7xxx wrought materials and production methods with improved tensile and toughness properties

Abstract

The present invention relates to a wrought 7xxx aluminum alloy containing, by weight percent, 6.7 to 7.4 Zn, 1.35 to 1.75 Mg, 1.85 to 2.35 Cu, 0.04 to 0.14 Zr, 0 to 0.5 Mn, 0 to 0.15 Ti, 0 to 0.15 V, 0 to 0.25 Cr, 0.05% or less Fe, and 0.05% or less Si, where Fe+Si is 0.08% or less, and the wrought 7xxx aluminum alloy is artificially aged at 155°C for a total equivalent aging time t(eq) of 24 to 45 hours, thereby optimizing the compromise between tensile yield strength and toughness and enabling improved cryogenic fracture toughness and fatigue resistance in corrosive environments.

Description

[Technical Field]

[0001] The present disclosure relates to methods for producing 7xxx aluminum wrought products having an improved compromise of tensile and toughness properties, as well as excellent cryogenic properties and fatigue resistance in corrosive environments, and more particularly to such manufacturing processes and rolled products and uses, especially designed for aviation and aerospace engineering and cryogenic applications. [Background technology]

[0002] High-strength 7xxx aluminum alloy products, also known as Al-Zn-Mg-Cu type alloy products, are widely used in aerospace structural applications, where material strength, fracture toughness, fatigue resistance, and corrosion resistance are simultaneously required. It is known that these diverse properties cannot all be optimized simultaneously and independently during the production of structural components and semi-finished products for aerospace structures. Changes in the alloy's chemical composition or the product manufacturing process parameters can tend to cause conflicting changes in several key properties. This is often the case for, first, what is commonly referred to as "static mechanical strength" (especially ultimate tensile stress UTS and tensile yield stress TYS) and, second, what is commonly referred to as "damage tolerance" (especially toughness and crack propagation resistance). Furthermore, several other properties, such as fatigue resistance, corrosion resistance, formability, and elongation at break, are related to these properties in complex and often unpredictable ways. Therefore, optimizing all the properties of mechanical structural materials, for example in the aerospace industry, often requires compromises between several key parameters.

[0003] Al-Zn-Mg-Cu alloys with high fracture toughness and high mechanical strength have been described in the prior art.

[0004] U.S. Patent No. 5,312,498 discloses a method for producing an aluminum-base alloy product with improved spallation resistance and fracture toughness, comprising providing an aluminum-base alloy composition consisting essentially of about 5.5-10.0 wt. % zinc, about 1.75-2.6 wt. % magnesium, about 1.8-2.75 wt. % copper, and the balance aluminum and other elements. The aluminum-base alloy is processed, heat treated, quenched, and aged to produce a product with improved corrosion resistance and mechanical properties.

[0005] US Patent No. 5,560,789 describes AA7000 series alloys with high mechanical strength and a method for obtaining them, containing, by weight, 7-13.5% Zn, 1-3.8% Mg, 0.6-2.7% Cu, 0-0.5% Mn, 0-0.4% Cr, 0-0.2% Zr, not more than 0.05% each and not more than 0.15% total of other elements, and the balance being aluminum.

[0006] U.S. Patent No. 5,865,911 describes an aluminum alloy consisting essentially of (by weight) about 5.9-6.7% zinc, 1.8-2.4% copper, 1.6-1.86% magnesium, 0.08-0.15% zirconium, the balance aluminum and incidental elements and impurities. The patent specifically addresses a compromise between static mechanical strength and toughness.

[0007] US Patent No. 6,027,582 describes a rolled, forged or extruded Al-Zn-Mg-Cu aluminum alloy product with a thickness of more than 60 mm, having a composition (by weight) of 5.7-8.7 Zn, 1.7-2.5 Mg, 1.2-2.2 Cu, 0.07-0.14 Fe, and 0.05-0.15 Zr, where Cu+Mg<4.1 and Mg>Cu.

[0008] US Pat. No. 6,972,110 teaches an alloy preferably containing (by weight) 7-9.5 Zn, 1.3-1.68 Mg, and 1.3-1.9 Cu, and recommends keeping Mg+Cu≦3.5.

