratio (volume ratio of S-oriented crystals / volume ratio of Cube-oriented crystals) is less than 0.3, volume ratio of Cube-oriented crystals is 10 to 25%, tensile strength is 250 MPa or more, yield strength is less than 130 MPa, elongation Is 30% or more, and the plane strain fracture limit is 0.22 or more.

  The aluminum alloy plate according to the first aspect preferably further contains 0.03 to 0.2% by mass of Cu.

The manufacturing method of the aluminum alloy plate which concerns on the 2nd aspect of this invention is a manufacturing method which manufactures the aluminum alloy plate which concerns on the 1st aspect of this invention , Comprising : Mg is 4.0-5.5 mass%, Aluminum alloy melt containing 0.005 to 0.10% by mass of Ti, the contents of Fe, Mn and Si as impurities being less than 0.10% by mass, and the balance being Al and inevitable impurities A slab manufacturing step for continuously casting to obtain a slab having a thickness of 2 to 15 mm, a winding step for winding the slab around a roll without hot rolling, and a slab wound around the roll An annealing precipitation treatment step for producing an annealing precipitation treatment material by holding at a holding temperature of 380 to 470 ° C. for 1 to 15 hours, and cold rolling at a final cold rolling ratio of 70 to 95% on the annealing precipitation treatment material. Final cold rolled material A final cold rolling step to obtain, and a final annealing step to obtain a final annealed material by performing a final annealing for holding the final cold rolled material at a holding temperature of 400 to 500 ° C. for 10 to 60 seconds. .

  In the method for producing an aluminum alloy plate according to the second aspect, the molten aluminum alloy preferably further contains 0.03 to 0.2% by mass of Cu.

The manufacturing method of the aluminum alloy plate which concerns on the 3rd aspect of this invention is a manufacturing method which manufactures the aluminum alloy plate which concerns on the 1st aspect of this invention , Comprising: 4.0-5.5 mass% of Mg, Aluminum alloy melt containing 0.005 to 0.10% by mass of Ti, the contents of Fe, Mn and Si as impurities being less than 0.10% by mass, and the balance being Al and inevitable impurities A slab manufacturing step of continuously casting to obtain a slab having a thickness of 2 to 15 mm, a winding step of winding the slab on a roll without hot rolling, and a slab wound on the roll An annealing precipitation treatment step for obtaining an annealing precipitation treatment material by holding at a holding temperature of 380 to 470 ° C. for 1 to 15 hours, and a first cold rolling material obtained by cold rolling the annealing precipitation treatment material. The next cold rolling process, An intermediate annealing step for obtaining an intermediate annealed material by performing an intermediate annealing on the primary cold rolled material, and a final cold rolled material obtained by subjecting the intermediate annealed material to cold rolling with a cold rolling rate of 10 to 30%. A final cold rolling step, and a final annealing step of obtaining a final annealed material by performing a final annealing of holding the final cold rolled material at a holding temperature of 400 to 500 ° C. for 10 to 60 seconds.

  In the method for producing an aluminum alloy plate according to the third aspect, it is preferable that the molten aluminum alloy further contains 0.03 to 0.2% by mass of Cu.

  In the method for producing an aluminum alloy plate according to the third aspect, the intermediate annealing step is preferably held at a holding temperature of 250 to 350 ° C. for 10 to 60 seconds using a continuous annealing furnace.

  In the method for producing an aluminum alloy plate according to the third aspect, the intermediate annealing step is preferably held at a holding temperature of 200 to 300 ° C. for 0.5 to 8 hours using a batch furnace.

  The aluminum alloy plate according to the present invention is excellent in press formability and shape freezing property. The method for producing an aluminum alloy plate according to the present invention can efficiently produce an aluminum alloy plate excellent in press formability and shape freezing property.

It is a figure which shows an example of a press-molded product. It is a figure (Example 2) which shows an example of the crystal orientation measurement result by EBSD. It is a figure (comparative example 1) which shows an example of the crystal orientation measurement result by EBSD. It is a top view which shows the shape and dimension of a test piece of a plane strain fracture limit.

[Aluminum alloy plate]
Prior to the description of the aluminum alloy plate according to the present embodiment, problems of the conventional 5000 series aluminum alloy plate will be described.

  Even if the conventional 5000 series aluminum alloy plate has high strength, defects such as cracks may occur in the vicinity of the plane strain region, particularly in press molding with a complicated shape. For this reason, the fracture limit was low in the plane strain region. Moreover, the conventional 5000 series aluminum alloy plate may have a high yield strength depending on the component composition, and in this case, a springback is likely to occur after press forming. If it does so, there also existed a problem that the so-called shape freezing property that the aluminum alloy plate after press molding did not fit in a predetermined design shape was bad. Furthermore, the conventional 5000 series aluminum alloy plate may have a rough surface appearance after press molding. In the conventional DC cast material, the average crystal grain size of the recrystallized grains is too large as 30 μm or more, which sometimes gives a rough skin appearance after press molding. For this reason, it has been desired for the conventional 5000 series aluminum alloy plate to reduce the average crystal grain size of the recrystallized grains to some extent.

  The conventional 5000 series aluminum alloy plate has the above-mentioned problems. For this reason, the 5000 series aluminum alloy sheet is currently required to have high strength, high elongation, low yield strength, and appropriately adjusted crystal grain size, volume ratio of Cube orientation crystal and S orientation crystal. Yes.

  As a method of improving the press formability of conventional 5000 series aluminum alloy plates, the intermetallic compound in the original slab is made fine by thin slab continuous casting, and the recrystallized grains in the final plate (annealed plate) are made as fine as possible. It is also possible to keep it. However, this method has a problem in that the solid solution amount of the transition element in the original slab is high, and particularly in an aluminum alloy plate having a high Mg composition, the yield strength becomes too high and the shape freezing property is poor. Moreover, since the solid solution amount of the transition element in the original slab becomes high, it becomes difficult to control the ratio of individual crystal orientations in the texture that governs plastic anisotropy in the subsequent cold rolling process. For this reason, when adopting the thin slab continuous casting method, in order to improve the formability by increasing the texture, particularly the volume ratio of the Cube orientation in the final annealed plate, the solid solution amount of the transition element in the original slab is increased. After lowering, it is necessary to adjust the subsequent processes such as cold rolling and to perform appropriate tempering.

  On the other hand, as a method for evaluating formability, conventionally, the value of elongation in a tensile test is often employed. In this case, since it is a uniaxial tensile test, the formability is evaluated in a so-called drawn region, and actual press forming is performed. It was unsuitable for evaluating the moldability. In general, cracks in press forming of an aluminum alloy plate are likely to occur in a plane strain region that is an intermediate region between the drawn region and the overhang region. For this reason, in order to reduce the incidence of defects such as cracks in press forming, it is necessary to evaluate the fracture limit in a plane strain region where the forming limit is the lowest in press forming of an aluminum alloy plate.

  The aluminum alloy sheet according to the present embodiment has been focused on the relationship between the volume ratio of the Cube orientation in the cold-rolled annealed material and the plane strain fracture limit, and as a result of earnestly examining the alloy composition and sheet-making conditions, press formability and shape freezing It came to obtain the aluminum alloy plate excellent in the property.

