CN112105752B

CN112105752B - Method for producing aluminum-copper-lithium alloys with improved compressive strength and improved toughness

Info

Publication number: CN112105752B
Application number: CN201980029564.9A
Authority: CN
Inventors: F·马斯; D·巴尔比耶; S·贾奇; A·丹尼路; G·普热; N·伯约那-卡里洛
Original assignee: Constellium Issoire SAS
Current assignee: Constellium Issoire SAS
Priority date: 2018-05-02
Filing date: 2019-04-24
Publication date: 2022-07-05
Anticipated expiration: 2039-04-24
Also published as: US20210189538A1; WO2019211546A1; CN112105752A; FR3080861B1; EP3788179A1; CA3098916A1; FR3080861A1

Abstract

The invention relates to a production method, wherein an alloy is produced, which contains the following elements: 3.5-4.7 wt.% Cu; 0.6-1.2 wt% Li; 0.2-0.8 wt.% Mg; 0.1-0.2 wt.% Zr; 0.0-0.3 wt% Ag; 0.0-0.8 wt.% Zn; 0.0-0.5 wt.% Mn; up to 0.20 wt% Fe + Si; optionally, an element selected from the group consisting of Cr, Sc, Hf and V, in an amount (if selected) of from 0.05 to 0.3 wt% for Cr and Sc and from 0.05 to 0.5 wt% for Hf and V; the other elements are each up to 0.05 wt% and up to 0.15 wt% in total, a refiner is introduced, the alloy is cast in coarse form, homogenized, hot deformed, solution heat treated, quenched, cold deformed and tempered, wherein the refiner comprises particles of TiC and/or the cold deformation ratio is 8-16%. The products obtained by the process according to the invention have an advantageous compromise between mechanical strength and toughness.

Description

Method for producing aluminum-copper-lithium alloys with improved compressive strength and improved toughness

Technical Field

The invention relates to a method for manufacturing a product made of an aluminium-copper-lithium alloy, in particular intended for aeronautical and aerospace construction.

Technical Field

Aluminium alloy products are developed to produce high strength parts intended for use in particular in the aerospace industry.

In this regard, lithium-containing aluminum alloys have attracted great interest because lithium can reduce the density of aluminum by 3% and increase the elastic modulus by 6% per 1 wt% added lithium. For these alloys to be selected for use in aircraft, their properties, related to other service characteristics, must reach those of the usual alloys, in particular in terms of a compromise between the static mechanical strength characteristics (tensile and compressive yield strength, ultimate tensile strength) and the damage tolerance characteristics (toughness, resistance to fatigue crack propagation), which are generally mutually exclusive. For some parts, such as the upper wing skin, compressive yield strength and in-plane stress toughness are important properties. Furthermore, these mechanical properties should preferably be stable over time and have good thermal stability, that is to say not significantly altered by ageing at the operating temperature.

These alloys must also have sufficient corrosion resistance, be able to be formed according to conventional methods, and have low residual stresses so that they can be fully machined. Finally, they must be able to be obtained by robust manufacturing methods, in particular on industrial plants where it is difficult to guarantee temperature uniformity within a few degrees of a large part.

Patent US 5,032,359 describes a large group of aluminium-copper-lithium alloys in which the addition of magnesium and silver, in particular from 0.3 to 0.5% by weight, allows the mechanical strength to be improved.

Patent US 5,455,003 describes a method of manufacturing an Al-Cu-Li alloy with improved mechanical strength and improved toughness at low temperature temperatures, in particular due to suitable work hardening and tempering (revenu). The patent recommends in particular the following composition in weight percent: cu-3.0-4.5, Li-0.7-1.1, Ag-0-0.6, Mg-0.3-0.6 and Zn-0-0.75.

Patent US 7,438,772 describes a composition comprising, in weight percent, Cu: 3-5, Mg: 0.5-2, Li: 0.01-0.9, and the use of higher levels of lithium is discouraged due to the deterioration of the compromise between toughness and mechanical strength.

Patent US 7,229,509 describes an alloy comprising (in 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 grain refiners such as Cr, Ti, Hf, Sc, V.

