Aluminum-copper-lithium alloy product for fuselage element having improved properties after a moderate-temperture hold, and transformation method

Abstract

The invention relates to a method for manufacturing a T8 rolled product with a thickness of 0.8 to 12.7 mm made of an aluminum-based alloy comprising, as percentages by weight, 2.05 to 2.25 of Cu, 1.25 to 1.45 of Li, 0.2 to 0.4 of Mg, 0.2 to 0.4 of Mn, an amount of Zr of less than or equal to 0.03, an amount of silver of less than or equal to 0.1%, 0.01 to 0.05 of Ti, an amount of Fe + Si of less than or equal to 0.2%, and inevitable impurities at a content of less than or equal to 0.05% by weight each and 0.15% by weight in total, the balance being aluminum, in which method in particular the tempering is carried out at a temperature of 150°C to 175°C and such that the equivalent tempering time calculated at 160°C is between 35 h and 45 h. The rolled products according to the invention exhibit improved thermal stability with respect to prolonged holds at moderate temperature, such as 1000 h at 85°C or 3000 h at 85°C.

Description

[0001] DESCRIPTION

[0002] Title: Aluminum-copper-lithium alloy product for fuselage components with improved properties after moderate temperature control and processing

[0003] technical field

[0004] The invention relates to thin sheets of aluminum-copper-lithium alloys, offering improved toughness after holding at moderate temperature, and the processes for producing them. These thin sheets are intended, in particular, for the aeronautical and aerospace industries.

[0005] Previous art

[0006] Aluminum alloy laminates are being developed to produce fuselage components, particularly for the aeronautical and aerospace industries. Aluminum-copper-lithium alloys are especially promising for manufacturing this type of product.

[0007] Patent EP 1 966 402 describes an alloy comprising 2.1 to 2.8 wt% of Cu, 1.1 to 1.7 wt% of Li, 0.1 to 0.8 wt% of Ag, 0.2 to 0.6 wt% of Mg, 0.2 to 0.6 wt% of Mn, an amount of Fe and Si less than or equal to 0.1 wt% each, and unavoidable impurities at a content less than or equal to 0.05 wt% each and 0.15 wt% in total, the alloy being substantially free of zirconium, particularly suitable for obtaining recrystallized thin sheets.

[0008] Patent EP EP2981632 describes a process for manufacturing a thin sheet of aluminum alloy with a thickness of 0.5 to 3.3 mm, essentially non-recrystallized in structure, in which, successively, a) a liquid metal bath is prepared comprising 2.6 to 3.4 wt% Cu, 0.5 to 1.1 wt% Li, 0.1 to 0.4 wt% Ag, 0.2 to 0.8 wt% Mg, 0.11 to 0.20 wt% Zr, 0.01 to 0.15 wt% Ti, optionally at least one element selected from Mn, V, Cr, Sc, and Hf, the quantity of the element, if selected, being 0.01 to 0.8 wt% for Mn, 0.05 to 0.2 wt% for V, 0.05 to 0.3% by weight for Cr, 0.02 to 0.3% by weight for Sc, 0.05 to 0.5% by weight for Hf, an amount of Zn less than 0.6% by weight, an amount of Fe and Si less than or equal to 0.1% by weight each, and unavoidable impurities at a content less than or equal to 0.05% by weight each and 0.15% by weight in total;b) a plate is cast from said molten metal bath; c) said plate is homogenized at a temperature between 450 °C and 515 °C; d) said plate is hot-rolled into a sheet with a thickness between 4 and 12 mm; e) said sheet is cold-rolled into a thin sheet with a final thickness between 0.5 and 3.3 mm, the thickness reduction achieved by cold rolling being between 1 and 3.5 mm; f) a heat treatment is carried out during which the sheet reaches a temperature between 300 °C and 450 °C for at least thirty minutes; g) said thin sheet is solution-treated at a temperature between 450 °C and 515 °C and quenched; h) said sheet is subjected to controlled tensile stress with a permanent deformation of 0.5 to 5%, the cold deformation after solution treatment being less than 15%;(i) income is generated including heating at a temperature between 130 and 170 °C and preferably between 150 and 160 °C for 5 to 100 hours and preferably from 10 to 40 hours.

