2xxx alloy wrought products with optimal corrosion resistance and methods of making the same

Abstract

Method of thermomechanical treatment of a forged product made of an aluminum alloy of the 2000 series, said aluminum alloy comprising in weight % Cu 3.5-5.8; Mg 0.2-1.5; Mn≤0.9; Fe≤0.15; Si≤0.15; Zr≤0.25; Ag≤0.8; Zn≤0.8; Ti 0.02-0.15; unavoidable impurities each ≤0.05 and total ≤0.15; the balance being aluminum, capable of improving the stress corrosion resistance. Said method comprises a tempering consisting of two sequences. The first sequence is defined by a maximum temperature T1 max of 130°C to 180°C, and a holding time at a temperature of 130°C to 180°C, said holding time being equal to an equivalent time calculated at 160°C of 10h to 80h (formula i). The second sequence is defined by a temperature T2 max lower than T1 ℃ (t) and a holding time t2 at a temperature of 100°C to 130°C, said holding time t2 being equal to an equivalent time calculated at 160°C (formula ii), such that (formula ii) is between 0.3% and 15% of the equivalent time calculated for the first sequence (formula iv). Formula i: Formula ii: Formula iii: Formula iv:

Description

TECHNICAL FIELD

[0001] The present invention relates to a forged product made of a 2XXX alloy having improved stress corrosion properties, and to a thermomechanical treatment method of a forged product made of a 2XXX series aluminum alloy, aiming at improving its resistance to corrosion under stress, while maintaining a good compromise between yield strength, ductility and damage tolerance, in particular toughness. BACKGROUND

[0002] Aeronautical applications generally require a very specific set of properties. In general, alloys having high mechanical strength are required, but depending on the intended use, other properties are generally also required, such as high fracture strength or ductility, and good resistance to corrosion, in particular to stress corrosion.

[0003] The resistance to stress corrosion of 2000 alloys is evaluated after an alternate immersion-floating test according to standard ASTM G47-98 (2019). In general, the products are tested in tension according to standard ASTM G49-85 (2019) for more than 30 mm. Depending on the chosen device, the test is carried out under constant deformation or constant load. The choice depends on the intended application and the chosen standard. As mentioned in standard ASTM G49-85 (2019), the corrosion test under constant load tensile stress is more severe than the corrosion test under constant strain tensile stress. Therefore, the maximum acceptable stress determined by the corrosion test under constant load tensile stress is generally less than or equal to the maximum acceptable stress determined by the corrosion test under constant strain tensile stress. This difference is related to the fact that under constant strain, in particular when a crack appears, there is a relaxation of the stress. Then, the product is subjected to a lower load than the initial load, which makes the test less severe. It can also be mentioned the article of N. Magaji et al. “Comparison of test methods used to analyze the stress corrosion cracking of differently tempered 7xxx alloys” - Materials and Corrosion 2019 - Volume 70 - pages 1192-1204.

[0004] 2000 alloys are known in the prior art. In the present text, the terms 2000 or 2xxx can be used interchangeably to designate aluminum alloys whose main element is the element Cu.

[0005] WO2004 / 106566 discloses an aluminium alloy with improved strength and ductility comprising Cu 3.5 to 5.8 wt.%, Mg 0.1 to 1.8 wt.%, Mn 0.1-0.8 wt.%, Ag 0.2-0.8 wt.%, Ti 0.02-0.12 wt.% and possibly one or more elements selected from the group comprising Cr 0.1-0.8 wt.%, Hf 0.1-1.0 wt.%, Sc 0.03-0.6 wt.% and V 0.05-0.15 wt.%, the remainder being aluminium, and wherein the alloy is essentially free of zirconium.

[0006] WO2020 / 123096 discloses a 2XXX alloy comprising a titanium content of 0.08 to 0.20 wt.% having at least two properties like mechanical strength, toughness, elongation and corrosion resistance with excellent trade-off. The application discloses a stress corrosion test performed at constant strain.

[0007] The standard practice of final thermomechanical treatment of these alloys after hot rolling comprises solutionizing, quenching as fast as possible, cold strain of at least 2% and tempering in a single isothermal stage.

[0008] The inventors have noticed that when the products according to WO2004 / 106566 are obtained according to standard thermomechanical treatment practice, these products do not obtain a lifetime of more than 10 days after corrosion test under 200 MPa constant load tensile stress.

[0009] FR2435535 discloses a heat treatment method of a wrought product made of a 2000 series aluminium alloy comprising (in wt.%) 3.5 to 5% copper, 0.2 to 0.1% magnesium, 0.25 to 1.2% silicon, wherein the Si / Mg ratio is greater than 0.8, characterised in that the tempering comprises at least two steps: a main tempering at a temperature higher than 225°C and lower than 285°C for a duration of 6 seconds to 60 minutes; and a complementary tempering at a temperature of 120°C to 175°C for a duration of 4 to 192 hours. FR2435535 differs from the present invention in that it applies to products with a silicon content greater than 0.25 wt.% and the first tempering step is performed at a temperature higher than 225°C.

[0010] US 3,305,410 discloses a two-stage tempering heat treatment for improving the corrosion resistance of aluminum alloys. This tempering is called "top-down" tempering. The first stage is performed at high temperature, typically at 190°C to 218°C, in order to initiate homogeneous precipitation and to minimize the precipitation at the grain boundaries. The second stage is performed at lower temperature, typically at 135°C to 163°C, in order to complete the precipitation. According to the invention, it is important that the hardening precipitation does not change significantly during the second stage. This can be achieved by choosing the tempering conditions of the invention.