Patent application US 2009/142222a1 describes an alloy comprising the following elements (in weight%): 3.4 to 4.2% of Cu, 0.9 to 1.4% of Li, 0.3 to 0.7% of Ag, 0.1 to 0.6% of Mg, 0.2 to 0.8% of Zn, 0.1 to 0.6% of Mn, and 0.01 to 0.6% of at least one element for controlling the grain structure. The application also describes a method of manufacturing an extruded product.

Patent application WO2009/036953 relates to an aluminium alloy product for structural elements, the chemical composition of which comprises (by weight): 3.4-5.0 Cu, 0.9-1.7 Li, 0.2-0.8 Mg, about 0.1-0.8 Ag, 0.1-0.9 Mn, up to 1.5 Zn, and one or more elements selected from the group consisting of: (about 0.05-0.3 Zr, 0.05-0.3 Cr, about 0.03-0.3 Ti, about 0.05-0.4 Sc, about 0.05-0.4 Hf), 0.15 Fe, 0.5 Si, conventional and unavoidable impurities.

Patent application WO 2012/085359a2 relates to a method of manufacturing a rolled product made of an aluminium-based alloy comprising: 4.2-4.6 wt.% Cu, 0.8-1.30 wt.% Li, 0.3-0.8 wt.% Mg, 0.05-0.18 wt.% Zr, 0.05-0.4 wt.% Ag, 0.0-0.5 wt.% Mn, up to 0.20 wt.% Fe + Si, less than 0.20 wt.% Zn, at least one element selected from Cr, Se, Hf and Ti, the elements (if selected) being in an amount of 0.05-0.3 wt.% for Cr and Se, 0.05-0.5 wt.% for Hf, 0.01-0.15 wt.% for Ti, the remaining elements each being up to 0.05 wt.% and totaling up to 0.15 wt.%, the remainder being aluminum, the method comprising the steps of preparing, casting, homogenizing, rolling at a temperature above 400 ℃, solution heat treating, quenching, drawing between 2 and 3.5%, and tempering.

Patent application US 2012/0225271 a1 relates to a wrought product having a thickness of at least 12.7mm, comprising: 3.00-3.80 wt.% Cu, 0.05-0.35 wt.% Mg, 0.975-1.385 wt.% Li, wherein-0.3 Mg-0.15Cu +1.65 ≦ Li ≦ -0.3Mg-0.15Cu +1.85, 0.05-0.50 wt.% of at least one grain structure control element, wherein the grain structure control element is selected from Zr, Sc, Cr, V, Hf, other rare earth elements, and combinations thereof, up to 1.0 wt.% Zn, up to 1.0 wt.% Mn, up to 0.12 wt.% Si, up to 0.15 wt.% Fe, up to 0.15 wt.% Ti, up to 0.10 wt.% other elements, and the total amount of other elements is no more than 0.35 wt.%.

Application WO 2013/169901 describes an alloy comprising the following elements (in weight percent): 3.5-4.4% of Cu, 0.65-1.15% of Li, 0.1-1.0% of Ag, 0.45-0.75% of Mg, 0.45-0.75% of Zn and 0.05-0.50% of at least one element for controlling the grain structure. Advantageously, the alloy has a Zn to Mg ratio of 0.60 to 1.67.

There is a need for aluminium-copper-lithium alloy products having even more improved properties than the known products, in particular in terms of a compromise between static mechanical strength properties (in particular tensile and compressive yield strengths) and damage tolerance properties (in particular toughness, thermal stability, corrosion resistance and machinability), and at the same time having a low density.

In addition, there is a need for a robust, reliable and economical method of manufacturing these products.

Disclosure of Invention

A first object of the invention is a method for manufacturing a product based on an aluminium alloy, in which, in turn,

a) preparing an aluminum-based liquid metal bath comprising 3.5 to 4.7 wt.% Cu; 0.6 to 1.2 wt% Li; 0.2 to 0.8 wt.% Mg; 0.1 to 0.2 wt.% Zr; 0.0 to 0.3 wt% Ag; 0.0 to 0.8 wt.% Zn; 0.0 to 0.5 wt.% Mn; up to 0.20 wt% Fe + Si; optionally, an element selected from Cr, Sc, Hf and V, if selected, in an amount of from 0.05 to 0.3 wt% for Cr and Sc and from 0.05 to 0.5 wt% for Hf and V; each of the other elements is up to 0.05 wt% and up to 0.15 wt% in total, the remainder being aluminum;