  Hereinafter, the aluminum alloy plate according to the present embodiment will be described. The aluminum alloy plate according to the present embodiment contains a predetermined amount of Mg and Ti, and the contents of Fe, Mn, and Si as impurities are less than a predetermined amount, respectively, and the balance is substantially Al and inevitable impurities. An aluminum alloy plate made of

(Mg: 4.0 to 5.5% by mass)
In the aluminum alloy plate according to the present embodiment, Mg is an essential element contained in order to enhance the strength of the aluminum alloy plate by strengthening the solid solution by solid solution in the matrix. Mg is also an element that uniformly plastically deforms the material and improves the fracture limit in the plane strain region in order to enhance work hardening ability during press molding.

  The aluminum alloy plate according to the present embodiment limits the Mg content of the aluminum alloy plate to a range of 4.0 to 5.5% by mass. A preferable Mg content is in the range of 4.3 to 5.2 mass%. A more preferable Mg content is in the range of 4.5 to 5.0 mass%. When the content of Mg in the aluminum alloy plate is less than 4.0% by mass, the strength and elongation of the aluminum alloy plate are decreased, the breaking limit in the plane strain region is decreased, and press formability is decreased. Absent. On the other hand, if the Mg content exceeds 5.5% by mass, the yield strength becomes too high, and the shape freezing property at the time of press molding is lowered, which is not preferable.

(Ti: 0.005 to 0.10% by mass)
In the aluminum alloy plate according to the present embodiment, Ti is an essential element included to act as a crystal grain refining agent during ingot casting and prevent casting cracks.

The aluminum alloy plate according to the present embodiment limits the Ti content of the aluminum alloy plate to a range of 0.005 to 0.10% by mass. The preferable Ti content is in the range of 0.005 to 0.07 mass%. A more preferable Ti content is in the range of 0.01 to 0.05 mass%. If the Ti content of the aluminum alloy plate is less than 0.005% by mass, the effect of refining at the time of ingot casting is insufficient, which may cause casting cracks, which is not preferable. On the other hand, if the Ti content exceeds 0.10% by mass, coarse intermetallic compounds such as TiAl ₃ may precipitate during ingot casting, which may reduce press formability in the final plate, which is not preferable. .

  In addition, in the aluminum alloy plate which concerns on this embodiment, when Ti and B coexist, the refinement | miniaturization effect of a crystal grain tends to become stronger. For this reason, it is preferable that the aluminum alloy plate according to this embodiment includes B in addition to Ti. Ti and B are contained in the aluminum alloy plate by adding a rod hardener (grain refiner) such as Al-5% Ti-1% B in the manufacturing process of the aluminum alloy plate.

(Fe, Mn and Si: each less than 0.10% by mass)
The aluminum alloy plate according to the present embodiment limits the contents of Fe, Mn, and Si as impurities within the range of less than 0.10% by mass of the aluminum alloy plate, respectively. In this way, by regulating the contents of Fe, Mn, Si, etc., even in the thin slab continuous casting method described later, it is possible to keep the solid solution amount of these transition elements as small as possible in the state of the original slab. Become. Among Fe, Mn, and Si, Mn is an element that is easily dissolved in a matrix (matrix). For this reason, when the content of Mn in the original slab is 0.10% by mass or more, the 0.2% proof stress of the aluminum alloy plate becomes too high, and the shape freezing property may be lowered. Further, solute Mn and _Al 6 in the matrix (Fe · Mn), _Al 6 fine Mn-based precipitates such as Mn is, prevent the growth of Cube orientation crystal during final annealing. For this reason, when the Mn content is 0.10% by mass or more, solid solution Mn and fine Mn-based precipitates are generated in the matrix, thereby reducing the fracture limit in the plane strain region of the aluminum alloy plate. The press formability may be reduced. Therefore, the preferable Mn content is in the range of less than 0.04% by mass. A more preferable content of Mn is in a range of less than 0.02% by mass.

Fe is an element that is easily crystallized as an intermetallic compound during casting. When the content of Fe contained in the molten aluminum alloy is 0.10% by mass or more, the size of intermetallic compounds such as Al ₆ Fe and Al—Fe—Si that are crystallized during casting increases, and the aluminum alloy There is a possibility that formability may be reduced due to concentration of strain around a relatively coarse intermetallic compound during press forming of a plate. Therefore, the content of Fe in the aluminum alloy plate is limited to a range of less than 0.10% by mass.

  Si is crystallized as an intermetallic compound at the time of casting, and part of the element is a solid solution in the matrix in the original slab. If the Si content of the aluminum alloy plate is 0.10% by mass or more, the following problems may occur. That is, the size of the intermetallic compound such as Al-Fe-Si that crystallizes during casting becomes large, and the moldability is reduced due to the concentration of strain around the relatively coarse intermetallic compound during press forming of the aluminum alloy plate. There is a fear. Therefore, the Si content of the aluminum alloy plate is limited to a range of less than 0.10% by mass.

(Cu: 0.2% by mass or less)
In the aluminum alloy plate according to the present embodiment, Cu is an element that increases the strength and is an arbitrary element.

  Even if the aluminum alloy plate according to the present embodiment contains Cu in a range of 0.2% by mass or less, the effect of the present invention is not hindered. The preferable Cu content of the aluminum alloy plate is in the range of 0.03 to 0.2 mass%. A more preferable Cu content is in the range of 0.03 to 0.15 mass%. Furthermore, preferable Cu content exists in the range of 0.03-0.1 mass%. When the content of Cu in the aluminum alloy plate is less than 0.03% by mass, the effect of increasing the strength cannot be exhibited sufficiently. On the other hand, if the Cu content exceeds 0.2% by mass, the corrosion resistance of the aluminum alloy plate is lowered, which is not preferable.

(Inevitable impurities)
Inevitable impurities are inevitably mixed from raw metal, return material and the like. Examples of inevitable impurities include Cr, Zn, Ni, Ga, V, Pb, Bi, Sn, Na, Ca, and Sr. Inevitable impurities contained in the aluminum alloy sheet include, for example, Cr of less than 0.02% by mass, Zn of less than 0.10% by mass, Ni of less than 0.02% by mass, and Ga and V of 0.05. It is less than mass%. Moreover, the content of inevitable impurities allowable in the aluminum alloy plate is, for example, Pb, Bi, Sn, Na, Ca and Sr are each less than 0.02% by mass, and other elements are each less than 0.05% by mass. It is. Even if the aluminum alloy plate according to the present embodiment contains inevitable impurities in the above amount, the effect of the present invention is not hindered.

(Average crystal grain size: less than 30 μm)
The aluminum alloy plate according to this embodiment has an average crystal grain size of less than 30 μm. If the average crystal grain size is less than 30 μm, rough skin after press molding can be prevented, and a press-molded product having an excellent surface appearance can be obtained.

(Ratio of volume fraction of S orientation crystal to volume fraction of Cube orientation crystal: less than 0.3)
In the aluminum alloy plate according to the present embodiment, the ratio of the volume ratio of the S orientation crystal to the volume ratio of the Cube orientation crystal (volume ratio of the S orientation crystal / volume ratio of the Cube orientation crystal) is less than 0.3. When the ratio of the volume ratio of the S-oriented crystal to the volume ratio of the Cube-oriented crystal (volume ratio of the S-oriented crystal / volume ratio of the Cube-oriented crystal) is less than 0.3, a Taylor factor in so-called plane strain deformation (Taylor Factor) Therefore, the aluminum alloy plate is excellent in press formability.

