WO2018189471A1

WO2018189471A1 - Aluminium-copper-lithium alloy products

Info

Publication number: WO2018189471A1
Application number: PCT/FR2018/050886
Authority: WO
Inventors: Juliette CHEVY
Original assignee: Constellium Issoire
Priority date: 2017-04-10
Filing date: 2018-04-09
Publication date: 2018-10-18
Also published as: CN110536972A; FR3065011A1; BR112019021170B1; EP3610047A1; BR112019021170A2; CN110536972B; US20210087665A1; EP3610047B1; DE18724941T1; FR3065011B1; CA3058021A1

Abstract

The invention relates to a product made of an aluminium-based alloy comprising, by wt. %, Cu: 2.5-3.4; Li: 1.6-2.2; Mg: 0.4-0.9; Mn: 0.2-0.6, Zr: 0.08-0.18; Zn: < 0.4; Ag: < 0.15; Fe + Si ≤ 0.20; at least one element selected from Ti, Se, Cr, Hf and V, the content of the element, if selected, being: Ti: 0.01-0.15; Se: 0.01-0.15; Cr: 0.01-0.3; Hf: 0.01-0.5; V: 0.01-0.3; other elements ≤ 0.05 each and ≤ 0.15 in total; the remainder being aluminium. The invention also relates to a method for manufacturing an aluminum alloy-based, extruded, rolled and/or forged product, and a structural element incorporating at least one product as described above.

Description

Aluminum-copper-lithium alloy products

Field of the invention

The invention generally relates to wrought products of aluminum-copper-lithium alloys, and more particularly to such products in the form of profiles intended to produce stiffeners in aeronautical construction. State of the art

A continuous research effort is being made to develop materials that can simultaneously reduce the weight and increase the efficiency of high performance aircraft structures. Aluminum alloys containing lithium are very interesting in this respect, 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. For these alloys to be selected in aircraft, their performance must reach that of commonly used alloys, in particular in terms of a compromise between the static mechanical strength properties (elastic limit, breaking strength) and the properties of damage tolerance ( toughness, resistance to the propagation of fatigue cracks), these properties being in general antinomic. 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 integrally. Several Al-Cu-Li alloys are known for which an addition of silver is made.

No. 5,032,359 discloses a broad family of aluminum-copper-lithium alloys in which the addition of magnesium and silver, in particular between 0.3 and 0.5 percent by weight, makes it possible to increase the mechanical strength. These alloys are often known under the trade name "Weldalite ™".

US Patent 5,198,045 discloses a family of Weldalite ™ alloys comprising (in% by weight) (2,4-3,5) Cu (1,35-1,8) Li (0.25-0.65). Mg, (0.25-0.65) Ag, (0.08-0.25) Zr. The Wrought products made with these alloys combine a density of less than 2.64 g / cm ³ and a compromise between strength and toughness of interest.

US Pat. No. 7,229,509 describes a family of Weldalite ™ alloys comprising (in% by weight) (2.5-5.5) Cu, (0.1-2.5) Li, (0.2-1.0). Mg, (0.2-0.8) Ag, (0.2-0.8) Mn, (up to 0.4) Zr or other elements such as Cr, Ti, Hf, Se and V. Examples presented have a compromise between mechanical strength and improved toughness but their density is greater than 2.7 g / cm ³ . Patent application WO2007 / 080267 discloses a Zirconium-free Weldalite ™ alloy for fuselage plates comprising (in% by weight) (2, 1-2.8) Cu, (1, 1-1, 7) Li, (0.2-0.6) Mg, (0.1-0.8) Ag, (0.2-0.6) Mn.

AA2196 alloy comprising (in% by weight) (2.5-3.3) Cu, (1, 4-2.1) Li, (0.25-0.8) Mg, is also known. , 25-0.6) Ag, (0.04-0.18) Zr and at most 0.35 Mn.

The limitation of the amount of money is economically very favorable. However, it can be seen that the products according to the prior art made of alloys containing essentially no silver do not make it possible to obtain properties as advantageous as those of products made with alloys containing silver such as alloy AA2196.

