Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent
  • C22C21/16—Alloys based on aluminium with copper as the next major constituent with magnesium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent
  • C22C21/14—Alloys based on aluminium with copper as the next major constituent with silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C21/00—Alloys based on aluminium
  • C22C21/12—Alloys based on aluminium with copper as the next major constituent
  • C22C21/18—Alloys based on aluminium with copper as the next major constituent with zinc
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/002—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working by rapid cooling or quenching; cooling agents used therefor
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22F—CHANGING THE PHYSICAL STRUCTURE OF NON-FERROUS METALS AND NON-FERROUS ALLOYS
  • C22F1/00—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working
  • C22F1/04—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon
  • C22F1/057—Changing the physical structure of non-ferrous metals or alloys by heat treatment or by hot or cold working of aluminium or alloys based thereon of alloys with copper as the next major constituent
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/02—Making non-ferrous alloys by melting
  • C22C1/026—Alloys based on aluminium

Definitions

• the present invention relates to a wrought 2XXX alloy product having improved stress corrosion properties and a process for the thermo-mechanical treatment of wrought aluminum alloy products of the 2XXX series intended to improve their resistance to stress corrosion while while maintaining an excellent compromise between yield strength, ductility, and damage tolerance, in particular toughness.
• Aircraft applications generally require a very specific set of properties.
• High strength alloys are generally desired, but depending on the intended use, other properties such as high fracture toughness or ductility, as well as good corrosion resistance are usually required, in particular, stress corrosion resistance.
• the resistance to corrosion under stress of alloy 2000 is evaluated after alternating immersion-emersion test according to standard ASTM G47 - 98 (2019). Products over 30mm are generally tensile tested according to ASTM G49 - 85 (2019). Depending on the device chosen, the test is carried out under constant deformation or under constant load. The choice depends on the intended application and the selection criteria. As mentioned in ASTM G49 - 85 (2019), tensile stress corrosion testing under constant load is more severe than tensile stress corrosion testing under constant strain. Thus, the maximum allowable stress defined by a tensile stress corrosion test under constant load is generally less than or equal to that determined by a tensile stress corrosion test under constant strain.
• WO2004/106566 discloses an aluminum alloy having improved strength and ductility, comprising Cu 3.5 - 5.8 wt%, Mg 0.1 - 1.8 wt%, Mn 0.1 - 0.8 by weight, Ag 0.2 - 0.8% by weight, Ti 0.02 - 0.12% by weight and optionally one or more selected from the group consisting of Cr 0.1 - 0.8% by weight, Hf 0.1 - 1.0 wt%, Sc 0.03 - 0.6 wt%, and V 0.05 - 0.15 wt%, remaining aluminum, and wherein the alloy is substantially free of zirconium .
• WO2020/123096 discloses a 2XXX alloy, with a titanium content of between 0.08 and 0.20 weight % which has an excellent compromise of at least two characteristics such as mechanical strength, toughness, elongation and resistance to corrosion. This application discloses stress corrosion tests performed under constant strain.
• Standard practice for the final thermo-mechanical treatment of these alloys after hot rolling includes solution quenching, the fastest possible quenching, cold deformation of at least 2% and tempering with a single isothermal step.
• FR2435535 discloses a heat treatment process for wrought aluminum alloy products of the 2000 series containing (by weight %) from 3.5 to 5% copper, from 0.2 to 0.1% magnesium, from 0, 25 to 1.2% silicon with an Si/Mg ratio greater than 0.8 characterized in that the tempering comprises at least two stages a main tempering at a temperature greater than 225°C and less than 285°C of a duration of between 6 s and 60 min and additional tempering at a temperature of between 120° C. and 175° C. for a duration of between 4 and 192 hours.
• FR2435535 differs from the invention in that it applies to products whose silicon content is greater than 0.25% by weight and in that the first tempering step is carried out at a temperature greater than 225°C .
• US 3,305,410 discloses a two-step tempering heat treatment for aluminum alloys to improve corrosion resistance. This income is referred to as “top-down” income.
• the first stage is carried out at high temperature, typically between 190° C. and 218° C., so as to initiate homogeneous precipitation and minimize precipitation at the grain boundaries.