(Volume ratio of Cube orientation crystal: 10-25%)
In the aluminum alloy plate according to the present embodiment, the volume ratio of Cube-oriented crystals is 10 to 25%. When the volume ratio of the Cube-oriented crystal is 10 to 25%, the Taylor factor in so-called plane strain deformation becomes small, and thus an aluminum alloy plate excellent in press formability is obtained. The volume ratio of the Cube-oriented crystal is preferably 12 to 25%. When the volume ratio of the Cube-oriented crystal is 12 to 25%, the Taylor factor in plane strain deformation becomes smaller, so that the aluminum alloy plate is more excellent in press formability.

  The aluminum alloy plate according to the present embodiment has the above-described composition, crystal grain size, and crystal orientation, and has a large tensile strength, elongation, and plane strain fracture limit, and a low yield strength. In addition, it shows that the amount of springback at the time of press molding becomes smaller and the shape freezing property is better as the proof stress is smaller.

  Therefore, the 5000 series aluminum alloy plate according to the present embodiment exhibits high strength, has excellent press formability and shape freezing property, and is suitable for uses such as body sheets for automobiles.

  Here, the high strength property of the aluminum alloy plate can be evaluated by the magnitude of the tensile strength when the tensile test is performed. Moreover, the press formability of an aluminum alloy plate can be evaluated by the numerical value of the plane strain fracture limit during a tensile test. Furthermore, the shape freezing property of the aluminum alloy plate can be evaluated by the yield strength during the tensile test. In addition, it shows that the amount of springback at the time of press molding becomes smaller and the shape freezing property is better as the proof stress is smaller.

  The aluminum alloy plate according to the present embodiment has the following numerical values such as tensile strength, yield strength, elongation, and plane strain fracture limit, and therefore is suitable for uses such as body sheets for automobiles.

(Tensile strength: 250 MPa or more)
The aluminum alloy plate according to this embodiment has a tensile strength of 250 MPa or more. When the tensile strength is 250 MPa or more, the aluminum alloy plate is suitable for uses such as automobile body sheets that require high strength.

(Yield strength: less than 130 MPa)
The aluminum alloy plate according to this embodiment has a yield strength of less than 130 MPa. The yield strength during the tensile test of the aluminum alloy sheet is an index for evaluating the shape freezing property. It shows that shape freezing property is so favorable that a yield strength is small. That is, the aluminum alloy plate according to the present embodiment has a good shape freezing property. When the proof stress is less than 130 MPa, the aluminum alloy plate is suitable for applications such as automobile body sheets that require good shape freezing properties.

(Elongation: 30% or more)
The aluminum alloy plate according to this embodiment has an elongation of 30% or more. When the elongation is 30% or more, the aluminum alloy plate is suitable for uses such as automobile body sheets that require high elongation.

(Plane strain fracture limit: 0.22 or more)
The aluminum alloy plate according to this embodiment has a plane strain fracture limit of 0.22 or more. A plane strain fracture limit of 0.22 or more is preferable because of excellent press formability. In the present specification, the fracture limit in the plane strain region is simply referred to as plane strain fracture limit.

  The aluminum alloy plate according to this embodiment is excellent in press formability and shape freezing property.

  The aluminum alloy plate according to the present embodiment is manufactured by, for example, the following method for manufacturing an aluminum alloy plate.

[Method for producing aluminum alloy sheet]
The manufacturing method of the aluminum alloy plate according to the present embodiment includes a first manufacturing method and a second manufacturing method. The difference between the first manufacturing method and the second manufacturing method is whether or not the intermediate annealing process is performed during the cold rolling process, and the other processes are substantially the same. Specifically, the first method is a method in which only the cold rolling process is continuously performed for several passes without performing the intermediate annealing step, and the second method is in the middle of the cold rolling process of several passes. This is a method of performing an intermediate annealing step. In this specification, the cold rolling process of the first method is referred to as a final cold rolling process. In the second method, the cold rolling process before the intermediate annealing process is called a primary cold rolling process, and the cold rolling process after the intermediate annealing process is called a final cold rolling process. Hereinafter, the first manufacturing method will be described in detail, and a part of the description of the second manufacturing method will be omitted or simplified.

(First manufacturing method)
The first manufacturing method includes a slab manufacturing process, a winding process, an annealing precipitation process, a final cold rolling process, and a final annealing process.

<Slab manufacturing process>
The slab manufacturing step is a step of continuously casting a molten aluminum alloy having a specific composition to obtain a slab having a thickness of 2 to 15 mm. The molten aluminum alloy used in the slab manufacturing process is a molten metal having the same composition as the aluminum alloy plate according to the present embodiment. For this reason, the description about the composition of the molten aluminum alloy is omitted.

  The molten aluminum alloy used in this process is cast into a slab using a thin slab continuous casting machine after the raw material is put into a melting furnace, through a melting and melting process, for example, as follows. .

  The melting / melting step is a step of melting a raw material to melt a molten aluminum alloy having a specific composition. As the melting / melting process, for example, the raw material is charged into a melting furnace, and when a predetermined melting temperature is reached, the flux is appropriately charged and stirred, and further, if necessary, degassing in the furnace using a lance or the like. After carrying out, a process of separating the soot from the surface of the molten metal by holding it calm is used.

  In this melting / melting step, in order to adjust the molten aluminum alloy to a specific alloy component, a raw material such as Mg is usually input, but may be input again as necessary. In the melting / melting process, it is extremely important to take a sufficient sedation time until the flux and soot float and separate from the molten aluminum alloy to the molten metal surface. The sedation time is usually 30 minutes or longer, preferably 45 minutes or longer.

  The molten aluminum alloy melted in the melting furnace is once transferred to a holding furnace and then cast, or directly discharged from the melting furnace and cast.

  In the melting / melting step, the molten aluminum alloy may be passed through an in-line degassing device or a filter as necessary. As the in-line degassing apparatus, for example, an apparatus in which an inert gas is blown into a molten aluminum from a rotating rotor, and hydrogen gas in the molten metal is diffused and removed in bubbles of the inert gas is used. When nitrogen gas is used as the inert gas, the dew point is controlled to, for example, −60 ° C. or lower.

  The ingot obtained through the melting and melting step has a hydrogen gas content of usually 0.20 cc / 100 g or less, preferably 0.15 cc / 100 g or less. If the amount of hydrogen gas contained in the ingot is large, porosity may occur in the final solidified portion of the ingot. For this reason, it is preferable to crush the porosity contained in the ingot by regulating the rolling reduction per pass in the cold rolling process to, for example, 20% or more. When the hydrogen gas content of the ingot is 0.15 cc / 100 g or less, swelling in the annealing precipitation treatment step can be prevented.

  In this step, the above molten aluminum alloy is continuously cast to obtain a slab having a thickness of 2 to 15 mm. Examples of a method for continuously casting the molten aluminum alloy include a method using a thin slab continuous casting machine.

  Next, a thin slab continuous casting machine and a continuous casting method using the same will be described. When a thin slab continuous casting machine is used, a thin slab having a thickness of 2 to 15 mm can be continuously cast from the molten aluminum alloy. Examples of the thin slab continuous casting machine used in this step include a twin belt casting machine and a twin roll casting machine.

  Here, the twin-belt casting machine is provided with a pair of rotating belt portions provided with an endless belt and facing each other, a cavity formed between the pair of rotating belt portions, and an inside of the rotating belt portion. And a cooling means, and a molten metal is supplied into the cavity through a nozzle made of a refractory to continuously cast a thin slab.