[0011] The present invention relates to a thermomechanical treatment method applicable to 2XXX alloys having a composition in wt% Cu 3.5 - 5.8; Mg 0.2 - 1.5; Mn < 0.9; Fe < 0.15; Si < 0.15; Zr < 0.25; Ag < 0.8; Zn < 0.8; Ti 0.02 - 0.15, unavoidable impurities each < 0.05 and total < 0.15; the balance being aluminum, allowing to improve the stress corrosion resistance while allowing to obtain an excellent compromise between the yield strength, ductility and damage tolerance, in particular toughness. In particular, the method allows to improve the corrosion resistance under constant load tensile stress. SUMMARY

[0012] The present invention relates to a thermomechanical treatment method of a wrought product made of a 2000 series aluminum alloy comprising in wt% Cu 3.5 - 5.8; Mg 0.2 - 1.5; Mn < 0.9; Fe < 0.15; Si < 0.15; Zr < 0.25; Ag < 0.8; Zn < 0.8; Ti 0.02 - 0.15, unavoidable impurities each < 0.05 and total < 0.15; the balance being aluminum. This thermomechanical treatment comprises solid solution, quenching, work hardening and tempering. The tempering is characterized in that it comprises at least two sequences:

[0013] - a first sequence, the temperature in °C is described by a function T1 ℃ (t) depending on time t, so that the maximum temperature T1 max reached is between 130°C and 180°C and the holding time t1 at a temperature between 130°C and 180°C is such that the equivalent duration is between 10h and 80h, the equivalent duration is calculated at a temperature of 160°C according to the following formula

[0014] [mathematical operation 1]

[0015]

[0016] - a second step, the passage of temperature in °C as a function of time t, T2 ℃ (t) is described, the temperature of which is such that T2 ℃ (t) is lower than T1 max and its holding time t2 in hours at a temperature of 100°C to 130°C is such that the equivalent duration calculated at a temperature of 160°C is 0.3% to 15% of the equivalent duration calculated for the first step .

[0017] [mathematical operation 2]

[0018]

[0019] In a preferred embodiment, the temperature T2 ℃ (t) of the second step is lower than 130°C.

[0020] In a preferred embodiment, the holding time t2 of the second step at 105°C to 130°C, preferably 105°C to 125°C or 110°C to 130°C or 110°C to 125°C corresponds to an equivalent duration which is 0.3% to 15% of the equivalent duration calculated for the first step .

[0021] Preferentially, the equivalent duration is longer or equal to 0.4% of the equivalent duration calculated for the first step , still more preferentially the equivalent duration is longer or equal to 0.5% or 1% or 2% or 3% of the equivalent duration calculated at 160°C.

[0022] In a preferred embodiment, the equivalent duration is shorter or equal to 10% of the equivalent duration calculated for the first step , still more preferentially the equivalent duration is shorter or equal to 5% or 3.5% of the equivalent duration calculated for the first step .

[0023] Preferentially, the first step comprises one single isothermal phase.

[0024] Preferentially, the forged product is a thin metal sheet or a thick metal sheet or a profile or a forged part. In a preferred embodiment, the forged product is a thick metal sheet or a profile or a forged part having a thickness greater than or equal to 30 mm, preferentially 50 mm, still more preferentially greater than or equal to 90 mm.

[0025] ​In a preferred embodiment, the wrought product is a thick metal plate which has been subjected to a forming step of high-energy hydroforming, preferably by explosion hydroforming, before tempering.

[0026] Preferably, the wrought product made of 2000-series aluminum alloy is selected from the group consisting of AA2139, AA2039, AA2040, AA2124, AA2024, AA2027, AA2022, AA2042.

[0027] Preferably, the wrought product made of 2000-series aluminum alloy comprises in weight % Cu 3.9-5.2; Mg 0.2-0.9; Mn 0.1-0.6; Fe < 0.15; Si < 0.5; Zr < 0.15; Ag < 0.6; Zn < 0.8; Ti 0.02-0.15, unavoidable impurities each < 0.05 and in total < 0.15; the remainder being aluminum.

[0028] Preferably, the wrought product made of 2000-series aluminum alloy comprises in weight % Cu 4.5-5.0; Mg 0.40-0.90; Mn 0.20-0.50; Fe < 0.15; Si < 0.15; Zr < 0.05; Ag 0.10-0.50; Zn < 0.5; Ti 0.02-0.15, unavoidable impurities each < 0.05 and in total < 0.15; the remainder being aluminum.

[0029] Preferably, the surface area value of the dissolution peak at about 200°C to 300°C after the second working procedure measured by DSC is substantially equal to the surface area value of the dissolution peak measured after the first working procedure, for substantially equal it is understood that the difference is less than or equal to 5%, advantageously less than or equal to 2%.

[0030] Furthermore, the present application relates to a wrought product made of 2000-series aluminum alloy having a thickness greater than or equal to 30 mm, comprising in weight % Cu 3.5-5.8; Mg 0.2-1.5; Mn < 0.9; Fe < 0.15; Si < 0.15; Zr < 0.25; Ag < 0.8; Zn < 0.8; Ti 0.02-0.15, unavoidable impurities each < 0.05 and in total < 0.15; the remainder being aluminum; obtainable by the thermomechanical treatment method of the present application. The product is characterized by an average service life of more than 10 days for each case of three specimens under corrosion of a stress of less than or equal to 200 MPa applied in the short transverse direction TC, the test being carried out according to the conditions of ASTM G47-98 (2019) with constant load tensioning device according to ASTM G49-85 (2019).

[0031] Preferably, the forged product made of 2000-series aluminum alloy having a thickness greater than or equal to 30 mm has a lifetime greater than or equal to 10 days for all the samples tested in short transverse direction TC under a stress less than or equal to 200 MPa, using a constant load tensioning device according to ASTM G49-85 (2019) in the conditions of ASTM G47-98 (2019).

[0032] Preferably, the forged product made of 2000-series aluminum alloy having a thickness greater than or equal to 30 mm has a yield strength greater than or equal to 400 MPa in long transverse direction TL.

[0033] Preferably, the forged product made of 2000-series aluminum alloy having a thickness greater than or equal to 30 mm comprises, in % by weight: Cu 3.9-5.2; Mg 0.2-0.9; Mn 0.1-0.6; Fe < 0.15; Si < 0.15; Zr < 0.15; Ag < 0.6; Zn < 0.8; Ti 0.02-0.15, unavoidable impurities each < 0.05 and total < 0.15; the remainder being aluminum.

[0034] Preferably, the forged product made of 2000-series aluminum alloy having a thickness greater than or equal to 30 mm comprises, in % by weight: Cu 4.5-5.0; Mg 0.40-0.90; Mn 0.20-0.50; Fe < 0.15; Si < 0.15; Zr < 0.05; Ag 0.10-0.50; Zn < 0.5; Ti 0.02-0.15, unavoidable impurities each < 0.05 and total < 0.15; the remainder being aluminum.