b) introducing a refiner into the molten bath to provide a Ti content of 0.01 to 0.15 wt%;

c) casting a coarse form from the liquid metal bath;

d) homogenizing the crude form at a temperature of 450 ℃ to 550 ℃, preferably 480 ℃ to 530 ℃, for 5 to 60 hours;

e) hot deforming the homogenized raw form, preferably by rolling;

f) solution heat treating the heat deformed product at 490-530 ℃ for 15 min-8 h, and then quenching the solution heat treated product;

g) cold-deforming the product at a cold deformation rate of 2% to 16%;

h) tempering, wherein the product thus cold deformed is brought to a temperature of 130 ℃ to 170 ℃, preferably 140 ℃ to 160 ℃ for 5 to 100 hours, preferably 10 to 70 hours;

wherein the refiner comprises particles of the TiC type and/or the cold deformation ratio is 8 to 16%.

Another object of the invention is a product obtainable by the process of the invention and which is a rolled product, having a thickness between 8 and 50mm and having the following characteristics at intermediate thicknesses:

K_app(L-T)≥-0.5Rc_p0.2(L)+375，

preferably K_app(L-T)≥-0.5Rc_p0.2(L)+386

Wherein K_app(L-T), expressed in MPa m, according to the standard ASTM E561(2015)

The value of the apparent stress intensity factor at break determined by measurement on a CCT specimen having a width W of 406mm and a thickness B of 6.35mm, and

Rc_p0.2(L), expressed in MPa, isCompressive yield strength measured at 0.2% compression according to standard ASTM E9 (2018).

Another object is an aircraft structural member, preferably an aircraft upper wing skin element, comprising the product of the invention.

Drawings

FIG. 1: toughness K of the alloy of example 1_appL-T and compressive yield strength Rc_p0.2L is a compromise between.

FIG. 2: the figure shows the measured K of the alloy according to example 1_app(L-T) value and according to the formula-0.5R_cp0.2The difference between the values calculated for (L) +386 depends on the conventional yield strength R measured in the longitudinal direction of the product_p0.2A change in (c).

FIG. 3: toughness K of the alloy of example 2_appL-T and compressive yield strength Rc_p0.2L is a compromise between.

FIG. 4: the figure shows the measured K of the alloy according to example 2_app(L-T) value and according to the formula-0.5R_cp0.2The difference between the values calculated for (L) +375 is a function of the conventional yield strength R measured in the longitudinal direction of the product_p0.2A change in (c).

Detailed Description

Unless otherwise indicated, all indications relating to the chemical composition of the alloy are expressed as weight percentages based on the total weight of the alloy. The expression 1.4Cu refers to the copper content expressed in weight% multiplied by 1.4. The name of The alloy conforms to The aluminum Association (The aluminum Association) specifications known to those skilled in The art. When the concentration is expressed in ppm (parts per million), the index value also refers to the mass concentration.

Unless otherwise stated, the metallurgical state definitions given in the european standard EN 515(1993) apply.

Tensile static mechanical characteristics, in other words ultimate tensile strength R_mConventional yield strength at 0.2% elongation R_p0.2And an elongation at break a%, determined by means of a tensile test according to standard NF EN ISO 6892-1(2016), the sampling and direction of the test being defined by standard EN 485 (2016). R_p0.2(L) means R measured in the longitudinal direction_p0.2。

Compressive yield strength Rc_p0.2Measured at 0.2% compression according to standard ASTM E9-09 (2018). Rc (Rc)_p0.2(L) means Rc measured in the longitudinal direction_p0.2。

Stress intensity factor (K)_1C) Determined according to standard ASTM E399 (2012).

Standard ASTM E399 (2012) gives permission to determine K_QWhether or not it is K_1CA criterion of valid values of (a). For a given sample geometry, K of different materials obtained_QThe values may be comparable to each other, provided that the yield strengths of the materials are of the same order of magnitude.

Unless otherwise stated, the definition of the standard EN 12258(2012) applies.

Apparent stress intensity factor at break (K)_app) And the values of the stress strength factor at break (Kc) are as defined in the standard ASTM E561.

A curve of the effective stress intensity factor as a function of the effective crack extension, called curve R, is given according to the standard ASTM E561 (ASTM E561-10-2).

