FR2838135A1 - PRODUCTS CORROYED IN A1-Zn-Mg-Cu ALLOYS WITH VERY HIGH MECHANICAL CHARACTERISTICS, AND AIRCRAFT STRUCTURE ELEMENTS - Google Patents

Abstract

The invention consists of a rolled, extruded or forged product made of an Al-Zn-Mg-Cu alloy, characterized in that it contains (in mass percent): a) Zn 8, 3 - 14, 0 Cu 0, 3 - 2, 0 Mg 0, 5 - 4, 5 and preferably 0, 5 - 3, 6 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, Yb, the content of each of said elements, if selected, being between 0.02 and 0.7% , c) the remainder of aluminum and inevitable impurities, and in that it satisfies the conditions d) Mg / Cu> 2, 4 ete) (7, 9 - 0, 4 Zn)> (Cu + Mg)> (6, 4 - 0, 4 Zn), and preferably, Mg> 1. 95 + 0, 5 (Cu - 2, 3) + 0, 16 (Zn - 6) + 1, 9 (Si - 0, 04). according to the invention can be used in particular for the manufacture of stiffeners for the fuselage of civil aircraft.

Description

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PRODUCTS CORROYED IN AL-ZN-MG-CU ALLOYS
WITH VERY HIGH MECHANICAL CHARACTERISTICS,
AND ELEMENTS OF AIRCRAFT STRUCTURE
Technical field of the invention
The present invention relates to products wrought in alloys of Al-Zn-Mg-Cu type with very high mechanical characteristics, with a Zn content greater than 8.3%, as well as aircraft structural elements incorporating such products.

STATE OF THE ART Alloys of the Al-Zn-Mg-Cu type (belonging to the family of 7xxx alloys) are commonly used in aeronautical construction, and in particular in the construction of the wings of civil aircraft. For the extrados of the wings, for example, a skin made of heavy plates in alloys 7150,7055, 7449 is used, and possibly stiffeners in profiles of alloys 7150,7055, 7349 or 7449. Alloys 7150,7050 and 7349 are also used for the manufacture of fuselage stiffeners.

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 as well as good toughness and resistance to stress corrosion and exfoliating corrosion. More recently, it has appeared that for certain applications, the use of an alloy with a higher zinc content can have advantages because this makes it possible to further increase the elastic limit. Alloys 7349 and 7449 contain between 7.5 and 8.7% zinc. Wrought alloys richer in zinc have been described in the literature, but do not seem to be used in aircraft construction.

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The article Microstructure and properties of a new super-high-strength Al-Zn-Mg-Cu alloy C912 by Y. L Wu et al., Published in the journal Materials & Design, Vol 18, p. 211-
215 (1998) discloses an alloy Zn 8.7%, Mg 2.6%, Cu 2.5%, Si and Fe <0.05% (each) envisaged for the manufacture of structural elements for airfoils and fuselage.

US Patent 5,560,789 (Pechiney Research) discloses an alloy of composition Zn
10.7%, Mg 2.84%, Cu 0.92% which is transformed by spinning. The addition elements of this alloy very loaded with zinc, magnesium and copper are difficult to dissolve because the solution temperature of the product is limited by the melting temperature of the phases with the lowest melting point: this product has high mechanical strength, but very low elongation at break, due to the presence of coarse precipitates; said product is not very formable.

US Pat. No. 5,221,377 (Aluminum Company of America) discloses several alloys of the Al-Zn-Mg-Cu type with a zinc content of up to 11.4% and sufficiently loaded with copper. They are difficult to pour, and the addition elements are difficult to dissolve, which favors the presence, undesirable, of coarse precipitates.

Furthermore, it has been proposed to use Al-Zn-Mg-Cu alloys with a high zinc content for the manufacture of hollow bodies intended to withstand high pressures, such as, for example, compressed gas cylinders. European patent application EP 020 282 A1 (Société Métallurgique de Gerzat) discloses alloys with a zinc content of between 7.6% and 9.5%. European patent application EP 081441 A1 (Société Métallurgique de Gerzat) discloses a process for obtaining such bottles. European patent application EP 257 167 A1 (Société Métallurgique de Gerzat) notes that none of the known Al-Zn-Mg-Cu type alloys enables the severe technical requirements imposed by this specific application to be satisfied in a reliable and reproducible manner; 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 cylinders, in particular with regard to maximizing the burst pressure of these cylinders, and cannot be transferred to other wrought products.

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In general, in alloys of the Al-Zn-Mg-Cu type, a high content of zinc, but also of Mg and Cu is necessary to obtain good static mechanical characteristics (elastic limit, breaking limit) , provided that these elements can be put into solution. But it is also well known (see for example US
5,221,377) than when the zinc content is increased in an alloy of the family
7xxx above about 7 to 8%, there are problems associated with insufficient resistance to exfoliating corrosion and stress corrosion. More generally, it is known that the most charged Al-Zn-Mg-Cu alloys are liable to pose corrosion problems. These problems are generally solved with the aid of specific heat or thermomechanical treatments, in particular by pushing the tempering treatment beyond the peak, for example during a T7 type treatment. But these treatments can then lead to a drop in the static mechanical characteristics. In other words, for a minimum level of corrosion resistance targeted, the optimization of an Al-Zn-Mg-Cu type alloy must seek a compromise between the static mechanical characteristics (elastic limit Rpo, 2, limit of rupture Rm, elongation at rupture A) and the damage tolerance characteristics (toughness, crack propagation speed etc.). Depending on the minimum level of corrosion resistance targeted, a state close to the tempered peak is used (T6 states), which in general offers a toughness - Rpo, 2 compromise favoring the static mechanical characteristics, or the tempering is pushed beyond the peak (T7 states), seeking a compromise favoring tenacity.