• the second level is carried out at a lower temperature, typically between 135° C. and 163° C., so as to complete the precipitation.
• the invention relates to a thermo-mechanical treatment process applied to 2XXX alloys of composition in % by weight Cu 3.5 - 5.8; Mg 0.2 - 1.5; M n ⁇ 0.9; Fe ⁇ 0.15; If ⁇ 0.15; Zr ⁇ 0.25; Ag ⁇ 0.8; Zn ⁇ 0.8; Ti 0.02-0.15, unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; remains aluminum allowing to improve resistance to stress corrosion while allowing to obtain an excellent compromise between elastic limit, ductility, and tolerance to damage, in particular toughness.
• the process makes it possible to improve resistance to corrosion under tensile stress under constant load.
• the invention relates to a process for the thermo-mechanical treatment of wrought aluminum alloy products of the 2000 series comprising, in% by weight, Cu 3.5 - 5.8; Mg 0.2 - 1.5; M n ⁇ 0.9;Fe ⁇ 0.15; If ⁇ 0.15;Zr ⁇ 0.25;Ag ⁇ 0.8;Zn ⁇ 0.8; Ti 0.02-0.15, unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; remains aluminum.
• This thermo-mechanical treatment includes solution treatment, quenching, hardening, and tempering.
• Tempering is characterized in that it comprises at least two sequences: a first sequence whose temperature expressed in °C is described by a function T1° c (t) depending on time t, such that the maximum temperature reached T1 max 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 time is between 1 Oh and 80h, equivalent duration calculated at a temperature of 160°C according to the formula [Math 1] and a second sequence whose temperature expressed in °C is described by a time-dependent function t whose temperature is such that T2° c (t) is less than T1 max and whose holding time t2 expressed in hours at a temperature between 100°C and 130°C is such that the equivalent duration calculated at a temperature of 160°C according to the formula
• [Math 2] is between 0.3% and 15% of the equivalent duration calculated for the first sequence.
• the temperature T2° c (t) of the second sequence is less than 130°C.
• the holding time t2 of the second sequence comprised between 105°C and 130°C, preferentially between 105°C and 125°C or between 110°C and 130°C, or between 110°C and 125°C, corresponds to an equivalent duration between 0.3% and 15% of the equivalent duration °calculated for the first sequence.
• the equivalent duration t2 ⁇ °° is greater than or equal to 0.4% of the equivalent duration calculated for the first sequence, even more preferably the duration equivalent is greater than or equal to 0.5% or 1% or 2% or 3% of the equivalent duration calculated at 160°C.
• the equivalent duration is less than or equal to 10% of the equivalent duration calculated for the first sequence, even more preferred, the equivalent duration is less than or equal to 5%, or 3.5%.
• the first sequence comprises a single isothermal plateau.
• the wrought product is a thin sheet or a thick sheet or a profile or a forged part.
• the wrought product is a thick sheet or a section or a forged part with a thickness greater than or equal to 30 mm, preferably 50 mm, even more preferably greater than or equal to 90 mm.
• the wrought product is a thick sheet having undergone a step of shaping by high-energy hydroforming before tempering, preferably shaping by hydroforming by explosion.
• the wrought aluminum alloy product of the 2000 series is preferably chosen from a designation AA2139, AA2039, AA2040, AA2124, AA2024, AA2027, AA2022, AA2042.
• the wrought aluminum alloy product of the 2000 series comprises, in% by weight, Cu 3.9-5.2; Mg 0.2 - 0.9; Mn 0.1 - 0.6; Fe ⁇ 0.15; If ⁇ 0.15; Zr ⁇ 0.15; Ag ⁇ 0.6; Zn ⁇ 0.8; Ti 0.02-0.15, unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; remains aluminum.
• the wrought aluminum alloy product of the 2000 series comprises, in% by weight, Cu 4.5-5.0; Mg 0.40 - 0.90; Mn 0.20 - 0.50; Fe ⁇ 0.15; If ⁇ 0.15; Zr ⁇ 0.05; Ag 0.10 - 0.50; Zn ⁇ 0.5; Ti 0.02-0.15, unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; remains aluminum.