[0035] Advantageously, the product according to the application or obtained according to the method is used for aerospace applications for monolithic structures such as fuselage, rib or spar elements. BRIEF DESCRIPTION OF DRAWINGS

[0036] [ Figure 1 ] Figure 1 Schematic representation of tempering according to one embodiment of the application, wherein the two processes are carried out sequentially without any room temperature step.

[0037] [ Figure 2 ] Figure 2 Schematic representation of tempering according to one embodiment of the application, wherein the two processes are carried out sequentially through one room temperature step.

[0038] [ Figure 3 ] Figure 3 Schematic representation of tempering according to one embodiment of the application, wherein the first process is single stage.

[0039] [ Figure 4 ] Figure 4Thermograms obtained after differential scanning calorimetry or DSC measurements of samples A13 and A14 of Example 6 are shown.

[0040] [ Figure 5 ] Figure 5 Determination of the surface area value of the dissolution peak after DSC measurements is illustrated. DETAILED DESCRIPTION

[0041] Unless otherwise specified, all indications relating to the chemical composition of the alloys are expressed as a percentage by weight based on the total weight of the alloy. The expression 1.4 Cu means the copper content expressed in wt% multiplied by 1.4. The alloy designation is in accordance with the Aluminum Association regulations known to the person skilled in the art. The density depends on the composition and is determined by calculation rather than gravimetric methods. These values are calculated according to the Aluminum Association method described on pages 2-12 and 2-13 of “Aluminum Standards and Data”.

[0042] Unless otherwise specified, the definitions of the metallurgical conditions are those indicated in European Standard EN 515 (1993).

[0043] Unless otherwise specified, the static mechanical properties, in other words the breaking strength Rm, the conventional yield strength at 0.2% elongation Rp0.2 (“yield strength”) and the elongation at break A%, are determined by tensile test according to Standard EN 10002-1, the sampling and testing direction being defined by Standard EN 485-1.

[0044] Unless otherwise specified, the stress intensity factor (K Q ) is determined according to Standard ASTM E 399. Standard ASTM E 399 gives the criteria for determining whether K Q is a valid value. For a given specimen geometry, the K 1C values obtained for different materials are comparable with each other as long as the yield strength of the materials is of the same order of magnitude. Q

[0045] Stress corrosion tests at the center of the medium thickness of the specimens have been carried out according to Standards ASTM G47-98 (2019) and ASTM G49-85 (2019) on short transverse TC. Unless otherwise specified, the stress corrosion tests are carried out using tensile specimens. Generally, the tensile specimens are cylindrical with a diameter of 3.17 ± 0.01 mm. Nevertheless, flat specimens can also be used. These specimens are tested at a given stress using a device ensuring a constant load according to the recommendations of ASTM G49-85 (2019). At least three specimens are tested for each case.

[0046] ​The terms used for aluminum and aluminum alloy products are defined by the standard NF EN 12258-1, unless otherwise specified. In particular, a thin sheet metal is a rolled product having a rectangular cross section with a uniform thickness of 0.20 mm to 6 mm, unless otherwise specified. Rolled products with a thickness greater than 6 mm are called thick sheets.

[0047] A wrought product resistant to stress corrosion in short transverse direction (i.e. TC) means that the product does not have any cracking before 10 days of testing under a stress of 200 MPa applied in short transverse direction, said testing being performed according to the recommendations of ASTM G49-85 (2019) using a device ensuring a constant load. The product of the invention has a resistance to stress corrosion in short transverse direction. In a preferred mode, the product has an average lifetime and a standard deviation such that the difference between the average lifetime and the standard deviation is greater than 10 days.

[0048] Unless otherwise specified, tempering is a heat treatment aimed at modifying the properties of the product by precipitation of intermetallic phases from a supersaturated solution. According to the prior art, it can consist of one or more steps. By "step", it is understood a heating phase or an isothermal phase or a cooling phase. The heating phase and / or the cooling phase can be linear and defined by a heating rate or a cooling rate.

[0049] According to the invention, a "process" consists of one or more steps. A process can be defined by a temperature curve as a function of time T ℃ (t).

[0050] For a step or a process, a holding time equivalent to a reference temperature T ref can be calculated.

[0051] According to the invention, the precision of the tempering temperatures mentioned in the present application is preferably + / - 5°C, still more preferably + / - 3°C.

[0052] The holding time of a process defined by T ℃ (t) over the time interval t' to t" is equivalent to the duration of the process performed at the reference temperature T ref .

[0053] is defined by:

[0054] [mathematical operation 3]

[0055]

[0056] where T ℃ (t) is the instantaneous temperature (in °C) of the process as a function of time t (in hours) and T ref is the reference temperature. in hours. The constant Q corresponds to the activation energy of diffusion. According to the application, the constant Q is considered equal to 136,000 J / mol, which corresponds to the activation energy of diffusion of copper Cu in aluminum. The ideal gas constant R is equal to 8.314 J / K / mol.

[0057] The wrought product made of 2000 series aluminum alloy comprises, in weight %, Cu 3.5 - 5.8; Mg 0.2 - 1.5; Mn < 0.9; Fe < 0.15; Si < 0.15; Zr < 0.25; Ag < 0.8; Zn < 0.8; Ti 0.02 - 0.15, unavoidable impurities each < 0.05 and total < 0.15; the remainder being aluminum.

[0058] The copper content is at least 3.5 wt%, preferably at least 3.9 wt%, advantageously at least 4.1 wt% and still more preferably at least 4.4 wt% in order to obtain sufficient yield strength. The copper content is at most 5.8 wt%, preferably at most 5.2 wt%, advantageously at most 5.0 wt%. In one embodiment, the copper content of the wrought product is between 3.9 and 5.2 wt%, advantageously between 4.5 and 5.0 wt%. A too low copper content value leads to too low mechanical strength and yield strength. A too high copper content value leads to insufficient toughness.

[0059] The Mg content is at least 0.2 wt%, preferably at least 0.20 wt%, advantageously at least 0.40 wt%. The Mg content is at most 1.5 wt%, preferably at most 0.9 wt%, still more preferably 0.90 wt%. In one embodiment, the Mg content of the wrought product is between 0.2 and 0.9 wt%, advantageously between 0.40 and 0.90 wt%. A too low magnesium content value leads to too low mechanical strength and yield strength. A too high magnesium content value leads to insufficient toughness.