[0009] Patent EP2981631 describes a 0.5 to 8 mm thick aluminum alloy sheet comprising 2.6 to 3.0 wt% Cu, 0.5 to 0.8 wt% Li, 0.1 to 0.4 wt% Ag, 0.2 to 0.7 wt% Mg, 0.06 to 0.20 wt% Zr, 0.01 to 0.15 wt% Ti, optionally at least one element selected from Mn, V, Cr, Sc, and Hf, the quantity of the element, if selected, being 0.01 to 0.8 wt% for Mn, 0.05 to 0.2 wt% for V, 0.05 to 0.3 wt% for Cr, 0.02 to 0.3 wt% for Sc, 0.05 to 0.5 wt% for Hf, an amount of Zn less than 0.2% by weight, an amount of Fe and Si less than or equal to 0.1% by weight each, and unavoidable impurities at a content less than or equal to 0.05% by weight each and 0.15% by weight in total, said sheet being obtained by a process comprising casting, homogenization, hot rolling and optionally cold rolling, solution heating, quenching and tempering,the composition and the income being combined so that the yield strength in the longitudinal direction RpO,2(L) is between 395 and 435 MPa.

[0010] For certain fuselage applications, it is particularly important that the toughness of thin steel sheets be high in the TL direction. This is because a large portion of the fuselage is designed to withstand the aircraft's internal pressure. Since the longitudinal direction of the steel sheets is generally aligned with the aircraft's length, they are subjected to transverse stress. Consequently, cracks are driven along the TL direction.

[0011] 11 is known from patent EP 1 891 247 that, for sheets with a thickness between 4 and

[0012] At 12 mm, it may be advantageous for the microstructure to be completely non-recrystallized or completely recrystallized.

[0013] Patent EP3802897 describes a process for manufacturing a thin sheet of aluminum alloy comprising, in % by weight, 2.3 to 2.7% of Cu, 1.3 to 1.6% of Li, 0.2 to 0.5% of Mg, 0.1 to 0.5% of Mn, 0.01 to 0.15% of Ti, an amount of Zn less than 0.3, an amount of Fe and Si less than or equal to 0.1% each, and unavoidable impurities at a content less than or equal to 0.05% by weight each and 0.15% by weight in total, wherein in particular the hot rolling inlet temperature is between 400 °C and 445 °C and the hot rolling outlet temperature is less than 300 °C. Sheet metal according to patent EP3802897 has advantageous mechanical properties and is notably used for the manufacture of fuselage panels.

[0014] Application W02021 / 111069 describes a process for manufacturing a thin sheet of aluminum alloy comprising, by weight percentages, 2.2 to 2.7% Cu, 1.3 to 1.6% Li, less than 0.1% Ag, 0.2 to 0.5% Mg, 0.1 to 0.5% Mn, 0.01 to 0.15% Ti, less than 0.3% Zn, 0.1% or less of Fe and Si, and unavoidable impurities with a content of 0.05% or less by weight each and 0.15% by weight in total, remaining aluminum, wherein, in particular, the hot rolling inlet temperature is between 400°C and 460°C and the hot rolling outlet temperature is less than 300°C, and the average heating rate during the process is solution is at least about 17°C / min between 300 °C and 400 °C, tempering conditions such that the yield strength in the cross direction RpO,2(TL) is between 350 and 380 MPa.Sheet metal according to request W02021 / 111069 has advantageous mechanical properties and is used in particular for the manufacture of fuselage panels.

[0015] In the field of aluminum alloys used in aeronautics, maintaining mechanical properties throughout the aircraft's service life is crucial. Materials used in aircraft structures are exposed to moderate temperatures over extended periods. In aeronautical terminology, a moderate temperature generally refers to temperatures between 70°C and 85°C. These service conditions can lead to changes in the alloy's mechanical properties, particularly due to microstructural modifications associated with prolonged exposure to these moderate temperatures (known in English as "LTE," for Long Temperature Exposure). It is generally accepted that prolonged exposure to moderate temperatures can be simulated by holding the alloy at 85°C for 1000 hours, or even 3000 hours at 85°C.

[0016] There is a need to design products offering good thermal stability after prolonged exposure to moderate temperature, simulated according to the invention by maintaining 1000h at 85 °C or 3000h at 85 °C.

[0017] The present invention defines a range of Al-Cu-Li alloy compositions, a manufacturing process, and a product manufactured according to this process, which combines high yield strength and toughness after prolonged exposure to moderate temperatures. Compared to other prior art alloys, the composition of the inventive alloy avoids the problem of decreased fracture toughness during prolonged exposure to moderate temperatures.