Calculating the critical stress intensity factor K from the curve R_CIn other words, the strength factor destabilizes the crack. Stress intensity factor K_COIt is also calculated by assigning the length of the initial crack at the onset of monotonic load to the critical load. These two values are calculated for a sample having the desired shape. K_appRepresenting the factor K corresponding to the sample used for the test of curve R_CO。K_effRepresenting the factor K corresponding to the sample used for the test of curve R_C。

The mechanical parts for which the static and/or dynamic mechanical properties are particularly important for the performance of the structure and which usually require or are calculated structurally are referred to herein as "structural elements" or "structural elements" of the mechanical construction. They are generally elements whose failure can compromise the security of the construction, its user, its consumer or others. For aircraft, these structural elements include, in particular, the elements making up the fuselage (for example fuselage skins), stiffeners (stringers) of the fuselage, watertight bulkheads (bulkheads), fuselage frames (circular frames), wings (for example upper or lower wing skins), stiffeners (stringers or stiffers), stiffeners (ribs) and spars (spars) and empennages, in particular consisting of horizontal and vertical stabilizers), as well as floor beams (floor beams), seat rails (seat tracks) and doors.

According to the invention, such aluminium alloys selected comprising lithium, copper, magnesium and zirconium, in particular in specific and critical amounts, allow the production of products, in particular rolled products, with an improved compromise between toughness, tensile yield strength and compressive yield strength under certain deformation conditions.

The inventors have noted that, surprisingly, it is possible to improve the use properties of products made from these alloys, in particular those which make them suitable for making structural elements in the aeronautical and aerospace sector. In particular, the products of the invention are particularly well suited for the preparation of aircraft upper wing skin elements, since they have a particularly improved compressive yield strength Rc_p0.2(L) -toughness Kapp (L-T) tradeoff.

In particular, the invention relates to a method wherein an alloy is prepared comprising the following elements: 3.5-4.7 wt.% Cu; 0.6-1.2 wt% Li; 0.2-0.8 wt.% Mg; 0.1-0.2 wt.% Zr; 0.0-0.3 wt% Ag; 0.0-0.8 wt.% Zn; 0.0-0.5 wt.% Mn; up to 0.20 wt% Fe + Si; optionally, an element selected from the group consisting of Cr, Sc, Hf and V, in an amount (if selected) of from 0.05 to 0.3 wt% for Cr and Sc and from 0.05 to 0.5 wt% for Hf and V; the other elements are each up to 0.05 wt% and up to 0.15 wt% in total, a refiner is introduced, the alloy is cast in coarse form, homogenized, hot deformed, solution heat treated, quenched, cold deformed and tempered, wherein the refiner comprises particles of TiC and/or the cold deformation ratio is 8-16%.

The copper content of the product of the invention is from 3.5 to 4.7% by weight, preferably from 4.0 to 4.6% by weight. In a particularly advantageous embodiment, the copper content is from 4.1 to 4.5% by weight, preferably from 4.2 to 4.4% by weight. The increase in copper content contributes to the improvement in tensile yield strength and compressive yield strength. However, too high an amount of copper results in a decrease in the plane stress toughness Kapp.

The lithium content of the products of the invention is between 0.6 and 1.2% by weight. Advantageously, the lithium content is between 0.8 and 1.0% by weight; preferably 0.85 to 0.95 wt%. An increase in the lithium content has a favourable effect on the density, however the inventors have noted that for the alloy of the invention the selected lithium content allows to improve the mechanical strength, in particular the tensile yield strength and the compromise between the compressive yield strength and the toughness. Too high a lithium content may result in deterioration of toughness.

The magnesium content of the product of the invention is between 0.2 and 0.8% by weight. Preferably, the magnesium content is at least 0.3 wt.%, or even 0.4 wt.% or 0.5 wt.%, which improves both static mechanical strength and toughness. Preferably, the magnesium content is less than 0.7 wt% or even 0.65 wt%. In fact, high magnesium content causes deterioration of toughness.

The alloy may contain up to 0.8 wt.% zinc. In an advantageous embodiment, the Zn content is from 0.05 to 0.6 wt.%, preferably from 0.2 to 0.5 wt.%, and still more preferably from 0.30 to 0.40 wt.%. In another embodiment, the alloy comprises less than 0.05 wt.% Zn, preferably less than 0.02 wt.%.

