EP3201370B1 - Wrought product of an alloy of aluminium, magnesium, lithium - Google Patents

Description

Field of the invention

The invention relates to wrought aluminum-magnesium-lithium alloy products, more particularly such products with an improved compromise in properties, in particular an improved compromise between tensile elastic limit and toughness of said products. The invention also relates to a manufacturing process as well as the use of these products intended in particular for aeronautical and aerospace construction.

State of the art

Wrought aluminum alloy products are developed to produce high strength parts intended in particular for the aeronautical industry and the aerospace industry. Aluminum alloys containing lithium are very interesting in this regard, since lithium can reduce the density of aluminum by 3% and increase the modulus of elasticity by 6% for each weight percent of lithium added. In particular, aluminum alloys containing simultaneously magnesium and lithium make it possible to achieve particularly low densities and have therefore been extensively studied.

The patent GB 1,172,736 teaches an alloy containing 4 to 7% by weight Mg, 1.5 - 2.6% Li, 0.2 - 1% Mn and / or 0.05 - 0.3% Zr, aluminum residue, useful for processing of products with high mechanical strength, good corrosion resistance, low density and high elastic modulus. Said products are obtained by a process comprising an optional quenching followed by tempering. By way of example, the products resulting from the process according to GB 1,172,736 have a tensile strength ranging from approximately 440 MPa to approximately 490 MPa, a tensile elastic limit ranging from approximately 270 MPa to approximately 340 MPa and an elongation at rupture of the order of 5-8%.

International demand WO 92/03583 describes an alloy useful for aeronautical structures having a low density and of general formula Mg _a Li _b Zn _c Ag _d Al _bal , in which a is between 0.5 and 10%, b is between 0.5 and 3% , c is between 0.1 and 5%, d is between 0.1 and 2% and bal indicates that the rest is aluminum. This document also discloses a process for obtaining said alloy comprising the steps: a) pouring an ingot of the composition described above, b) removing the residual stresses from said ingot by heat treatment, c) homogenizing by heating and maintaining temperature then cool the ingot, d) hot roll said ingot to its final thickness, e) dissolve and then soak the product thus laminated, f) tract the product and g) achieve an income of said product by heating and maintaining temperature .

The patent US 5,431,876 teaches a group of ternary aluminum alloys lithium and magnesium or copper, including at least one additive such as zirconium, chromium and / or manganese. The alloy is prepared according to methods known to a person skilled in the art, comprising, for example, extrusion, dissolving, quenching, pulling the product from 2 to 7% and then tempering.

The patent US 6,551,424 describes a process for manufacturing rolled aluminum-magnesium-lithium alloy products with a composition (in% by weight) Mg: 3.0 - 6.0; Li: 0.4 - 3.0; Zn up to 2.0; Mn up to 1.0; Ag up to 0.5; Fe up to 0.3; If up to 0.3; Cu up to 0.3; 0.02 - 0.5 of an element selected from the group consisting of Sc, Hf, Ti, V, Nd, Zr, Cr, Y, Be, said method including cold rolling lengthwise and in the sense of width.

The patent US 6,461,566 describes an alloy of composition (in% by weight) Li: 1.5 - 1.9; Mg: 4.1 - 6.0; Zn 0.1 - 1.5; Zr 0.05 - 0.3; Mn 0.01 - 0.8; H 0.9 x 10 ^-5 - 4.5 x 10 ^-5 and at least one element selected from the group Be 0.001 - 0.2; Y 0.001 - 0.5 and Sc 0.01 - 0.3.

The patent application WO 2012/16072 describes a wrought aluminum alloy product of composition in% by weight, Mg: 4.0 - 5.0; Li: 1.0 - 1.6; Zr: 0.05-0.15; Ti: 0.01 - 0.15; Fe: 0.02 - 0.2; If: 0.02 - 0.2; Mn: ≤ 0.5; Cr ≤ 0.5; Ag: ≤ 0.5; Cu ≤ 0.5; Zn ≤ 0.5; Sc <0.01; other items <0.05; remains aluminum. Said product is in particular obtained according to a manufacturing process comprising in particular successively the casting of the alloy in raw form, its deformation hot and optionally cold, the dissolution then the quenching of the product thus deformed, optionally the cold deformation of the product thus put in solution and quenched and finally the tempering of the product wrought at a temperature below 150 ° C. The metallurgical state obtained for the rolled products is advantageously a T6 or T6X or T8 or T8X state and for the extruded products advantageously a T5 or T5X state in the case of press quenching or a T6 or T6X or T8 or T8X state.

IN Fridlyander "Aluminum alloys containing lithium and magnesium", Metallovedenie i termicheskaya obrabotka metallov (RU), no. 9 (2003) pages 13-16 (ISSN: 0026-0819 ) discloses an Al-Li-Mg alloy, which comprises Mg 5.0-6.0%; Li 1.9-2.3%; Zr 0.09-0.15%; If 0.1-0.3%; Fe ≤ 0.3%; Ti ≤ 0.1%; Mn ≤ 0.3%; Na ≤ 0.05%.

Wrought aluminum-magnesium-lithium alloy products have a low density and are therefore particularly interesting in the extremely demanding field of aeronautics. For new products to be selected in such a field, their performance must be significantly improved compared to that of existing products, in particular their performance in terms of compromise between the properties of static mechanical resistance (in particular tensile elastic limit and in compression, resistance to rupture) and the properties of tolerance to damage (toughness, resistance to the propagation of cracks in fatigue), these properties being in general contradictory.

These alloys must also have sufficient corrosion resistance, be able to be shaped according to the usual methods and have low residual stresses so that they can be machined without substantial distortion during said machining.