• the value of the area of the dissolution peak, after the second sequence, measured by DSC, dissolution peak between approximately 200° C. and 300° C. is substantially equal to the value of the area of the dissolution peak measured after the first sequence, by substantially equal is meant a difference less than or equal to 5%, advantageously less than or equal to 2%.
• the invention also relates to a wrought product in aluminum alloy of the 2000 series with a thickness greater than or equal to 30 mm comprising, in% by weight, Cu 3.5-5.8; Mg 0.2 - 1.5; M n ⁇ 0.9; Fe ⁇ 0.15; If ⁇ 0.15; Zr ⁇ 0.25; Ag ⁇ 0.8; Zn ⁇ 0.8; Ti 0.02-0.15, unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; rest aluminum; capable of being obtained by the thermo-mechanical treatment process according to the invention.
• This product is characterized in that the average stress corrosion life at a stress less than or equal to 200 MPa applied in the short transverse direction TC is greater than 10 days for three specimens per case, the tests being carried out according to the conditions of ASTM G47 - 98 (2019) using a tension device under constant load according to ASTM G49 - 85 (2019).
• the wrought aluminum alloy product of the 2000 series with a thickness greater than or equal to 30 mm is such that the service life of all the specimens tested in the short transverse direction TC at a stress less than or equal to 200 MPa under the conditions of ASTM G47 - 98 (2019) using a tension device under constant load per ASTM G49 - 85 (2019) is greater than or equal to 10 days.
• the wrought aluminum alloy product of the 2000 series with a thickness greater than or equal to 30 mm has an elastic limit in the long transverse direction TL greater than or equal to 400 MPa.
• the wrought aluminum alloy product of the 2000 series with 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; If ⁇ 0.15; Zr ⁇ 0.15; Ag ⁇ 0.6; Zn ⁇ 0.8; Ti 0.02-0.15, unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; remains aluminum.
• the wrought aluminum alloy product of the 2000 series with 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; If ⁇ 0.15; Zr ⁇ 0.05; Ag 0.10 - 0.50; Zn ⁇ 0.5; Ti 0.02-0.15, unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; remains aluminum.
• the product according to the invention or obtained according to the process of is used for aeronautical applications of integral structures such as fuselage, rib or spar elements.
• FIGURES
• Figure 1 is a schematic representation of the tempering of an embodiment of the invention where the two sequences are performed successively without going through a step at room temperature.
• FIG. 2 shows a schematic representation of the tempering of an embodiment of the invention where the two sequences are carried out successively by going through a step at room temperature.
• Figure 3 shows a schematic representation of the income of an embodiment of the invention where the first sequence is a single step.
• Figure 4 shows the thermograms obtained after measurement by differential scanning calorimetry or DSC on samples A13 and A14 of example 6.
• Figure 5 illustrates the determination of the value of the area of the dissolution peak after DSC measurement.
• the static mechanical characteristics in other words the breaking strength R m , the conventional yield strength at 0.2% elongation R p 0.2 ("yield strength") and the elongation at break A%, are determined by a tensile test according to standard EN 10002-1, the sampling and direction of the test being defined by standard EN 485-1.
• the stress intensity factor (KQ) is determined according to the ASTM E 399 standard.
• the ASTM E 399 standard gives the criteria for determining whether KQ is a valid value of Kic.
• KQ values obtained for different materials are comparable with each other provided that the elastic limits of the materials are of the same order of magnitude.
• Stress corrosion tests were performed according to ASTM G47 - 98 (2019) and ASTM G49 - 85 (2019) in the short through TC direction for specimens centered at mid-thickness. Unless otherwise stated, stress corrosion tests are carried out using tensile specimens. Typically the tensile specimens are cylindrical with a diameter of 3.17 +0.01 mm. It is however possible to use flat specimens. 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 per case.
• a thin sheet is a rolled product of rectangular cross-section whose uniform thickness is between 0.20 mm and 6 mm.
• a thick plate is a rolled product with a thickness greater than 6 mm.
• a wrought product resistant to corrosion under stress in the short cross direction means that the product does not show any rupture before 10 days of testing at a stress of 200 MPa applied in the short cross direction, using a device ensuring a constant load according to the recommendations of ASTM G49 - 85 (2019).