Whatever approach is chosen, the development and use of such products poses two problems: on the one hand, these alloys highly loaded with zinc and magnesium are difficult to cast and to transform, in particular by extrusion, rolling or forging. . For example, the maximum force that a spinning press can provide can be a limiting factor. In particular, among the alloys of the 7xxx family, the alloys 7349 and 7449 require very high spinning forces. On the other hand, there are applications in which the shaping ability of said extruded and rolled products is an important factor. This is particularly the case with fuselage stiffeners.

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Therefore, it is to be feared that the search for an alloy with even higher strength than those of the 7349 and 7449 alloys will result in an alloy which is difficult to cast and process, and difficult to shape.

Problem Raised The problem which the present invention tries to answer is to provide new wrought products made of an alloy of the Al-Zn-Mg-Cu type with a high zinc content, greater than 8.3%, and in particular extruded products, which are characterized by a very high tensile strength, a very high elastic limit, sufficient corrosion resistance, good formability, and which can be manufactured industrially under conditions of reliability compatible with the high demands of the aviation industry.

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

A first object of the present invention consists of a rolled, extruded or forged product made of an Al-Zn-Mg-Cu alloy, characterized in that it contains (in mass percent): a) Zn 8.3 - 14.0 Cu 0.3 - 2.0
Mg 0.5 - 4.5 and preferably 0.5 - 3.6
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, Yb, the content of each of said elements, if it is selected, being between 0.02 and 0.7%, c) the remainder of aluminum and impurities inevitable, and in that it satisfies the conditions

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d) Mg / Cu> 2.4 and e) (7.9 - 0.4 Zn)> (Cu + Mg)> (6.4 - 0.4 Zn).

A second object of the present invention consists of a rolled, extruded or forged product made of an Al-Zn-Mg-Cu alloy, characterized in that it contains (in mass percent): a) Zn 9.5 - 14.0 Cu 0.3 - 2.0
Mg 0.5 - 4.5 and preferably 0.5 - 3.6
Fe + Si <0.25 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 of said elements, if selected, being between 0.02 and 0.7%, c ) the remainder of aluminum and inevitable impurities, and in that it satisfies the conditions d) Mg / Cu> 2.4 and e) (7.9 - 0.4 Zn)> (Cu + Mg)> (6.4 - 0.4 Zn).

A third object of the present invention is an aircraft structural element which incorporates at least one of said products, and in particular a structural element used in the construction of the fuselage of civil aircraft, such as a fuselage stiffener.

Description of the figures Figure 1 shows the section of the Tl profile.

Figure 2 shows the section of profile T2.

Figure 3 shows the section of profile T3. In figures 1, 2 and 3, the dimensions indicated are approximate and expressed in millimeters.

In Figures 1, 2 and 3, the letter a designates the "heel" of the profile, and the letter b the "sole".

FIG. 4 schematically shows the zone of a fuselage stiffener which has undergone shaping by jogging. The benchmarks are as follows:

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a Jog depth b Jog width c Upper sole: appearance of significant plane deformations d Bottom sole: appearance of significant plane deformations
Figure 5 shows schematically the place on the Tl profile where the sample is taken for the 3-point bending test.

Figure 6 shows schematically the definition of the bend angle. Figure 7 shows schematically the geometric parameters important for the three-point bending test.

Detailed description of the invention Unless otherwise stated, all the indications relating to the chemical composition of the alloys are expressed in percent by mass. Therefore, in a mathematical expression, 0.4 Zn means: 0.4 times the zinc content, expressed as a mass percent; this applies mutatis mutandis to the other chemical elements. The designation of the alloys follows the rules of The Aluminum Association. The metallurgical states are defined in European standard EN 515. Unless otherwise stated, the static mechanical characteristics, that is to say the tensile strength Rm, the elastic limit Rpo, 2, and the elongation at break A , are determined by a tensile test according to standard EN 10002-1. The term spun product includes so-called drawn products, that is to say products which are produced by spinning followed by drawing.

The Applicant, during a number of preparatory studies, has come to the conclusion that a new material exhibiting a significantly better compromise between mechanical strength and formability should in any event have a sufficient zinc content, typically higher. at approximately 8.3%, and preferably greater than 9.0%. This condition is not sufficient, however.

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In the context of the present invention, the Applicant has found a very particular field of composition which allows the production of wrought products, and in particular of extruded products, which have both very high static mechanical characteristics and corrosion resistance. acceptable, and good formatting ability. The Applicant has thus been able to develop spun products which can be used very advantageously as stiffeners for the fuselage of civil aircraft. In this application, the damage tolerance is not a limiting factor, and one can therefore afford to optimize the yield strength and the breaking limit to the detriment of the damage tolerance, while being careful not to degrade corrosion resistance. On the other hand, pushing the elastic limit and the breaking limit to the maximum, making it possible to lighten the structure of the airplane, usually results in a degradation of the formability. However, fuselage stiffeners are subject to complex and very specific shaping operations. To develop a more resistant alloy for fuselage stiffeners, it is therefore necessary to ensure that the formability does not deteriorate compared to known alloys, or, preferably, is better than that of known alloys. .