There is a need for aluminum-copper-lithium alloy products, especially spun products, having a reduced density and properties substantially equivalent to those of known silver-containing products, particularly in terms of a compromise between the properties of static mechanical resistance and damage tolerance properties. The thermal stability, the corrosion resistance, the machinability and the density of these products in particular must also be satisfactory compared to those of known products containing silver while having a low density. Object of the invention

A first subject of the invention is an aluminum-based alloy product comprising, in% by weight,

Cu: 2.5-3.4; preferably 2.8-3.2;

Li: 1.6-2.2; preferentially 1.65-1.8;

Mg: 0.4-0.9; preferentially 0.5-0.8;

Mn: 0.2 - 0.6; preferably 0.3-0.6;

Zr: 0.08 - 0.18; preferentially 0.12-0.16;

Zn: <0.4, preferably 0.05-0.4; more preferably 0.2-0.4;

Ag: <0.15; preferentially <0.1; more preferably still <0.05;

Fe + Si <0.20;

at least one element selected from

Ti: 0.01-0.15; preferably 0.01-0.05;

Se: 0.01-0.15, preferentially 0.02-0.1;

Cr: 0.01 - 0.3, preferably 0.02-0.1;

Hf: 0.01 - 0.5; preferably 0.02-0.1;

V: 0.01-0.3, preferably 0.01-0.05;

other elements <0.05 each and <0, 15 in total, remains aluminum.

A second object of the invention is a method of manufacturing a spun, rolled and / or forged product based on aluminum alloy comprising the steps:

a) developing a bath of liquid metal comprising, in percentage by weight, Cu:

2.5-3.4; Li: 1.6-2.2; Mg: 0.4-0.9; Mn: 0.2 - 0.6; Zr: 0.08 - 0.18; Zn: <0.4; Ag: <0.15; Fe + Si <0.20; at least one element selected from Ti, Se, Cr, Hf and V, the content of said element, if selected, being Ti: 0.01 - 0.15; Se, 0.01-0.15; Cr: 0.01 - 0.3; Hf: 0.01 - 0.5; V: 0.01 - 0.3; other elements <0.05 each and <0.15 in total, remaining aluminum

b) pouring a raw form from said bath of liquid metal;

c) homogenizing said raw form;

d) hot deformation and, optionally, cold deformation of the raw form into a spun, rolled and / or forged product; e) dissolving and quenching said product;

f) controlled traction of said product with a permanent deformation of 1 to 15%, preferably 2 to 4%;

g) the income of the said product by heating at 140 to 170 ° C for 5 to 70 hours.

Advantageously, the income is made so that said product has a conventional yield strength measured at 0.2% elongation in the direction L, R _p o, 2 (L), of at least 510 MPa and a tenacity KQ (LT), in the LT direction, of at least 21

MPaVn and as KQ (LT)> -0.2667 * R _P o, 2 (L) + 169. Yet another object of the invention is a structural element incorporating at least one product according to the invention.

Description of figures

Figure 1: Shape of the profile W of the example (the term "shape" means the cross section of said profile). The dimensions are given in mm. The samples used for the mechanical characterizations were taken from the area indicated by the dots.

Figure 2: Shape of the profile Z of the example (the term "shape" means the cross section of said profile). The dimensions are given in mm. The samples used for the mechanical characterizations were taken from the area indicated by the dots.

3: Compromise between toughness and mechanical strength obtained for the profiles of the example.

Description of the invention

Unless stated otherwise, all the information concerning the chemical composition of the alloys is expressed as a percentage by weight based on the total weight of the alloy. The designation of alloys is 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 method of measuring weight. The values are calculated in accordance with the procedure of The Aluminum Association, which is described pages 2-12 and 2.13 of "Aluminum Standards and Data". The definitions of the metallurgical states are given in the European standard EN 5 15 (2009).

Unless otherwise stated, the static mechanical characteristics, in other words the tensile strength R _m , the conventional yield stress at 0.2% elongation R _p o, 2 ("yield strength") and elongation at break A, are determined by a tensile test according to EN 10002-1 (2001), the sampling and the direction of the test being defined by EN 485-1 (2016).