• the product according to the invention is resistant to stress corrosion in the short transverse direction.
• 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.
• tempering is a heat treatment aimed at modifying the properties of a product by precipitation of the intermetallic phases from the supersaturated solution. Depending on the state of the art, it may consist of one or more steps. “Step” means a temperature rise phase or an isothermal plateau or a cooling phase. The rising and/or cooling phases can be linear and defined by a heating or cooling rate.
• a “sequence” consists of one or more steps.
• a sequence can be defined by a curve of temperature as a function of time T° c (t).
• the tempering temperatures mentioned in the application are preferably with an accuracy of +/- 5°C, even more preferably +/- 3°C.
• the duration of maintenance of a sequence defined by T° c (t) during a time interval between t' and t" is equivalent to a duration sequence carried out at a reference temperature T ref . is defined by the formula:
• T° c (t) is the instantaneous temperature in °C of a sequence which evolves with time t (in hours), and Tref is the reference temperature. is expressed in hours.
• the constant Q corresponds to the activation energy for diffusion. According to the invention, the constant Q is taken as equal to 136000 J/mol which corresponds to the activation energy of the diffusion of copper Cu in aluminium.
• the ideal gas constant R is equal to 8.314 J/K/mol.
• the wrought aluminum alloy product of the 2000 series comprises in wt% Cu 3.5 - 5.8; Mg 0.2 - 1.5; M n ⁇ 0.9; Fe ⁇ 0.15; If ⁇ 0.15; Zr ⁇ 0.25; Ag ⁇ 0.8; Zn ⁇ 0.8; Ti 0.02-0.15, unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; remains aluminum.
• the Cu content is at least 3.5% by weight, preferably at least 3.9% by weight, advantageously at least 4.1% and even more preferably at least 4.4% by weight in order to obtain a sufficient elastic limit.
• the Cu content is at most 5.8% by weight, preferably at most 5.2%, advantageously at most 5.0% by weight.
• the wrought product has a Cu content of between 3.9 and 5.2% by weight, advantageously between 4.5 and 5.0% by weight. Too low a value of the copper content leads to too low a mechanical resistance and an elastic limit. Too high a copper content value leads to insufficient toughness.
• the Mg content is at least 0.2% by weight, preferably at least 0.20% by weight, advantageously at least 0.40% by weight.
• the Mg content is at most 1.5% by weight, preferably at most 0.9%, even more preferably 0.90% by weight.
• the wrought product has a Mg content of between 0.2 and 0.9% by weight, advantageously between 0.40 and 0.90% by weight.
• a value that is too low for the magnesium content leads to too low a mechanical strength and an elastic limit. Too high a magnesium content value leads to insufficient toughness.
• the Mn content is preferably at least 0.05% by weight, even more preferably at least 0.1% and even more preferably at least 0.20% by weight. weight.
• the Mn content is at most 0.9% by weight, preferably at most 0.6% by weight, even more preferably at most 0.50% by weight. In one embodiment, the Mn content is between 0.1 and 0.6% by weight, preferably between 0.20 and 0.50% by weight.
• the addition of manganese makes it possible to control the growth of recrystallization grains, and thus makes it possible to increase the mechanical strength of the product and its elastic limit, but too high a content leads to a drop in toughness.
• the Zr content is at most 0.25% by weight, preferably at most 0.15% by weight, even 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 observed that a Zr content of less than or equal to 0.05% by weight makes it possible to improve the formability of the product. In another preferred embodiment, the Zr content is between 0.05 and 0.15% by weight.
• the Ag content is at most 0.8% by weight, preferably at most 0.6%. In a preferred embodiment, the Ag content is between 0.10 and 0.50% by weight.
• 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%.
• 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, even more advantageously between 0.02 and 0.05% by weight. weight.
• the titanium has the effect of controlling the casting microstructure, in particular of refining the grain size.
• the other elements have a content of at most 0.05% by weight each and 0.15% by weight in total. These are unavoidable impurities, the rest is aluminum.