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

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:

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

The alloys according to the invention must contain at least 0.5% of magnesium, since it is not possible to obtain satisfactory static mechanical characteristics with a lower content of magnesium. According to the observations of the Applicant, with a zinc content of less than 8.3%, no result is obtained which is better than those obtained with the known alloys. Preferably, the zinc content is greater than 9.0%, and even more preferably greater than 9.5%. However, it

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It is necessary to respect certain relationships between certain elements, as explained below. In any case, we do not want to exceed a zinc content of about
14%, because beyond this value, whatever the magnesium and copper content, the results are not satisfactory. Adding at least 0.3% copper improves corrosion resistance. But to ensure satisfactory dissolution, the Cu content should not exceed about 2%, and the Mg content should not exceed about 4.5%; maximum content of 3.6% is preferred for magnesium.

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

First of all, the alloy must be sufficiently loaded with addition elements liable to precipitate during a maturation or a tempering treatment, in order to be able to exhibit interesting static mechanical characteristics. For this, according to the observations of the applicant, in addition to the minimum and maximum limits for the zinc, magnesium and copper contents indicated above, the content of these addition elements must meet the condition Mg + Cu> 6.4 - 0.4 Zn.

To enhance this effect, it is necessary to add a sufficient content of so-called anti-crystallizing elements. More precisely, 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, Tb, Dy, Ho, Er, Yb, Cr, Mn with, for each element present, a concentration of between 0.02 and 0.7%.

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

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According to the invention, for alloys with a zinc content of 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 in 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 Applicant has observed that for said anti-recrystallizing elements, it is advantageous, whatever the zinc content, not to exceed the following maximum content: Cr 0.40; Mn0.60; Sc 0.50; Zr 0.15; 0.60; 0.15; 0.35 and preferably 0.30; Nd 0.35 and preferably 0.30; Eu 0.35 and preferably 0.30; Gd0.35; Tb 0.35; 0.40; 0.40; 0.40; 0.40; 0.20; 0.35 and preferably 0.30.

The Applicant has observed that in order to improve the breaking point and the elastic limit, it is preferable to observe a Mg / Cu ratio> 2.4, and preferably at least 2.8 or even 4.0.

Another technical characteristic is linked 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 observed during numerous tests that this occurrence of cracks or cracks was much more probable when the 7000 alloys completed their solidification below 470 C. To significantly reduce the probability of the occurrence of cracks or cracks during casting up 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 between 473 C and 478 C, and make it possible to achieve industrial reliability of the metal production processes (that is to say a constancy of the quality

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cast plates or billets) compatible with the high requirements of the aeronautical industry.

Another technical characteristic of the invention is related to the need to minimize as much as possible the quantity of insoluble precipitates after the homogenization and dissolution treatments, since this decreases the toughness, the elongation at break and the fitness skills; for this, we choose a content of Mg, Cu and
Zn such that Mg + Cu <7.9 - 0.4 Zn. Said precipitates are typically S, M or T type Al-Zn-Mg-Cu ternary or quaternary phases.

And finally, the incorporation of a small amount, between 0.02 and 0.15% per element, of one or more elements chosen from the group consisting of Sn, Cd, Ag, Ge, In makes it possible to improve the response of the alloy to the tempering treatment, and has beneficial effects on the mechanical strength and on the corrosion resistance of the product.

Adding a small amount of silver or another element such as Cd, Ge, In, Sn (in the range of 0.05 to 0.10%) improves the efficiency of the tempering, and a positive effects on the mechanical resistance and the stress corrosion resistance of the product. 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. The profiles also benefit from an increase in their mechanical strength, which is all the greater as the width or the thickness of the profile is low; this so-called press effect is well known to those skilled in the art. The Applicant has observed that when the added anti-recrystallizing element is scandium, a content of between 0.02 and 0.50% is advantageous.

The products according to the invention are in particular spun products. They can be used advantageously for the manufacture of structural elements in aircraft construction. A preferred application of the products according to the invention is the application as a structural element in the fuselage of a civil aircraft. These elements, in particular the stiffeners, are first of all dimensioned in terms of mechanical strength. For this use, damage tolerance is usually not a design property, as long as it is of a reasonable level: we

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can, if necessary and to a certain extent, optimize the mechanical resistance to the detriment of the tolerance to damage, and without fear of diminishing the usefulness of the product.
Corrosion resistance should always remain at an acceptable level. The increase in the mechanical strength of said fuselage stiffeners makes it possible, at the choice of the manufacturer, to reduce their weight, or to have, for equal weight, a more rigid fuselage structure. The first option can make it possible, by increasing the spacing between two neighboring stiffeners (within the limit of the resistance to folding of the fuselage sheets), to reduce the number of stiffeners, which leads to a reduction in the number of fasteners or dots. 'assembly between stiffener and wing skin. This can prove to be very advantageous, since fasteners or assembly points, such as rivets or bolts, enter significantly into the cost of manufacturing such structures. A particularly advantageous use of the product according to the invention is therefore the application as a structural element in the field of aircraft construction, and more precisely in the construction of aircraft comprising a fuselage assembled from a plurality of stiffeners and 'a plurality of sheets, at least part of said stiffeners being structural elements according to the invention.