[0018] Description of the invention

[0019] The first object of the invention relates to a method for manufacturing a rolled product with a thickness between 0.8 and 12.7 mm, based on an aluminum alloy, comprising the following steps: a) Preparation of a liquid metal bath comprising, in weight percentage:

[0020] Cu: 2.05-2.25

[0021] Li: 1.25-1.45

[0022] Mg: 0.2-0.4

[0023] Mn: 0.2-0.4

[0024] Zr: < 0.03

[0025] Ag: < 0.1

[0026] Ti: 0.01-0.05

[0027] Fe + Si: < 0.2 other elements < 0.05 each and < 0.15 in total, remainder aluminum; b) Casting of a plate from said liquid metal bath; c) Homogenization of said cast plate, preferably at a temperature of 490 °C to 530 °C for a period of 5 to 60 hours; d) Hot rolling and, optionally, cold rolling of the homogenized plate to obtain a product of thickness of 0.8 to 12.7 mm, preferably 0.8 mm to 8 mm; preferably the hot rolling inlet temperature is between 400 and 460 °C and the outlet temperature is less than 300 °C; e) Solution heating and quenching of said rolled product, preferably at a temperature of 450 to 535 °C for a period of 5 minutes to 8 hours; f) Controlled traction of said product in solution with a permanent deformation of 1 to 6%;(g) Income of said product drawn to obtain a state T8 such that the income comprises a sequence whose temperature expressed in °C is described by a function T°; c (t) depending on the time t expressed in hours, such that the maximum temperature reached Tmax is 150 °C to 175 °C, preferably 150 °C to 160 °C, and the income period is such that the equivalent period t eq 160 ° c calculated at a temperature of 160 °C, the time frame is between 35 and 45 hours, where teq 160 C is calculated according to the formula:

[0028] According to a preferred method, the liquid metal bath comprises 2.05 to 2.20 by weight of Cu, preferably 2.05 to 2.15% by weight.

[0029] Preferably, the income duration is such that the equivalent duration t eq 160 ° cThe calculated temperature at 160°C is between 38 and 42 hours. In a preferred mode, the maximum temperature reached during the Tmax return is 155°C to 160°C.

[0030] A second object of the invention relates to a rolled product with a thickness of 0.8 to 12.7 mm in the T8 state, based on an aluminum alloy whose composition comprises, in weight percentage: Cu: 2.05-2.25

[0031] Li: 1.25-1.45

[0032] Mg: 0.2-0.4

[0033] Mn: 0.2-0.4

[0034] Zr: < 0.03

[0035] Ag: < 0.1

[0036] Ti: 0.01-0.05

[0037] Fe + Si: < 0.2 other elements < 0.05 each and < 0.15 in total, remainder aluminum, and such that, the difference in the area of ​​the dissolution peak of phases 8' measured between the state after tempering and holding for 1000 hours at 85 °C and the state after tempering is less than 2.0 J / g, where the area of ​​dissolution peak is measured by differential calorimetry after heating at a rate of 20 °C / min from room temperature to a temperature of about 620 °C.

[0038] According to a preferred method, the rolled product comprises 2.05 to 2.20 by weight of Cu, preferably 2.05 to 2.15% by weight.

[0039] According to another preferred mode, the rolled product is such that the difference in the area of ​​the dissolution peak of the phases 8' measured between the state after holding for 3000 hours at 85 °C and the state after tempering is less than 5.0 J / g, where the area of ​​dissolution peak is measured by differential calorimetry after heating at a rate of 20 °C / min from room temperature up to a temperature of about 620 °C.

[0040] According to another preferred method, the evolution of the elastic limit R p 0.2 in the TL direction of the rolled product after holding for 1000 hours at 85 °C compared to the after-tempering state is less than or equal to 20 MPa, and the difference in toughness K app in the TL direction between the tempered product and the tempered product having undergone a holding period of 1000 hours at 85 °C is less than or equal to 10 MPaVm.

[0041] According to another preferred method, the evolution of the elastic limit R p0.2 in the TL direction of the rolled product after holding for 3000 hours at 85 °C compared to the after-tempering state is less than or equal to 40 MPa, and the difference in toughness K app in the TL direction between the tempered product and the tempered product having undergone a holding period of 3000 hours at 85 °C is less than or equal to 30 MPaVm.

[0042] Figures

[0043] Figure 1 shows the effect of holding 1000 at 85 °C and 3000h at 85 °C on the yield strength in the TL direction and the stress intensity factor Kapp TL measured on CCT760 type specimens for A and C sheets under the conditions of example 1.

