EP1492895B1 - Al-zn-mg-cu alloy products - Google Patents

Abstract

The invention relates to alloys and associated products which are laminated, extruded or forged in Al-Zn-Mg-Cu alloy. Alloys of the invention generally comprise (in mass percentage): a) Zn 8.3-14.0=Cu 0.3-4.0=Mg 0.5-4.5 Zr 0.03-0.15 Fe+Si<0.25 b) at least one element selected from the group consisting of Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y and Yb, the content of each elements; if included, being between 0.02 and 0.7%, and c) the aluminum remainder and inevitable impurities, and wherein Mg/Cu<2.4 and (7.7-0.4 Zn)>(Cu+Mg)>(6.4-0.4 Zn). Products of the present invention are useful as structural elements (for example wing unit caisson, wing unit extrados) in aeronautical construction.

Description

Technical field of the invention

The present invention relates to alloys of Al-Zn-Mg-Cu type with compromised static mechanical characteristics - improved damage tolerance, with a Zn content greater than 8.3%, as well as structural elements for aeronautical construction incorporating half wrought products made from these alloys.

State of the art

Al-Zn-Mg-Cu alloys (belonging to the family of 7xxx alloys) are commonly used in aircraft construction, and in particular in the construction of civil aircraft wings. For the extrados of the wings is used for example a skin made of alloy plates 7150, 7055, 7449, and possibly stiffeners profiles in alloys 7150, 7055, or 7449. These alloy designations, well known to the man of business, correspond to those of The Aluminum Association.

Some of these alloys have been known for decades, such as alloys 7075 and 7175 (zinc content between 5.1 and 6.1% by weight), 7050 (zinc content between 5.7 and 6.7%). , 7150 (zinc content between 5.9 and 6.9%) and 7049 (zinc content between 7.2 and 8.2%). They have a high yield strength, good toughness and good resistance to stress corrosion and exfoliating corrosion. More recently, it has been found that for certain applications, the use of an alloy with a higher zinc content may have advantages because it makes it possible to further increase the yield strength. Alloys 7349 and 7449 contain between 7.5 and 8.7% zinc. of the Wrought alloys richer in zinc have been described in the literature, but do not appear to be used in aeronautical construction.
The patent US5,560,789 (Pechiney Research) discloses an alloy of composition Zn 10.7%, Mg 2.84%, Cu 0.92% which is processed by spinning. These alloys are not optimized specifically for a compromise static mechanical characteristics - toughness.
The patent US5,221,377 (Aluminum Company of America) discloses several Al-Zn-Mg-Cu alloys with a zinc content up to 11.4%. These alloys, as will be explained below, do not meet the objectives of the present invention either.

In addition, it has been proposed to use Al-Zn-Mg-Cu alloys with a high zinc content for the manufacture of hollow bodies designed to withstand high pressures, such as for example compressed gas bottles. The European patent application EP 020 282 A1 (Société Metallurgique de Gerzat) discloses alloys with a zinc content of between 7.6% and 9.5%. The European patent application EP 081 441 A1 (Société Métallurgique de Gerzat) discloses a process for obtaining such bottles. The European patent application EP 257 167 A1 (Société Métallurgique de Gerzat) notes that none of the known Al-Zn-Mg-Cu type alloys satisfies in a reliable and reproducible manner the severe technical requirements imposed by this specific application; it proposes to move towards a lower zinc content, namely between 6.25% and 8.0%.
The teaching of these patents is specific to the problem of compressed gas bottles, in particular as regards the maximization of the bursting pressure of these bottles, and can not be transferred to other wrought products.

Generally speaking, in Al-Zn-Mg-Cu type alloys, a high content of zinc, but also of Mg and Cu is necessary to obtain good static mechanical characteristics (yield strength, ultimate strength). . But he is also well known (see for example US5,221,377 ) that when the zinc content in an alloy of the 7xxx family is increased beyond about 7 to 8%, problems related to resistance to exfoliating corrosion and stress corrosion are encountered insufficient. More generally, it is known that the most heavily loaded Al-Zn-Mg-Cu alloys are likely to cause corrosion problems. These problems are generally solved by means of special thermal or thermomechanical treatments, in particular by pushing the treatment of income beyond the peak, for example during a treatment of the T7 type. But these treatments can then lead to a decrease in static mechanical characteristics. In other words, for a desired minimum level of corrosion resistance, the optimization of an Al-Zn-Mg-Cu type alloy must seek a compromise between the static mechanical characteristics (elastic limit R _p0,2 , limit at rupture R _m , elongation at break A) and the characteristics of damage tolerance (toughness, speed of propagation of cracks, etc.). According to the minimum level of corrosion resistance aimed at, a state close to the income peak (T6 states) is used, which in general offers a toughness compromise - R _p0.2 emphasizing the static mechanical characteristics, or the income is pushed beyond the peak (T7 states), seeking a compromise that favors tenacity. These metallurgical states are defined in the EN 515 standard.