Such an aircraft is characterized by a structure that is lighter, but at least as rigid, or by a structure that is more rigid, but not heavier than existing aircraft.

As with the attachments between structural elements of different type (for example stiffener and fuselage skin), it is desirable to minimize the number of assemblies between two structural elements of the same type, and in particular between two stiffeners. For this purpose, sheets or extruded products of as large a relevant dimension as possible should be used; in the context of spun products, this relevant dimension is essentially length. However, the manufacture of very long profiles in highly charged Al-Zn-Mg-Cu alloys requires excellent mastery of the casting, spinning and heat treatment processes, and may require an adaptation of the chemical composition according to the invention. More particularly, the Applicant has observed that the product according to the invention can be obtained with a reduced spinning pressure compared to known products of comparable zinc content, which makes it possible to manufacture sections of greater length.

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Another problem which arises in particular when using said products as fuselage stiffeners is their formability.

A shaping method used during the industrial manufacture of fuselage stiffeners from sections is joggling. This is an introduction of a localized step over an area of a few millimeters (cf. figure 4). This can be done, in the case of profiles according to the invention, either hot (preferably at 130 ° C.) or cold.

In the case of cold jogging, the section delivered in the W (unstable) state will advantageously be put back into solution, followed by quenching. Then the shaping is carried out by jogging. Cold joggling does not allow for as deep shaping as hot joggling, but when applicable it is often more convenient.

Joggling as an industrial shaping process does not lend itself to use for the study of materials under development. However, it is known that the failure of the material on jogging is directly linked to the maximum plane deformations that the material can bear. This allows the ability of a material to be jogged to be evaluated using the 3-point bending test. According to DIN 50111 (September 1987, in particular section 3.1), the sample must be sufficiently large in relation to its thickness to be under conditions of plane deformation at the center of the test specimen.

In the context of the present invention, in order to evaluate the formability at 130 ° C. (lukewarm formability of the product in the final state), the flat test piece is deformed in an oven at 130 ° C. until the beginning of the drop of the product. applied force (which means the initiation of a crack) while always making sure that the temperature of the sample is indeed at 130 C. Since the strain is done hot, the strain rate is a parameter which influences the result. It was fixed by a crosshead speed of 50 mm / min. The higher the bending angle (see definition in Figure 6), the greater the ability to be jogged. For mechanical reasons, it is important that the samples to be compared have the same thicknesses. If two samples of different thickness are to be compared, the face is machined in compression to the required thickness. In the case

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of a profile, the sample is taken from which the flat test piece is prepared at a representative location as shown in Figure 5 for the Tl profile.

The 3-point bending tests at 130 C are carried out on the T6x or T7x state of the product.

Nevertheless, it is possible to characterize the formability in the as-quenched state W with this test, provided that the time between the tensile stress relief following quenching and the execution of the three-point bending test is controlled. In the case of extruded products, the bending angle at 130 C is expressed as an average value calculated from individual measurements taken on samples taken at different places distributed over the length of the profile.

A particularly preferred product according to the present invention is a spun product which exhibits in the T6511 state, measured on specimens taken from a flat area, a bending angle, measured at 130 ° C. by a 3-point bending test according to DIN 50 111 (section 3.1) on a sample with a thickness of 1.6 mm, at least 34, and an elastic limit Rpo, 2 of at least 720 MPa, and preferably a bending angle of at least 35 and a elastic limit of at least 750 MPa.

Another particularly advantageous product according to the invention is a spun product which in the T76511 state, measured on specimens taken from a flat area, has a bending angle, measured at 130 ° C. by a 3-point bending test according to DIN 50 111 (section 3.1) on a sample with a thickness of 1.6 mm, at least 36, and an elastic limit Rpo, 2 of at least 660 MPa, and preferably of at least 670 MPa. This product can be used in cases where the corrosion resistance must be at least EB level during an EXCO test (ASTM G34 standard) performed on unmachined specimens.

These two preferred products lend themselves well to the manufacture of fuselage stiffeners for civil aircraft.

As indicated above, the Applicant has surprisingly found that compared to known products, including those with a comparable zinc content, the products according to the invention show good hot-forming ability. In

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on the other hand, the cold forming ability in the unstable state W after redissolution and quenching is slightly less good. For the manufacture of aircraft structural elements, such as fuselage stiffeners, the Applicant therefore prefers the hot forming process, if said forming is deep.

The products according to the invention can also be used as a structural element for an aircraft floor, as well as, in the form of profiles, as seat rails.

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

Examples Example 1: Several Al-Zn-Mg-Cu alloys were prepared by semi-continuous casting of plates, and they were subjected to a standard transformation range, comprising a homogenization step, the parameters of which were determined according to l 'teaching of US Pat. No. 5,560,789, followed by hot rolling, by a solution step followed by quenching and stress relieving operations, and finally by tempering in the T651 state. Sheets with a thickness of 20 mm were thus obtained in the T651 state. The compositions of the sheets making up this test are shown in Table 1.