There is therefore a need for wrought products of aluminum-magnesium-lithium alloy having a low density as well as improved properties compared to those of known products, in particular in terms of compromise between the properties of static mechanical strength and the properties of damage tolerance. Regarding damage tolerance properties, wrought products must in particular have a high toughness as well as a low propensity for delamination. Such products must also be able to be obtained according to a reliable, economical and easily adaptable manufacturing process to a conventional manufacturing line.

Subject of the invention

A first object of the invention is a wrought aluminum alloy product of composition, in% by weight, Mg: 4.0 - 5.0; Li: 1.0 - 1.8; Mn: 0.35 - 0.45; Zr: 0.05-0.15; Ag: ≤ 0.5; Fe: ≤ 0.1; Ti: <0.15; If: ≤ 0.05; other elements ≤ 0.05 each and ≤ 0.15 in combination; remains aluminum.

1. (a) on coule une forme brute en alliage d'aluminium de composition, en % en poids : Mg : 4,0 - 5,0 ; Li : 1,0 - 1,8; Mn: 0,35 - 0,45 ; Zr : 0,05 - 0,15; Ag : ≤ 0,5 ; Fe : ≤ 0,1 ; Ti : < 0,15 ; Si : ≤ 0,05 ; autres éléments ≤ 0,05 chacun et ≤ 0,15 en association ; reste aluminium ;
2. (b) optionnellement, on homogénéise ladite forme brute ;
3. (c) on déforme à chaud ladite forme brute pour obtenir un produit déformé à chaud;
4. (d) optionnellement, on met en solution ledit produit déformé à chaud à une température de 360°C à 460°C, préférentiellement de 380°c à 420°C, pendant 15 minutes à 8 heures ;
5. (e) on trempe ledit produit déformé à chaud ;
6. (f) optionnellement, on effectue un dressage/planage dudit produit déformé et trempé ;
7. (g) optionnellement, on déforme à froid de façon contrôlée le produit déformé et trempé pour obtenir une déformation permanente à froid de 1 à 10 %, de préférence de 2 à 6%, plus préférentiellement encore de 3 à 5% et, plus préférentiellement encore de 4 à 5%;
8. (h) on réalise un revenu dudit produit déformé et trempé.

The invention also relates to a process for manufacturing said wrought product in which:

1. (a) pouring a crude form of aluminum alloy of composition, in% by weight: Mg: 4.0 - 5.0; Li: 1.0 - 1.8; Mn: 0.35 - 0.45; Zr: 0.05-0.15; Ag: ≤ 0.5; Fe: ≤ 0.1; Ti: <0.15; If: ≤ 0.05; other elements ≤ 0.05 each and ≤ 0.15 in combination; remains aluminum;
2. (b) optionally, said raw form is homogenized;
3. (c) said raw form is hot deformed to obtain a hot deformed product;
4. (d) optionally, said hot-deformed product is dissolved in a temperature of 360 ° C to 460 ° C, preferably from 380 ° c to 420 ° C, for 15 minutes to 8 hours;
5. (e) soaking said hot-deformed product;
6. (f) optionally, a straightening / leveling of said deformed and hardened product is carried out;
7. (g) optionally, the deformed and quenched product is cold deformed in a controlled manner to obtain a permanent cold deformation of 1 to 10%, preferably 2 to 6%, more preferably still 3 to 5% and, more preferably another 4 to 5%;
8. (h) an income of said deformed and quenched product is produced.

Another subject of the invention is the use of said wrought product to produce an aircraft structural element.

Description of the figures

• Figure 1 : Profile for fuselage frame of Example 1
• Figure 2 : Yield strength, Rp0,2, depending on the toughness, K _Q * for a flat bar 10 mm thick (* all values of K _Q are invalid due to the criterion P _max / P _Q ≤ 1 , 10 of ASTM E399)
• Figure 3 : Yield strength, Rp0.2, as a function of the stress intensity factor corresponding to the maximum force, K _max (evaluated according to standard ASTM E399) for a flat bar 10 mm thick

Description of the invention

Unless otherwise stated, all indications concerning the chemical composition of the alloys are expressed as a percentage by weight based on the total weight of the alloy. By way of example, the expression 1.4 Cu means that the copper content expressed in% by weight is multiplied by 1.4. The designation of the alloys is done in accordance with the regulations of The Aluminum Association, known to those skilled in the art. The density depends on the composition and is determined by calculation rather than by a weight measurement method. The values are calculated in accordance with the procedure of The Aluminum Association, which is described on pages 2-12 and 2-13 of "Aluminum Standards and Data". The definitions of metallurgical states are given in European standard EN 515.

The static mechanical characteristics in tension, in other words the tensile strength R _m , the conventional elastic limit at 0.2% elongation R _p0.2 , and the elongation at break A%, are determined by a tensile test according to standard NF EN ISO 6892-1, the sampling and the direction of the test being defined by standard EN 485-1. The toughness is determined by a toughness test K1c according to standard ASTM E399. A curve giving the effective stress intensity factor as a function of the effective crack extension is determined according to standard ASTM E399. The tests were carried out with a CT8 test piece (B = 8mm, W = 16mm). In the case of invalid K _Q values according to ASTM E399, in particular with respect to the criterion P _max / P _Q ≤ 1.10, the results were also presented in K _max (stress intensity factor corresponding to the maximum force P _max ).

The increase in stresses on the product during the K1c toughness test according to ASTM E399 may be indicative of the propensity of the product to delamination. The term “delamination” (“crack delamination” and / or “crack divider” in English) is understood here to mean cracking in planes orthogonal to the front of the main crack. The orientation of these plans corresponds to that of grain boundaries not recrystallized after deformation by wrought. Low delamination is a sign of less fragility in the planes concerned and minimizes the risk of crack deviation towards the longitudinal direction during propagation in fatigue or under monotonous stress.