Problem

The problem to which the present invention attempts to respond is therefore to propose new wrought products of high zinc content Al-Zn-Mg-Cu type alloy, greater than 8.3%, which are characterized by an improved compromise between toughness. and static mechanical characteristics (ultimate strength, yield strength), which have sufficient corrosion resistance and high elongation, and which can be industrially manufactured under conditions of reliability compatible with the high demands of the industry aeronautics.

Objects of the invention

The Applicant has found that the problem can be solved by adjusting the concentration of the Zn, Cu and Mg addition elements and certain impurities (especially Fe and Si) in a fine way, and possibly adding other elements.

1. a) Zn 8,3 - 14,0 Cu 0,3 - 4,0 et préférentiellement 0,3 - 3,0
   Mg 0,5 - 4,5 et préférentiellement 0,5 - 3,0
   Zr 0,03 - 0,15 Fe + Si < 0,25
2. b) au moins un élément sélectionné dans le groupe composé de Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, la teneur de chacun desdits éléments, s'il est sélectionné, étant comprise entre 0,02 et 0,7%,
3. c) le reste aluminium et impuretés inévitables,
   et en qu'il satisfait aux conditions
4. d) Mg / Cu < 2,4 et
5. e) (7,7 - 0,4 Zn) > (Cu + Mg) > (6,4 - 0,4 Zn).

A first object of the present invention is constituted by a rolled, spun or forged product made of Al-Zn-Mg-Cu alloy, characterized in that it contains (in percent by mass):

1. a) Zn 8.3 - 14.0 Cu 0.3 - 4.0 and preferably 0.3 - 3.0
   Mg 0.5 - 4.5 and preferably 0.5 - 3.0
   Zr 0.03 - 0.15 Fe + Si <0.25
2. b) at least one element selected from the group consisting of Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, the content of each of said elements, if is selected, being between 0.02 and 0.7%,
3. (c) the remaining aluminum and unavoidable impurities,
   and that he satisfies the conditions
4. d) Mg / Cu <2.4 and
5. e) (7.7 - 0.4 Zn)> (Cu + Mg)> (6.4 - 0.4 Zn).

1. a) Zn 9,5 - 14,0 Cu 0,3 - 4,0 et préférentiellement 0,3 - 3,0
   Mg 0,5 - 4,5 et préférentiellement 0,5 - 3,0
   Fe + Si < 0,25
2. b) au moins un élément sélectionné dans le groupe composé de Zr, Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, Cr, Mn, la teneur de chacun desdits éléments, s'il est sélectionné, étant comprise entre 0,02 et 0,7 % ,
3. c) le reste aluminium et impuretés inévitables,
   et en ce qu'il satisfait les conditions
4. d) Mg / Cu < 2,4 et
5. e) (7,7 - 0,4 Zn) > (Cu + Mg) > (6,4 - 0,4 Zn).

A second object of the present invention is constituted by a rolled, spun or forged product made of Al-Zn-Mg-Cu alloy, characterized in that it contains (in percent by mass):

1. a) Zn 9.5 - 14.0 Cu 0.3 - 4.0 and preferably 0.3 - 3.0
   Mg 0.5 - 4.5 and preferably 0.5 - 3.0
   Fe + Si <0.25
2. b) at least one element selected from the group consisting of Zr, Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, Cr, Mn, the content of each said elements, if selected, being between 0.02 and 0.7%,
3. (c) the remaining aluminum and unavoidable impurities,
   and in that it satisfies the conditions
4. d) Mg / Cu <2.4 and
5. e) (7.7 - 0.4 Zn)> (Cu + Mg)> (6.4 - 0.4 Zn).

A third object of the present invention is a structural element for aircraft construction which incorporates one of said products, including a structural element used in the construction of the wing boxes of civil aircraft, such as a wing extrados.

Description of figures

The figure 1 schematically shows a wing box of an airplane.

The landmarks are: 1, 4 extrados 2 intrados 3 spar 5 Stiffener 6 Box height 7 Width of the box

The figure 2 represents the mechanical resistance - damage tolerance compromise in an R _p0.2 - K _app diagram for the alloys of Example 3.
The figure 3 represents the mechanical resistance - damage tolerance compromise in an R _p0.2 - K _app diagram for the alloys of Example 5.

Detailed description of the invention

Unless stated otherwise, all the information relating to the chemical composition of the alloys is expressed in percent by weight. Therefore, in a mathematical expression, "0.4 Zn" means: 0.4 times the zinc content, expressed in mass percent; this applies mutatis mutandis to other chemical elements. The designation of the alloys follows the rules of The Aluminum Association. The metallurgical states are defined in the European standard EN 515. Unless stated otherwise, the static mechanical characteristics, that is to say the breaking strength R _m , the yield strength R _p0,2 , and the elongation at the rupture A, are determined by a tensile test according to EN 10002-1. The static mechanical characteristics in compression were determined according to the ASTM E9 standard. The K _IC toughness in planar deformations was determined according to the ASTM E399 standard. The K _app parameter was measured according to ASTM E561 standard on CT type specimens of W width equal to 127 mm. The term "spun product" includes so-called "stretched" products, i.e., products that are made by spinning followed by stretching.