Table 1

<tb>
<tb> Alloy <SEP> Zn <SEP> Mg <SEP> Cu <SEP> Fe <SEP> Si <SEP> Zr <SEP> Ti <SEP> Mn <SEP> Sc <SEP> Mg / Cu
<tb> A <SEP> 8.40 <SEP> 2.11 <SEP> 1.83 <SEP> 0.09 <SEP> 0.06 <SEP> 0.11 <SEP> 0.017 <SEP> 0 <SEP > 0 <SEP> 1.15
<tb> B <SEP> 10.27 <SEP> 3.2 <SEP> 0.71 <SEP> 0.08 <SEP> 0.03 <SEP> 0.11 <SEP> 0.017 <SEP> 0 <SEP > 0 <SEP> 4.57 <SEP>
<tb> C <SEP> 10.08 <SEP> 2.69 <SEP> 0.95 <SEP> 0.08 <SEP> 0.03 <SEP> 0.11 <SEP> 0.014 <SEP> 0 <SEP > 0 <SEP> 2.83
<tb> D <SEP> 9.97 <SEP> 2.14 <SEP> 1.32 <SEP> 0.09 <SEP> 0.03 <SEP> 0.11 <SEP> 0.017 <SEP> 0 <SEP > 0 <SEP> 1.62
<tb>

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The static mechanical characteristics were determined by a tensile test according to standard EN 10002-1. The K1C toughness was determined according to ASTM E399. The results are shown in Table 2:
Table 2

<tb>
<tb> Alloy <SEP> Traction <SEP> direction <SEP> Long <SEP> Traction <SEP> direction <SEP> TL <SEP> Toughness <SEP> LT
<tb> RpO, 2 <SEP> Rm <SEP> A <SEP> RpO, 2 <SEP> Rm <SEP> A <SEP> K1C
<tb> MPa <SEP> MPa <SEP>% <SEP> MPa <SEP> MPa <SEP>% <SEP> MPam
<tb> A <SEP> 627 <SEP> 665 <SEP> 14.7 <SEP> 566 <SEP> 623 <SEP> 13.6 <SEP> 31.9 <SEP>
<tb> B <SEP> 716 <SEP> 726.5 <SEP> 6.5 <SEP> 640 <SEP> 696 <SEP> 5.2 <SEP> 21.1
<tb> C <SEP> 700 <SEP> 717 <SEP> 9.2 <SEP> 629 <SEP> 676 <SEP> 8.1 <SEP> 21 <SEP>
<tb> D <SEP> 665 <SEP> 685 <SEP> 12.2 <SEP> 608 <SEP> 649 <SEP> 11 <SEP> 26.8
<tb>
It is noted that the sheet C, in accordance with the invention, presents a good compromise between mechanical strength and elongation. Compared to sheet D, outside the invention, its mechanical strength is significantly better. Compared to sheet A, made of alloy 7449 according to the state of the art, alloy C has a very improved mechanical strength. The fact that the toughness of sheet C is less good than that of sheet B limits its application to certain uses for which the toughness is not dimensioned, but which require both excellent mechanical strength and good workability. formatting. Compared to sheet B, outside the invention, the elongation at break of sheet C is significantly better. Moreover, in order for the sheet B to be able to achieve the results indicated in Table 2, it must be subjected to a fairly long solution which does not lend itself to the requirements of industrial production. And even, it is observed that there are too many coarse phases in the product which have a detrimental effect on the homogeneity of the mechanical properties, both within the same batch and within the same product (sheet or profiled); prohibits the use of product B as an aircraft structural component.

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<tb>
<tb>

5
<tb> 10
<tb> 15
<tb> 20
<tb> 25
<tb> 30
<tb>

Example 2:
Several alloy plates were cast, the composition of which is indicated in the
Table 3, with an Si content approximately equal to 0.04% for all alloys.

Alloys G1, G2, G3 and G4 and B are outside the present invention. The composition of the alloys B and D, outside the invention, is indicated in Example 1, as well as that of Example C (according to the invention). All these alloys exhibited satisfactory flowability during the tests, that is to say that no cracks or cracks were observed during the casting tests on an industrial scale.

Alloys G5, G6, G7, G8 are outside the present invention, and alloy G9 is a 7060 alloy according to the state of the art; these alloys exhibited cracks during casting tests.

The difficulties appearing during the casting of these alloys do not necessarily make the wrought products obtained from these plates unsuitable for use, but are at the origin of additional costs because the implementation (that is to say) ie the quantity of salable metal relative to the quantity of metal charged, a parameter which is directly linked to the quantity of discarded plates) will be greater than for the alloys corresponding to the preferred field of the invention. In addition, the propensity of these alloys to form slits during their solidification makes it very difficult to make the casting process more reliable within the framework of a quality assurance program through statistical process control.

It is found that all the 7000 alloys exhibiting a very pronounced propensity for the formation of slits or cracks during 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 flow criterion.