Unless otherwise stated, the definitions of standard EN 12258 apply.

Furthermore, here a structural element or a structural element of a mechanical construction is called a mechanical part for which the static and / or dynamic mechanical properties are particularly important for the performance of the structure and for which a structural calculation is usually prescribed or performed. These are typically elements whose failure is likely to endanger the safety of said construction, its users, its users or others. For an aircraft, these structural elements include in particular the elements that make up the fuselage (such as the fuselage skin, the stiffeners or stringers of the fuselage (stringers), the bulkheads, the frames of fuselage (circumferential frames), the wings (such as upper or lower wing skin), stiffeners (stringers or stiffeners), ribs (ribs), spars, floor beams and the seat rails) and the tail unit composed in particular of horizontal and vertical stabilizers (horizontal or vertical stabilizers), as well as the doors. The wrought aluminum alloy product according to the invention has the following particular composition, in% by weight: Mg: 4.0 - 5.0; Li: 1.0 - 1.8; Mn: 0.35 - 0.45; Zr: 0.05 - 0, 15; Ag: ≤ 0.5; Fe: ≤ 0.1; Ti: <0.15; Si: ≤ 0.05; other elements ≤ 0.05 each and ≤ 0.15 in combination aluminum alloy products having such a composition associated in particular with the particular Mn content selected exhibit improved static mechanical properties as well as a low propensity for delamination. According to an even more advantageous embodiment, the Mn content, in% by weight, is preferably from 0.35 to 0.40.

According to an advantageous embodiment, the raw form of aluminum alloy has a silver content of less than or equal to 0.25% by weight, more preferably a silver content of 0.05% to 0.1% by weight. This element contributes in particular to static mechanical properties. In addition, according to an even more advantageous embodiment, the shape crude aluminum alloy has a total Ag and Cu content of less than 0.15% by weight, preferably less than or equal to 0.12%. Control of the maximum content of these two elements in combination makes it possible in particular to improve the resistance to intergranular corrosion of the wrought product.

According to a particular embodiment, the raw form has a zinc content, in% by weight, of less than 0.04%, preferably less than or equal to 0.03%. Such a limitation of the zinc content in the particular alloy described above has given excellent results in terms of density and corrosion resistance of the alloy.

According to another embodiment compatible with the preceding modes, the raw aluminum alloy form has an Fe content, in% by weight, of less than 0.08%, preferably less than or equal to 0.07%, more preferably still less than or equal to 0.06%. The present inventors believe that a minimum content of Fe, and possibly that of Si, can contribute to improving the mechanical properties and in particular the fatigue properties of the alloy. Excellent results have in particular been obtained for an Fe content of 0.02 to 0.06% by weight and / or an Si content of 0.02 to 0.05% by weight.

The lithium content of the products according to the invention is between 1.0 and 1.8% by weight. According to an advantageous embodiment, the crude form of aluminum alloy has a Li content, in% by weight, less than 1.6%, preferably less than or equal to 1.5%, preferably still less than or equal to 1 , 4%. A minimum lithium content of 1.1% by weight and preferably 1.2% by weight is advantageous. The present inventors have found that a limited lithium content, in the presence of certain addition elements, makes it possible to very significantly improve the toughness, which largely compensates for the slight increase in density and the decrease in static mechanical properties.

According to a preferred embodiment, the raw form of aluminum alloy has a Zr content, in% by weight, of 0.10 to 0.15%. The inventors have indeed found that such a Zr content makes it possible to obtain an alloy having a favorable fiber structure for improved static mechanical properties.

According to an advantageous embodiment, the raw form of aluminum alloy has an Mg content, in% by weight, of 4.5 to 4.9%. Excellent results have been obtained for alloys according to this embodiment in particular with regard to static mechanical properties.

According to an advantageous embodiment, the Cr content of the products according to the invention is less than 0.05% by weight, preferably less than 0.01% by weight. Such a limited Cr content in combination with the other elements of the alloy according to the invention makes it possible in particular to limit the formation of primary phases during casting.

The Ti content of the products according to the invention is less than 0.15% by weight, preferably between 0.01 and 0.05% by weight. The Ti content is limited in the particular alloy of the present invention, in particular to avoid the formation of primary phases during casting. On the other hand, it may be advantageous to control the Ti content to control the granular structure and in particular the grain size during the casting of the alloy.

Certain elements can be harmful for Al-Mg-Li alloys as described above, in particular for reasons of transformation of the alloy such as toxicity and / or breakage during deformation. It is therefore preferable to limit these elements to a very low level, i.e. less than 0.05% by weight or even less. In an advantageous embodiment, the products according to the invention have a maximum content of 10 ppm of Na, preferably of 8 ppm of Na, and / or a maximum content of 20 ppm of Ca. According to a particularly advantageous embodiment, the raw form of aluminum alloy is substantially free of Sc, Be, Y, more preferably said raw form comprises less than 0.01% by weight of these elements taken in combination.

• Mg : 4,0 - 5,0, préférentiellement 4,5 - 4,9;
• Li : 1,1 -1,6, préférentiellement 1,2 - 1,5 ;
• Zr : 0,05 - 0,15, préférentiellement 0,10 - 0,15 ;
• Ti : < 0,15, préférentiellement 0,01-0,05 ;
• Fe : 0,02 - 0,1, préférentiellement 0,02 - 0,06 ;
• Si : 0,02 - 0,05 ;
• Mn : 0,35 à 0,45, préférentiellement de 0,35 à 0,40 ;
• Cr : < 0,05, préférentiellement < 0,01 ;
• Ag : ≤ 0,5 ; préférentiellement ≤ 0,25 ; plus préférentiellement encore ≤ 0,1 ;
• Sc : < 0,01 ;
• autres éléments ≤ 0,05 chacun et ≤ 0,15 en association ;
• reste aluminium. D'excellents résultats ont été obtenus avec un alliage présentant une telle composition.