  In addition, the twin roll casting machine is provided with a pair of rotating roll parts provided with endless rolls and facing each other, a cavity formed between the pair of rotating roll parts, and an inside of the rotating roll part. A cooling means, and a molten metal is supplied into the cavity through a nozzle made of a refractory to continuously cast a thin slab.

  The thickness of the slab obtained by continuously casting the molten aluminum alloy is limited to a range of 2 to 15 mm. The preferred slab thickness is in the range of 3-12 mm. A more preferable slab thickness is in the range of 5 to 10 mm. When the slab thickness is less than 2 mm, it is difficult to obtain a final plate having a predetermined thickness when the final cold rolling rate is set to 70 to 95%. On the other hand, when the thickness of the slab exceeds 15 mm, it is difficult to wind the slab directly on the roll. When the thickness of the slab is in the range of 2 to 15 mm, the solidification cooling rate of the slab is preferably about 40 to 1000 ° C./sec in the vicinity of the slab thickness ¼.

Similar to the composition of the molten aluminum alloy, the slab produced using the thin slab continuous casting machine has contents of Fe, Mn, and Si as inevitable impurities, each less than 0.10% by mass. For this reason, the metal structure of the slab is a finely crystallized intermetallic compound such as Al ₆ Fe or Al—Fe—Si. For this reason, when the annealing precipitation process described below is performed on a slab produced using a thin slab continuous casting machine, transition elements such as Fe, Mn, and Si dissolved in the original slab are Al ₆ Fe, Al-Fe. Since it is diffused and absorbed by fine intermetallic compounds such as -Si and Al- (Fe.Mn) -Si, the solid solution amount of these transition elements can be further reduced.

  Thus, the solid solution amount of the transition element in the slab can be further reduced by the annealing precipitation process described later.

<Winding process>
The winding process is a process of winding the slab around a roll without hot rolling. At this process, it winds up on a roll as it is, without performing the hot rolling normally performed with respect to a slab.

<Annealing precipitation treatment process>
The annealing precipitation treatment step is a step of producing an annealing precipitation treatment material by holding the slab (coil) wound around the roll at a holding temperature of 380 to 470 ° C. for 1 to 15 hours using a batch annealing furnace.

The annealing precipitation treatment step is an important step for reducing the solid solution amount of Fe, Mn and Si dissolved in the matrix (matrix phase) in the first production method and the second production method described later. . Specifically, when an annealing precipitation treatment step is performed, Al ₆ Fe, Al—Fe that finely crystallizes transition elements such as Fe, Mn, and Si dissolved in the slab wound around the roll. It is diffused and absorbed by intermetallic compounds such as -Si and Al- (Fe.Mn) -Si. Thereby, the solid solution amount of transition elements such as Fe, Mn and Si in the slab can be reduced.

  As described above, the annealing precipitation treatment step can reduce the amount of the transition element in the slab in advance, so that it is possible to promote the growth of the Cube orientation crystal in the final annealing. Therefore, the final annealed plate finally obtained using this slab has an average crystal grain size of less than 30 μm, and the ratio of the volume ratio of the S-oriented crystal to the volume ratio of the Cube-oriented crystal (volume ratio of S-oriented crystal / Cube The volume ratio of the orientation crystal) is less than 0.3, and the volume ratio of the Cube orientation crystal is in the range of 10 to 25%. In the present specification, the final annealed plate is an aluminum alloy plate according to the present embodiment.

  As an annealing furnace used in the annealing precipitation treatment step, for example, a batch annealing furnace can be used. The holding temperature is limited to the range of 380 to 470 ° C. A preferable holding temperature is in the range of 400 to 450 ° C. If the holding temperature is less than 380 ° C., the amount of transition element dissolved cannot be sufficiently reduced. On the other hand, if the holding temperature exceeds 470 ° C., it takes too much time to cool the coil, and productivity is lowered, which is not preferable.

  The holding time in the annealing precipitation treatment step is limited to a range of 1 to 15 hours. Preferred holding times are in the range of 2 to 10 hours. If the holding time is less than 1 hour, the solid solution amount of the transition element may not be sufficiently reduced. On the other hand, when the holding time exceeds 15 hours, the productivity decreases.

  After completion of the annealing precipitation treatment step, the slab (coil) wound around the roll is passed through a cold rolling machine, and a cold rolling treatment is performed. This cold rolling process usually consists of several passes of cold rolling process. In the first method, the final cold rolling process is performed in which only the cold rolling process is continuously performed for several passes without performing the intermediate annealing process.

<Final cold rolling process>
The final cold rolling step is a step of obtaining the final cold rolled material by performing cold rolling with a final cold rolling rate of 70 to 95% on the annealed precipitation treated material. After the final cold rolling process, a final annealing process, which will be described later, is performed on the final cold rolled material.

  The final cold rolling rate of the final cold rolled material is limited to a range of 70 to 95%. A preferable final cold rolling rate is in the range of 70 to 90%. A more preferable final cold rolling rate is in the range of 70 to 85%. When the final cold rolling rate is in the range of 70 to 95%, a final annealed plate having an average crystal grain size of less than 30 μm can be obtained. As a result, the appearance skin of the aluminum alloy plate after press forming can be finished finely.

  If the final cold rolling rate is less than 70%, the amount of work strain accumulated during cold rolling is too small, and it becomes difficult to obtain a recrystallized structure having an average crystal grain size of less than 30 μm by final annealing. On the other hand, if the final cold rolling rate exceeds 95%, the amount of work strain accumulated during cold rolling is too large, and thus the edge cracks at the edges, making rolling difficult.

<Final annealing process>
The final annealing step is a step of obtaining a final annealed material by subjecting the final cold-rolled material to continuous annealing at a holding temperature of 400 to 500 ° C. for 10 to 60 seconds using a continuous annealing furnace. This final annealing material becomes the aluminum alloy plate according to the present embodiment.

  When the holding temperature is less than 400 ° C., recrystallization is delayed, and it becomes difficult to obtain a complete recrystallized structure having an average crystal grain size of less than 30 μm. On the other hand, when the holding temperature exceeds 500 ° C., thermal strain becomes severe and the plate during the continuous annealing process may be burned.

  If the holding time is less than 10 seconds, the actual temperature of the plate does not reach a predetermined temperature, and the annealing process may be insufficient. On the other hand, if the holding time exceeds 60 seconds, the process takes too much time and productivity is lowered. In the final annealing step, it is preferable to perform continuous annealing using a continuous annealing furnace.

  In the final annealing step, batch processing annealing using an annealing furnace or continuous annealing using a continuous annealing furnace is performed. Among these, continuous annealing using a continuous annealing furnace is preferable because it can be rapidly cooled after annealing.

  By subjecting the final cold-rolled sheet to a final annealing treatment, the average crystal grain size is less than 30 μm, and the ratio of the volume ratio of the S-oriented crystal to the volume ratio of the Cube-oriented crystal (volume ratio of the S-oriented crystal / volume ratio of the Cube-oriented crystal) ) Is less than 0.3, and a final annealed plate having a Cube-oriented crystal volume ratio of 10 to 25% can be obtained. Further, the final annealing step can also serve as a softening treatment for increasing the elongation.

  The aluminum alloy plate obtained through the final annealing step is an annealed material and has high press formability in the forming step.

(Second manufacturing method)
The second manufacturing method includes a slab manufacturing step, a winding step, an annealing precipitation treatment step, a primary cold rolling step, an intermediate annealing step, a final cold rolling step, and a final annealing step. Have.