[0044] Figure 2 shows the effect of holding 1000 at 85 °C and 3000h at 85 °C on the yield strength in the TL direction and the stress intensity factor Kapp TL measured on CCT760 type specimens for A and D sheets under the conditions of example 1.

[0045] Figure 3 illustrates the evolution of the elastic limit after holding 1000 at 85°C and 3000h at 85°C as a function of the evolution of the area of ​​the dissolution peak of the 8' phases measured by differential scanning calorimetry (DSC) tests according to the conditions of example 2.

[0046] Figure 4 illustrates the differential scanning calorimetry (DSC) used to quantify the presence of 6' precipitates in the sample, comparing standard tempering conditions of 48h at 152°C (Figure 4a) and tempering conditions according to the invention of 40h at 160°C (Figure 4b), after tempering, holding for 1000h at 85°C and holding for 3000h at 85°C.

[0047] Detailed description of the invention

[0048] Unless otherwise stated, all indications concerning the chemical composition of alloys are expressed as a percentage by weight based on the total weight of the alloy. The expression 1.4 Cu means that the copper content expressed as a percentage by weight is multiplied by 1.4. The designation of alloys is in accordance with the regulations of The Aluminium Association, which are known to those skilled in the art. Density depends on the composition and is determined by calculation rather than by a method of weight measurement. The values ​​are calculated in accordance with the procedure of The Aluminium Association, which is described on pages 2-12 and 2-13 of "Aluminum Standards and Data".

[0049] Unless otherwise stated, the definitions of metallurgical states given in European standard EN 515 (1993) apply. Unless otherwise stated, the static mechanical properties, in other words the tensile strength R m , the tensile yield strength Rp The 0.2 and elongation at break A% are determined by a tensile test according to ASTM E8. The location at which the parts are taken and their direction of stress are defined by EN 485-1. Unless otherwise specified, the definitions of EN 12258 apply.

[0050] Within the framework of the invention, the mechanical characteristics are measured in full thickness.

[0051] In the context of the present invention, thin sheet metal means sheet metal having a thickness of 0.8 mm to 12.7 mm.

[0052] The present inventors have obtained thin sheets, of thickness from 0.8 to 12.7 mm, preferably from 0.8 mm to 8 mm, even more preferably from 1.2 mm to 6.5 mm, exhibiting good thermal stability after 1000h at 85 °C and 3000h at 85 °C thanks to a narrow selection of composition and controlled tempering conditions.

[0053] The thin sheets according to the invention have particularly advantageous properties, especially with regard to toughness in the TL direction in the T8 state and after prolonged holding at moderate temperature of 1000 at 85 °C and 3000h at 85 °C.

[0054] The aircraft is held at temperatures of 85°C for 1000 hours and 3000 hours to simulate the service conditions it will encounter throughout its lifespan. These tests are used to evaluate the thermal stability of the product.

[0055] In the process according to the invention, a liquid metal bath is prepared whose composition in percentage by weight (wds%) is as follows:

[0056] Cu: 2.05-2.25

[0057] Li: 1.25-1.45

[0058] Mg: 0.2-0.4

[0059] Mn: 0.2-0.4

[0060] Zr: < 0.03

[0061] Ag: < 0.1

[0062] Ti: 0.01-0.05

[0063] Fe + Si: < 0.2 other elements or impurities < 0.05 each and < 0.15 in total, remains aluminium.

[0064] The copper content of the products according to the invention is 2.05 to 2.25% by weight. If the copper content exceeds 2.25%, a significant decrease in toughness is observed after prolonged exposure to moderate temperatures. When the copper content is too low, the static mechanical properties, particularly the yield strength, are not achieved in the T8 state. In an advantageous embodiment of the invention, the copper content is preferably 2.05 to 2.20% by weight to improve thermal stability. In another advantageous embodiment of the invention, the copper content is 2.05 to 2.15% by weight, and preferably 2.05 to 2.10% by weight.

[0065] The lithium content of the products according to the invention is 1.25 to 1.45% by weight. Advantageously, the lithium content is 1.30 to 1.40% by weight, and preferably 1.35 to 1.40% by weight. A maximum lithium content of 1.45% by weight, and preferably 1.40% by weight, is advantageous, particularly for improving the trade-off between toughness and mechanical strength. The addition of lithium contributes to increasing mechanical strength and toughness. Furthermore, the addition of lithium allows for a reduction in density.

[0066] Advantageously the density of the products according to the invention is less than 2.65.