The applicant, in a number of preparatory studies, has come to the conclusion that a new material with a significantly better compromise should in any case have a sufficient zinc content, typically greater than about 8.3. %. This condition is not enough, however.

According to the invention, the problem is solved by finely adjusting the contents of the alloying elements and certain impurities, and by adding a controlled concentration of certain other elements to the composition of the alloy.

• Zn 8,3-14,0   Cu 0,3-4,0   Mg 0,5-4,5

ainsi que certains autres éléments spécifiés ci-dessous, et le reste étant l'aluminium avec ses impuretés inévitables.The present invention applies to Al-Zn-Mg-Cu alloys containing:

• Zn 8.3-14.0 Cu 0.3-4.0 Mg 0.5-4.5

as well as some other elements specified below, and the rest being aluminum with its inevitable impurities.

The alloys according to the invention must contain at least 0.5% magnesium, since it is not possible to obtain satisfactory static mechanical characteristics with a lower magnesium content. According to the findings of the applicant, with a zinc content of less than 8.3%, one does not obtain a result that is better than those obtained with known alloys. Preferably, the zinc content is greater than 9.0%, and even more preferably greater than 9.5%. However, it is necessary to respect certain relationships between certain elements, as explained later. In another advantageous embodiment, the zinc content is between 9.0 and 11.0%. In any case, we do not want to exceed a zinc content of about 14%, because beyond this value, regardless of the magnesium and copper content, the results are not satisfactory.

The addition of at least 0.3% copper improves corrosion resistance. But to ensure a satisfactory dissolution, the Cu content should not exceed about 4%, and the Mg content should not exceed about 4.5%; maximum contents of 3.0% are preferred for each of these two elements.

The Applicant has found that in order to solve the problem, it is necessary to take into account, in an Al-Zn-Mg-Cu type alloy, several technical characteristics:

First of all, the alloy must be sufficiently loaded with addition elements capable of precipitating during a maturation or a treatment of income, in order to be able to present interesting static mechanical characteristics. For this, according to the findings of the applicant, in addition to the minimum and maximum limits for the zinc, magnesium and copper contents indicated above, the content of these additive elements must fulfill the condition Mg + Cu> 6.4 0.4 Zn.

Furthermore, the Applicant has found that to obtain a sufficient level of toughness, it is necessary that Mg / Cu <2.4, preferably <2.0 and even more preferentially <1.7.

To reinforce this effect, it is necessary to add a sufficient content of so-called anti-recrystallizing elements. More specifically, for alloys with more than 9.5% zinc, at least one element selected from the group comprising the elements Zr, Sc, Hf, La, Ti, Y, Ce, Nd, Eu, Gd, must be added. Tb, Dy, Ho, Er, Yb, Cr, Mn with, for each element present, a concentration of between 0.02 and 0.7%. It is preferable that the concentration of all the elements of said group does not exceed 1.5%.

These anti-recrystallizing elements, in the form of fine precipitates formed during thermal or thermomechanical treatments, block the recrystallization. However, the Applicant has found that when the alloy is heavily loaded with zinc (Zn> 9.5%) it will be necessary to avoid a too abundant precipitation during the quenching of the wrought product. A compromise must therefore be found as to the content of anti-recrystallizing elements which influence the precipitation during quenching.

According to the invention, for alloys with a zinc content between 8.3% and 9.5%, it is necessary to add zirconium with a content of between 0.03% and 0.15%, and in addition at least an element selected from the group comprising the elements Sc, Hf, La, Ti, Y, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Yb, with, for each element present, a concentration of between 0, 02 and 0.7%. The plaintiff has found that for the said anti-recrystallizing elements, it is advantageous, irrespective of the zinc content, not to exceed the following maximum levels: Cr 0.40; Mn 0.60; Sc 0.50; Zr 0.15; Hf 0.60; Ti, 0.15; This 0.35 and preferably 0.30; Nd 0, 35 and preferably 0.30; Eu 0.35 and preferably 0.30; Gd 0.35; Tb 0.35; Ho, 0.40; Dy 0.40; Er 0.40; Yb 0.40; Y, 0.20; 0.35 and preferably 0.30. Advantageously, the total of these elements does not exceed 1.5%.

Another technical characteristic is related to the need to be able to industrially produce wrought products under conditions of reliability compatible with the high requirements of the aeronautical industry, as well as under satisfactory economic conditions. It is therefore necessary to choose a chemical composition which minimizes the occurrence of cracks or cracks during the solidification of the plates or billets, said cracks or cracks being unacceptable defects leading to the scrapping of said plates or billets. The Applicant has found in numerous tests that this occurrence of cracks or splits was much more likely when the 7000 alloys complete their solidification below 470 ° C. To significantly reduce the probability of occurrence of cracks or splits at casting to an industrially acceptable level, it is better to choose a chemical composition such as

Mg> 1.95 + 0.5 (Cu - 2.3) + 0.16 (Zn - 6) + 1.9 (Si - 0.04).