The alloy may also contain up to 0.3 wt% silver. In one embodiment, the alloy comprises more than 0.05 wt%, preferably more than 0.1 wt% and still more preferably 0.2 to 0.3 wt% Ag. In one embodiment, the maximum Ag content is 0.27 wt%.

The presence of zinc and/or silver allows to obtain a compressive yield strength value close to the tensile yield strength value. In one embodiment, the Ag content is 0.1 to 0.27 wt% and/or the Zn content is 0.2 to 0.40 wt%. The alloy may also contain up to 0.5 wt.% manganese. Advantageously, the manganese content is between 0.05 and 0.4% by weight. In one embodiment, the manganese content is from 0.2 to 0.37 wt%, preferably from 0.25 to 0.35 wt%. In another embodiment, the manganese content is from 0.1 to 0.2 wt.%, preferably from 0.10 to 0.20 wt.%. In particular, the addition of Mn allows to obtain high toughness. However, if the Mn content is too high, the fatigue life may be significantly reduced.

The Zr content of the alloy is 0.1 to 0.2 weight percent. In an advantageous embodiment, the Zr content is from 0.10 to 0.15% by weight, preferably from 0.11 to 0.14% by weight.

The alloy also contains titanium, the Ti content being 0.01 to 0.15 wt.%, preferably 0.02 to 0.08 wt.%. In one embodiment, the refiner introduced into the aluminum alloy melt pool comprises TiC type particles. Advantageously, the refiner has the formula AlTi_xC_yIt is also written as ATxCy, where x and y are the contents of Ti and C in weight% for 1 weight% of Al, and x/y>4. Unexpectedly, the inventors have noted that, in the particular case of the alloy of the invention, the presence of TiC particles in the refiner and therefore in the alloy at the start of a particular refinement of the alloy during casting (AlTiC refinement) allows to obtain a product with an optimal compromise of properties. In particular, the grain refining rods of the embodiments of the method of the present invention neutralize the TiC particles present in the alloy, allowing the toughness K to be improved_appL-T and compressive yield strength Rc_p0.2L is a compromise between.

The sum of the iron content and the silicon content is at most 0.20% by weight. Preferably, the iron content and the silicon content are each at most 0.08 wt.%. In an advantageous embodiment of the invention, the iron content and the silicon content are at most 0.06% by weight and 0.04% by weight, respectively. The controlled and limited iron and silicon content contributes to an improved compromise between mechanical strength and damage tolerance.

The alloy may also contain at least one element selected from the group consisting of Cr, Sc, Hf, and V that may help control grain size, in amounts (if selected) of 0.05 to 0.3 wt.% for Cr and Sc, and 0.05 to 0.5 wt.% for Hf and V.

The content of the alloying elements may be selected to minimize density. Preferably, the additive elements contributing to the increase in density, such as Cu, Zn, Mn and Ag, are minimized, and the elements contributing to the decrease in density, such as Li and Mg, are maximized, thereby achieving 2.73g/cm or less³And preferably less than or equal to 2.72g/cm³The density of (c).

The content of other elements is up to 0.05% by weight each and up to 0.15% by weight in total. Other elements are usually unavoidable impurities.

The method of manufacturing a product of the present invention comprises the steps of: preparation, casting, introduction of a refiner, homogenization, hot deformation, solution heat treatment and quenching, cold deformation, and tempering.

In a first step, a liquid metal bath is prepared in order to obtain an aluminium alloy having the composition of the present invention. A refiner is then introduced into the melt pool such that the Ti content is 0.01 to 0.15 wt%, optionally the refiner comprises TiC type particles. Advantageously, the Ti content is between 0.02 and 0.08% by weight, preferably between 0.03 and 0.06% by weight. In one embodiment, the refiner comprises TiC type particles. Advantageously, the TiC type particle-containing refiner is introduced in such a form and amount that the amount of TiC added is the same as the amount added in the form of refiner AT3C0.15 in an amount of 2 to 5kg/t of aluminium alloy. Preferably, the TiC type particle-containing refiner is introduced in the form of AT3C0.15 in an amount of 2 to 5kg/t of aluminium alloy.

The liquid metal bath is then cast into a coarse form, preferably in the shape of a rolled ingot.