[0067] The magnesium content of the products according to the invention is 0.2 to 0.4% by weight, and preferably 0.25 to 0.35% by weight, and more preferably 0.30 to 0.35% by weight. A minimum magnesium content of 0.25% by weight is advantageous. A maximum magnesium content of 0.35% by weight, and preferably 0.30% by weight, is advantageous.

[0068] The manganese content is 0.2 to 0.4% by weight, preferably 0.25 to 0.35% by weight. A minimum manganese content of 0.2% by weight, and preferably 0.25% by weight, is advantageous. A maximum manganese content of 0.4% by weight, and preferably 0.35% by weight or even 0.33% by weight, is advantageous.

[0069] The zirconium content is less than or equal to 0.03% by weight. Preferably, the zirconium content is less than or equal to 0.02% by weight, and even more preferably less than or equal to 0.01% by weight.

[0070] The silver content of the products according to the invention is less than or equal to 0.1% by weight. Advantageously, the silver content is less than or equal to 0.05% by weight, and even more preferably less than or equal to 0.01% by weight. When the silver content is too high, the product incurs an excessively high industrial cost. Reducing the silver content to levels below 0.1% by weight is economically advantageous.

[0071] The titanium content is 0.01 to 0.05% by weight. The addition of titanium, possibly combined with boron and / or carbon, helps to control the granular structure, particularly during casting.

[0072] The sum of the iron and silicon contents is less than or equal to 0.2% by weight. Preferably, the iron and silicon contents are each at most 0.1% by weight. In an advantageous embodiment of the invention, the iron and silicon contents are at most 0.08% and preferably at most 0.04% by weight. A controlled and limited iron and silicon content contributes to improving the trade-off between mechanical strength and damage tolerance.

[0073] The manufacturing process for the rolled product according to the invention then includes the steps of casting, homogenization, hot rolling and optionally cold rolling, solution heating, controlled tensile testing, quenching and tempering.

[0074] The prepared molten metal bath is poured into a slab. The slab can be poured using conventional casting techniques such as semi-continuous casting. The slab has a substantially parallelepiped shape, preferably with a thickness of 300 mm or more, preferably 400 mm or more, for example 500 mm or 600 mm, or any other intermediate values. After pouring, the slab is generally scalped to remove segregation zones near the surface while maintaining a substantially parallelepiped shape.

[0075] The plate is then homogenized, preferably at a temperature of 490 °C to 535 °C. Preferably, the homogenization time is 5 to 60 hours. Advantageously, the homogenization temperature is at least 500 °C. In one embodiment, the homogenization temperature is below 515 °C.

[0076] After homogenization, the plate is generally cooled to room temperature before being preheated for hot rolling. The preheating aims to reach a hot rolling inlet temperature of 400 to 460 °C, preferably 420 to 445 °C, and even more preferably 420 to 440 °C, enabling deformation by hot rolling. It is also possible to reach this hot rolling inlet temperature directly after homogenization. Preheating before rolling is therefore optional.

[0077] Hot rolling is generally carried out to obtain a sheet with a thickness typically ranging from 3 to 12.7 mm, preferably 4 to 12.7 mm. In a preferred mode, the hot rolling exit temperature is below 300 °C and preferably below 290 °C in order to control the energy stored in the sheet.

[0078] After hot rolling, the resulting sheet can optionally be cold rolled, notably to obtain a final thickness of 0.8 to 4 mm. A range of thicknesses between 3 and 4 mm exists according to the invention, where the product can be finished hot or cold.

[0079] Preferably, the final thickness is at most 8.0 mm, preferably at most 7.0 mm, and even more preferably at most 6.5 mm. Advantageously, the final thickness is at least 0.9 mm, and preferably at least 1.2 mm. The resulting rolled product, also called sheet metal, is then solution-treated, preferably at a temperature of 450 to 535 °C, even more preferably from 450 to 525 °C, for at least 5 minutes, preferably at least 10 minutes. The duration of solution treatment is advantageously from 5 minutes to 8 hours, even more preferably from 10 minutes to 1 hour.

[0080] Optionally, the average heating rate of the sheet metal during solution heating can be at least about 17 °C / min in the temperature range between 300 °C and 400 °C, preferably at least about 19 °C / min, and even more preferably at least about 25 °C / min.

[0081] The sheet metal thus placed in the solution is then quenched. Preferably, quenching is carried out by immersion in a liquid, typically an aqueous solution, which can be maintained at ambient temperature, typically at a temperature of 10 °C to 40 °C.