  As compared with the first manufacturing method, the second manufacturing method replaces the final cold rolling step of the first manufacturing method with a primary cold rolling step, an intermediate annealing step, and a final cold rolling step. It differs in that it performs the process. For this reason, description of the 2nd manufacturing method abbreviate | omits or simplifies description about the process same as the process of 1st manufacturing method, and is about a primary cold rolling process, an intermediate annealing process, and a final cold rolling process. explain.

  In the second manufacturing method, the following first cold rolling step is performed after the slab manufacturing step to the annealing precipitation treatment step are performed as in the first manufacturing method.

<First cold rolling process>
A primary cold rolling process is a process of cold-rolling the said annealing precipitation treatment material obtained at the annealing precipitation treatment process, and obtaining a primary cold-rolled material. In addition, this primary cold rolling process is a cold rolling process performed before an intermediate annealing process, and distinguishes it from the below-mentioned cold rolling process (final cold rolling process) performed after an intermediate annealing process. Therefore, it is particularly called a primary cold rolling process. The cold rolling rate of the primary cold rolled material is limited to a range of 70 to 95%. The cold rolling rate of a preferable primary cold-rolled material is in the range of 80 to 90%. When the cold rolling rate of the primary cold rolled material is in the range of 70 to 95%, nuclei of Cube oriented crystals are generated during intermediate annealing, which is preferable.

<Intermediate annealing process>
The intermediate annealing step is a step of performing intermediate annealing on the primary cold rolled material to obtain an intermediate annealing material. This intermediate annealing process is a process in which the cold-rolled material that has become a rolling texture by the first cold rolling process described above is subjected to a partial annealing process that is held at a relatively low temperature to be partially recrystallized. In the first cold rolling process described above, the compressive stress in the ND direction and the tensile stress in the RD direction act on the cold-rolled material by the rolling roll, and a number of dislocations are introduced by plastic deformation. Dislocations are deposited in the vicinity of the region corresponding to the crystal grain boundaries. Therefore, in the intermediate annealing step, a large number of small recrystallized grains grow from the vicinity of the region corresponding to the crystal grain boundary of the original slab.

  Intermediate annealing is performed using a continuous annealing furnace or a batch annealing furnace. The treatment conditions for intermediate annealing vary depending on whether a continuous annealing furnace or a batch annealing furnace is used.

  When the intermediate annealing is continuous annealing using a continuous annealing furnace, the intermediate annealing step is preferably a step of holding the primary cold rolled material at a holding temperature of 250 to 350 ° C. for 10 to 60 seconds. A preferred holding temperature is in the range of 250-350 ° C. A more preferable holding temperature is in the range of 250 to 300 ° C.

  When the holding temperature is less than 250 ° C., partial recrystallization does not occur and the metal structure becomes an unrecrystallized structure, which is not preferable. On the other hand, if the holding temperature exceeds 350 ° C., recrystallization proceeds excessively, which is not preferable. If the holding time is less than 10 seconds, the temperature of the plate may be uneven, which is not preferable. If the holding time exceeds 60 seconds, productivity is lowered, which is not preferable.

  When the intermediate annealing is batch annealing using a batch annealing furnace, the intermediate annealing step is preferably a step of holding the primary cold rolled material at a holding temperature of 200 to 300 ° C. for 0.5 to 8 hours. A preferable holding temperature is in the range of 200 to 300 ° C. A more preferable holding temperature is in the range of 250 to 300 ° C.

  When the holding temperature is less than 200 ° C., partial recrystallization does not occur and the metal structure becomes an unrecrystallized structure, which is not preferable. On the other hand, when the holding temperature exceeds 300 ° C., recrystallization proceeds excessively, which is not preferable. If the holding time is less than 0.5 hours, the temperature of the coil may be non-uniform, which is not preferable. When the holding time exceeds 8 hours, productivity is not preferable.

  Through the intermediate annealing process as described above, many small recrystallized grains grow from the vicinity of the region corresponding to the grain boundary of the original slab, but many small recrystallized grains obtained by this partial annealing treatment However, the Cube orientation crystal does not grow preferentially.

<Final cold rolling process>
The final cold rolling step is a step of obtaining the final cold rolled material by performing cold rolling at a final cold rolling rate of 10 to 30% on the intermediate annealed material. In addition, this final cold rolling process is a cold rolling process performed after an intermediate annealing process, and is distinguished from the above-mentioned cold rolling process (primary cold rolling process) performed before an intermediate annealing process. Therefore, it is called the final cold rolling process. Since this final cold rolling process is the second cold rolling process in the second manufacturing method, it should be referred to as a secondary cold rolling process.

  The final cold rolling rate of the final cold rolled material is limited to a range of 10 to 30%. A preferable final cold rolling rate is in the range of 10 to 25%. A more preferable final cold rolling rate is in the range of 15 to 25%. When the final cold rolling rate is in the range of 10 to 30%, among the many small recrystallized grains obtained by the partial annealing described above, the Cube oriented crystal is maintained around its Cube oriented crystal while maintaining its crystal structure. Strain energy can be accumulated in this region, and the volume ratio of the Cube-oriented crystals can be increased by the final annealing process described later.

  If the final cold rolling rate is less than 10%, the amount of processing strain accumulated during cold rolling is too small, and the driving force necessary for crystal growth from the nucleus of the Cube orientation crystal is insufficient during final annealing. It becomes difficult to increase the volume ratio of the Cube orientation crystal in the plate. On the other hand, if the final cold rolling rate exceeds 30%, the crystal structure of the Cube orientation crystal formed in the metal structure by the intermediate annealing may be crushed by plastic deformation, leading to a decrease in the Cube orientation volume ratio in the final annealing plate. This is not preferable.

  In the final cold rolling as described above, among the large number of small recrystallized grains obtained by the above-mentioned partial annealing treatment, within the recrystallized grains that are Cube-oriented crystals, the Taylor factor in the so-called rolling process is small, and slipping occurs. The activity of dislocation is increasing. For this reason, the recrystallized grains that have been Cube-oriented crystals easily undergo slip deformation and can maintain their crystal structure even when subjected to rolling. In the region around the Cube orientation crystal, the metal structure has not been recrystallized although a certain degree of recovery has occurred due to the above-described partial annealing treatment. For this reason, dislocations are further deposited in the region around the Cube-oriented crystal even in the final cold rolling under relatively light pressure.

  On the other hand, among the many small recrystallized grains obtained by the above-mentioned partial annealing treatment, in the recrystallized grains other than the Cube orientation, the so-called rolling factor has a relatively large Taylor factor, and the slip dislocation activity Has fallen. For this reason, when the recrystallized grains that are oriented crystals other than the Cube orientation are subjected to a rolling process, the amount of dislocations introduced increases, making it difficult to maintain the crystal structure.

  After the final cold rolling step, the final annealing step is performed as in the first manufacturing method. In this final annealing process, among the many small recrystallized grains obtained by the above-mentioned partial annealing process, the recrystallized grains that were Cube orientation crystals acted as nuclei (seed crystals), and the surrounding area was recrystallized. Turn into. As described above, the region around the Cube-oriented crystal is not recrystallized even by the partial annealing treatment, and dislocations are further accumulated by the final cold rolling. Therefore, this strain energy becomes a driving force for recrystallization, and the growth of the Cube-oriented crystal is promoted.