The stress intensity factor (KQ) is determined according to ASTM E 399 (2012). Thus, the proportion of specimens defined in paragraph 7.2.1 of this standard is always verified, as is the general procedure defined in paragraph 8. ASTM E 399 (2012) gives paragraphs 9. 1 .3 and 9.1. criteria to determine if KQ is a valid Kic value. Thus, a Kic value is always a KQ value, the reciprocal being not true. In the context of the invention, the criteria of paragraphs 9.1 .3 and 9. 1 .4 of ASTM E399 (2012) are not always verified, however for a given specimen geometry, the KQ values presented are always comparable with each other, the geometry of the specimen making it possible to obtain a valid value of Kic not being always accessible taking into account the constraints related to the dimensions of the sheets or profiles.

Unless otherwise specified, the definitions of EN 12258 (2012) apply. The thickness of the profiles is defined according to 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 can be considered as the thickness of the elementary rectangle.

Here, a "structural element" or "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 realized. These are typically elements whose failure is likely to endanger the safety of said construction, its users, its users or others. For an airplane, these elements of These structures include the elements that make up the fuselage (such as fuselage skin (fuselage skin), stiffeners or stringers, bulkheads, circumferential frames, wings (such as wing skin), stiffeners (stiffeners), ribs (ribs) and spars) and empennage composed in particular of horizontal and vertical stabilizers (horizontal or vertical stabilizers), as well as the floor beams, the seat tracks and the doors.

According to the invention, a selected class of aluminum alloys containing specific and critical levels of copper, lithium, magnesium, zinc, manganese and zirconium but essentially free of silver makes it possible to prepare products wrought with an improved compromise between toughness and strength compared to products containing essentially no money.

The present inventors have found that, surprisingly, it is possible for products to achieve a compromise at least equivalent between the static mechanical strength properties and the damage tolerance properties that that obtained with an aluminum-copper-lithium alloy containing silver, such as alloy AA2196, by carefully selecting the amounts of lithium, copper, magnesium, manganese, zinc and zirconium.

The copper content of the products according to the invention is between 2.5 and 3.4% by weight. In an advantageous embodiment of the invention, the copper content is at least 2.8 or preferably at least 2.9% by weight and / or at most 3.2 and preferably at most 3.1% by weight. weight.

The lithium content of the products according to the invention is between 1, 6 and 2.2% by weight. Advantageously, the lithium content is between 1.65% and 1.8% by weight. Preferably, the lithium content is at most 1.75% by weight. The magnesium content of the products according to the invention is between 0.4 and 0.9% by weight and preferably it is at least 0.5% by weight and more preferably still greater than 0.6%. in weight. Advantageously, the magnesium content is from plus 0.8% by weight. The present inventors have found that when the magnesium content is less than 0.30% by weight the advantageous compromise between mechanical strength and damage tolerance is not achieved. The manganese content of the products according to the invention is between 0.2 and 0.6% by weight and, preferably, it is at least 0.3% by weight and, more preferably still, at least 0.33% by weight and more preferably at least 0.4% by weight. In another embodiment, the manganese content is between 0.2 and 0.4% by weight, preferably between 0.25 and 0.35% by weight. The present inventors have found that when the manganese content is less than 0.2% by weight, the KQ (LT) toughness, in the LT direction, advantageous according to the invention is not obtained.

The zirconium content of the products according to the invention is between 0.08 and 0.18% by weight and, preferably, it is 0.12 to 0.16% by weight and more preferably 0% by weight. , 14 to 0.15% by weight. In another embodiment, the zirconium content is advantageously between 0.09 and 0.12% by weight, preferably between 0.09 and 0.11% by weight, and even between 0.09 and 0.10% by weight. in weight.

The zinc content is less than 0.4% by weight, preferably it is 0.05 and 0.35% by weight. Advantageously, the zinc content is 0.2 to 0.3% by weight, which can contribute to achieving the desired compromise between toughness and strength.