This criterion is called in the context of the present invention the "flowability criterion". The alloys produced according to this variant of the invention complete their solidification at a temperature of between 473 ° C. and 478 ° C., and make it possible to achieve an industrial reliability of the processes for producing the metal (that is to say a consistent quality of cast plates) compatible with the high demands of the aerospace industry.

Another technical feature of the invention is related to the need to minimize as much as possible the amount of insoluble precipitates after the homogenization and dissolution treatments, as this reduces the toughness; for this, we choose a content of Mg, Cu and Zn such that Mg + Cu <7.7 - 0.4 Zn. Said precipitates are typically ternary or quaternary phases Al-Zn-Mg-Cu type S, M or T.

And finally, the Applicant has found that the incorporation of a small amount, between 0.02 and 0.15% per element, of one or more elements selected from the group consisting of Sn, Cd, Ag, Ge, In allows to improve the response of the alloy to the treatment of income, and has beneficial effects on the mechanical strength and on the corrosion resistance of the product. A content of between 0.05 and 0.10% is preferred. Among these elements, money is the preferred element.

The products according to the invention are in particular rolled or spun products. They can be used advantageously for the manufacture of structural elements in aeronautical construction. A preferred application of the products according to the invention is the application as a structural element in a wing box, and in particular in its upper part (extrados) which is first dimensioned in compressive strength. The figure 1 schematically shows a section of the wing box of a civil aircraft. Such a wing box typically has a length of between 10 m and 40 m and a width of between 2 m and 10 m; its height varies according to the place on the wing and is typically between 0.2 m and 2 m. The box consists of the extrados (1) and the intrados (2). The extrados (1) of a civil aircraft consists of a strong plate of a typical thickness during delivery between 15 mm and 60 mm, and stiffeners (5) which can be made from profiles and attached to the skin using mechanical fasteners (such as rivets or bolts) or welding techniques (such as arc welding, laser beam welding, or friction welding). The extrados structure (skin - stiffeners) can also be obtained by assembling other aluminum alloy semi-finished products. It can also be obtained by integral machining of heavy plates or profiles, that is to say without assembly.

In general, in order to reduce as much as possible the weight of such a structure, it is desirable to reduce the number of fastening means (rivets, bolts, etc.) or solder joints. Therefore, it is desirable to use sheets or spun products whose dimensions are as close as possible to those of the finished wing box. This need to use half-products of very large dimensions, for example of a width between 0.5 m and 4 m, with a thickness of between 10 mm and 60 mm or even 100 mm, and a length between 6 m and more than 20 m, limits the choice of usable materials. More particularly, in the case of rolled products, it is necessary to be able to obtain these plates of very large dimensions with sufficient industrial reliability. For very large aircraft, the length of the airplane wings may exceed 20 m and even 30 m, which requires the use of sheets or profiles longer than 20 m or 30 m, to minimize the assembly of the structural elements. The manufacture of sheets or profiles of such a size in highly charged Al-Zn-Mg-Cu alloys requires excellent control of the casting, rolling and thermal and thermomechanical processes, and requires an adaptation of the chemical composition. according to the invention.

It should be noted that the profiles of small thickness or width, in addition to a considerable increase in static mechanical characteristics due to the press effect well known to those skilled in the art. This effect is not observed for thick sections.

The products according to the invention can be used as structural elements in aeronautical construction. For the application as extrados, a metallurgical state of T6 type, for example T651, is preferred. One can also consider the use in the T7 state.

Rolled, extruded or forged semi-finished products can be produced which have a very interesting compromise of properties, particularly for the aeronautical construction: a yield strength R _p0.2 (L) greater than 630 MPa and even greater than 640 MPa, a toughness K _IC (LT) greater than 23 MPa√m and even greater than 25 MPa√m, an elongation at break A% higher than 8% and even greater than 10%, while maintaining the resistance to exfoliating corrosion and stress corrosion at a level at least comparable to that of known Al-Zn-Mg-Cu alloys. These products may have a value of K _{app (LT)} , measured according to ASTM E561 at T / 2 on a test piece of width W = 406 mm, of at least 70 MPa√m, and preferably at least equal to at 75 MPa√m.

The product according to the invention is particularly suitable for use as a structural element in a wing box, for example in the form of an extrados or a stiffener. The advantages of the products according to the invention allow in particular their use as structural elements of very large aircraft, including civil aircraft, and especially in the form of rolled and spun products. In a particularly advantageous application, these structural elements are made from sheets with a thickness greater than 60 mm.

In the case of a profile, the addition of one or more anti-recrystallizing elements, such as scandium, is particularly advantageous; such an effect is also observed in the case of heavy plates. When the added anti-recrystallizing element is scandium, a content of between 0.02 and 0.50% is advantageous. Adding a small amount of money or some other element such as Cd, Ge, In, Sn (in the order of 0.05 to 0.10%) improves income efficiency, and positive effects on the mechanical strength and stress corrosion resistance of the product.

The invention will be better understood with the aid of the examples, which are however not limiting in nature.