• the wrought aluminum alloy product of the 2000 series is chosen from the designations AA2139, AA2039, AA2040, AA2124, AA2024, AA2027, AA2022, AA2042.
• the wrought aluminum alloy product of the 2000 series is advantageously a thin sheet, a thick sheet, a profile or a forging.
• the wrought product is a sheet at least 30 mm thick, preferably greater than or equal to 50 mm, even more preferably greater than or equal to 90 mm.
• the wrought aluminum alloy product of the 2000 series is obtained by a standard production process.
• a raw form is cast from a bath of liquid metal of composition in % by weight Cu 3.5 - 5.8; Mg 0.2 - 1.5; M n ⁇ 0.9; Fe ⁇ 0.15; If ⁇ 0.15; Zr ⁇ 0.25; Ag ⁇ 0.8; Zn ⁇ 0.8; Ti 0.02-0.15, unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; remains aluminum.
• the raw form is advantageously a plate, or a billet.
• the raw shape is then homogenized, then hot shaped to obtain a wrought alloy product aluminum of the 2000 series.
• the homogenization is carried out at a temperature of between 490° C. and 530° C. for a period of 1 Oh to 50 h.
• the plate is homogenized and then hot rolled to obtain a wrought aluminum alloy product of the 2000 series.
• the wrought aluminum alloy product of the 2000 series is a sheet with a thickness greater than or equal to 30 mm, preferably greater than or equal to 50 mm, even more preferably greater than or equal to 90 mm.
• the wrought aluminum alloy product of the 2000 series is a sheet with a thickness less than or equal to 180 mm, preferably less than or equal to 150 mm.
• the wrought aluminum alloy product of the 2000 series comprising in % by weight, Cu 3.5 - 5.8; Mg 0.2 - 1.5; M n ⁇ 0.9; Fe ⁇ 0.15; If ⁇ 0.15; Zr ⁇ 0.25; Ag ⁇ 0.8; Zn ⁇ 0.8; Ti 0.02-0.15, unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; rest aluminum undergoes a thermo-mechanical treatment comprising solution treatment, quenching, work hardening and tempering.
• the wrought product undergoes solution treatment at a temperature of between 490° C. and 530° C. for a period of 5 h to 20 h.
• the quenching is carried out by immersing the product put into solution in water at room temperature, conventionally at around 22° C. (+/- 10° C.) or by sprinkling the product using a spray.
• Hardening is then carried out.
• this hardening is carried out cold. It can be achieved by traction or compression.
• the permanent deformation rate is between 1 and 9%, preferably between 3 and 5%.
• an additional shaping step can be performed before tempering.
• This shaping step can be performed by a high energy hydroforming process.
• this process is carried out on a thick sheet, typically with a thickness greater than or equal to 30 mm, preferably greater than or equal to 50 mm and even more preferably greater than or equal to 90 mm.
• This process may be an explosion hydroforming process. This type of process is described in the publication “Applications and capabilities of explosive forming” by DJ. Mynor et al. Journal of Materials Processing Technology 125-126 (2002) pp 1-25.
• the wrought product is tempered, comprising at least two sequences.
• the wrought product is tempered comprising two sequences.
• the first sequence aims to obtain the final mechanical properties of the product.
• the first sequence is such that it makes it possible to obtain the best toughness/yield strength compromise.
• the first sequence consists of one or more stages of heating, and/or isothermal holding and/or cooling.
• the evolution of the temperature during the first sequence can be described by a function T1° c (t) depending on the time t.
• the temperature reaches a maximum temperature T1 max between 130°C and 180°C.
• the maximum temperature T1 max is reached during an isothermal plateau.
• the duration of the first sequence is such that the duration of maintenance at a temperature comprised between 130°C and 180°C is equivalent to an equivalent duration comprised between 1 Oh and 80h, equivalent duration calculated at the reference temperature of 160°C according to the formula [Math 1]
• the function is integrated over the period of time where the temperature expressed in °C is between 130°C and 180°C. That is to say that the function is integrated over the period of time corresponding to the first crossing of the temperature 130° C. on ascent, and the first crossing of the temperature 130° C. during the descent. In the case where the time period is discontinuous, the function must be integrated according to each of the time periods where the temperature is between 130°C and 180°C.