According to a particularly advantageous embodiment, the raw form of aluminum alloy has a composition, in% by weight:

• Mg: 4.0 - 5.0, preferably 4.5 - 4.9;
• Li: 1.1 -1.6, preferably 1.2-1.5;
• Zr: 0.05 - 0.15, preferably 0.10 - 0.15;
• Ti: <0.15, preferably 0.01-0.05;
• Fe: 0.02 - 0.1, preferably 0.02 - 0.06;
• If: 0.02 - 0.05;
• Mn: 0.35 to 0.45, preferably 0.35 to 0.40;
• Cr: <0.05, preferably <0.01;
• Ag: ≤ 0.5; preferably ≤ 0.25; more preferably still ≤ 0.1;
• Sc: <0.01;
• other elements ≤ 0.05 each and ≤ 0.15 in combination;
• remains aluminum. Excellent results have been obtained with an alloy having such a composition.

The process for manufacturing the products according to the invention comprises the successive stages of preparing a bath of liquid metal so as to obtain an Al-Mg-Li alloy of particular composition, the casting of said alloy in raw form, optionally the homogenization of said raw form thus cast, the hot deformation of said raw form to obtain a hot deformed product, optionally dissolving the product thus hot deformed, quenching of said hot deformed product, optionally dressing / leveling of the deformed and quenched product, optionally the cold deformation in a controlled manner of the deformed and quenched product to obtain a permanent cold deformation of 1 to 10%, preferably 2 to 6%, more preferably still 3 to 5%, the income of said deformed and quenched product. According to an advantageous embodiment, the tempering step is carried out before the cold deformation step in a controlled manner.

The manufacturing process therefore firstly consists in casting a raw form of Al-Mg-Li alloy with a composition, in% by weight: Mg: 4.0 - 5.0; Li: 1.0 -1.8; Mn: 0.35 - 0.45; Zr: 0.05-0.15; Ag: ≤ 0.5; Fe: ≤ 0.1; Ti: <0.15; If: ≤ 0.05; other elements ≤ 0.05 each and ≤ 0.15 in combination; remains aluminum. A bath of liquid metal is therefore produced and then poured in raw form, typically a rolling plate, a spinning billet or a forge blank.

Following the step of casting the raw form, the manufacturing process optionally includes a step of homogenizing the raw form so as to reach a temperature between 450 ° C and 550 ° C and, preferably, between 480 ° C and 520 ° C for a period of between 5 and 60 hours. The homogenization treatment can be carried out in one or more stages. According to a preferred embodiment of the invention, the hot deformation is carried out directly following a simple reheating without carrying out homogenization.

The raw form is then deformed when hot, typically by spinning, rolling and / or forging, to obtain a deformed product. This hot deformation is preferably carried out at an inlet temperature above 400 ° C and, advantageously, from 420 ° C to 450 ° C. According to an advantageous embodiment, the hot deformation is a deformation by spinning of the raw form.

In the case of sheet metal fabrication by rolling, it may be necessary to carry out a cold rolling step (which then constitutes an optional first cold deformation step) for products whose thickness is less than 3 mm. It may prove useful to carry out one or more intermediate heat treatments, typically carried out at a temperature between 300 and 420 ° C, before or during cold rolling.

The product deformed hot and, optionally cold, is optionally subjected to a separate dissolution at a temperature of 360 ° C to 460 ° C, preferably from 380 ° C to 420 ° C, for 15 minutes to 8 hours.

The deformed product and, optionally, dissolved, is then quenched. The quenching is carried out with water and / or air. It is advantageous to carry out air quenching because the intergranular corrosion properties are improved. In the case of a spun product, it is advantageous to carry out quenching on a press (or quenching on spinning heat), preferably a quenching on an air press, such quenching making it possible in particular to improve the static mechanical properties . According to another embodiment, it can also be a quenching on a water press. In the case of hardening on a press, the product is dissolved in heat on spinning.

The hot deformed and quenched product can optionally be subjected to a dressing or leveling step depending on whether it is a profile or a sheet. The term “dressing / leveling” is understood here to mean a cold deformation step without permanent deformation or with a permanent deformation of less than 1%.

The product hot deformed, quenched and, optionally upright / planed, is also cold deformed in a controlled manner to obtain a permanent cold deformation of 1 to 10%, preferably 2 to 6%, more preferably still 3 to 5 %, and more preferably still from 4 to 5%. According to an advantageous embodiment, the permanent cold deformation is 2 to 4%. Cold deformation can in particular be carried out by traction, compression and / or rolling. According to a preferred embodiment, the cold deformation is carried out by traction.

The deformed, hardened and optionally straightened / leveled product undergoes a tempering stage. Advantageously, the tempering is carried out by heating, in one or more stages, at a temperature below 150 ° C, preferably at a temperature of 70 ° C to 140 ° C, for 5 to 100 hours.

According to a first embodiment, the tempering step is carried out after the cold deformation step in a controlled manner. The metallurgical state obtained for the wrought products corresponds in particular to a T8 state according to standard EN515.

According to a second embodiment, the tempering step is carried out before the cold deformation step in a controlled manner. The product hot deformed and tempered is then cold deformed in a controlled manner to obtain a permanent cold deformation of 1 to 10%, preferably 2 to 6%, more preferably still 3 to 5%, and more preferably still 4 to 5%. According to an advantageous embodiment, the permanent cold deformation is 2 to 4%. Quite unexpectedly, it has indeed been demonstrated that, when it is carried out after the tempering step, the cold deformation in a controlled manner of a wrought product of composition as described above makes it possible to obtain an excellent compromise between static mechanical properties and those of damage tolerance, in particular toughness. The metallurgical state obtained for the wrought products corresponds in particular to a T9 state according to standard EN515.