The crude form is then homogenized to reach a temperature of 450 ℃ to 550 ℃, preferably 480 ℃ to 530 ℃ for 5 to 60 hours. The homogenization treatment may be performed in one stage or in multiple stages.

After homogenization, the crude form is typically cooled to room temperature and then preheated for hot deformation. In particular, the hot deformation may be extrusion or hot rolling. Preferably, it is a hot rolling step. The hot rolling is carried out to a thickness of preferably 8 to 50mm and preferably 15 to 40 mm.

The product thus obtained is then subjected to a solution heat treatment to reach a temperature of 490 to 530 ℃ for 15min to 8h, then quenched with water, usually at room temperature.

The product is then subjected to cold deformation at a cold deformation rate of 2 to 16%. In one embodiment, cold deformation is controlled stretching with a set of 2 to 6%, preferably 2.0% to 4.0%. In one embodiment, the product is cold deformed at a cold deformation ratio of 8-16%. In one embodiment, cold deformation is performed in two steps: firstly, cold rolling the product, wherein the thickness reduction rate is 8-12%, and preferably 9-11%; the stretching is then carried out in a controlled manner with a permanent set of 0.5 to 4%, preferably 0.5% to 2%.

The product is then subjected to a tempering step by heating at a temperature of 130 to 170 ℃, preferably 140 to 160 ℃, for 5 to 100 hours and preferably 10 to 70 hours. In a particularly advantageous embodiment, the tempering is carried out at a temperature of 140 to 155 ℃, preferably 145 to 150 ℃, preferably for 18 to 22 hours.

The inventors have noted that, unexpectedly, the process of the invention allows to obtain an advantageous product. The specific amounts and critical amounts of the alloy of the invention in relation to the specific manufacturing method thus allow to achieve excellent properties. In particular, the product of the invention is advantageously a rolled product having a thickness of 8 to 50mm and having, at a medium thickness, the following characteristics:

K_app(L-T)≥-0.5Rc_p0.2(L)+375，

preferably K_app(L-T)≥-0.5Rc_p0.2(L)+386

Even more preferably K_app(L-T)≥-0.5Rc_p0.2(L)+391，

Rc_p0.2(L), expressed in MPa, is the compressive yield strength measured at 0.2% compression according to the standard ASTM E9 (2018).

Advantageously, the product of the invention is a rolled product having a thickness of 8 to 50mm and having, at a medium thickness, the following characteristics:

K_app(L-T)≥-0.5R_cp0.2(L)+375

and a yield strength value R_p0.2(L) is at least 580MPa, preferably 600MPa, even morePreferably the pressure of the mixture is 615MPa,

wherein K is_app(L-T), expressed in MPa m, according to the standard ASTM E561(2015)

The value of the apparent stress intensity factor at break determined by measurement on a CCT sample having a width W of 406mm and a thickness B of 6.35mm, and

And R_p0.2(L), conventional yield strength at 0.2% elongation measured in the longitudinal direction of the product, determined by tensile testing according to standard NF EN ISO 6892-1 (2016).

The inventors have in particular noticed that, surprisingly, it is advantageous to introduce a refining agent containing particles of TiC type into the liquid metal bath so as to obtain a Ti content of 0.01 to 0.15% by weight and a cold deformation after solution heat treatment with a cold deformation rate of 8 to 16%. In particular, this combination allows to obtain a rolled product having a thickness of 8 to 50mm and, at intermediate thicknesses, having the following characteristics:

K_app(L-T)≥-0.5Rc_p0.2(L)+386,

preferably K_app(L-T)≥-0.5Rc_p0.2(L)+391

Advantageously, the combination of the introduction of a refining agent containing TiC type particles into the liquid metal bath so as to obtain a Ti content of 0.01 to 0.15% by weight and a cold deformation rate after solution heat treatment of 8 to 16%, allows to obtain a rolled product with a thickness of 8 to 50mm and having, at medium thicknesses, the following characteristics:

K_app(L-T)≥-0.5Rc_p0.2(L)+386，

preferably K_app(L-T)≥-0.5Rc_p0.2(L)+391

And a yield strength value R_p0.2(L) is at least 600MPa, even more preferably at least 615MPa, where K_app(L-T), expressed in MPa m, according to the standard ASTM E561(2015)

Rc_p0.2(L), expressed in MPa, is the compressive yield strength measured at 0.2% compression according to the standard ASTM E9(2018), and

R_p0.2(L), the conventional yield strength at 0.2% elongation measured in the longitudinal direction of the product, determined by means of a tensile test according to standard NF EN ISO 6892-1 (2016).