[0060] Preferably, the Mn content is at least 0.05 wt%, still more preferably at least 0.1 wt%, still more preferably at least 0.20 wt%. The Mn content is at most 0.9 wt%, preferably at most 0.6 wt%, still more preferably at most 0.50 wt%. In one embodiment, the Mn content is between 0.1 and 0.6 wt%, preferably between 0.20 and 0.50 wt%. The addition of manganese allows to control the growth of recrystallized grains, allowing to increase the mechanical strength of the product and its yield strength, but a too high content leads to a decrease in toughness.

[0061] The Zr content is at most 0.25% by weight, preferably at most 0.15% by weight, still more preferably at most 0.05% by weight. In one embodiment, the Zr content is less than or equal to 0.04% by weight, advantageously the Zr content is less than or equal to 0.01% by weight. The inventors have noted that a Zr content less than or equal to 0.05% by weight allows to improve the formability of the product. In another preferred embodiment, the Zr content is between 0.05 and 0.15% by weight.

[0062] The Ag content is at most 0.8% by weight, preferably at most 0.6% by weight. In one preferred embodiment, the Ag content is between 0.10 and 0.50% by weight.

[0063] The Zn content is at most 0.8% by weight. In one embodiment, the Zn content is less than 0.5%, advantageously less than 0.25%.

[0064] The Ti content is between 0.02 and 0.15% by weight. In one embodiment, the Ti content is between 0.02 and 0.10% by weight, advantageously between 0.02 and 0.09% by weight, still more advantageously between 0.02 and 0.05% by weight. Titanium has a role in controlling the microstructure of the cast, in particular in refining the grain size.

[0065] The content of the other elements is at most 0.05% by weight each and at most 0.15% by weight in total. They consist of unavoidable impurities, the remainder being aluminium.

[0066] Each of these embodiments can be combined in whole or in part.

[0067] Advantageously, the wrought product made of 2000-series aluminium alloy is selected from the type AA2139, AA2039, AA2040, AA2124, AA2024, AA2027, AA2022, AA2042.

[0068] Advantageously, the wrought product made of 2000-series aluminium alloy is a thin metal sheet, a thick metal sheet, a profile or a forged part. In one preferred embodiment, the wrought product is a metal sheet having a thickness of at least 30 mm, preferably greater than or equal to 50 mm, still more preferably greater than or equal to 90 mm.

[0069] The wrought product made of 2000-series aluminium alloy is obtained by standard preparation methods. The original form is cast from a liquid metal bath having a composition in % by weight Cu 3.5 - 5.8; Mg 0.2 - 1.5; Mn < 0.9; Fe < 0.15; Si < 0.15; Zr < 0.25; Ag < 0.8; Zn < 0.8; Ti 0.02 - 0.15, unavoidable impurities < 0.05 each and < 0.15 in total; the remainder being aluminium.

[0070] Advantageously, the raw form is a plate, or a cast blank. The raw form is then homogenized, then hot formed, to obtain a wrought product made of a 2000 series aluminum alloy. Advantageously, the homogenization is performed at a temperature of 490°C to 530°C, for a duration of 10h to 50h. Advantageously, in the case of a plate, the plate is homogenized, then hot rolled to obtain a wrought product made of a 2000 series aluminum alloy. Advantageously, the wrought product made of a 2000 series aluminum alloy is a metal plate having a thickness greater than or equal to 30mm, preferably greater than or equal to 50mm, still more preferably greater than or equal to 90mm. Advantageously, the wrought product made of a 2000 series aluminum alloy is a metal plate having a thickness less than or equal to 180mm, preferably less than or equal to 150mm.

[0071] The wrought product made of a 2000 series aluminum alloy is subjected to a thermo-mechanical treatment comprising solid solution, quenching, work hardening and tempering, said 2000 series aluminum alloy comprising in wt% Cu 3.5 - 5.8; Mg 0.2 - 1.5; Mn < 0.9; Fe < 0.15; Si < 0.15; Zr < 0.25; Ag < 0.8; Zn < 0.8; Ti 0.02 - 0.15, unavoidable impurities each < 0.05 and total < 0.15; the remainder being aluminum.

[0072] Advantageously, the wrought product is solid-solved at a temperature of 490°C to 530°C, for a duration of 5h to 20h. Advantageously, the quenching is performed by immersion of the solid-solved product in water at room temperature (typically about 22°C (+ / - 10°C)), or by spraying the product using a spray.

[0073] Work hardening is then performed. Advantageously, this work hardening is performed at cold. It can be performed by stretching or compression. Advantageously, the permanent strain rate is 1% to 9%, preferably 3% to 5%.

[0074] Optionally, a further shaping step can be performed prior to tempering. This shaping step can be performed by a high energy hydraulic forming method. Preferably, this method is performed on a thick metal plate, typically having a thickness greater than or equal to 30mm, preferably greater than or equal to 50mm, and still more preferably greater than or equal to 90mm. This method can be an explosive hydraulic forming method. This type of method is described in the publication D.J. Mynor et al. "Applications and capabilities of explosive forming" Journal of Materials Processing Technology 125-126 (2002) pages 1-25.

[0075] According to the application, the forged product is subjected to a tempering comprising at least two sequences. Preferably, the forged product is subjected to a tempering comprising two sequences.

[0076] According to the present application, when it is mentioned that the temperature interval is "130°C to 180°C", it is meant that the temperature boundary values are included. Thus, it should be understood that when it is mentioned "130°C to 180°C", it is understood "from 130°C to 180°C".