  On the other hand, among the many small recrystallized grains obtained by the above-mentioned partial annealing treatment, in the recrystallized grains that are orientation crystals other than the Cube orientation, many dislocations are deposited in the crystal structure by the final cold rolling. ing. For this reason, the recrystallized grains that were orientation crystals other than the Cube orientation are less likely to act as nuclei (seed crystals) during the final annealing treatment.

  As described above, according to the second manufacturing method, it is possible to further increase the volume ratio of the Cube orientation crystal in the final annealed plate, the average crystal grain size is less than 30 μm, and the S orientation crystal with respect to the volume ratio of the Cube orientation crystal. A final annealed plate having a volume ratio (volume ratio of S-oriented crystals / volume ratio of Cube-oriented crystals) of less than 0.3 and a volume ratio of Cube-oriented crystals of 10 to 25% can be obtained.

  According to the aluminum alloy plate manufacturing method according to the present embodiment (the first manufacturing method and the second manufacturing method), an aluminum alloy plate excellent in press formability and shape freezing property can be efficiently manufactured.

  The aluminum alloy plate of the present invention is suitable as a vehicle body panel and a structural member. For example, it is suitable as outer panels, inner panels, and reinforcements such as the hood 10, the door 11, the fender 12, the roof 13, and the trunk 14 shown in FIG.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.

(Preparation of original slab material)
An alloy melt having the composition shown in Table 1 (alloys No. 1 to No. 6) is melted, and a thin slab having a thickness of 10 mm is continuously cast (CC casting) by a twin belt casting machine, and this thin slab is directly used as a coil. Winded up. Next, a slab material (original slab material) having a predetermined size was collected from the thin slab. Alloy No. 4-No. The original slab material No. 6 is an original slab material whose component composition is outside the specified range of the present invention. In the following examples and comparative examples, these original slab materials were used as raw materials.

[Example 1]
First, alloy no. After inserting the original slab material No. 1 into the annealer and performing annealing precipitation treatment at 440 ° C. for 10 hours, cold rolling was performed without intermediate annealing treatment to obtain a final cold rolled material having a thickness of 1.0 mm. Obtained. In this case, the final cold rolling rate of the final cold rolled material was 90%.

  Next, after cutting this final cold-rolled material into a predetermined size, the final cold-rolled material is inserted into a salt bath to simulate the final annealing treatment by continuous annealing, and held at 460 ° C. for 15 seconds, and then from the salt bath. The final annealing process which took out rapidly and water-cooled was performed, and the final annealing board with a board thickness of 1.0 mm was obtained. Table 2 shows the manufacturing conditions. The production conditions of the following examples and comparative examples are also shown in Table 2.

[Example 2]
First, alloy no. No. 1 slab material was inserted into an annealer and annealed at 440 ° C. for 10 hours, followed by cold rolling to obtain a primary cold rolled material having a thickness of 1.33 mm.

  Next, this primary cold-rolled material is inserted into a salt bath and held at 290 ° C. for 15 seconds, and then subjected to an intermediate annealing treatment in which it is quickly taken out from the salt bath and water-cooled, and then the final cold-rolling rate is 25%. Cold rolling was performed to obtain a final cold rolled material having a thickness of 1.0 mm.

  Furthermore, after cutting this final cold-rolled material to a predetermined size, the final cold-rolled material is inserted into a salt bath simulating the final annealing process by continuous annealing, held at 460 ° C. for 15 seconds, and then quickly removed from the salt bath. The final annealing process which took out and water-cooled was performed, and the final annealing board with a board thickness of 1.0 mm was obtained.

[Example 3]
Alloy No. In place of the original slab material No. 1 A final annealed plate having a thickness of 1.0 mm was obtained in the same manner as in Example 2 except that the original slab material No. 2 was used.

[Example 4]
First, alloy no. The original slab material No. 2 was inserted into an annealer and subjected to annealing precipitation treatment at 440 ° C. for 10 hours, followed by cold rolling to obtain a primary cold rolled material having a plate thickness of 1.25 mm.

  Next, after inserting this primary cold-rolled material into an annealer and holding it at 240 ° C. for 1 hour, after performing an intermediate annealing treatment to air-cool, perform cold rolling with a final cold rolling rate of 20%, A final cold rolled material having a thickness of 1.0 mm was obtained.

  Furthermore, after cutting this final cold-rolled material to a predetermined size, the final cold-rolled material is inserted into a salt bath simulating the final annealing process by continuous annealing, held at 460 ° C. for 15 seconds, and then quickly removed from the salt bath. The final annealing process which took out and water-cooled was performed, and the final annealing board with a board thickness of 1.0 mm was obtained.

[Example 5]
Alloy No. In place of the original slab material No. 1 A final annealed plate having a thickness of 1.0 mm was obtained in the same manner as in Example 2 except that the former 3 slab material was used.

[Example 6]
Alloy No. In place of the original slab material No. 2, alloy no. A final annealed plate having a thickness of 1.0 mm was obtained in the same manner as in Example 4 except that the former 3 slab material was used.

[Comparative Example 1]
First, alloy no. No. 1 slab material was used, and cold rolling with a final cold rolling rate of 90% was performed without performing annealing precipitation treatment and intermediate annealing treatment to obtain a cold rolled material having a plate thickness of 1.0 mm. Next, after cutting this final cold-rolled material into a predetermined size, the final cold-rolled material is inserted into a salt bath to simulate the final annealing treatment by continuous annealing, and held at 460 ° C. for 15 seconds, and then from the salt bath. The final annealing process which took out rapidly and water-cooled was performed, and the final annealing board with a board thickness of 1.0 mm was obtained.

[Comparative Example 2]
Alloy No. In place of the original slab material No. 1 A final annealed plate having a thickness of 1.0 mm was obtained in the same manner as in Comparative Example 1 except that the original slab material of No. 4 was used.

[Comparative Example 3]
First, alloy no. No. 4 slab material was used, and cold rolling with a final cold rolling rate of 90% was performed without performing annealing precipitation treatment and intermediate annealing treatment to obtain a cold rolled material having a plate thickness of 1.0 mm.

  Next, after cutting this cold-rolled material to a predetermined size, the cold-rolled material is inserted into an annealer, imitating the final annealing process by batch annealing, held at 390 ° C. for 1 hour, and then furnace-cooled to 200 ° C. Furthermore, the final annealing process which air-cools was performed, and the final annealing board with a board thickness of 1.0 mm was obtained.

[Comparative Example 4]
Alloy No. In place of the original slab material No. 1 A final annealed plate having a plate thickness of 1.0 mm was obtained in the same manner as in Example 1 except that No. 4 original slab material was used. The final cold rolling rate of the cold rolled material was 90%.
[Comparative Example 5]
Alloy No. In place of the original slab material No. 1 A final annealed plate having a thickness of 1.0 mm was obtained in the same manner as in Example 1 except that the original slab material of No. 5 was used. The final cold rolling rate of the cold rolled material was 90%.

[Comparative Example 6]
Alloy No. In place of the original slab material No. 1 A final annealed plate having a thickness of 1.0 mm was obtained in the same manner as in Comparative Example 1 except that the original slab material No. 6 was used. The final cold rolling rate of the cold rolled material was 90%.

(Evaluation)
About the aluminum alloy plates of the above examples and comparative examples, tensile properties (tensile strength, 0.2% yield strength, elongation), average crystal grain size, crystal orientation, plane strain fracture limit, skin roughness are as follows. , Strength, shape freezing property, and press formability were evaluated.