[0082] The sheet metal then undergoes controlled tensile cold forming with a permanent deformation of 1 to 6%, and preferably 3 to 5%. Known processing steps such as rolling, planishing, straightening, and shaping can optionally be carried out after solution heating and quenching, and before or after controlled tensile testing. However, the total cold deformation after solution heating and quenching must remain below 15%, and preferably below 10%. High cold deformations after solution heating and quenching cause the formation of numerous shear bands across multiple grains, which are undesirable. Cold rolling is preferably not performed after solution heating.

[0083] The sheet metal then undergoes tempering at a temperature of 150°C to 175°C, preferably 150°C to 160°C, or even 155°C to 160°C. The tempering time is such that the equivalent time calculated at 160°C is equal to the time required for tempering. 160 C is 35 to 45 hours, preferably 38 to 42 hours.

[0084] Income can be described by a temperature function T° c (t) as a function of time. This function T° c (t) is such that, according to the invention, the maximum temperature T max reached during the heating period is between 150 °C and 175 °C. Preferably, the maximum temperature T max The temperature reached during the heating period is between 150°C and 160°C. The heating period is adjusted to obtain an equivalent calculated at 160°C. eq 160 ° c 35 to 45 hours, preferably 38 to 42 hours. This equivalent duration is calculated using a formula based on the integration of the temperature function. c(t) with respect to time over the income time interval. The formula is as follows:

[0085] The temperature is expressed in degrees Celsius (°C) and the time in hours.

[0086] In general, prolonged holding at a moderate temperature tends to decrease toughness and increase the yield strength of AlCuLi products after tempering, depending on the lithium content. This behavior is mainly observed for AlCuLi products with a lithium content greater than 1.2% by weight. While an increase in yield strength is not a disadvantage in itself, even though manufacturers prefer minimal changes in yield strength, it is important that toughness does not decrease excessively. The inventors thus found that the combined choice of the selected composition and tempering at a temperature of 150°C to 175°C for an equivalent time calculated at 160°C resulted in a significant decrease in toughness. eq 160 °c A holding period of 35 to 45 hours maintains satisfactory toughness properties after prolonged holding at moderate temperatures, particularly after holding for 1000 hours at 85°C or 3000 hours at 85°C. The Kapp (TL) toughness difference between the tempered product and the tempered product held for 1000 hours at 85°C is less than or equal to 10 MPaVm. The Kapp (TL) value is measured according to ASTM E561-2022 in the TL direction on 760 mm wide CCT specimens. This small change indicates that the material maintains good fracture resistance, which is desirable to ensure structural integrity throughout the aircraft's service life. In a preferred mode, after 3000 hours of holding at 85°C, the Kapp (TL) difference remains less than or equal to 30 MPaVm.

[0087] After holding at 85 °C for 1000 hours, the change in yield strength RpO2 (TL) compared to the tempered state is less than or equal to 20 MPa. Preferably, after holding at 85 °C for 3000 hours, the difference in RpO2 (TL) does not exceed 40 MPa. Maintaining stable yield strengths is advantageous in order to preserve the initial properties obtained after tempering at temperature T8.

[0088] The minimal variation in yield strength (Rp0,2(TL)) and toughness (Kapp(TL)) after holding periods of 1000 and 3000 hours at 85 °C demonstrates that these products maintain their mechanical strength and resistance to crack propagation. This stability ensures the reliability and durability of the materials in demanding applications such as aerospace.

[0089] The inventors attribute these properties to a particular microstructure that limits the precipitation of the 8' phases after prolonged holding at moderate temperatures. This was observed using differential scanning calorimetry (DSC). DSC is an analytical technique used to measure the amount of heat released or absorbed by a sample during heating. This allows for the determination of any phase dissolution or precipitation. In the case of the product according to the invention, the inventors found that the difference in the area of ​​the 8' phase dissolution peak measured between the state after holding for 1000 hours or 3000 hours at 85 °C (corresponding to a product that, after tempering at temperature T8, underwent a holding period of 1000 hours or 3000 hours at 85 °C) and the state after tempering is less than 5.0 J / g.This difference is less than 2.0 J / g between the state after holding at 85 °C for 1000 hours and the cooled state. This dissolution peak area is measured by differential scanning calorimetry at a heating rate of 20 °C / min, from ambient temperature to approximately 620 °C. Dissolution is observed at a temperature close to 200 °C ± 20 °C.