The silver content is less than 0.15% by weight, preferably less than 0.10% by weight and more preferably less than 0.05% by weight. The present inventors have found that the advantageous compromise between known mechanical strength and damage tolerance for alloys typically containing 0.2 to 0.4% by weight of silver can be obtained for alloys containing essentially no silver. with the composition selection made. The sum of the iron content and the silicon content is at most 0.20% by weight. Preferably, the iron and silicon contents are each at most 0.08% by weight. In In an advantageous embodiment of the invention, the iron and silicon contents are at most 0.06% and 0.04% by weight, respectively.

The alloy also contains at least one element that can contribute to controlling the grain size selected from Ti, Se, Cr, Hf and V, the content of the element, if selected, being from 0.01 to 0 15% by weight, preferably 0.01 to 0.05% by weight for Ti; from 0.01 to 0.15% by weight, preferably 0.02 to 0.1% by weight for Se; 0.01 to 0.5% by weight, preferably 0.02 to 0.1% by weight for Hf and from 0.01 to 0.3% by weight, preferably from 0.02 to 0.1% by weight for Cr and from 0.01 to 0.3% by weight, preferably 0.01 to 0.05% by weight for V. Preferably, between 0.02 and 0.04% by weight of titanium is chosen.

The alloy according to the invention is particularly intended for the manufacture of rolled, spun and / or forged products and, more particularly, spun products. The products according to the invention have a compromise between mechanical strength and particularly advantageous toughness.

The products according to the invention have a spun, solution, quenched, triturated and tempered state, especially for thicknesses up to 50 mm or between 8 and 50 mm, or even between 15 and 35 mm. conventional yield strength measured at 0.2% elongation in the L direction, Rp0.2 (L), of at least 510 MPa and a KQ (LT) toughness in the LT direction of at least 21 MPaVm and such that KQ (LT)> - 0.2667 * RpO, 2 (L) + 169. According to a particularly advantageous embodiment, they have, under the conditions described above, a conventional yield strength measured at 0.2% elongation in the L, Rp0.2 (L) direction of at least 525 MPa and a KQ (LT) toughness in the LT direction of at least 23 MPaVm and such that KQ (LT) )> - 0.2667 * RPO, 2 (L) + 171. In the present invention, the test pieces used for KQ measurements are CT type 20mm thick and 50mm wide. The manufacturing process of the products according to the invention comprises stages of production, casting, rolling, extrusion and / or forging, dissolving, quenching, stripping and tempering.

In a first step, a bath of liquid metal is produced so as to obtain an aluminum alloy of composition according to the invention.

The liquid metal bath is then cast in a crude form typically a rolling plate, an extrusion billet or a forging blank.

The crude form is then homogenized at a temperature between 450 ° C and 550 ° and preferably between 520 ° C and 530 ° C for a period of between 6 and 15 hours. After homogenization, the raw form is optionally cooled to room temperature before being preheated to be hot deformed. The hot deformation is carried out by rolling, extruding and / or forging so as to obtain a rolled product, spun and / or forged, preferably a spun product.

The product thus obtained is then dissolved by heat treatment at 490-550 ° C for 15 minutes to 8 hours, and then typically quenched with water at room temperature.

The product then undergoes controlled stress relief, preferably by traction, with a permanent deformation of 1 to 15% and preferably 2 to 4%.

Advantageously, the spun product exhibits at the end of the above-described process steps a thickness of up to 50 mm or between 8 and 50 mm, or even between 15 and 35 mm.

An income is achieved comprising heating at a temperature between 140 and 170 ° C for 5 to 70 hours so that said product has a conventional yield strength measured at 0.2% elongation in the L direction, R _p o, 2 (L), of at least 510 MPa and a tenacity KQ (LT), in the LT direction, of at least 21 MPaVm and such that KQ (L-T)> -0.2667 * R _p o, 2 (L) + 169. The present inventors have found that the compromise between mechanical strength and toughness can be improved by producing the temperature at a temperature of between 150 and 165 ° C. for a time equivalent to t at 160 ° C. between 15 and 28h, preferably between 20 and 27h, ¾ being defined by the formula: f exp (-16400 / T) dt

= ^A

where T (in Kelvin) is the instantaneous metal processing temperature, which changes with time t (in hours), and T _re f is a reference temperature set at 433 K.