[0077] First process

[0078] The first sequence aims at obtaining the final mechanical properties of the product. In particular, the first sequence makes it possible to obtain the best toughness-yield strength compromise. According to the application, the first sequence consists of one or more heating and / or isothermal holding and / or cooling steps. The variation of the temperature during the first sequence can be described by a function T1 ℃ (t) depending on time t. During the first sequence, the temperature reaches a maximum temperature T1 max of 130°C to 180°C. Preferably, the maximum temperature T1 max is reached during the isothermal phase. The duration of the first sequence is such that the holding time at a temperature of 130°C to 180°C is equal to an equivalent duration of 10h to 80h , where the equivalent duration is calculated according to the following formula at a reference temperature of 160°C:

[0079] [mathematical operation 1]

[0080]

[0081] The function is integrated over the period of time for which the temperature expressed in °C is between 130°C and 180°C. This means that the function is integrated over the period of time corresponding to the first passage at a temperature of 130°C in an ascending manner and to the first passage at a temperature of 130°C in a descending manner. In the case where the period of time is not continuous, the function should be integrated according to each period of time for which the temperature is between 130°C and 180°C.

[0082] Preferably, the holding time at a temperature of 130°C to 180°C during the first sequence is equal to an equivalent duration of at least 15h, 20h, 24h or 30h in order to obtain sufficient mechanical strength. Indeed, if the equivalent duration is too short, it is not possible to reach sufficient elastic limit, generally it is not possible to reach a yield strength of at least 400MPa in the TL (long transverse) direction. Preferably, the holding time at a temperature of 130°C to 180°C during the first sequence is such that the equivalent duration Shorter than 70 h, advantageously shorter than 60 h, or 50 h, or 40 h, in order to obtain sufficient ductility and toughness. Indeed, if the equivalent duration is too long, the ductility and toughness decrease.

[0083] A ripening step can be performed at room temperature before the first process. The duration of the ripening step can vary between a few minutes, a few hours or a few days. Preferably, the ripening duration is between 10 minutes and 10 hours, preferably up to 4 hours.

[0084] In a preferred embodiment of the application, the first process is a single stage (see Figure 3 ) By "single stage", it is understood to mean a process comprising one single isothermal stage. Typically, the first single stage process comprises a temperature ramping step, an isothermal hold at 130°C to 180°C and a cooling step.

[0085] Second process

[0086] The second process aims at improving the stress corrosion resistance.

[0087] According to the application, the second process induces negligible changes in mechanical properties such as the yield strength, the breaking strength or the toughness. The change in yield strength, breaking strength or toughness between the end of the first process and the end of the second process is less than 10%, advantageously less than 5%, still more advantageously less than 3% or 2%. Preferably, the change in yield strength is less than 3%, preferably less than 2%. Preferably, the change in toughness is less than 3%, preferably less than 2%.

[0088] The inventors have noticed that the second process does not significantly change the amount of precipitates formed at the end of the first process.

[0089] DSC, for Differential Scanning Calorimetry, is a thermal analysis technique. It measures the difference in heat exchange between the sample to be analyzed and a reference sample (in this case, alumina). This DSC technique is based on the fact that during a physical transition (for example a phase change), a certain amount of heat is exchanged with the sample to keep it at the same temperature as the reference sample. The direction of this heat exchange between the sample and the device depends on the endothermic or exothermic nature of the conversion process. Thus, for example, if the product contains precipitates, when it is heated, these precipitates can dissolve over a certain temperature range under the effect of heat. The product will then absorb more heat in order to be able to raise its temperature at the same rate as the reference sample. Its dissolution is therefore an endothermic phase change, since it absorbs heat. Furthermore, the sample can undergo an exothermic process, for example precipitation, when it transfers heat to the system.

[0090] By measuring the difference in heat flux between the sample and the reference sample, the differential scanning calorimeter can measure the heat absorbed or released during the transition.

[0091] Using this technique, the amount of dissolved phase can be estimated from the thermogram by calculating the surface area of the endothermic peak or of the dissolution peak, expressed in J / g. According to the application, the dissolution peak is between about 200°C and 300°C. By "about 200°C to 300°C", it is understood that the dissolution peak can extend in a range of + / - 50°C with respect to the range 200°C-300°C.

[0092] The inventors have noted that the surface area of the dissolution peak varies by less than 5% between the two procedures. Indeed, the inventors have noted that the surface area value of the dissolution peak after the second procedure, measured by DSC, where the dissolution peak is between about 200°C and 300°C, is substantially equal to the surface area value of the dissolution peak measured after the first procedure. By substantially equal, it is understood that the difference is less than or equal to 5%, advantageously less than or equal to 2%.

[0093] According to the application, the second procedure consists of one or more heating and / or isothermal holding and / or cooling steps.

[0094] The temperature variation during the second procedure can be described by a function T2 ℃ (t) depending on time. The second procedure is carried out at a temperature T2 max lower than the maximum temperature T1 ℃ of the first procedure. This means that during the second procedure, the function T2 max (t) is lower than the maximum temperature T1 ℃ .

[0095] Preferably, the second procedure is carried out at a temperature T2

[0096] The second procedure is characterized by a holding time t2 at a temperature of 100°C to 130°C. This holding time t2 at a temperature of 100°C to 130°C can be defined by an equivalent duration calculated at a temperature of 160°C according to the following formula ,

[0097] [mathematical operation 2]

[0098]

[0099] The temperature T2 ℃ (t) is expressed in °C.

[0100] The function is integrated over the time domain in which the product is held at 100°C to 130°C after the first procedure. According to the application, the equivalent duration thus calculated is shorter than or equal to 15% of the equivalent duration calculated for the first procedure .

[0101] Preferably, the second process is characterized by a holding time t2 at a temperature of 105°C to 130°C, or 105°C to 125°C, or 110°C to 130°C, or 110°C to 125°C, such that the equivalent duration calculated at 160°C is shorter than or equal to the equivalent duration calculated at 160°C for the first process by 15%.

[0102] Holding for longer at a temperature lower than 100°C, preferably lower than 105°C, still more preferably 110°C, does not improve the corrosion resistance in the short transverse direction.

[0103] the equivalent duration calculated at 160°C corresponding to a holding time t2 at a temperature of 100°C to 130°C, or 105°C to 130°C, or 105°C to 125°C, or 110°C to 130°C, or 110°C to 125°C, is shorter than or equal to the equivalent duration calculated for the first process by 15%.

[0104] Preferably, the equivalent duration corresponding to a holding time t2 at a temperature of 100°C to 130°C, or 105°C to 130°C, or 105°C to 125°C, or 110°C to 130°C, or 110°C to 125°C is shorter than or equal to the equivalent duration calculated at 160°C for the first process by 10%, 5% or 3.5%.