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Table 3

<tb>
<tb> Alloy <SEP> Zn <SEP> Mg <SEP> Cu <SEP> Screenability <SEP> Content <SEP>Mg> Mgcriti
<tb> (weight%) <SEP> (weight%) <SEP> (weight%) <SEP> observed <SEP> critical <SEP> in <SEP> Mg
<tb> Gl <SEP> 7. <SEP> 5 <SEP> 3 <SEP> 3 <SEP> Low <SEP> 2.54 <SEP> Yes
<tb> G2 <SEP> 8. <SEP> 5 <SEP> 3 <SEP> 2,3 <SEP> Low <SEP> 2.35 <SEP> Yes
<tb> G3 <SEP> 7. <SEP> 5 <SEP> 3 <SEP> 1. <SEP> 6 <SEP> Low <SEP> 1. <SEP> 84 <SEP> Yes
<tb> G4 <SEP> 6. <SEP> 5 <SEP> 3 <SEP> 2. <SEP> 3 <SEP> Low <SEP> 2. <SEP> 03 <SEP> Yes
<tb> B <SEP> 10.27 <SEP> 3.2 <SEP> 0.71 <SEP> Low <SEP> 1.82 <SEP> Yes
<tb> C <SEP> 10.08 <SEP> 2.69 <SEP> 0.95 <SEP> Low <SEP> 1.91 <SEP> Yes
<tb> D <SEP> 9.97 <SEP> 2.14 <SEP> 1.32 <SEP> Low <SEP> 2.08 <SEP> Yes
<tb> G5 <SEP> 8. <SEP> 5 <SEP> 2. <SEP> 3 <SEP> 3 <SEP> Strong <SEP> 2.7 <SEP> No <SEP>
<tb> G6 <SEP> 6. <SEP> 5 <SEP> 2. <SEP> 3 <SEP> 3 <SEP> Strong <SEP> 2. <SEP> 38 <SEP> No
<tb> G7 <SEP> 8. <SEP> 5 <SEP> 1. <SEP> 6 <SEP> 2. <SEP> 3 <SEP> Strong <SEP> 2. <SEP> 35 <SEP> No
<tb> G8 <SEP> 7. <SEP> 5 <SEP> 1. <SEP> 6 <SEP> 1. <SEP> 6 <SEP> Strong <SEP> 1. <SEP> 84 <SEP> No
<tb> G9 <SEP> 7 <SEP> 1.65 <SEP> 2.1 <SEP> Strong <SEP> 2.01 <SEP> No
<tb>
Example 3: Spinning billets were prepared with alloys whose composition is summarized in Table 4. The alloys were homogenized as follows:
Samples Q1 and Q2: 4 h at 465 C + 20 h at 476 C
Samples Q3 and Q4: 4 h at 465 C + 20 h at 471 C
Samples P1 to P4: 8 p.m. at 471 C.

The M, T and S phases were completely dissolved during the homogenization treatment; this was verified by differential enthalpy analysis (see US Pat. No. 5,560,789).

<Desc / Clms Page number 18>

The diameter of the billets was 200 mm for billets P3 and Q1 to Q4, and 155 mm for billets P1 and P2.

Table 4

<tb>
<tb> billet <SEP> Zn <SEP> Mg <SEP> Cu <SEP> Cr <SEP> Mn <SEP> Si <SEP> Fe <SEP> Zr <SEP> Ti <SEP> Mg / Cu
<tb> P1 <SEP> 8.10 <SEP> 2.48 <SEP> 1.65 <SEP> 0.14 <SEP> 0.17 <SEP> 0.01 <SEP> 0.08 <SEP> 0 , 15 <SEP> 0.03 <SEP> 1.50
<tb> P2 <SEP> 8.45 <SEP> 2.60 <SEP> 1.76 <SEP> 0.18 <SEP> 0.18 <SEP> 0.05 <SEP> 0.14 <SEP> 0 , 12 <SEP> 0.02 <SEP> 1.48
<tb> P3 <SEP> 8.39 <SEP> 2.55 <SEP> 1.71 <SEP> 0.18 <SEP> 0.16 <SEP> 0.04 <SEP> 0.15 <SEP> 0 , 11 <SEP> 0.02 <SEP> 1.49
<tb> QI <SEP> 10.20 <SEP> 3.41 <SEP> 0.68 <SEP> 0.17 <SEP> 0.17 <SEP> 0.07 <SEP> 0.08 <SEP> 0 , 13 <SEP> 0.04 <SEP> 5.01
<tb> Q2 <SEP> 10.20 <SEP> 2.84 <SEP> 0.95 <SEP> 0.18 <SEP> 0.17 <SEP> 0.06 <SEP> 0.11 <SEP> 0 , 13 <SEP> 0.03 <SEP> 2.99
<tb> Q3 <SEP> 9.98 <SEP> 2.10 <SEP> 1.24 <SEP> 0.18 <SEP> 0.17 <SEP> 0.06 <SEP> 0.14 <SEP> 0 , 12 <SEP> 0.03 <SEP> 1.69
<tb> Q4 <SEP> 10.00 <SEP> 2.15 <SEP> 1.25 <SEP> 0.18 <SEP> 0.17 <SEP> 0.07 <SEP> 0.14 <SEP> 0 , 12 <SEP> 0.03 <SEP> 1.72
<tb>
From these homogenized and peeled billets, three types of profiles T1, T2 and T3 were developed, the sections of which are shown in Figures 1, 2 and 3. The temperature of the container and of the tool was greater than 400 C, the spinning speed was less than 0.50 m / min.

The maximum spinning pressures are summarized in Table 5. It is surprisingly found that for the alloys according to the invention, the spinning pressure does not increase, and, surprisingly, even decreases, for certain types of profiles.