According to a particularly advantageous embodiment, the product spun with a conventional yield strength measured at 0.2% elongation in the direction L, Rp0.2 (L), of at least 525 MPa and a KQ toughness ( LT), in the LT direction, of at least 23 MPaVm and such that KQ (LT)> -0.2667 * RpO, 2 (L) + 171. In said embodiment, the spun product advantageously has a thickness, up to 50 mm or between 8 and 50 mm, or even between 15 and 35 mm.

The products according to the invention can advantageously be used in structural elements, in particular aircraft. Thus, an object of the invention is a structural element incorporating at least one product according to the invention or a product manufactured from a method according to the invention.

The use of a structural element incorporating at least one product according to the invention or manufactured from such a product is advantageous, in particular for aeronautical construction. The products according to the invention are particularly advantageous for the production of structural elements such as stiffeners or frames for the manufacture of intrados or extrados elements of aircraft wings, preferably stiffeners, longitudinal members and ribs, or also floor beams and seat rails.

These and other aspects of the invention are explained in more detail with the aid of the following illustrative and non-limiting examples.

Example In this example, several billets (384 mm in diameter) of Al-Cu-Li alloy whose composition is given in Table 1 were cast (alloys 67, 74 a and b, 66, 68 and 69). The composition of two alloys of the prior art AA2196 has also been given in Table 1 below.

Table 1. Composition in% by weight and density of Al-Cu-Li alloys used

For all alloys 67, 74a and b, 66, 68 and 69, Fe and Si <0.20% by weight and other elements less than 0.05% by weight each, o.i5% by total weight. The alloy billets 67, 74a and b, 66, 68 and 69 were then homogenized from 8 to 10h at 524 ° C. The billet alloy 2 was homogenized 8h at 500 ° C and 24h at 527 ° C while the alloy 5 was homogenized 8h at 520 ° C.

After homogenization, the billets were heated to 450 ° C. +/- 40 ° C. and then hot-spun to obtain profiles W according to FIG. 1 for the alloys 2, 67, 74 a and b, 66, 68 and 69 and Z according to Figure 2 for the alloys 5. The profiles thus obtained were dissolved at 524 ° C, quenched and tractionned with a permanent elongation of between 2 and 5%.

The profiles were subjected to an income as indicated in Table 2: 30h at 152 ° C, 48h at 152 ° C, 30h at 160 ° C. For the alloys 2 and 5, the income was made for 48h to 152 ° C. The equivalent times t; at 160 ° C were calculated taking into account the rise time up to the income level and considering a rise speed of 20 ° C / h.

Samples taken at the end of the profile were tested to determine their static mechanical properties as well as their toughness (KQ). The location of the samples is indicated in dashed lines in FIGS. 1 and 2. The reverts used for the measurement of the static properties were of diameter 10 mm and taken in such a way that the direction of the axis of the specimen corresponds to the direction of spinning (L direction). The specimens used for the toughness measurements were of CT type and had characteristics of B = 20 mm and W = 50 mm and were machined in such a way that the direction of loading corresponded to the direction of spinning and the direction of propagation was perpendicular. to the spinning direction and contained in the plane of Figures 1 and 2 (LT configuration).

The results obtained are given in Table 2 below and illustrated in FIG. 3 for the alloys of Table 1.

Table 2. Income conditions and properties Rp0.2 (L) and Kq (L-T) alloys teq 160 ° C Rp0.2 (L) Kq (L-T)

Returned

(h) (MPa) (MPaVm)