[0105] The inventors have noted that if the second process makes it possible to implement a sufficient duration at 100°C to 130°C, the corrosion under stress of the wrought product is improved. The equivalent duration calculated at 160°C is longer than or equal to 0.3%. The equivalent duration is shorter than 0.3% does not make it possible to stress corrosion sensitize the product. Still more preferentially, the equivalent duration is longer than or equal to the equivalent duration calculated at 160°C for the first process by 0.4%, 0.5%, 1%, 2% or 3%.

[0106] In one embodiment of the application, the first process and the second process are carried out in succession, without passing through room temperature in between. In this case, the start of the second process is at a temperature T1 ℃ (t) lower than 130°C, as shown in Figure 1 .

[0107] In another embodiment of the application, the first process and the second process are carried out in succession, with a holding at room temperature in between. In this case, the start of the second process is at a temperature T1℃ (t) the time at less than 130°C, such as Figure 2 As illustrated, the holding time t2 is equal to the cumulative holding time of the process in the temperature range from 100°C to 130°C.

[0108] The forged product obtained according to the application is suitable for aerospace applications, in particular for parts made as monolithic structures. A monolithic structure is a monolithic structure composed of a skin and stiffeners in one piece. Advantageously, the forged product obtained according to the application is used for monolithic structures, such as fuselage, rib or spar elements.

[0109] The inventors have noted that the thermomechanical treatment according to the application allows to obtain a better resistance to stress corrosion. In a preferred embodiment, the thermomechanical treatment is particularly beneficial for forged products expected to be resistant to stress corrosion in the short transverse TC, said forged products having a thickness greater than or equal to 30 mm, preferably greater than or equal to 50 mm or 90 mm, such as thick metal sheets, profiles or forged parts. A forged product made of 2000 series aluminum alloy having a thickness greater than or equal to 30 mm comprises, in weight %, Cu 3.5 - 5.8; Mg 0.2 - 1.5; Mn < 0.9; Fe < 0.15; Si < 0.15; Zr < 0.25; Ag < 0.8; Zn < 0.8; Ti 0.02 - 0.15, unavoidable impurities each < 0.05 and total < 0.15; the remainder being aluminum; which can be obtained by the thermomechanical treatment method of the application, which allows to have a corrosion average life over 10 days under a stress in the short transverse TC of less than or equal to 200 MPa. The test is carried out according to the conditions of ASTM G47-98 (2019) using a constant load tensioning device according to ASTM G49-85 (2019). In particular, in a preferred embodiment, the difference between the average life measured during the test and the standard deviation is greater than 10 days, the test being carried out according to the conditions of ASTM G47-98 (2019) using a constant load tensioning device according to ASTM G49-85 (2019).

[0110] The yield strength in the long transverse TL of the product is greater than or equal to 400 MPa.

[0111] The product of the application is used for aerospace applications for monolithic structures such as fuselages, ribs, spar elements.

[0112] Example

[0113] Example 1

[0114] The AA2139 alloy, the composition of which is indicated in Table 1, after homogenization at a temperature of 490°C to 530°C for a duration of 10 h to 50 h, is subjected to hot rolling to obtain a final thickness of 120 mm. The sheet is then solutionized at 490°C to 530°C for a duration of 5 h to 20 h, then quenched and stress relieved by controlled stretching, so as to obtain a permanent set of 2% to 4%. The sheet is then tested for stress corrosion after different tempering as indicated in Table 2.

[0115] As defined in the present application, the equivalent time is calculated taking into account the isothermal phase as well as the ramping up and ramping down phases.

[0116] The tempering comprising only one procedure is carried out with a ramping up to 150°C at a rate of 40°C / h, then to 160°C at a rate of 20°C / h. The cooling rate is 30°C / h.

[0117] The tempering comprising two procedures is carried out with the same ramping up and cooling rates. The two phases are carried out successively, without a phase held at room temperature.

[0118] [Table 1]

[0119] Si Fe Cu Mn Mg Ti Ag Zr Alloy A 0.04 0.08 4.8 0.3 0.5 0.05 0.33 <0.05

[0120] [Table 2]

[0121]

[0122] The stress corrosion tests (SCT) were carried out on the short transverse direction of the sheet using tensile specimens stressed at 200 MPa, under the conditions of ASTM G47-98 (2019). The specimens were subjected to immersion- floating cycles in a 3.5% NaCl salt solution, according to the conditions of ASTM G44-99 (2013). The tests were carried out under constant load, according to the recommendations of the standard ASTM G49-85 (2019). The tensile specimens had a diameter of 3.17 mm and were sampled at mid-thickness of the sheet. The results are indicated in Table 3.

[0123] The sheets were tested to determine their static mechanical properties and their toughness. The yield strength Rp0.2, the breaking strength Rm and the breaking elongation A in the TL direction are recorded in Table 4. The tensile specimens were sampled at mid-thickness and the toughness specimens used were CT20W40 (nomenclature according to the standard ASTM E399, thickness B = 20 mm, width W = 40 mm) sampled at quarter-thickness. In addition to the K q values obtained according to the standard ASTM E399, the K appThe value is taken as the test result. This includes the stress intensity factor of the test specimen obtained, the maximum load recorded during the test as the load, and the initial length of the crack after the fatigue pre-cracking as the crack length; it is the same as the length used to calculate K q

[0124] [Table 3]

[0125]

[0126] The tested products of the application A6 and A8 have a longer average lifetime than the products obtained after single-stage tempering. The lifetime of all the test specimens is not less than 10 days. The tested products of the application A6 and A8 have an average lifetime and a standard deviation such that the difference between the average and the standard deviation is greater than 10 days.

[0127] [Table 4]

[0128]

[0129] Example 2

[0130] Tests were carried out on the same metal sheet as in example 1 according to other tempering conditions shown in table 5. The stress corrosion tests were carried out under the same conditions as in example 1. The results are shown in table 6.

[0131] [Table 5]

[0132]

[0133] [Table 6]

[0134]

[0135] The tested product of the application A12 has a significantly longer average lifetime than the product A11, which is obtained after tempering comprising two sequences, but for which the holding time t2 at a temperature of 100°C to 130°C is equal to an equivalent duration This equivalent duration is 0.3% shorter than the calculated first sequence equivalent duration . The lifetime of all the test specimens numbered A12 tested is not less than 10 days. The tested product of the application A12 has an average lifetime and a standard deviation such that the difference between the average and the standard deviation is greater than 10 days.