<Tensile properties>
The obtained aluminum alloy sheet was measured for tensile strength (UTS), 0.2% yield strength (YS), and elongation (El) in a tensile test.

  Specifically, first, JIS No. 5 tensile test pieces were collected from the aluminum alloy sheet along three directions of the rolling parallel direction, the vertical direction, and the 45 ° direction.

Next, using a 50 kN autograph, at room temperature, the tensile test piece is pulled at a strain rate of 6.7 × 10 ⁻⁴ / sec in the region of 0.2% proof stress or less, and the region exceeds 0.2% proof stress. Then, it was pulled at a strain rate of 3.3 × 10 ⁻³ / sec. And the tensile strength (UTS) and 0.2% yield strength (YS) at this time were measured. Further, the elongation (%) is {(length L _{1 obtained} by joining tensile test pieces broken at the time of measuring tensile strength) − (length L ₀ of tensile test pieces before measuring tensile strength)} / (Length L ₀ of tensile test piece before measurement of tensile strength) × 100.

<Average crystal grain size>
First, a specimen was cut out from the obtained aluminum alloy sheet so that a longitudinal section parallel to the rolling direction of the aluminum alloy sheet (longitudinal section perpendicular to the LT direction) was observed. Next, this specimen is embedded in a thermoplastic resin, and the longitudinal section is mirror-polished, and then anodized in a borohydrofluoric acid aqueous solution, so that the recrystallized structure of the longitudinal section of the specimen can be clearly observed. I did it. When observing the recrystallized structure, the recrystallized structure is photographed using a polarizing microscope (area per field of view; 0.135 mm ² , 3 fields of view of each sample), and the crossing method is used from the obtained photographs. The average crystal grain size was measured.

<Crystal orientation>
The crystal orientation was measured using an EBSD (Electron Backscatter Diffraction) method.

  Specifically, first, a specimen was cut out from the obtained aluminum alloy sheet so that a longitudinal section parallel to the rolling direction (longitudinal section perpendicular to the LT direction) was observed. Next, after mirror-polishing the longitudinal section of this specimen, the polished surface was electrolytically polished to remove distortion caused by polishing.

  About the obtained test piece, the crystal orientation was measured using EBSD. Specifically, JSM6490A manufactured by JEOL Ltd. was used as the scanning electron microscope, and the acceleration voltage was set to 15 kV, the WD was 3 mm, and the sample tilt angle was 65 °. Then, an OIM type manufactured by TSL Solutions Inc. was used, and a 400 μm × 800 μm region was measured in 2 μm steps. The obtained results were analyzed by analysis software (OIM analysis), and the volume fraction of the Cube orientation crystal and the volume fraction of the S orientation crystal were obtained. Here, the Cube orientation was set to an orientation in the range of 15 ° from {100} <100>. The S direction was set to a range of 15 ° from {123} <634>.

  FIG. 2 is a diagram illustrating an example of a crystal orientation measurement result by EBSD of Example 2. FIG. 3 is a diagram showing an example of the crystal orientation measurement result by EBSD of Comparative Example 1. 2 and 3, reference numeral 20 denotes a Cube-oriented crystal.

<Plane strain fracture limit>
First, the test piece 40 shown in FIG. 4 was cut out from the obtained aluminum alloy plate as a test piece for measuring the plane strain fracture limit. 4 is a plan view of the test piece 40, and the thickness direction of the test piece 40 is perpendicular to the paper surface of FIG. Three types of test pieces 40 were produced by changing the method of cutting out from the aluminum alloy plate. Specifically, the aluminum is so arranged that the tensile direction (longitudinal direction, the direction of length of 200 mm in FIG. 4) is three directions, a direction parallel to the rolling direction, a 45 ° direction, and a 90 ° direction. A specimen was cut out from the alloy plate. A circular pattern of φ10 mm for the scribed circle test was drawn at the center of each of these test pieces.

Next, using these three types of test pieces, a tensile test was performed at a strain rate of 10 ⁻³ / sec. After the tensile test, the strain in the tensile direction (maximum strain) and the strain in the width direction at a plurality of measurement points in the center portion of the test piece and within a range of about 20 mm from the vicinity of the fracture portion were read from the scribed circle.

The major axis of the scribed circle extending in the pulling direction was deformed diameter d _1. Then, the true strain e at the plurality of measurement points is calculated by applying the post-deformation diameter d ₁ and the pre-deformation diameter d ₀ (10 mm) of the plurality of measurement points to the following equation (1). did.
_{e = Ln (d 1 / d} 0) (1)
(E: true strain, d ₁ : diameter after deformation, d ₀ : diameter before deformation)

On the other hand, using a point micrometer, the plate thickness strain was measured about every 1 mm from the vicinity of the fracture portion of the test piece. And the area | region of the uniform elongation of the test piece was specified from the strain distribution created based on the measured value of plate thickness distortion. Of the maximum strain value of a plurality of measurement points in the uniform elongation in the region, the largest maximum distortion value, and a plane strain fracture limit e _c.

The measurement of plane-strain fracture limit e _c was performed by 3 types of each 3 times for each specimen (n = 3).

Specifically, the tensile direction (longitudinal direction) of the plane strain fracture limit (rolling direction parallel with the test piece formed in a direction measured three times a plane strain fracture limit e _c, the average value to the rolling direction ) was _{e L.} The tensile direction (longitudinal direction) is 45 ° with a test piece formed in a direction measured three times a plane strain fracture limit e _c, the average value of the plane strain fracture limit (rolling direction 45 °) to the rolling direction e _X. Furthermore, the tensile direction (longitudinal direction) is 90 ° with a test piece formed in a direction measured three times a plane strain fracture limit e _c, the plane average breaking strain limit (rolling direction 90 °) to the rolling direction e _LT .

The plane strain rupture limit (rolling direction) e _L , the plane strain rupture limit (rolling direction 45 °) e _X , and the plane strain rupture limit (rolling direction 90 °) e _LT are applied to the following formula (2): The plane strain rupture limit (average value) e _ave was calculated.
e _ave. = (e _L + e _LT + 2e _X ) / 4 (2)
(E _ave .: Plane strain fracture limit (average value), e _L : plane strain fracture limit (rolling direction), e _LT : plane strain fracture limit (rolling direction 90 °) _, e _X : plane strain fracture limit (rolling direction) 45 °))

<Skin roughness>
About the test piece which measured the plane strain fracture | rupture limit, the visual evaluation which visually confirms the presence or absence of an orange peel (Yuzu skin) was performed about the scribed circle nearest to the crack part and not contacting the crack part. Here, the orange peel is a surface pattern having small irregularities generated on the surface of a test piece when a tensile test or stretch forming is performed on a metal such as an Al—Mg alloy. In an Al—Mg alloy, orange peel generally tends to occur as the Mg concentration increases. Those in which no orange peel was observed were evaluated as having good skin roughness (◯), and those in which orange peel was observed were evaluated as having poor skin roughness (×).

<Strength>
The tensile strength was measured using the test piece. Those having a tensile strength of 250 MPa or more were evaluated as having good strength (◯), and those having a tensile strength of less than 250 MPa were evaluated as having poor strength (x).

<Shape freezing>
The 0.2% proof stress was measured using the test piece. Those having a 0.2% proof stress of less than 130 MPa were evaluated as having good shape freezing properties (◯), and those having a 0.2% proof stress of 130 MPa or higher were evaluated as having poor shape freezing properties (×).