Examples Example 1

Several Al-Zn-Mg-Cu alloys were prepared by semi-continuous casting of plates, and were subjected to a conventional transformation range, including a homogenization step followed by hot rolling, dissolution step followed by quenching and stress relieving operations, and finally an income in state T651. Thus sheets of 20 mm thickness were obtained in the T651 1 state.
The compositions of the sheets composing this test are indicated in Table 1. <u> Table 1 </ u> Alloy Zn mg Cu Fe Yes Zr Ti mn sc AT 8.40 2.11 1.83 0.09 0.06 0.11 0,017 0 0 B 10,27 3.2 0.71 0.08 0.03 0.11 0,017 0 0 VS 10.08 2.69 0.95 0.08 0.03 0.11 0.014 0 0 D 9.97 2.14 1.32 0.09 0.03 0.11 0,017 0 0

The alloy A is a 7449 alloy according to the state of the art, the alloys B and C are alloys with a high Zn content, not respecting the technical characteristics of the invention, the alloy D is an alloy according to the invention. 'invention.

The static tensile strength properties according to EN 10002-1, the compressive yield strength R _p0.2 ^C (a dimensioning property for the upper surface) according to ASTM E9, and the toughness K _IC in plane deformations according to ASTM E399. The results are shown in Table 2: <u> Table 2 </ u> Alloy Long Traction TL sense traction Compression sense L Toughness LT R _p0.2 MPa R _m MPa AT % R _p0.2 MPa R _m MPa AT % R _p0.2 ^C MPa K _IC MPa√m AT 627 665 14.7 566 623 13.6 618 31.9 B 716 726.5 6.5 640 696 5.2 703 21.1 VS 700 717 9.2 629 676 8.1 675 21 D 665 685 12.2 608 649 11 656 26.8

It clearly appears that the alloy according to the invention has a better compromise static characteristics / toughness than the alloy 7449 according to the prior art (R _p0.2 in tension and in higher compression and K _IC similar), and that the alloys with a high zinc content which do not respect the technical characteristics of the invention are less efficient.

Example 2

Two alloys whose chemical composition is shown in Table 3 were cast and processed using a range similar to that of Example 1, except that the sheets obtained were 6 mm thick. <u> Table 3 </ u> Alloy Zn mg Cu Fe Yes Zr Ti mn sc E 8.42 2.09 1.9 0.07 0.02 0.10 0.016 0 0 F 8.34 2.11 1.84 0.07 0.03 0.11 0,018 0 0.083

The alloy E is a 7449 alloy, and the alloy F is an alloy according to the invention containing an addition of 0.083% Scandium.
The static mechanical characteristics obtained in the T651 state are presented in Table 4 below. Toughness has been characterized using the Kahn indicator, well known to those skilled in the art and described in particular in the article by JG Kaufman and AH Knoll, "Kahn-Type Tear Tests and Crack Toughness of Aluminum Sheet", published in Materials Research & Standards, pp. 151-155, in 1964 . The K _app parameter was measured according to ASTM E561 standard on CT type specimens of W width equal to 127 mm. The parameter K _app ("apparent K") is the stress intensity factor calculated using the maximum load measured during the test and the initial crack length (at the end of pre-cracking) in the formulas indicated by the standard. cited. These indicators are conventionally used to measure the toughness in plane stresses. The results of the tenacity measurements made during this test are shown in Table 5 below. <u> Table 4 </ u> Alloy Long Traction TL sense traction R _p0.2 MPa R _m MPa AT % R _p0.2 MPa R _m MPa AT % E 615 649 13.7 588 646 13.3 F 648 688 12.5 605 652 15.0 Alloy Kahn indicator (LT) MPa Kahn indicator (TL) MPa K _app (LT) MPa√m K _app (TL) MPa√m E 231 212 58 37 F 236 218 57 36

The results of Tables 4 and 5 clearly show the improvement of the static mechanical characteristics of the alloy object of the invention for similar toughness, or better than that of the alloy without scandium.

Example 3

Two alloys were cast whose chemical composition is shown in Table 6, and were processed using a range similar to that of Example 1, except that the sheets obtained were 25 mm and 10 mm thick. and that two income states have been developed: the state T651 (treatment of 48h at 120 ° C) defined as the peak of tensile strength and T7x51 state (24h 120 ° C + 17h 150C). <u> Table 6 </ u> Alloy Zn mg Cu Fe Yes Zr Ti mn sc R 8.3 2.13 1.85 0,030 0,032 0.11 0,017 0 0 S 8.6 2.1 1.9 0.07 0.03 0.11 0,017 0 0.078

The alloy R is a 7449 alloy, and the alloy S is an alloy according to the invention containing an addition of 0.078% of scandium.