According to an advantageous embodiment, the method for manufacturing a wrought product does not include any cold deformation step inducing a permanent deformation of at least 1% between the hot deformation step or, if this step is present, solution and the income stage.

The combination of the chosen composition, in particular of the content of Mg, Li and Mn and of the processing parameters, in particular the order of the stages of the manufacturing process, advantageously makes it possible to obtain wrought products having an improved compromise in properties. very particular, especially the compromise between mechanical resistance and tolerance to damage, while having a low density and good corrosion performance.

The wrought products according to the invention are preferably spun products such as profiles, rolled products such as sheets or thick sheets and / or forged products.

The wrought products according to the invention have particularly advantageous characteristics in comparison with identical wrought products but having the only difference in their Mn content, in particular an Mn content, in% by weight, of less than 0.3% or greater than 0.5%. The term "identical wrought products" means aluminum alloy products of the same composition, in% by weight, with the exception of Mn, and obtained according to the same manufacturing process, in particular wrought products in the same metallurgical state. according to standard EN515 and having the same rate of deformation in permanent traction in traction obtained by traction in a controlled manner.

According to an advantageous embodiment, the wrought products according to the invention exhibit less delamination on the rupture surfaces of the K1c test pieces obtained according to ASTM E399 than identical wrought products but having the only difference in their Mn content, in particular a Mn content, in% by weight, less than 0.3% or more than 0.5%.

According to an embodiment compatible with the previous mode, the wrought products according to the invention have at mid-thickness, for a thickness between 0.5 and 15 mm, a tensile strength Rm (L) greater than that of products identical wrought but with the only difference being their Mn content, in particular an Mn content, in% by weight, less than 0.3% or more than 0.5%.

According to an embodiment compatible with the preceding modes, the wrought products according to the invention have, at mid-thickness, for a thickness between 0.5 and 15 mm, a yield strength in tension Rp0,2 (L) higher than that of identical wrought products but having the only difference in their Mn content, in particular an Mn content, in% by weight, less than 0.3% or more than 0.5%.

1. (i) une résistance à la rupture Rm (L) ≥ 450 MPa, de préférence Rm (L) ≥ 455 MPa;
2. (ii) une limite d'élasticité en traction Rp0,2 (L) ≥ 330 MPa ; de préférence Rp0,2 (L) ≥ 335 MPa et, plus préférentiellement encore Rp0,2 (L) ≥ 350 MPa;
3. (iii) une limite d'élasticité en traction R p0,2 (TL) ≥ 300 MPa,de préférence Rp0,2 (TL) ≥ 305 et, plus préférentiellement encore Rp0,2 (TL) ≥ 320 MPa;
4. (iv) une ténacité, mesurée selon la norme ASTM E399 avec des éprouvettes CT8 de largeur W = 16 mm et d'épaisseur = 8 mm, K_Q (L-T) ≥ 24 MPa√m, de préférence K_Q (L-T) ≥ 26 MPa√m ;
5. (v) un facteur d'intensité de contrainte correspondant à la force maximale Pmax, mesurée selon la norme ASTM E399 avec des éprouvettes CT8 de largeur W = 16 mm et d'épaisseur = 8mm, K_max (L-T) ≥ 30 MPa√m, de préférence K_max (L-T) ≥ 32 MPa√m.

According to an advantageous embodiment, the products wrought in the T8 state, advantageously in the T8 state with a permanent cold deformation greater than 4%, according to the invention have, at mid-thickness, for a thickness of between 0 , 5 and 15 mm, at least one property of static mechanical resistance among properties (i) to (iii) and at least one property of tolerance to damage among properties (iv) to (v):

1. (i) a tensile strength Rm (L) ≥ 450 MPa, preferably Rm (L) ≥ 455 MPa;
2. (ii) a tensile elastic limit Rp0,2 (L) ≥ 330 MPa; preferably Rp0.2 (L) ≥ 335 MPa and, more preferably still Rp0.2 (L) ≥ 350 MPa;
3. (iii) a yield strength in tension R p0,2 (TL) ≥ 300 MPa, preferably Rp0,2 (TL) ≥ 305 and, more preferably still Rp0,2 (TL) ≥ 320 MPa;
4. (iv) toughness, measured according to ASTM E399 standard with CT8 test pieces of width W = 16 mm and thickness = 8 mm, K _Q (LT) ≥ 24 MPa√m, preferably K _Q (LT) ≥ 26 MPa√m;
5. (v) a stress intensity factor corresponding to the maximum force Pmax, measured according to standard ASTM E399 with CT8 test pieces of width W = 16 mm and thickness = 8mm, K _max (LT) ≥ 30 MPa√m , preferably K _max (LT) ≥ 32 MPa√m.

1. (i) une résistance à la rupture Rm (L) ≥ 450 MPa, de préférence Rm (L) ≥ 460 MPa;
2. (ii) une limite d'élasticité en traction Rp0,2 (L) ≥ 380 MPa, de préférence Rp0,2 (L) ≥ 390 MPa et, plus préférentiellement encore, Rp0,2 (L) ≥ 410 MPa;
3. (iii) une limite d'élasticité en traction Rp0,2 (TL) ≥ 320 MPa, de préférence Rp0,2 (TL) ≥ 335 MPa plus préférentiellement Rp0,2 (TL) ≥ 340 MPa et, plus préférentiellement encore, Rp0,2 (TL) ≥ 350 MPa;
4. (iv) une ténacité, mesurée selon la norme ASTM E399 avec des éprouvettes CT8 de largeur W = 16 mm et d'épaisseur = 8 mm, K_Q (L-T) ≥ 20 MPa√m, de préférence K_Q (L-T) ≥ 22 MPa√m ;
5. (v) un facteur d'intensité de contrainte correspondant à la force maximale Pmax, mesurée selon la norme ASTM E399 avec des éprouvettes CT8 de largeur W = 16 mm et d'épaisseur = 8mm, K_max (L-T) ≥ 22 MPa√m, de préférence K_max (L-T) ≥ 25 MPa√m.