Table 5: Spinning pressure

<tb>
<tb> Pressure <SEP> Pressure <SEP> Pressure <SEP> Pressure <SEP> Pressure <SEP> Ratio <SEP> of
<tb> [bars] <SEP> for <SEP> [bars] <SEP> for <SEP> [bars] <SEP> for <SEP> [bars] <SEP> for <SEP> [bars] <SEP> for <SEP> spinning
<tb> billet <SEP> Pl <SEP> billet <SEP> Q1 <SEP> billet <SEP> Q2 <SEP> billet <SEP> Q3 <SEP> billet <SEP> Q4
<tb> Profile <SEP> Tl <SEP> 179 <SEP> 175 <SEP> 170 <SEP> 164 <SEP> 164 <SEP> 58
<tb> Profile <SEP> T2 <SEP> 151 <SEP> 145 <SEP> 142 <SEP> 137 <SEP> 139 <SEP> 24
<tb> Profile <SEP> T3 <SEP> 203 <SEP> 208 <SEP> 200 <SEP> 193 <SEP> 195 <SEP> 13
<tb>

<Desc / Clms Page number 19>

The profiles Q1 to Q4 were dissolved at 471 C, the profiles P1 to P3 to 472 C (profiles Tl and T3) or (profile T2). All the profiles have been soaked in water and pulled with a permanent elongation between 1.5 and 2%. No straightening was applied after controlled traction.

The static mechanical characteristics are summarized in Table 6, for three different thicknesses of the test specimen in the T6511 state, taken from a flat zone of the profile. These states were obtained by artificial aging under the following conditions:
Alloys Q1 and Q2: 18 hours at 120 C
Alloys P1 to P3, Q3 and Q4: 36 hours at 120 C.

Table 6

<tb>
<tb> Alloy <SEP> Rm <SEP> [MPa] <SEP> Rp0,2 <SEP> [MPa] <SEP> A <SEP> [%
<tb> profile <SEP> Tl <SEP> T3 <SEP> T2 <SEP> Tl <SEP> T3 <SEP> T2 <SEP> Tl <SEP> T3 <SEP> T2
<tb> Ql <SEP> 755 <SEP> 753 <SEP> 788 <SEP> 743 <SEP> 736 <SEP> 783 <SEP> 8.4 <SEP> 7.0 <SEP> 4.7
<tb> Q2 <SEP> 746 <SEP> 750 <SEP> 778 <SEP> 731 <SEP> 729 <SEP> 771 <SEP> 9.8 <SEP> 8.7 <SEP> 6.0
<tb> Q3 <SEP> 698 <SEP> 699 <SEP> 728 <SEP> 674 <SEP> 673 <SEP> 712 <SEP> 13.6 <SEP> 12.3 <SEP> 9.3
<tb> Q4 <SEP> 697 <SEP> 696 <SEP> 723 <SEP> 673 <SEP> 670 <SEP> 704 <SEP> 13.3 <SEP> 11.7 <SEP> 10.7
<tb> Pl <SEP> 708 <SEP> 694 <SEP> 745 <SEP> 671 <SEP> 656 <SEP> 718 <SEP> 12.5 <SEP> 11.7 <SEP> 7.7
<tb>

Sample :
Tl = sole of the T1 profile. T2 = heel of section T2. T3 = heel of profile T3.

The characteristics in the T76511 state, obtained by artificial aging under the following conditions:
QlàQ4: 12h to 120 C + 8h to 150 C
PI: 12 h at 120 C + 10 h at 56 C

<Desc / Clms Page number 20>

are summarized in Table 7.
Table 7

<tb>
<tb> alloy <SEP> Rm <SEP> [MPa] <SEP> Rp0,2 <SEP> [MPa] <SEP> A <SEP> [%]
<tb> profile <SEP> Tl <SEP> T3 <SEP> T2 <SEP> Tl <SEP> T3 <SEP> T2 <SEP> Tl <SEP> T3 <SEP> T2
<tb> QI <SEP> 694 <SEP> 706 <SEP> 712 <SEP> 674 <SEP> 687 <SEP> 696 <SEP> 9.9 <SEP> 7.7 <SEP> 8.3
<tb> Q2 <SEP> 694 <SEP> 704 <SEP> 708 <SEP> 675 <SEP> 686 <SEP> 693 <SEP> 10.3 <SEP> 9.0 <SEP> 8.3
<tb> Q3 <SEP> 674 <SEP> 676 <SEP> 697 <SEP> 662 <SEP> 664 <SEP> 684 <SEP> 9.6 <SEP> 9.7 <SEP> 10.0
<tb> Q4 <SEP> 673 <SEP> 677 <SEP> 687 <SEP> 657 <SEP> 663 <SEP> 672 <SEP> 11.1 <SEP> 9.7 <SEP> 10.0
<tb> P1 <SEP> 659 <SEP> 644 <SEP> 686 <SEP> 615 <SEP> 589 <SEP> 643 <SEP> 12.1 <SEP> 10.3 <SEP> 9.1
<tb>

Sample :
Tl = sole of profile Tl. T2 = heel of profile T2. T3 = heel of profile T3.

It is noted that compared to the alloy P1, the alloys Q1, Q2 and Q3 have a significantly higher mechanical resistance.

Corrosion resistance was characterized according to the EXCO test (ASTM G34 standard) of products Q1 to Q4 in the T6511 state (unmachined samples) was EA or EB level and overall at least as good or better than that of samples PI to P3.