[0090] The process according to the invention minimizes the difference in the area of ​​the dissolution peak of secondary phases, measured by differential scanning calorimetry (DSC), between the alloy state after 1000 hours and 3000 hours of holding at 85 °C, compared to the product state after tempering. Thanks to this optimization, the area of ​​the dissolution peak is maintained at less than 2.0 J / g after 1000 hours of holding at 85 °C. In a preferred mode, the area of ​​the dissolution peak is maintained at less than 5.0 J / g after 3000 hours at 85 °C.

[0091] This small variation indicates that the product retains stable and adequate mechanical properties, even after prolonged exposure to conditions simulating the service life of an aircraft.

[0092] Examples

[0093] Example 1

[0094] Four plates (A, B, C and D) were cast, the composition of which is indicated in Table 1 below. Alloys A and B correspond to a composition according to the invention, and C and D are reference compositions.

[0095] [Table 1] - Chemical composition (% by weight) The plates were homogenized at a temperature of 508 °C for 12 hours and then cooled to room temperature. The plates were then reheated before rolling at a temperature of 460 °C for 17 hours and then at 450 °C for 3 hours before being hot-rolled to a final thickness of 5 mm for composition A and 4 mm for compositions B, C, and D. For each of the sheets, the rolling exit temperature was between 280 and 300 °C.

[0096] The rolled sheets were then placed in solution at a temperature of 500 °C for 30 minutes with a temperature rise rate of at least 17 °C / min, and then quenched in water at ambient temperature. The sheets then underwent a plastic deformation of 3.5%.

[0097] Following these transformation steps, the sheets underwent a tempering step, depending on the case, of 40h 160 °C according to the invention or of 48h 152°C according to a reference tempering (in both cases the rate of temperature rise is approximately 30 °C / h), corresponding respectively to a time equivalent at 160 °C of 40.4 h and 23.8 h (table 2).

[0098] In order to evaluate the thermal stability of the tempered sheets, tests of maintenance at moderate temperature were carried out according to 1000h at 85 °C and 3000h at 85 °C.

[0099] In each case, the tempered sheets before and after holding were characterized in tension according to the recommendations of ASTM E8 in the direction perpendicular to the rolling direction, denoted TL. The value of the apparent stress intensity factor at break, Kapp, expressed in MPaVm, defined according to ASTM E561-2022, was measured in the TL direction on CCT specimens with a width of 760. All the results are reported in Table 2 and illustrated in Figures 1 and 2. [Table 2] - Mechanical Properties

[0100] Figure 1 shows the evolution of the compromise Rp0.2 (TL) -Kapp (TL) as a function of the holding time for the plate A of the invention and the reference plate C.

[0101] It is generally observed that the yield strength increases and the toughness decreases as a function of the prolonged time at 85 °C. The Kapp toughness of sheet A which underwent a tempering of 40h at 160 °C remains unchanged after 1000 at 85 °C (AKapp = 0 MPaVm) and decreases slightly after 3000h at 85h (AKapp = 16 MPaVm), unlike sheet C which underwent the same tempering (AKapp = 6 MPaVm after 1000 at 85 °C and 28 MPaVm after 3000h at 85 °C).

[0102] Figure 2 highlights the cumulative effect of composition and tempering on the evolution of the toughness value during holding. Sheet D, which differs from the invention not only in composition but also in tempering, shows a greater decrease in the Kapp value (AKapp = 10 MPaVm after 1000h at 85 °C and 35 MPaVm after 3000h at 85 °C).

[0103] Example 2

[0104] In this example, the 4 mm B sheet, processed according to the conditions described in Example 1, underwent two tempering conditions, either according to the reference conditions (sheet B1) or according to the invention (sheet B-2). Each was then held at 85 °C for 1000 h and 85 °C for 3000 h.

[0105] The B1 and B2 sheets were tensile tested to measure the yield strength of the product in the TL direction according to ASTM E8 after tempering and holding for 1000 and 3000 hours at 85 °C (Table 3). Similarly, differential scanning calorimetry (DSC) tests were performed on the products to quantify the amount of precipitate. The tests consisted of heating each product at a rate of 20 °C / min from ambient temperature to approximately 620 °C and recording the temperature change of the differential signal.

[0106] At around 200 °C, a dissolution peak is recorded, which is representative of the initial quantity of 8' precipitates. The proportion of 6' precipitates can be quantified by the peak area, expressed in J / g. The larger the area, the greater the quantity of 6' precipitates (Figure 4). Figure 4a) corresponds to the tests performed on sheet B1, and Figure 4b) to those performed on sheet B-2.