The static mechanical characteristics obtained in states T651 and T7951 and measured at mid-thickness are presented in Table 7 below.
The toughness in plane deformations K _IC was determined according to the ASTM E399 standard, at mid-thickness. Tenacity in plane stresses was characterized at mid-thickness using the parameter K _app, measured according to ASTM standard E561 on CCT type test pieces of width W equal to 406 mm. The results of the tenacity measurements made during this test are shown in Table 8 below. <u> Table 7 </ u> Thickness Alloy State Long Traction TL sense traction R _p0.2 MPa R _m MPa AT % R _p0.2 MPa R _m MPa AT % S-10 mm T651 632 655 7.9 612 649 9.6 T7x51 598 619 8.6 601 622 7.5 S-25 mm T651 647 681 12.8 606 649 13.2 T7x51 611 644 12.4 588 622 11.9 R-25 mm T651 601 637 10.4 584 620 10.2 T7x51 584 622 10.9 565 597 10.8 Thickness Alloy State K _IC (LT) MPa√m K _IC (TL) MPa√m K _app (LT) MPa√m S-10mm T651 Not measured 72.8 T7x51 73.7 S-25mm T651 24 24 81.6 T7x51 25 22 72.6 R-25mm T651 231 212 56.1 T7x51 236 218 84.4

We have shown on the figure 2 the compromise mechanical resistance - damage tolerance in a diagram R _p0.2 - K _app for the alloys of Example 3. It appears that the reference alloy "R" has the usual compromise (the toughness decreases when the resistance mechanical increases). Conversely, and surprisingly, the alloy according to the invention "S" has a very low decay (thickness 10 mm) or even a net increase (thickness 25 mm) of the toughness when the mechanical strength increases. Moreover, the alloy according to the invention has levels of mechanical strength significantly higher than those of the reference alloy and comparable toughness or greater.

Example 4

Several alloys were cast whose composition is shown in Table 9, with an Si content of approximately 0.04% for all alloys.

The alloys G1, G2, G3 and G4 are outside the present invention, as well as the alloys B and C, described in Example 1. The alloy D is an alloy according to the invention described in Example 1. All of these alloys showed satisfactory flowability during the tests, i.e. splits or cracks were not observed in the casting tests on an industrial scale.

The alloys G5, G6, G7, G8 are outside the present invention, and the alloy G9 is a 7060 alloy according to the state of the art; these alloys showed slits during casting tests.
The difficulties arising during the casting of these alloys do not necessarily make the wrought products obtained from these plates unsuitable for use, but are the cause of additional costs because the implementation (that is to say the quantity of salable metal relative to the quantity of metal fired, a parameter which is directly related to the quantity of scraped plates) will be greater than for the alloys corresponding to the preferred domain of the invention. In addition, the propensity of these alloys for the formation of slits during their solidification makes it very difficult to make the casting process reliable in the context of a quality assurance program by statistical process control.

It is found that all 7xxx alloys having a very pronounced propensity for the formation of cracks or cracks in the casting have a magnesium content lower than the critical magnesium content; this critical value was obtained by calculating the limit value in Mg defined by the flowability criterion. <u> Table 9 </ u> Alloy Zn (%) Mg (%) Cu (%) Observed reliability Critical content in Mg (%) Mg> Critical Mg 01 7.5 3 3 Low 2.54 Yes G2 8.5 3 2.3 Low 2.35 Yes G3 7.5 3 1.6 Low 1.84 Yes G4 6.5 3 2.3 Low 2.03 Yes B 10,27 3.2 0.71 Low 1.82 Yes VS 10.08 2.69 0.95 Low 1.91 Yes D 9.97 2.14 1.32 Low 2.08 Yes G5 8.5 2.3 3 Strong 2.7 No G6 6.5 2.3 3 Strong 2.38 No G7 8.5 1.6 2.3 Strong 2.35 No G8 7.5 1.6 1.6 Strong 1.84 No G9 7 1.65 2.1 Strong 2.01 No

Example 5

Rolling plates were developed by a process similar to that described in Example 1. The chemical composition is given in Table 10. By a method similar to that described in Example 1, it was prepared by hot rolling. 25 mm thick sheets. They were dissolved for 2 hours at a temperature of between 472 and 480 ° C. (these temperatures are determined by preliminary calorimetry tests on the raw rolling sheets, a procedure that is conventional for those skilled in the art), quenched by spraying. and tractionned with a permanent elongation of between 1.5 and 2%. Then the sheets were subjected to a tempering treatment at a temperature of 135 ° C. <u> Table 10 </ u> Alloy Zn mg Cu Fe Yes Zr Ti mn sc Mg / Cu M 9.94 3.02 0.78 0.04 0.03 0.10 0,063 0 0 3.87 NOT 10.00 2.72 0.77 0.06 0.04 0.10 0,055 0 0.10 3.53 K 9.90 2.03 1.55 0.03 0.03 0.10 0.05 0 0.10 1.31

The static mechanical tensile and compressive properties as well as the toughness K _app as specified in the preceding examples were measured at mid-thickness. Table 11 Alloy Duration of income h R _p0.2 MPa R _m MPa AT % R _p0.2 ^C MPa K _app (LT) MPa√m L-shaped traction Compression sense L NOT 14.5 692 699 9.7 669 52.7 NOT 35 657 672 11.2 634 61.9 M 14.5 676 690 10.0 658 33.4 M 35 648 658 9.9 635 47.0 K 12.5 Not Measured 645 79.4 K 14.5 671 689 11.7 649 76.2 K 35 659 672 11.4 648 84.8 K 120 Not measured 567 115.0

It has been verified that for the sheets N, M and K, the income of 14.5 h leads to the state T651. For significantly longer revenues, the parameters R _p0.2 , R _p0.2 ^C and R _m degrade while the toughness in plane stresses K _app increases.