Example 4 The formability of the Tl-type profiles of Example 3 was studied using the 3-point bending test according to DIN 50 111 of September 1987 (section 3.1). The location of the sample, a flat area, is shown in Figure 5. Important parameters of the 3-point bending device are shown in Figure 7. The test was performed at 130 C.

The T6511 and T76511 states have been tested. The bending angles are presented in Table 8. These are average values calculated from half a dozen individual measurements taken on samples taken at different places distributed over the length of the profiles.

<Desc / Clms Page number 21>

Table 8

<tb>
<tb> Angle <SEP> of <SEP> bending
<tb> alloy <SEP> to <SEP> state <SEP> T76511 <SEP> to <SEP> state <SEP> T6511
<tb> Q1 <SEP> 43.4 <SEP> Q2 <SEP> 38.1 <SEP> 36.9
<tb> Q3 <SEP> 33.90 <SEP> 33.8
<tb> P1 <SEP> 41.50 <SEP> 35.2
<tb>
In all cases, the profiles according to the invention (Q1 and Q2) have a formability comparable to that of the profiles according to the state of the art (Q3 and P1).

Example 5: We studied the cold forming ability of samples similar to those of Example 4 (in the unstable state W after redissolution and quenching), with the same 3-point bending technique , but at room temperature. There is a low dispersion of the bending angle as a function of the length of the profiles. Table 9 refers to the values measured at state W.

Table 9:

<tb>
<tb> Sample <SEP> Angle <SEP> of <SEP> bending
<tb> QI <SEP> 27.1 '<SEP>
<tb> Q2 <SEP> 27.3 '<SEP>
<tb> Q3 <SEP> 33.6 <SEP>
<tb> P1 <SEP> 34.5
<tb>

Claims (15)

1. Rolled, extruded or forged product of Al-Zn-Mg-Cu alloy, characterized in that it contains (in mass percent): a) Zn 8.3 - 14.0 Cu 0.3 - 2.0 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, Yb, the content of each of said elements, if it is selected, being between 0.02 and 0.7%, c) the remainder of aluminum and impurities inevitable, and in that it satisfies the conditions d) Mg / Cu> 2.4 and e) (7.9 - 0.4 Zn)> (Cu + Mg)> (6.4 - 0.4 Zn). 2. Rolled, extruded or forged product of Al-Zn-Mg-Cu alloy, characterized in that it contains (in mass percent): a) Zn 9.5 - 14.0 Cu 0.3 - 2.0 Mg 0.5 - 4.5 Fe + Si <0.25 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 of said elements, if selected, being between 0.02 and 0.7%, c ) the remainder of aluminum and inevitable impurities, and in that it satisfies the conditions d) Mg / Cu> 2.4 and e) (7.9 - 0.4 Zn)> (Cu + Mg)> (6.4 - 0.4 Zn). 3. Product according to claim 1, wherein Zn> 9.0%. 4. Product according to any one of claims 1 to 3, wherein Mg 0.5 - 3.6. 5. Product according to any one of claims 1 to 4, wherein Mg / Cu> 2.8 <Desc / Clms Page number 23> 6. Product according to any one of claims 1 to 5, wherein Mg / Cu> 4.0. 7. Product according to any one of claims 1 to 6, wherein Mg> 1.95 + 0.5 (Cu - 2.3) + 0.16 (Zn - 6) + 1.9 (Si - 0.04). 8. Product according to any one of claims 1 to 7, wherein the following maximum concentrations are not exceeded: Cr 0.40 Mn 0.60 Sc 0.50 Zr 0.15 Hf 0.60 Ti 0.15 Ce, Nd, La and Eu 0.35 each and preferably 0.30 each Gd0.35 Tb 0.35 Ho 0.40 Dy 0.40 Er 0.40 Yb 0.40 Y 0.20 9. Extruded product according to any one of claims 1 to 7, characterized in that it has in the T6511 state, measured on specimens taken from a flat area, a) a bending angle, measured at 130 C by a 3-point bending test according to DIN 50 111 (section 3.1) on a sample of thickness 1.6 mm, and expressed as an average value calculated from individual measurements carried out on samples taken at different places distributed over the length of the profile, of at least 34, and b) an elastic limit Rpo, 2 of at least 720 MPa, and preferably a bending angle of at least 35 and an elastic limit of at least 750 MPa. 10. Spun product according to one of claims 1 to 7, characterized in that it has in the state T76511, measured on specimens taken from a flat area, a) a bending angle, measured at 130 C by a 3-point bending test according to DIN 50 111 (section 3.1) on a sample with a thickness of 1.6 mm, and expressed as an average value calculated from individual measurements carried out on samples taken at different places distributed over the length of the profile, at least 37 and preferably of at least 40, and b) an elastic limit Rpo, 2 of at least 670 MPa. <Desc / Clms Page number 24> 11. Spun product according to claim 10, characterized in that the corrosion resistance, determined according to the EXCO test (ASTM G34 standard), the T6511 state on unmachined samples, is at least EB level. 12. Aircraft structural element, produced in a product according to any one of claims 1 to 11. 13. Structural element according to claim 12, characterized in that said element is a fuselage stiffener. 14. Structural element according to claim 13, characterized in that said element is made from a spun product. 15. Aircraft comprising a fuselage assembled from a plurality of stiffeners and a plurality of sheets, characterized in that at least part of said stiffeners are structural elements according to any one of claims 12 to 14.