• the duration of maintenance at a temperature between 130° C. and 180° C. during the first sequence is equivalent to an equivalent duration of at least 15 hours, 20 hours, 24h, or 30h in order to obtain sufficient mechanical resistance. Indeed, if the equivalent duration is too short, it is not possible to reach a sufficient elastic limit, typically to reach an elastic limit of at least 400 MPa in the TL (Travers Long) direction.
• the duration of maintenance at a temperature between 130° C. and 180° C. during the first sequence is such that the equivalent duration is less than 70h, advantageously less than 60h, or 50h, or 40h in order to obtain sufficient ductility and toughness. Indeed, if the equivalent duration is too long, the ductility and toughness drop.
• the first sequence can be preceded by a maturation step at ambient temperature.
• the duration of the maturation step can vary between a few minutes, a few hours or a few days.
• the maturation time is between 10 minutes and 10 hours, preferably at most 4 hours.
• the first sequence is a single step (see Figure 3).
• the term “mono-level” means a sequence comprising a single isothermal level.
• a first single-level sequence comprises a temperature rise step, isothermal maintenance between 130° C. and 180° C. and a cooling step.
• the purpose of the second sequence is to improve resistance to stress corrosion.
• the second sequence induces a negligible change in the mechanical properties such as the elastic limit, the breaking stress or the toughness.
• the elastic limit, the breaking stress, or the tenacity evolves by less than 10% between the end of the first sequence and the end of the second sequence, advantageously by less than 5%, even more advantageously by less than 3% or 2%.
• the elastic limit changes by less than 3%, preferably by less than 2%.
• the tenacity changes by less than 3%, preferably by less than 2%.
• the inventors have observed that the second sequence does not significantly modify the quantity of precipitates formed at the end of the first sequence.
• DSC Differential Scanning Calorimetry
• a reference in this case, alumina
• This DSC technique relies on the fact that during a physical transformation, such as a phase transition, a certain amount of heat is exchanged with the sample to keep it at the same temperature as the reference.
• the direction of this heat exchange between the sample and the equipment depends on the endothermic or exothermic nature of the transition process. Thus, for example, if a product contains precipitates, when it is heated, these precipitates can dissolve in a temperature range under the effect of heat.
• the product will then absorb more heat to be able to increase its temperature at the same rate as the reference.
• the dissolution of precipitates is an endothermic phase transition because it absorbs heat.
• the sample can undergo exothermic processes, such as precipitation, when it transfers heat to the system.
• a differential scanning calorimeter can measure the amount of heat absorbed or released during a transition.
• This dissolution peak according to the invention is between about 200°C and 300°C.
• about 200°C and 300°C is meant that the dissolution peak may extend within a range between +/- 50°C relative to the range of 200°C-300°C.
• the inventors have observed that the area of the dissolution peak varies by less than 5% between the two sequences.
• the inventors have in fact observed that the value of the area of the dissolution peak after the second sequence, measured by DSC, dissolution peak between approximately 200° C. and 300° C., is substantially equal to the value of the area of the dissolution peak measured after the first sequence.
• substantially equal is meant a difference less than or equal to 5%, advantageously less than or equal to 2%.
• the second sequence consists of one or more stages of heating, and/or isothermal holding and/or cooling.
• the evolution of the temperature during the second sequence can be described by a time-dependent function T2° c (t).
• the second sequence is carried out at a temperature T2 lower than the maximum temperature T1 max of the first sequence. That is to say that during the second sequence, the function T2° c (t) is lower than the maximum temperature T1 max .
• the second sequence is carried out at a temperature T2 below 130°C, even more preferably below 125°C.
• the second sequence is characterized by a holding time t2 at a temperature between 100°C and 130°C.
• This holding time t2 at a temperature between 100°C and 130°C can be defined by an equivalent time calculated at the temperature of 160°C according to formula
• the temperature T2° c (t) is expressed in °C.
• the equivalent duration thus calculated is less than or equal to 15% of the equivalent duration calculated for the first sequence.