According to an advantageous embodiment, the products wrought in the T9 state, advantageously in the T9 state with a permanent cold deformation greater than 4%, according to the invention have, at mid-thickness, for a thickness between 0 , 5 and 15 mm, at least one property of static mechanical resistance among properties (i) to (iii) and at least one property of tolerance to damage among properties (iv) to (v):

1. (i) a tensile strength Rm (L) ≥ 450 MPa, preferably Rm (L) ≥ 460 MPa;
2. (ii) a tensile elastic limit Rp0,2 (L) ≥ 380 MPa, preferably Rp0,2 (L) ≥ 390 MPa and, more preferably still, Rp0,2 (L) ≥ 410 MPa;
3. (iii) a yield strength in tension Rp0,2 (TL) ≥ 320 MPa, preferably Rp0,2 (TL) ≥ 335 MPa more preferably Rp0,2 (TL) ≥ 340 MPa and, more preferably still, Rp0, 2 (TL) ≥ 350 MPa;
4. (iv) toughness, measured according to ASTM E399 standard with CT8 test pieces of width W = 16 mm and thickness = 8 mm, K _Q (LT) ≥ 20 MPa√m, preferably K _Q (LT) ≥ 22 MPa√m;
5. (v) a stress intensity factor corresponding to the maximum force Pmax, measured according to standard ASTM E399 with CT8 test pieces of width W = 16 mm and thickness = 8mm, K _max (LT) ≥ 22 MPa√m , preferably K _max (LT) ≥ 25 MPa√m.

According to a preferred embodiment, the products wrought in the T8 or T9 state mentioned above have, for a thickness of between 0.5 and 15 mm, at mid-thickness at least two properties of static mechanical resistance chosen from the properties ( i) to (iii) and at least one damage tolerance property chosen from properties (iv) to (v).

The wrought products according to the invention also have a lower propensity for delamination, the latter being evaluated on the fracture surfaces of test pieces K1c according to standard ASTME399 (test piece CT8, B = 8 mm, W = 16 mm).

The products spun according to the invention have particularly advantageous characteristics. The spun products preferably have a thickness of between 0.5 mm and 15 mm, but products with a thickness greater than 15 mm, up to 50 mm or even 100 mm or more may also have advantageous properties. The thickness of the extruded products is defined according to standard EN 2066: 2001: the cross section is divided into elementary rectangles of dimensions A and B; A being always the largest dimension of the elementary rectangle and B being able to be considered as the thickness of the elementary rectangle. The sole is the elementary rectangle with the largest dimension A.

The wrought products according to the invention are advantageously used to produce structural elements for aircraft, in particular for aircraft. Preferred aircraft structural elements are in particular a fuselage skin, a fuselage frame, a stiffener or a fuselage beam or even a wing skin, a wing stiffener, a rib or a spar. These and other aspects of the invention are explained in more detail with the aid of the following illustrative and nonlimiting examples.

Examples Example 1

Several raw forms of Al-Mg-Li alloy, the composition of which is given in Table 1, were cast. Alloy B has a composition according to the invention. The density of alloys A and B, calculated in accordance with the procedure of The Aluminum Association described on pages 2-12 and 2-13 of "Aluminum Standards and Data", is 2.55. Table 1 - Composition in% by weight and density of the Al-Mg-Li alloys used Alloy Ag Li Yes Fe Cu Ti Mn Mg Zn Zr Na (ppm) Ca (ppm) Density AT 0.10 1.39 0.04 0.05 0.01 0.03 0.14 4.56 0.03 0.12 8 22 2.55 B 0.11 1.39 0.03 0.06 0.01 0.03 0.41 4.57 0.03 0.11 8 15 2.55

• pour les produits à l'état final T6 : un revenu bi-palier effectué pendant 30h à 120°C suivi de 10h à 100°C ;
• pour les produits à l'état final T8 : une traction contrôlée avec déformation permanente de 3 ou 5% (respectivement T8-3% et T8-5%) puis un revenu bi-palier effectué pendant 30h à 120°C suivi de 10h à 100°C;
• pour les produits à l'état final T9 : un revenu bi-palier effectué pendant 30h à 120°C suivi de 10h à 100°C puis une traction contrôlée avec déformation permanente de 3 ou 5% (respectivement T9-3% et T9-5%).

Billet 358 mm in diameter were produced in the raw forms. They were reheated to 430-440 ° C and then deformed hot by spinning on a press in the form of a profile for the fuselage frame as shown in FIG. figure 1 . The products thus spun were quenched in air (quenching on a press). They then underwent:

• for products in the final state T6: two-stage tempering carried out for 30 hours at 120 ° C followed by 10 hours at 100 ° C;
• for products in the T8 final state: controlled traction with permanent deformation of 3 or 5% (respectively T8-3% and T8-5%) then two-stage tempering carried out for 30 hours at 120 ° C followed by 10 hours at 100 ° C;
• for products in the final state T9: two-stage tempering carried out for 30 hours at 120 ° C followed by 10 hours at 100 ° C then a controlled traction with permanent deformation of 3 or 5% (respectively T9-3% and T9- 5%).