30h - 152 ° C 16.8 506 27.3

66 48h - 152 ° C 26.7 541 18.8

30h - 160 ° C 30.6 545 16.6

30h - 152 ° C 16.8 517 37.8

48h - 152 ° C 26.7 564 24.8

30h - 160 ° C 30.6 569 20.2

67

30h -155 ° C 21,545 33.1

40h - 152 ° C 22.2 548 29.0

21h - 160 ° C 21.6 542 27.7

30h - 152 ° C 16.8 524 17.3

68 48h - 152 ° C 26.7 548 15.1

30h - 160 ° C 30.6 545 14.9

30h - 152 ° C 16.8 551 20.9

69 48h - 152 ° C 26.7 566 16.6

30h - 160 ° C 30.6 560 15.7 30h-152 ° C 16.8 518 32.4a 48h-152 ° C 26.7 552 22.0

30h-160 ° C 30.6 552 18.4

30h-152 ° C 16.8 515 38.7b 48h-152 ° C 26.7 550 23.0

30h-160 ° C 30.6 557 18.5

48h-152 ° C 26.7 522 37.6

48h-152 ° C 26.7 536 38.2

Claims

claims

1) Aluminum alloy product comprising, in% by weight,

Cu: 2.5-3.4; preferably 2.8-3.2;

Li: 1.6-2.2; preferentially 1.65-1.8;

Mg: 0.4-0.9; preferentially 0.5-0.8;

Mn: 0.2 - 0.6; preferably 0.3-0.6;

Zr: 0.08 - 0.18; preferentially 0.12-0.16;

Zn: <0.4, preferably 0.05-0.4; more preferably 0.2-0.4;

Ag: <0.15; preferentially <0.1; more preferably still <0.05;

Fe + Si <0.20;

at least one element selected from Ti, Se, Cr, Hf and V, the content of the element, if selected, being:

Ti: 0.01-0.15; preferably 0.01-0.05;

Se: 0.01-0.15, preferentially 0.02-0.1;

Cr: 0.01 - 0.3, preferably 0.02-0.1;

Hf: 0.01 - 0.5; preferably 0.02-0.1;

V: 0.01-0.3, preferably 0.01-0.05;

other elements <0.05 each and <0.15 in total, remains aluminum.

2) The product of claim 1 wherein the copper content is 2.9 to 3.1% by weight.

3) Product according to any one of claims 1 to 2 wherein the lithium content is 1.65 to 1.75% by weight.

4) Product according to any one of claims 1 to 3 wherein the manganese content is 0.4 to 0.6% by weight. 5) Product according to any one of claims 1 to 3 wherein the zirconium content is 0.14 to 0.15% by weight. 6) A process for producing a spun, rolled and / or forged aluminum alloy product comprising the steps of:

a) developing a bath of liquid metal comprising, in percentage by weight, Cu:

b) pouring a raw form from said bath of liquid metal;

c) homogenizing said raw form;

d) hot deformation and, optionally, cold deformation of the raw form into a spun, rolled and / or forged product;

e) dissolving and quenching said product;

g) returning said product spun by heating at 140 to 170 ° C for 5 to 70 hours so that said product has a conventional yield strength measured at 0.2% elongation in the direction L, R _p o , 2 (L), of at least 510 MPa and toughness

KQ (LT), in the LT direction, of at least 21 MPaVm and such that KQ (LT) - 0.2667 * R _P o, ₂ (L) + 169.

7) The method of claim 6 wherein the homogenization temperature is between 520 ° C and 530 ° C and the treatment time is between 6 and 15 hours.

8) Process according to any one of claims 6 to 7 wherein the income is made a temperature between 150 to 165 ° C for a time equivalent t; at 160 ° C between 15 and 28h, preferably between 20 and 27h, t _; - being defined by the formula:

where T (in Kelvin) is the instantaneous temperature of metal treatment, which evolves with the time t (in hours), and T _ref is a reference temperature set at 433 K.

9) Product obtained according to any one of claims 6 to 8 characterized in that it has a conventional yield strength measured at 0.2% elongation in the direction L, Rp0.2 (L), d at least 525 MPa and a KQ (LT) toughness in the LT direction of at least 23 MPaVm and such that KQ (LT)> -0.2667 * RpO, 2 (L) + 171.

10) Structure element incorporating at least one product according to any one of claims 1 to 5 or made from a product obtained according to any one of claims 6 to 8.

1 1) structural element according to claim 10 characterized in that it is used as a stiffener or frame for the manufacture of intrados or extrados elements of aircraft wing, preferably stiffeners, spars and ribs, or floor beams and seat rails.