<Press formability>
The press formability was evaluated from the average value e _ave of the plane strain rupture limit. When the average value e _ave of the plane strain rupture limit is 0.22 or more, the press formability is evaluated as good (◯), and when the average value e _ave of the plane strain rupture limit is less than 0.22, the press formability is It was evaluated as defective (x).

<Comprehensive evaluation>
What was evaluated as good (◯) in all items of rough skin property, strength, shape freezing property, and press formability was evaluated as good (◯). Of the rough skin, the strength, the shape freezing property, and the press formability, one that was evaluated as defective (×) was evaluated as being poor (×).

  Table 3 shows the results of tensile properties (tensile strength, 0.2% proof stress, elongation), average crystal grain size, crystal orientation, plane strain breaking limit, skin roughness, strength, shape freezing property, and press formability. .

  In Examples 1 to 6, the alloy composition is within the scope of the present invention, and the production conditions are within the scope of the present invention. Examples 1-6 were favorable ((circle)) in all the evaluation items of rough skin property, intensity | strength, shape freezing property, and press moldability, and the comprehensive evaluation was favorable ((circle)).

  In Comparative Example 1, the alloy composition was within the range of the present invention, but since the annealing precipitation treatment was not performed, the evaluation of press formability was poor (x).

  In Comparative Example 2, the alloy composition had a low Mg content, and the Fe and Mn contents were too high, and because the annealing precipitation treatment was not performed, the shape freezeability and press formability were poorly evaluated (× )Met.

  Further, in Comparative Example 3, the Mg content in the alloy composition was low, the Fe and Mn contents were too high, and the annealing precipitation treatment was not performed, and the final annealing treatment was performed by batch annealing in an annealer. Therefore, the evaluation of shape freezing property and press formability was poor (x).

  In Comparative Example 4, the Mg content in the alloy composition was low, and the Fe and Mn contents were too high. Therefore, although the annealing precipitation treatment was performed, the evaluation of shape freezeability and press formability was poor (x). It was.

  Further, in Comparative Example 5, since the Fe content was too high in the alloy composition, the annealing process was performed, but the evaluation of press formability was poor (x).

  Further, in Comparative Example 6, since the Fe and Mn contents were too high in the alloy composition and the annealing precipitation treatment was not performed, the evaluation of shape freezing property and press formability was poor (x).

From the above results, within the range of the component composition of the present invention, the ratio of the volume ratio of the S-oriented crystal to the volume ratio of the Cube-oriented crystal (the volume ratio of the S-oriented crystal / Cube is set to less than 30 μm). By having a recrystallized structure in which the volume ratio of the orientation crystal is less than 0.3 and the volume ratio of the Cube orientation crystal is in the range of 10 to 25%, the tensile strength is 250 MPa or more, the proof stress is less than 130 MPa, the elongation is 30% or more, It can be seen that the characteristic that the plane strain breaking limit at a strain rate of 10 ⁻³ / sec is 0.22 or more can be exhibited.

  The entire contents of Japanese Patent Application No. 2014-133554 (application date: June 30, 2014) are incorporated herein by reference.

  As mentioned above, although this invention was demonstrated by embodiment, this invention is not limited to these, A various deformation | transformation is possible within the range of the summary of this invention.

  The aluminum alloy plate according to the present invention can be used for automobile body sheets and the like. The method for manufacturing an aluminum alloy plate according to the present invention can be used for manufacturing body sheets for automobiles and the like.

20 Cube orientation crystal 40 test piece

Claims (8)

Mg contains 4.0 to 5.5 mass%, Ti contains 0.005 to 0.10 mass%, and the contents of Fe, Mn, and Si as impurities are each less than 0.10 mass%, and The balance is an aluminum alloy plate made of Al and inevitable impurities,
The average crystal grain size is less than 30 μm, the ratio of the volume ratio of the S orientation crystal to the volume ratio of the Cube orientation crystal (volume ratio of the S orientation crystal / volume ratio of the Cube orientation crystal) is less than 0.3, and the volume ratio of the Cube orientation crystal Is 10-25%,
An aluminum alloy sheet having a tensile strength of 250 MPa or more, a proof stress of less than 130 MPa, an elongation of 30% or more, and a plane strain breaking limit of 0.22 or more.   The aluminum alloy plate according to claim 1, further comprising 0.03 to 0.2% by mass of Cu. A manufacturing method for manufacturing the aluminum alloy plate according to claim 1,
Mg contains 4.0 to 5.5 mass%, Ti contains 0.005 to 0.10 mass%, and the contents of Fe, Mn, and Si as impurities are each less than 0.10 mass%, and A slab manufacturing step of continuously casting a molten aluminum alloy composed of Al and inevitable impurities to obtain a slab having a thickness of 2 to 15 mm;
A winding step of winding the slab on a roll without hot rolling;
An annealing precipitation treatment step in which the slab wound around the roll is held at a holding temperature of 380 to 470 ° C. for 1 to 15 hours to produce an annealing precipitation treatment material,
A final cold rolling step of obtaining a final cold rolled material by performing cold rolling at a final cold rolling rate of 70 to 95% on the annealed precipitation treated material;
A final annealing step in which the final cold rolled material is subjected to final annealing for 10 to 60 seconds at a holding temperature of 400 to 500 ° C. to obtain a final annealed material;
A method for producing an aluminum alloy plate, comprising:   The said aluminum alloy molten metal contains 0.03-0.2 mass% of Cu further, The manufacturing method of the aluminum alloy plate of Claim 3 characterized by the above-mentioned. A manufacturing method for manufacturing the aluminum alloy plate according to claim 1,
Mg contains 4.0 to 5.5 mass%, Ti contains 0.005 to 0.10 mass%, and the contents of Fe, Mn, and Si as impurities are each less than 0.10 mass%, and A slab manufacturing step of continuously casting a molten aluminum alloy composed of Al and inevitable impurities to obtain a slab having a thickness of 2 to 15 mm;
A winding step of winding the slab on a roll without hot rolling;
An annealing precipitation treatment step in which the slab wound around the roll is held at a holding temperature of 380 to 470 ° C. for 1 to 15 hours to obtain an annealing precipitation treatment material,
A first cold rolling step of cold rolling the annealed precipitation treated material to obtain a primary cold rolled material;
An intermediate annealing step for obtaining an intermediate annealing material by performing an intermediate annealing on the primary cold-rolled material;
A final cold rolling step of obtaining a final cold rolled material by performing cold rolling at a final cold rolling rate of 10 to 30% on the intermediate annealed material;
A final annealing step in which the final cold rolled material is subjected to final annealing for 10 to 60 seconds at a holding temperature of 400 to 500 ° C. to obtain a final annealed material;
A method for producing an aluminum alloy plate, comprising:   The said aluminum alloy molten metal contains 0.03-0.2 mass% of Cu further, The manufacturing method of the aluminum alloy plate of Claim 5 characterized by the above-mentioned.   The said intermediate annealing process hold | maintains for 10 to 60 second with the holding temperature of 250-350 degreeC using a continuous annealing furnace, The manufacturing method of the aluminum alloy plate of Claim 5 or 6 characterized by the above-mentioned.   The method for producing an aluminum alloy plate according to claim 5 or 6, wherein the intermediate annealing step is carried out at a holding temperature of 200 to 300 ° C for 0.5 to 8 hours using a batch furnace.