[0136] Example 3

[0137] ​An AA2139 alloy, the composition of which is indicated in Table 7, after homogenization at 490°C to 530°C for a duration of 10 h to 50 h, is subjected to hot rolling to obtain a final thickness of 120 mm. The metal sheet is then solutionized at 490°C to 530°C for a duration of 5 h to 20 h, then quenched and stress relieved by controlled stretching, so as to obtain a permanent set of 2% to 4%. The metal sheet is then tested for stress corrosion after different tempering as indicated in Tables 8 and 9.

[0138] [Table 7]

[0139] Si Fe Cu Mn Mg Ti Ag Zr Alloy B 0.05 0.09 4.9 0.3 0.5 0.09 0.32 <0.05

[0140] The stress corrosion tests are performed under the same conditions as for Example 1.

[0141] [Table 8]

[0142]

[0143] [Table 9]

[0144]

[0145] The tempering according to the application, which comprises two stages, significantly improves the stress corrosion resistance.

[0146] Example 4

[0147] The stress corrosion tests are performed on a metal sheet made of AA2139 under the same conditions as for Example 1, which has already been subjected to a single-stage tempering at 160°C for 36 h. The metal sheet is tested in the short transverse direction under a constant load of 200 MPa stress and under a constant strain of 276 MPa stress. The results are indicated in Table 10.

[0148] [Table 10]

[0149]

[0150] It should be observed that the average lifetime obtained under constant strain is longer than that obtained under constant load, despite the higher stress applied. This example demonstrates that the tests under constant strain are less severe than those performed under constant load.

[0151] Example 5

[0152] Stress under seawater corrosion exposure tests were performed on the same metal sheets as described in example 1. The tests consisted in placing tensile specimens under a constant load applying a stress of 200 MPa (constant load) in a seawater atmosphere. This is the same stress condition as those used in example 1. They correspond to the conditions of ASTM G49-85 (2019).

[0153] The metal sheets were tested for their resistance to seawater corrosion exposure under stress in two tempering conditions, which are the same as those disclosed in example 1 and correspond to a single stage tempering at 160°C for 36h and the tempering of the application at 160°C 36h + 120°C 20h.

[0154] The results are reported in table 11.

[0155] [Table 11]

[0156]

[0157] The metal sheets subjected to the tempering of the application have a better resistance to stress corrosion in a seawater atmosphere. After 18 months (about 540 days) of exposure, none of the specimens were damaged.

[0158] Example 6

[0159] Stress corrosion tests were performed on the same metal sheets made of AA2139 as in example 1, which have been subjected to the single stage tempering and the two stage tempering of the application. The single stage tempering consists in only one procedure and is performed with a ramp up to 150°C at a rate of 40°C / h and then to 168°C at a rate of 20°C / h. The cooling rate is 30°C / h. The first procedure of the tempering according to the application, which consists in two procedures, undergoes the same ramp up or cooling rate as the tempering which consists in only one single procedure. After the first procedure, the second procedure is performed without passing through the ambient temperature. At the end of the second procedure, the metal sheet is cooled at a rate of 30°C / h.

[0160] [Table 12]

[0161]

[0162] The products were tested in the short transverse under a constant load applying a stress of 200 MPa. The results are shown in table 13.

[0163] [Table 13]

[0164]

[0165] Differential scanning calorimetry measurements, also called DSC (Differential Scanning Calorimetry) measurements, were performed on the two products A13 and A14. Figure 4The obtained thermograms are shown. The skilled person can note that the two thermograms are similar.

[0166] In both cases, a dissolution peak between 200 and 300°C (10, 10') is observed. Figure 4 The precipitate present dissolves during heating, which is accompanied by a drop in the measured enthalpy. The amount of precipitate present after tempering is estimated by integrating the surface area of the peak contained under the baseline of the curve. If the sample does not undergo any physical transformation, the baseline represents the variation of enthalpy as a function of temperature. This baseline can be obtained by using the baseline of a reference sample that does not undergo any physical transformation in the temperature range considered. It can also be estimated by extrapolation of the curve measured (see Figure 5 ). In the case of this example, the dissolution peak surface area of sample A13 measured is 4.98 J / g, and that of sample A14 is 4.90 J / g. The difference between the two is 1.6%.

[0167] The amount of precipitate formed after tempering is similar for the two heat treatments considered. However, for sample A14, which has been subjected to the tempering of the application, an increase in corrosion resistance is practically observed.

Claims

1. A method for the thermomechanical treatment of a wrought product made of a 2000 series aluminium alloy, said aluminium alloy comprising in weight % Cu 3.5-5.8; Mg 0.2-1.5; Mn < 0.9; Fe < 0.15; Si < 0.15; Ag < 0.8; Zn < 0.8; Ti 0.02-0.15; unavoidable impurities each < 0.05 and in total < 0.15; the balance being aluminium, said tempering comprising at least two sequences, [mathematical operation 1] [mathematical operation 2] said first sequence comprising a single isothermal stage.

2. The method according to claim 1, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 200 and 300°C.

3. The method according to claim 1 or 2, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 220 and 280°C.

4. The method according to any one of claims 1 to 3, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 230 and 270°C.

5. The method according to any one of claims 1 to 4, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 240 and 260°C.

6. The method according to any one of claims 1 to 5, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 245 and 255°C. Zr≤0.25； 7. The method according to any one of claims 1 to 6, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 250 and 255°C.

8. The method according to any one of claims 1 to 7, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 250 and 252°C.

9. The method according to any one of claims 1 to 8, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251 and 252°C.

10. The method according to any one of claims 1 to 9, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251 and 251.5°C. The thermomechanical treatment comprises solution, quenching, work hardening and tempering, characterized in that, 11. The method according to any one of claims 1 to 10, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252°C. a first step, in which the temperature expressed in °C, by a function T1 ℃ (t), is described, so that the maximum temperature T1 max is comprised between 130 °C and 180 °C, and the holding time t1 at a temperature comprised between 130 °C and 180 °C is such that the equivalent duration is comprised between 10 h and 80 h, wherein the equivalent duration is calculated at a temperature of 160 °C according to the following formula, 12. The method according to any one of claims 1 to 11, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C. and a second step in which the temperature expressed in °C passes through a function T2 ℃ (t) to a temperature such that T2 ℃ (t) < T1 max and its holding time t2 at a temperature of 100 to 130 °C is such that the equivalent duration calculated at a temperature of 160 °C according to the following formula is 0.3 to 15% of the equivalent duration calculated for the first step .