Samples were tested to determine their static mechanical properties (yield strength R _p0.2 in MPa, breaking strength R _m in MPa, and elongation A in%).

The results obtained are given in Tables 2 (L direction) and 3 (TL direction) below. These results are the means of 4 measurements made on full thickness samples taken from 4 positions on the fuselage frame (positions referenced a, b, c and d on the figure 1 ) for direction L and 2 measurements made on full thickness samples taken from 1 single position, referenced c on the figure 1 , for the sense TL. Table 2 - Mechanical properties of the products obtained (direction L) Alloy Mechanical property T6 T8 (3%) T8 (5%) T9 (3%) T9 (5%) AT Rm (MPa) 427 447 449 449 460 Rp0.2 (MPa) 298 330 346 382 409 AT (%) 12 11 10 9 9 B Rm (MPa) 441 453 459 460 468 Rp0.2 (MPa) 321 340 354 398 418 AT (%) 11 10 9 8 7 Alloy Mechanical property T6 T8 (3%) T8 (5%) T9 (3%) T9 (5%) AT Rm (MPa) 441 441 439 441 454 Rp0.2 (MPa) 308 308 302 335 371 AT (%) 14 14 13 11 9 B Rm (MPa) 444 456 459 456 467 Rp0.2 (MPa) 298 309 333 328 347 AT (%) 15 14 14 10 11

An Mn content of the Al-Mg-Li alloy of approximately 0.4% by weight (alloy B) makes it possible to significantly improve the mechanical resistance of the alloy (Rp0.2 and Rm), in particular the mechanical resistance in the direction L, relative to that of an alloy having an Mn content of approximately 0.14% by weight (alloy A). Furthermore, the mechanical properties, in particular for alloy B, increase with the increase in controlled traction (T6 <TX-3% <TX-5% with TX = T8 or T9). Finally, the best results are generally obtained when controlled traction is carried out after tempering (T8 <T9).

Example 2

Several raw forms of Al-Mg-Li alloy, the composition of which is given in Table 1 of the previous example, were cast. Alloy B has a composition according to the invention.

• pour les produits à l'état final T6 : un revenu bi-palier effectué pendant 30h à 120°C suivi de 10h à 100°C ;
• pour les produits à l'état final T8 : une traction contrôlée avec déformation permanente de 3 ou 5% (respectivement T8-3% et T8-5%) puis un revenu bi-palier effectué pendant 30h à 120°C suivi de 10h à 100°C;
• pour les produits à l'état final T9 : un revenu bi-palier effectué pendant 30h à 120°C suivi de 10h à 100°C puis une traction contrôlée avec déformation permanente de 3 ou 5% (respectivement T9-3% et T9-5%).

Billet 358 mm in diameter were produced in the raw forms. They were reheated to 430-440 ° C and then deformed hot by spinning on a press in the form of a flat bar (100 mm x 10 mm). The products thus spun were quenched in air (quenching on a press). They then underwent:

• for products in the final state T6: two-stage tempering carried out for 30 hours at 120 ° C followed by 10 hours at 100 ° C;
• for products in the T8 final state: controlled traction with permanent deformation of 3 or 5% (respectively T8-3% and T8-5%) then two-stage tempering carried out for 30 hours at 120 ° C followed by 10 hours at 100 ° C;
• for products in the final state T9: two-stage tempering carried out for 30 hours at 120 ° C followed by 10 hours at 100 ° C then a controlled traction with permanent deformation of 3 or 5% (respectively T9-3% and T9- 5%).

Cylindrical samples with a diameter of 4 mm were tested to determine their static mechanical properties (yield strength, R _p0.2 , in MPa; breaking strength, Rm, in MPa and elongation, A, in%).

The results obtained are given in Tables 4 (L direction) and 5 (TL direction) below. Table 4 - Mechanical properties of the products obtained (direction L). Alloy Mechanical property T6 T8 (3%) T8 (5%) T9 (3%) T9 (5%) AT Rm (MPa) 421 439 441 444 453 Rp0.2 (MPa) 286 319 330 381 398 AT (%) 13 11 11 9 10 B Rm (MPa) 439 453 456 451 462 Rp0.2 (MPa) 309 337 352 383 424 AT (%) 11 10 8 9 6 Alloy Mechanical property T6 T8 (3%) T8 (5%) T9 (3%) T9 (5%) AT Rm (MPa) 400 428 417 430 438 Rp0.2 (MPa) 267 300 303 334 345 AT (%) 16 17 15 14 14 B Rm (MPa) 423 437 447 448 449 Rp0.2 (MPa) 290 315 323 339 371 AT (%) 16 16 16 14 12

An Mn content of the Al-Mg-Li alloy of approximately 0.4% by weight (alloy B) makes it possible to significantly improve the mechanical resistance of the alloy (Rp0.2 and Rm), in particular the mechanical resistance in the direction L, relative to that of an alloy having an Mn content of approximately 0.14% by weight (alloy A). Furthermore, the mechanical properties, in particular Rp0.2, increase with the increase in controlled traction (T6 <TX-3% <TX-5% with TX = T8 or T9). Finally, the best results are generally obtained when controlled traction is carried out after tempering (T8 <T9).