The alloy product of the invention allows in particular the manufacture of structural elements, in particular aircraft structural elements. In an advantageous embodiment, the preferred aircraft structural element is an aircraft upper wing skin element.

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

Examples

Example 1

In this example, two plates of 406mm thickness were cast for each alloy, the composition of each alloy being given in Table 1. Alloy 1 was refined using 2.7kg/t AT 3B. Alloy 2 was refined using 4kg/t of AT3C0.15.

TABLE 1 compositions in weight% of

alloys

1 and 2

Alloy (I)	Si	Fe	Cu	Mn	Mg	Zn	Ti	Zr	Li	Ag
											1	0.02	0.03	4.3	0.31	0.60	0.35	0.03	0.12	0.91	0.24
2	0.02	0.04	4.3	0.14	0.61	0.36	0.05	0.13	0.88	0.25

The plates were homogenized at about 510 ℃. The homogenized plate was hot rolled at an input temperature of about 450 ℃ and an output temperature of about 390 ℃ to obtain a plate thickness of 28mm for each alloy. The plates were solution heat treated at about 510 ℃ for 3h and then water quenched at 20 ℃. One sheet of each

alloy

1 and 2 was then cold rolled at a thickness reduction of 10% ("LAF 10%" condition) and then stretched at a permanent elongation of about 1%. For each alloy, the other sheet was also stretched at a 3% set without prior cold rolling.

The plate was subjected to a single stage tempering as shown in table 2. Samples were taken at medium thickness to measure static mechanical characteristics in tension and compression and toughness K_Q. The width W of the test piece used for the toughness measurement was 40mm, and the thickness B was 20 mm. The measurements made are valid according to ASTM E399 standard. In addition, planar stress toughness at intermediate thicknesses was measured during the curve R test using CCT samples 406mm wide and 6.35mm thick. The results are shown in table 2 and fig. 1.

FIG. 2 shows measured K_app(L-T) value with a value according to the formula "-0.5R_cp0.2The difference between the values calculated for (L) + 386' is a function of the conventional yield strength R measured in the longitudinal L direction of the product_p0.2(L) is changed.

TABLE 2 temper conditions for different sheets and mechanical properties obtained

Example 2

Plates with a cross-section of 406X 1520mm were cast, the composition of which is given in Table 3. The refiner used was AT 3B.

TABLE 3 compositions in weight% of

alloys

3, 4 and 5

Alloy (I)	Si	Fe	Cu	Mn	Mg	Zn	Ti	Zr	Li	Ag
												3	0.05	0.05	4.5	0.37	0.35	0.02	0.03	0.11	1.02	0.21
4	0.03	0.05	4.5	0.34	0.71	0.04	0.04	0.11	1.02	0.21
											5	0.03	0.04	4.6	0.35	0.23	0.04	0.02	0.14	1.05	0.22

The plates were homogenized at about 510 ℃. After homogenization, the plate was hot rolled to obtain a plate with a thickness of 25 mm. The plates were solution heat treated at about 510 ℃ for 5 hours and then quenched in cold water. One sheet of each alloy was cold rolled at a 10% reduction in thickness ("LAF 10%" condition) and then stretched at a permanent elongation of about 1.2%. The other sheet of each alloy was drawn at a certain permanent elongation without prior cold rolling. The values of permanent elongation are shown in Table 4.

The panels were then subjected to tempering at 155 ℃ for 10 to 25 hours as shown in table 2. In whichSampling at equal thickness to measure static mechanical characteristics in tension and compression and plane stress toughness K_app(L-T). The specimen used for toughness measurement was CCT with width W406 mm and thickness B6.35 mm. The results obtained are shown in table 4 and fig. 3.

FIG. 4 shows measured K_app(L-T) value and according to the formula-0.5R_cp0.2The difference between the values calculated for (L) +375 is a function of the conventional yield strength R measured in the longitudinal L direction of the product_p0.2A change in (c).

Table 4: the tempering conditions and the mechanical properties obtained for the plates made of

alloys

3, 4 and 5.