13. The method according to any one of claims 1 to 12, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

2. The thermo-mechanical treatment method according to claim 1, wherein the temperature T2 of the second working step is lower than 130°C. ℃ (t) less than 130°C.

3. The thermomechanical treatment method according to claim 1 or 2, characterized in that, The holding time t2 at 105°C to 130°C of the second process corresponds to an equivalent duration The equivalent duration The first process equivalent duration calculated 0.3% to 15%.

4. The thermomechanical treatment method according to claim 1 or 2, characterized in that, the equivalent duration time longer than or equal to the calculated first process equivalent duration time 0.5%.

5. The thermomechanical treatment method according to claim 4, characterized in that, the equivalent duration time longer than or equal to the calculated first process equivalent duration time 1%.

6. The thermomechanical treatment method according to claim 1 or 2, characterized in that, the equivalent duration less than or equal to 10% of the calculated first process equivalent duration the equivalent duration 7. The thermomechanical treatment method according to claim 6, characterized in that, the equivalent duration time less than or equal to 5% of the calculated first process equivalent duration time of the calculated first process equivalent duration time.

8. The thermomechanical treatment method according to claim 1 or 2, characterized in that, 14. The method according to any one of claims 1 to 13, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

9. The thermomechanical treatment method according to claim 1 or 2, characterized in that, 15. The method according to any one of claims 1 to 14, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

10. The thermomechanical treatment method according to claim 1 or 2, characterized in that, 16. The method according to any one of claims 1 to 15, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

11. The thermomechanical treatment method according to claim 1 or 2, characterized in that, 17. The method according to any one of claims 1 to 16, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

12. The thermomechanical treatment method of claim 1 or 2, wherein 18. The method according to any one of claims 1 to 17, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

13. The thermomechanical treatment method of claim 1 or 2, wherein 19. The method according to any one of claims 1 to 18, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

14. The thermomechanical treatment method of claim 1 or 2, wherein 20. The method according to any one of claims 1 to 19, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

21. The method according to any one of claims 1 to 20, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

22. The method according to any one of claims 1 to 21, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

23. The method according to any one of claims 1 to 22, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

24. The method according to any one of claims 1 to 23, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

25. The method according to any one of claims 1 to 24, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C. Zr≤0.15； 26. The method according to any one of claims 1 to 25, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

27. The method according to any one of claims 1 to 26, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

28. The method according to any one of claims 1 to 27, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

29. The method according to any one of claims 1 to 28, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

15. The thermomechanical treatment method of claim 1 or 2, wherein 30. The method according to any one of claims 1 to 29, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

31. The method according to any one of claims 1 to 30, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

32. The method according to any one of claims 1 to 31, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

33. The method according to any one of claims 1 to 32, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

34. The method according to any one of claims 1 to 33, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

35. The method according to any one of claims 1 to 34, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C. Zr≤0.05； 36. The method according to any one of claims 1 to 35, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

37. The method according to any one of claims 1 to 36, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

38. The method according to any one of claims 1 to 37, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

39. The method according to any one of claims 1 to 38, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

16. The thermomechanical treatment method of claim 1 or 2, wherein 40. The method according to any one of claims 1 to 39, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

17. The thermomechanical treatment method of claim 16, wherein, 41. The method according to any one of claims 1 to 40, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

42. The method according to any one of claims 1 to 41, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

43. The method according to any one of claims 1 to 42, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

44. The method according to any one of claims 1 to 43, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

45. The method according to any one of claims 1 to 44, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

46. The method according to any one of claims 1 to 45, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C.

47. The method according to any one of claims 1 to 46, wherein said first sequence comprises a single isothermal stage at a temperature comprised between 251.5 and 252.5°C. Zr≤0.25； 48. The method according to ​ ​ ​ obtained by the thermomechanical treatment method according to one of claims 1 to 12, characterized in that The average service life of three specimens in each case was more than 10 days under corrosion with a stress of less than or equal to 200 MPa applied on the short transverse TC, the test being carried out according to the conditions of ASTM G47-98 (2019) with constant load tensioning according to ASTM G49-85 (2019).

19. The forged product made of 2000-series aluminium alloy having a thickness greater than or equal to 30 mm according to claim 18, the service life of all specimens of which is longer than or equal to 10 days.

20. The forged product made of 2000-series aluminium alloy having a thickness greater than or equal to 30 mm according to claim 18 or 19, the yield strength in the long transverse direction TL of which is greater than or equal to 400 MPa.

21. The forged product made of 2000-series aluminium alloy having a thickness greater than or equal to 30 mm according to claim 18 or 19, comprising in weight % Cu 3.9-5.2; Mg 0.2-0.9; Mn 0.1-0.6; Fe < 0.15; Si < 0.15; Ag < 0.6; Zn < 0.8; Ti 0.02-0.15; unavoidable impurities each < 0.05 and in total < 0.15; the remainder being aluminium.

22. The forged product made of 2000-series aluminium alloy having a thickness greater than or equal to 30 mm according to claim 18 or 19, comprising in weight % Cu 4.5-5.0; Mg 0.40-0.90; Mn 0.20-0.50; Fe < 0.15; Si < 0.15; Ag 0.10-0.50; Zn < 0.5; Ti 0.02-0.15; unavoidable impurities each < 0.05 and in total < 0.15; the remainder being aluminium.

23. Use of the forged product according to any one of claims 18 to 22 or of the forged product obtained according to any one of claims 1 to 17 for an aeronautical application of monolithic structures.

24. Use of the forged product according to claim 23 for an aeronautical application of fuselage, rib or spar elements. ​ ​ Zr≤0.15； ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Zr≤0.05； ​ ​ ​ ​ ​ ​

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