The toughness of the products was characterized by the test of K1c according to standard ASTM E399. The tests were carried out with a CT8 test piece (B = 8mm, W = 16 mm) taken at mid-thickness. The values of K _Q have always been invalid according to the ASTM E399 standard, in particular with respect to the criterion P _max / P _Q ≤ 1.10. For this, the results are presented in K _max (stress intensity factor corresponding to the maximum force P _max ). The results are reported in Tables 6 and 7 and illustrated in figures 2 and 3 (LT and TL test pieces respectively). These results are the means of at least two 2 values. Table 6 - Results of the tenacity tests on LT specimens (K _max and K _Q in MPa√m) Alloy Tenacity T8 (3%) T8 (5%) T9 (3%) T9 (5%) AT K _max LT 32.2 33.6 32.5 25.9 K _Q LT 24.6 26.3 25.2 22.3 B K _max LT 30.0 32.2 25.9 - K _Q LT 24.6 26.2 22.0 - Alloy Tenacity T8 (3%) T8 (5%) T9 (3%) T9 (5%) AT K _max TL 30.8 29.5 29.9 - K _Q TL 25.4 25.0 24.7 - B K _max TL 28.5 28.2 25.2 - K _Q TL 24.2 24.3 22.4 -

The products according to the invention have a satisfactory toughness whatever the Mn content of the alloy.

The figure 2 illustrates the elastic limit, Rp0,2, of the products of this example as a function of the toughness, K _Q (all the values of K _Q are invalid due to the criterion P _max / P _Q ≤ 1.10). The figure 3 illustrates the elastic limit, Rp0,2, of the products of this example as a function of the stress intensity factor corresponding to the maximum stress, K _max .

The products in T9 exhibit an excellent compromise between their static properties, in particular Rp0.2, and their toughness, K _Q , or their stress intensity factor corresponding to the maximum force, K _max .

Delamination was quantified semi-quantitatively on the rupture surfaces of the K1c test pieces previously described according to a score of 0 to 2: score 0 = no visible delamination, score 1 = weak delamination, score 2 = marked delamination (several sheets / secondary cracks in the visible L direction). Tables 8 and 9 summarize the scores assigned to the different test pieces (LT and TL test pieces respectively). Table 8 - Evaluation of delamination on LT specimens (scores) Alloy T8 (3%) T8 (5%) T9 (3%) T9 (5%) AT 1 2 2 1 B 0 1 0 - Alloy T8 (3%) T8 (5%) T9 (3%) T9 (5%) AT 0 1 1 - B 0 0 0 -

Alloy B products exhibit lower delamination than Alloy A products.

Claims (13)

1. Wrought product made of aluminium alloy having the composition, in % by weight, Mg: 4.0 - 5.0; Li: 1.0 - 1.8; Mn: 0.35 - 0.45; Zr: 0.05 - 0.15; Ag: ≤ 0.5; Fe: ≤ 0.1; Ti: < 0.15; Si: ≤ 0.05; other elements ≤ 0.05 each and ≤ 0.15 in combination; the balance being aluminium.
2. Wrought product according to claim 1 having a concentration of Mn, in % by weight, of 0.35 to 0.40.
3. Wrought product according to claim 1 or 2 having a concentration of Zn, in % by weight, of less than 0.04%, preferably less than or equal to 0.03%.
4. Wrought product according to any one of claims 1 to 3 having a concentration of Fe, in % by weight, of less than 0.08%, preferably less than or equal to 0.07%, more preferably less than or equal to 0.06%.
5. Wrought product according to any one of claims 1 to 4 having a concentration of Li, in % by weight, of less than 1.6%, preferably less than or equal to 1.5%, more preferably less than or equal to 1.4%.
6. Wrought product according to any one of claims 1 to 5, having less delamination on the rupture surfaces of the K1c test pieces obtained according to the standard ASTM E399 than a wrought product identical but having the sole difference of a concentration of Mn, in % by weight, of less than 0.3.
7. Wrought product according to any one of claims 1 to 6, having at mid-thickness, for a thickness between 0.5 and 15mm, an ultimate strength in the direction L Rm (L) greater than that of a wrought product identical but having the sole difference of a concentration of Mn, in % by weight, of less than 0.3.
8. Wrought product according to any one of claims 1 to 6, having at mid-thickness, for a thickness between 0.5 and 15mm, an elastic limit under tension in the direction L Rp0.2(L) greater than that of a wrought product identical but having the sole difference of a concentration of Mn, in % by weight, of less than 0.3.
9. Method for manufacturing a wrought product, wherein:

   (a) an unwrought product is cast from aluminium alloy having the composition, in % by weight, Mg: 4.0 - 5.0; Li: 1.0 - 1.8; Mn: 0.35 - 0.45; Zr: 0.05 - 0.15; Ag: ≤ 0.5; Fe: ≤ 0.1; Ti: < 0.15; Si: ≤ 0.05; other elements ≤ 0.05 each and ≤ 0.15 in combination; the balance being aluminium;

   (b) optionally, said unwrought product is homogenised;

   (c) said unwrought product is hot worked to obtain a hot-worked product;

   (d) optionally, said hot-worked product is solution heat treated at a temperature from 360°C to 460°C, preferably from 380°C to 420°C for 15 minutes to 8 hours;

   (e) said hot-worked product is quenched;

   (f) optionally, a straightening of said worked and quenched product is carried out;

   (g) optionally, the worked product is cold worked in a controlled manner to obtain a cold permanent set of 1 to 10%, preferably of 2 to 6%, even more preferably of 3 to 5%;

   (h) an ageing of said worked and quenched product is carried out.
10. Method according to claim 9, wherein the step of ageing (h) is carried out before the step of cold working in a controlled manner (g).
11. Method according to claim 9 or 10, wherein the hot working of step (c) is a working by extrusion of the unwrought product.
12. Method according to any one of claims 9 to 11, wherein the quenching of step (e) is press quenching.
13. Use of a wrought product according to any one of claims 1 to 8 or obtained according to any one of claims 9 to 12, to produce an aircraft structural element, preferably a fuselage skin, a fuselage frame, a fuselage stiffener or stringer or a rib.

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