Claims

1. A method of manufacturing an aluminium alloy based product, wherein, in sequence,

a) preparing an aluminum-based liquid metal bath comprising 3.5 to 4.7 wt.% Cu; 0.6 to 1.2 wt% Li; 0.2 to 0.8 wt.% Mg; 0.1 to 0.2 wt.% Zr; 0.0 to 0.3 wt% Ag; 0.0 to 0.8 wt.% Zn; 0.0 to 0.5

Mn in weight%; up to 0.20 wt% Fe + Si; optionally, selected from Cr, Sc,

Elements of Hf and V, if selected, in amounts of, for Cr and Sc

0.05 to 0.3 wt%, for Hf and V0.05 to 0.5 wt%; each of the other elements is up to 0.05 wt% and up to 0.15 wt% in total, the remainder being aluminum;

c) casting a coarse form from the liquid metal bath;

d) homogenizing the crude form at a temperature of 450 ℃ to 550 ℃ for 5 to 60 hours;

e) hot deforming the homogenized coarse form;

f) the hot deformed product is subjected to solution heat treatment at 490-530 ℃ for 15 min-8 h,

then quenching the solution heat treated product;

g) cold-deforming the product at a cold deformation rate of 2% to 16%;

h) tempering, wherein the product thus cold deformed is brought to a temperature of 130 ℃ to 170 ℃ for 5 to 100 hours;

2. The process of claim 1, wherein d) the crude form is homogenized at a temperature of 480 ℃ to 530 ℃ for 5 to 60 hours.

3. The method of claim 1, wherein e) the homogenized, coarse form is hot deformed by rolling.

4. The method according to claim 1, wherein h) tempering is performed, wherein the product thus cold deformed is brought to a temperature of 140 ℃ to 160 ℃.

5. The process according to claim 1, wherein h) tempering is carried out for 10 to 70 hours.

6. The process according to claim 1, wherein the refining agent comprising TiC type particles is introduced in such a form and in such an amount that the amount of TiC added is the same as the amount added in the following way: added in the form of a refiner AT3C0.15 in an amount of 2 to 5kg/t of aluminium alloy.

7. The method according to any one of claims 1-6, wherein the cold-deformation of step g) comprises the steps of:

g1) cold rolling the product with a thickness reduction of 8-12%;

g2) stretching the product in a controlled manner with a permanent set of 0.5-4%.

8. The method of any one of claims 1-6, wherein tempering is performed at a temperature of 140 to 155 ℃ for 18 to 22 hours.

9. The method of claim 8, wherein tempering is performed at a temperature of 145 to 150 ℃ for 18 to 22 hours.

10. A process according to any one of claims 1 to 6, wherein the copper content is from 4.0 to 4.6% by weight.

11. The method of claim 10, wherein the copper content is 4.1-4.5 wt%.

12. The method according to any one of claims 1 to 6, wherein the manganese content is 0.05-0.4 wt%.

13. The method according to any one of claims 1-6, wherein the Ag content is 0.1-0.27 wt% and/or the Zn content is 0.2-0.40 wt%.

14. An aluminium alloy based product obtainable by the method according to any one of claims 1-13.

15. The product according to claim 14, which is a rolled product having a thickness of 8 to 50mm, and which has the following characteristics at intermediate thicknesses:

K_app(L-T)≥-0.5Rc_p0.2(L)+375，

16. The product of claim 15, wherein K is_app(L-T)≥-0.5Rc_p0.2(L)+386。

17. The product according to claim 14, which is a rolled product having a thickness of 8 to 50mm, and which has the following characteristics at intermediate thicknesses:

K_app(L-T)≥-0.5Rc_p0.2(L) +386, and

R_p0.2(L)>600Mpa，

Rc_p0.2(L), expressed in MPa, is the compressive yield strength measured at 0.2% compression according to standard ASTM E9 (2018); and

R_p0.2(L), conventional yield strength at 0.2% elongation measured in the longitudinal direction of the product, determined by tensile testing according to standard NF EN ISO 6892-1 (2016).

18. The product of claim 17, wherein K is_app(L-T)≥-0.5Rc_p0.2(L)+391。

19. The product of claim 17, wherein R_p0.2(L)>615Mpa。

20. An aircraft structural element comprising the product according to any one of claims 14-19.

21. The aircraft structural element of claim 20, being an aircraft upper wing skin element.