[0107] Table 3 shows that products B1 and B2 exhibit an increase in yield strength after holding. However, the increase is smaller for the product according to the invention. This difference can be correlated with the amount of precipitate formed during holding. This can be evaluated by calculating the difference in peak area between the state after holding and the cooled state.

[0108] All the results are reported in Table 3 and illustrated in Figure 3. [Table 3] -

Claims

DEMANDS 1. A process for manufacturing a rolled product with a thickness between 0.8 and 12.7 mm, based on an aluminum alloy, comprising the following steps: a) Preparation of a liquid metal bath comprising, as a percentage by weight: Cu: 2.05-2.25 Li: 1.25-1.45 Mg: 0.2-0.4 Mn: 0.2-0.4 Zr <0.03 Ag < 0.1 Ti: 0.01-0.05 Fe + Si < 0.2 other elements < 0.05 each and < 0.15 in total, remainder aluminum; b) Casting a plate from said molten metal bath; c) Homogenizing said cast plate; d) Hot rolling and, optionally, cold rolling of the homogenized plate to obtain a product with a thickness of 0.8 to 12.7 mm; e) Solution heating and quenching said rolled product; f) Controlled tensile heating of said solution-heated product with a permanent deformation of 1 to 6%; g) Tempering said tensile heating product to obtain a T8 condition such that the tempering comprises a sequence whose temperature, expressed in °C, is described by a function T° c (t) depending on the time t expressed in hours, such that the maximum temperature reached Tmax is 150 °C to 175 °C and the income period is such that the equivalent time teq 160 C calculated at a temperature of 160 °C, the time frame is between 35 and 45 hours, where teq 160 C is calculated using the formula: 136100 / 1 1 \1 8, .314 \.T c (t) + 273 160 4- 273 1 2. A manufacturing process according to claim 1 such that the maximum temperature reached Tmax is 150 °C to 160 °C.

3. Manufacturing process according to claim 1 or 2 wherein the liquid metal bath comprises from 2.05 to 2.20 by weight of Cu, preferably from 2.05 to 2.15% by weight.

4. A manufacturing method according to any one of claims 1 to 3, wherein the tempering time is such that the equivalent time t eq 160 ° c calculated at a temperature of 160 °C is between 38h and 42h.

5. Manufacturing process according to any one of claims 1 to 4 wherein the maximum temperature reached during tempering Tmax is 155 °C to 160 °C.

6. Rolled product with a thickness of 0.8 to 12.7 mm in the T8 condition, based on aluminum alloy whose composition comprises, as a percentage by weight: Cu: 2.05-2.25 Li: 1.25-1.45 Mg: 0.2-0.4 Mn: 0.2-0.4 Zr: < 0.03 Ag: < 0.1 Ti: 0.01-0.05 Fe + Si: < 0.2 other elements < 0.05 each and < 0.15 in total, remainder aluminum, and such that, the difference in the area of ​​the dissolution peak of phases 8' measured between the state after tempering and holding for 1000 hours at 85 °C and the state after tempering is less than 2.0 J / g, where the area of ​​dissolution peak is measured by differential calorimetry after heating at a rate of 20 °C / min from room temperature to a temperature of about 620 °C.

7. Rolled product according to claim 6 comprising from 2.05 to 2.20 by weight of Cu, preferably from 2.05 to 2.15% by weight.

8. Rolled product according to claim 6 or 7 such that the difference in the area of ​​the dissolution peak of phases 8' measured between the state after holding for 3000 hours at 85 °C and the state after tempering is less than 5.0 J / g, where the area of ​​dissolution peak is measured by differential calorimetry after heating at a rate of 20 °C / min from room temperature up to a temperature of approximately 620 °C.

9. Rolled product according to any one of claims 6 to 8 characterized in that, after holding for 1000 hours at 85 °C, the change in yield strength Rp0.2 in the TL direction relative to the tempered state is less than or equal to 20 MPa, and the difference in toughness Kapp in the TL direction between the tempered product and the tempered product that has undergone a holding period of 1000 hours at 85 °C is less than or equal to 10 MPaVm.

10. Laminated product according to any one of claims 6 to 8 characterized in that, after holding for 3000 hours at 85 °C, the evolution of the yield strength R p 0.2 in the TL direction relative to the after-temperature state is less than or equal to 40 MPa, and the difference in toughness K ap p in the TL direction between the tempered product and the tempered product that has undergone a holding period of 3000 hours at 85 °C is less than or equal to 30 MPaVm.

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