As in Example 3, we have represented the mechanical resistance - damage tolerance compromise in an R _p0.2 - K _app diagram. This diagram is provided at figure 3 for the alloys of Example 5.
With an equal zinc content, and an equal scandium content, the sheet K with a lower Mg / Cu ratio shows significantly better toughness values than the N sheet.

Example 6

Spinning billets 291 mm in diameter with an alloy according to the invention were prepared by vertical casting, the composition of which is given in Table 12. Table 12 Alloy Zn mg Cu Cr mn Yes Fe Zr Ti Mg / Cu T 9.43 1.96 1.67 - 0.01 0.05 0.07 0.12 0.03 1.17

Billet homogenized (7h 460 ° C + 23h 466 ° C) and peeled were extruded, the temperature of the container and the tool being greater than 400 ° C, and the spinning speed being less than 0.50 m / min . The geometry of the profiles comprises a sole (thickness 15 mm, width 152 mm), a rib (thickness 15 mm, height 38 mm) and a reinforcement (thickness 23 mm, width 76 mm).

After dissolving (4h 472 ° C at the bearing), quenching and controlled traction, the profiles were subjected to a T7A511 tempering treatment (6h 120 ° C + 7h 135 ° C) and T7B511 (6h 120 ° C + 28h 135 ° C ); the letters A and B here symbolize these different income conditions.

Profiles of similar geometry in alloy 7449, the precise composition of which does not correspond to the present invention, have also been developed for reference in the T79511 state.

The results of the characterization of these profiles are given in Table 13 below. (the letter X indicates that the characteristic has not been determined for this product). <u> Table 13 </ u> Alloy (Position) State Static Characteristics Sens L Tenacity Traction Compression K _IC K _IC R _p0,2 R _m AT R _p0.2 ^C (LT) (TL) MPa MPa % MPa MPa m MPa m 7449 (Reinforcement) T79511 625 650 13.0 645 30 20 T (reinforcement) T7A511 694 707 11.5 712 46.8 20.4 T (sole) 669 689 12.3 665 34.2 22.1 T (Rib) 664 678 11.6 659 X X T (reinforcement) T7B511 681 685 10.6 707 37.0 20.3 T (sole) 663 670 11.0 676 29.0 22.8 T (Rib) 661 666 10.2 666 X X

It clearly appears that the alloy "T" according to the invention has a much better compromise mechanical strength - toughness.

Claims (25)

1. Rolled, extruded or forged product made of an Al-Zn-Mg-Cu alloy, characterised in that it contains (in percent by mass):

   a) Zn 8.3 - 14.0 Cu 0.3 - 4.0 Mg 0.5 - 4.5
   Zr 0.03 - 0.15 Fe + Si < 0.25

   b) at least one element selected from the group composed of Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, the content of each of the said elements, if selected, being between 0.02 and 0.7%,

   c) the remainder aluminium and inevitable impurities,
   and in that it satisfies the conditions

   d) Mg / Cu < 2.4 and

   e) (7.7 - 0.4 Zn) > (Cu + Mg) > (6.4 - 0.4 Zn).
2. Product according to claim 1, characterised in that its maximum content of the following elements is (in percent by mass):

   Sc 0.50; Hf 0.60; La 0.35 and preferably 0.30; Ti 0.15; Ce 0.35 and preferably 0.30; Nd 0.35 and preferably 0.30; Eu 0.35 and preferably 0.30; Gd 0.35; Tb 0.35; Dy 0.40; Ho 0.40; Er 0.40; Yb 0.40; Y 0.20.
3. Product according to either claim 1 or 2,
   characterised in that the total concentration by mass of elements Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, Cr, Mn does not exceed 1.5%.
4. Rolled, extruded or forged product made of Al-Zn-Mg-Cu alloy, characterised in that it contains (in percent by mass):

   a) Zn 9.5 - 14.0 Cu 0.3 - 4.0 Mg 0.5 - 4.5
   Fe + Si < 0.25

   b) at least one element selected from the group composed of Zr, Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, Cr, Mn, the content of each of the said elements, if selected, being between 0.02 and 0.7%,

   c) the remainder aluminium and inevitable impurities,
   and in that it satisfies the conditions

   d) Mg / Cu < 2.4 and

   e) (7.7 - 0.4 Zn) > (Cu + Mg) > (6.4 - 0.4 Zn)
5. Product according to claim 4, characterised in that its maximum content of the following elements is (in percent by mass):