• the second sequence is characterized by a holding time t2 at a temperature between 105°C and 130°C, or between 105°C and 125°C, or between 110°C and 130°C, or between 110°C and 125°C, such as the equivalent time calculated at 160°C is less than or equal to 15% of the equivalent duration calculated at 160°C for the first sequence.
• Prolonged maintenance at a temperature below 100° C., preferably below 105° C., even more preferably 110° C. does not make it possible to improve the resistance to corrosion in the short transverse direction.
• the equivalent duration calculated at a temperature of 160°C, corresponding to the holding time t2 at a temperature between 100°C and 130°C, or between 105°C and 130°C, or between 105°C and 125°C, or between 110°C and 130°C, or between 110°C and 125°C is less than or equal to 15% of the equivalent duration calculated for the first sequence.
• the equivalent duration corresponding to the duration of the hold t2 at a temperature between 100°C and 130°C or between 105°C and 130°C, or between 105°C and 125°C, or between 110°C and 130°C, or between 110°C and 125°C is less than or equal to 10%, 5%, or 3.5% of the equivalent duration calculated at 160°C for the first sequence.
• the inventors have observed that the stress corrosion of the wrought product is improved if the second sequence is such that a sufficient duration of between 100° C. and 130° C. is carried out.
• the equivalent duration calculated at 160°C is greater than or equal to 0.3%.
• a equivalent duration of less than 0.3% does not desensitize the product to stress corrosion.
• the equivalent duration is greater than or equal to 0.4%, 0.5%, 1%, 2% or 3% of the equivalent duration calculated at 160°C for the first sequence.
• the first and the second sequence are carried out successively without going through the ambient temperature between the two.
• the start of the second sequence takes place when the temperature T1° c (t) is less than 130° C. as shown in FIG. 1.
• the first and the second sequence are carried out successively with maintenance at room temperature between the two.
• the start of the second sequence takes place when the temperature T1° c (t) is less than 130° C. as shown in FIG. 2, the hold time t2 is equal to the cumulative hold times of the sequences in the temperature range between 100°C and 130°C.
• the wrought product obtained according to the invention is suitable for aeronautical applications, in particular for components produced as an integral structure.
• An integral structure is a monolithic structure consisting of a skin and a stiffener in one piece.
• the wrought product obtained according to the invention is advantageously used for integral structures, such as fuselage, rib or spar elements.
• thermo-mechanical treatment makes it possible to obtain better stress corrosion resistance.
• the thermo-mechanical treatment is particularly interesting on wrought products with a thickness greater than or equal to 30 mm, preferably greater than or equal to 50 mm or 90 mm, such as a thick sheet, a profile or a forged product for which the resistance to stress corrosion in the short transverse direction TC is sought.
• a wrought aluminum alloy product of the 2000 series with a thickness greater than or equal to 30 mm comprising, in% by weight, Cu 3.5-5.8; Mg 0.2 - 1.5; M n ⁇ 0.9;Fe ⁇ 0.15; If ⁇ 0.15;Zr ⁇ 0.25;Ag ⁇ 0.8;Zn ⁇ 0.8; Ti 0.02-0.15 unavoidable impurities ⁇ 0.05 each and ⁇ 0.15 total; rest aluminum; capable of being obtained by the thermo-mechanical treatment process according to the invention makes it possible to obtain an average lifetime in stress corrosion at a stress less than or equal to 200 MPa imposed in the short transverse direction TC greater than 10 days .
• the tests are carried out according to the conditions of ASTM G47 - 98 (2019) using a tension device under constant load according to ASTM G49 - 85 (2019).
• the difference between the average lifetime and the standard deviation measured during the test is greater than 10 days, the tests being carried out according to the conditions of ASTM G47 - 98 (2019 ) using a tension device under constant load according to ASTM G49 - 85 (2019).
• This product has a yield strength in the long transverse direction TL greater than or equal to 400 MPa.
• the product according to the invention is used for aeronautical applications of integral structures such as fuselage, rib or spar elements.
• An AA2139 alloy the composition of which is indicated in Table 1, underwent, after homogenization at a temperature of between 490° C. and 530° C. for a period of 1 Oh to 50 h, hot rolling to obtain a final thickness of 120 mm.
• the sheet was then placed in solution between 490° C. and 530° C. for a period of 5 to 20 hours then quenched and stress-relieved by controlled traction so as to obtain a permanent deformation between 2 and 4%.
• the sheet was then tested for stress corrosion after different tempers as indicated in Table 2.
• Tempering comprising only one sequence is carried out with a heating rate of 40°C/h up to 150°C, then at 20°C/h up to 160°C.
• the cooling rate is 30°C/h.
• Tempers with two sequences are carried out with the same heating and cooling rates. The two levels are made one after the other without going through a maintenance at room temperature.
• SCC Stress corrosion testing
• the sheets were tested to determine their static mechanical properties and toughness.
• the yield strength Rp0.2, the breaking strength Rm and the elongation at break A, in the TL direction are presented in Table 4.
• the K q value obtained according to ASTM E399 the value of K app is used as the test result. This is the stress intensity factor obtained for the specimen tested using as load the maximum load recorded during the test, and as crack length, the initial length of the crack after pre-cracking in fatigue; it is the same length as that used for the calculation of K q . [Table 3]
• the products A6 and A8 tested according to the invention have a longer average lifetime than the products obtained after a single-level tempering. None of the specimens tested has a lifespan of less than 10 days.
• the products tested according to the invention A6 and A8 have an average lifetime and a standard deviation such that the difference between the average and once the standard deviation is greater than 10 days.
• Example 5 The same sheet as Example 1 was tested under other tempering conditions as indicated in Table 5. The stress corrosion tests were carried out under the same conditions as Example 1. The results are shown in table 6. [Table 5]
• the product tested according to the invention A12 has a significantly longer average lifetime than the product Ail obtained after tempering comprising two sequences but whose holding time t2 at a temperature between 100° C. and 130° C. is equivalent to a equivalent duration less than 0.3% of the equivalent time duration calculated for the first sequence. None of the specimens tested for reference A12 has a lifetime of less than 10 days.
• the product tested according to the invention A12 has a mean lifetime and a standard deviation such that the difference between the mean and once the standard deviation is greater than 10 days.
• An AA2139 alloy the composition of which is indicated in Table 7, underwent, after homogenization between 490° C. and 530° C. for a duration of 1 Oh to 50 h, hot rolling to obtain a final thickness of 120 mm.
• the sheet was then placed in solution between 490° C. and 530° C. for a period of 5 to 20 hours then quenched and stress-relieved by controlled traction so as to obtain a permanent deformation between 2 and 4%.
• the sheet was then tested for stress corrosion after different tempers as indicated in Tables 8 and 9. [Table 7]
• the stress corrosion resistance in marine exposure of the sheet was tested for two tempering conditions, identical to those presented in Example 1, and corresponding to single-level tempering for 36 hours at 160° C. and tempering according to invention 36h at 160°C + 20h 120°C.
• Single-level tempering comprises only one sequence and is carried out with a heating rate of 40°C/h up to 150°C, then 20°C/h up to 168°C.
• the cooling rate is 30°C/h.
• the tempering according to the invention comprising two sequences underwent for the first sequence the same heating or cooling rates as the tempering comprising only a single sequence.
• the second sequence is carried out following the first sequence without going through the ambient temperature. At the end of the second sequence, the sheet is cooled at 30° C./h.
• a dissolution peak (10, 10') located between 200°C and 300°C is observed (FIG. 4) in both cases.
• the precipitates present are dissolved during the heating, which is accompanied by a drop in the measured enthalpy.
• the quantity of precipitates present on tempering is estimated by integrating the area of the peak comprised under the base line of the curve.
• the base line is representative of the evolution of the enthalpy with the temperature if the sample did not undergo any physical transformation.
• This baseline can be obtained by using the baseline of the reference sample which does not undergo any physical transformation in the temperature range considered. It can also be estimated by extrapolating the measured curve (see Figure 5).
• a dissolution peak area of 4.98 J/g is measured for sample A13 and a dissolution peak area of 4.90 J/g for sample A14.
• the difference between the two is 1.6%.
• the amount of precipitates formed on tempering is similar for the two heat treatments considered. However, an improvement in the resistance to corrosion is indeed observed for sample A14, having undergone tempering according to the invention.

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