   Sc 0.50; Hf 0.60; La 0.35 and preferably 0.30; Ti 0.15; Ce 0.35 and preferably 0.30; Nd 0.35 and preferably 0.30; Eu 0.35 and preferably 0.30; Gd 0.35; Tb 0.35; Dy 0.40; Ho 0.40; Er 0.40; Yb 0.40; Y 0.20; Cr 0.40; Mn 0.60.
6. Product according to either claim 4 or 5,
   characterised in that the total concentration by mass of elements Zr, Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, Cr, Mn does not exceed 1.5%.
7. Product according to any one of claims 1 to 4,
   characterised in that the Mg / Cu ratio is < 2.0 and preferably < 1.7.
8. Product according to any one of claims 1 to 7,
   characterised in that Zn > 9.0% and preferably < 9.5%.
9. Product according to any one of claims 1 to 8,
   characterised in the contents of Cu and / or Mn do not exceed 3.0% for each.
10. Product according to any one of claims 1 to 9,
    characterised in that the zinc content is between 9.0 and 11.0%.
11. Product according to any one of claims 1 to 10, characterised in that its magnesium, copper, zinc and silicon contents are chosen such that
    
            Mg > 1.95 + 0,5 (Cu - 2,3) + 0,16 (Zn - 6) + 1,9 (Si - 0,04).
    
    
12. Product according to any one of claims 1 to 11, characterised in that it also contains at least one element selected from the group consisting of Cd, Ge, In, Sn, Ag, with contents of between 0.05 to 0.15%, and preferably 0.05 to 0.10%, for each selected element.
13. Product according to any one of claims 1 to 12, characterised in that the yield point R_p0,2(L) > 630 MPa, and preferably > 640 MPa.
14. Product according to any one of claims 1 to 13, characterised in that K_IC(L-T) > 23 MPa√m.
15. Product according to any one of claims 1 to 14, characterised in that K_app(L-T) measured according to ASTM E561 at mid-thickness on a test piece with width W = 406 mm is at least equal to 70 MPa√m, and preferably at least equal to 75 MPa√m.
16. Product according to claim 15, characterised in that K_IC(L-T) > 25 MPa√m.
17. Product according to any one of claims 1 to 16, characterised in that the elongation at rupture A%(L) > 8%.
18. Structural member for aeronautical construction, including at least one rolled or extruded product made of Al-Zn-Mg-Cu alloy, characterised in that the said rolled or extruded product contains (in percent by mass):

    a) Zn 8.3 - 14.0 Cu 0.3 - 4.0 and preferably 0.3 - 3.0
    Mg 0.5 - 4.5 and preferably 0.5 - 3.0
    Zr 0.03 - 0.15 Fe + Si < 0.15

    b) at least one element selected from the group composed of Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, the content of each of the said elements, if selected, being between 0.02 and 0.7%,

    c) the remainder aluminium and inevitable impurities,
    and in that the said rolled or extruded product satisfies the conditions

    d) Mg / Cu < 2.4 and preferably < 1.7; and

    e) (7.7 - 0.4 Zn) > (Cu + Mg) > (6.4 - 0.4 Zn).
19. Wing box, in which the extrados is made from an Al-Zn-Mg-Cu alloy plate, characterised in that the said plate contains (in percent by mass):

    a) Zn 8.3 - 14.0 Cu 0.3 - 4.0 and preferably 0.3 - 3.0
    Mg 0.5 - 4.5 and preferably 0.5 - 3.0
    Zr 0.03 - 0.15 Fe + Si < 0.15

    b) at least one element selected from the group composed of Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, the content of each of the said elements, if selected, being between 0.02 and 0.7%,

    c) the remainder aluminium and inevitable impurities,
    and in that the said plate satisfies the conditions

    d) Mg / Cu < 2.4 and preferably < 1.7; and

    e) (7.7 - 0.4 Zn) > (Cu + Mg) > (6.4 - 0.4 Zn).
20. Wing box according to claim 19, characterised
    in that the said extrados is made from integral machining using a plate thicker than 60 mm.
21. Wing box according to either claim 19 or 20,
    characterised in that the said plate contains, between 0.02 and 0.50% of scandium.
22. Wing, box, in which at least one of the stiffeners is made from an Al-Zn-Mg-Cu alloy extruded product, characterised in that the said extruded product contains (in percent by mass) :

    a) Zn 8.3 - 141.0 Cu 0.3 - 4.0 and preferably 0.3 - 3.0
    Mg 0.5 - 4.5 and preferably 0.5 - 3.0
    Zr 0.03 - 0.15 Fe + Si < 0.15

    b) at.least one element selected from the group composed of Sc, Hf, La, Ti, Ce, Nd, Eu, Gd, Tb, Dy, Ho, Er, Y, Yb, the content of each of the said elements, if selected, being between 0.02 and 0.7%,

    c) the remainder aluminium and inevitable impurities,
    and in that the said plate satisfies the conditions

    d) Mg / Cu < 2.4 and

    e) (7.7 - 0.4 Zn) > (Cu + Mg) > (6.4 - 0.4 Zn).
23. Wing box according to claim 22, characterised in that the said extruded product contains between 0.02 and 0.50% of scandium.
24. Wing box according to any one of claims 19 to 24, characterised in that the said plate or the said section is used in the T6 or T651 metallurgical temper.
25. Wing box according to any one of claims 19 to 24, characterised in that the said plate or the said section is used in the T7 metallurgical temper.

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