[0009] PCT patent application WO 2004 / 090183 discloses an alloy containing essentially (in wt%) 6.0-9.5 Zn, 1.3-2.4 Cu, 1.5-2.6 Mg, less than 0.25 Mn and Zr, but preferably in the range of 0.05-0.15 for higher Zn contents, other elements less than 0.05 each and less than 0.25 total, balance aluminum, where (in wt%) 0.1[Cu]+1.3<[Mg]<0.2[Cu]+2.15, preferably 0.2[Cu]+1.3<[Mg]<0.1[Cu]+2.15.

[0010] US Patent Application Publication No. 2005 / 0006010 describes a method for producing a high strength Al-Zn-Cu-Mg alloy with improved fatigue crack growth resistance and high damage tolerance by casting an ingot having the following composition (by weight): 5.5-9.5 Zn, 1.5-3.5 Cu, 1.5-3.5 Mg, less than 0.25 Mn, less than 0.25 Zr, less than 0.10 Cr, less than 0.25 Fe, less than 0.25 Si, less than 0.10 Ti, less than 0.25 Hf and / or V, other elements less than 0.05 each and less than 0.15 total, balance aluminum. and artificially ageing the worked and heat-treated product, wherein the ageing step comprises a first heat treatment at a temperature in the range of 105°C to 135°C for more than 2 hours but less than 8 hours, and a second heat treatment at a temperature above 135°C but less than 170°C for more than 5 hours but less than 15 hours.

[0011] EP 1544315 discloses a product, particularly a rolled, extruded or forged product, made of an AlZnCuMg alloy of the following composition by weight percentages: 6.7-7.3 Zn, 1.9-2.5 Cu, 1.0-2.0 Mg, 0.07-0.13 Zr, less than 0.15 Fe, less than 0.15 Si, other elements not exceeding 0.05 each and a maximum total of 0.15%, balance aluminium, with Mg / Cu<1. The product is preferably processed by solution heat treatment, quenching, cold working and artificial ageing.

[0012] U.S. Patent No. 8,277,580 teaches a rolled or forged wrought Al-Zn-Cu-Mg aluminum alloy having a thickness of 2 to 10 inches. The product has been processed by solution heat treatment, quenching, and aging, and contains (by weight): 6.2 to 7.2% Zn, 1.5 to 2.4% Mg, 1.7 to 2.1% Cu, 0 to 0.13% Fe, 0 to 0.10% Si, 0 to 0.06% Ti, 0.06 to 0.13% Zr, 0 to 0.04% Cr, 0 to 0.04% Mn, and impurities and other incidental elements each of which is 0.05% or less.

[0013] U.S. Pat. No. 8,673,209 discloses an aluminum alloy product having a thickness of about 4 inches or less, which has the ability to achieve an improved combination of strength, fracture toughness, and corrosion resistance when solution heat treated, quenched, and artificially aged, and in components made from the product, the alloy consisting essentially of about 6.8 to about 8.5 weight percent Zn, about 1.5 to about 2.00 weight percent Mg, about 1.75 to about 2.3 weight percent Cu, about 0.05 to about 0.3 weight percent Zr, less than about 0.1 weight percent Mn, less than about 0.05 weight percent Cr, the balance Al, incidental elements, and impurities, and a method for making the same.

[0014] WO 2019 / 007817 relates to an extruded, rolled and / or forged aluminium-based alloy product having a thickness of at least 25 mm and containing (in % by weight) 6.70-7.40 Zn, 1.50-1.80 Mg, 2.20-2.60 Cu, with a Cu to Mg ratio of at least 1.30, and containing the following impurities: 0.04-0.14 Zr, 0-0.5 Mn, 0-0.15 Ti, 0-0.15 V, 0-0.25 Cr, 0-0.15 Fe, 0-0.15 Si, each not exceeding 0.05 and a total not exceeding 0.15.

[0015] EP 2322677 discloses aluminum alloy products, such as plates, forgings, and extrusions, suitable for use in the manufacture of aerospace structural components such as integral wing spars, ribs, and webs, containing approximately 6-10 wt.% Zn, 1.2-1.9 wt.% Mg, 1.2-2.2 wt.% Cu, where Mg is less than (Cu + 0.3), and 0.05-0.4 wt.% Zr, with the balance being Al, incidental elements, and impurities. Preferably, the alloy contains approximately 6.9-8.5 wt.% Zn, 1.2-1.7 wt.% Mg, and 1.3-2 wt.% Cu. This alloy offers an improved combination of strength and fracture toughness in thick gauges. When artificially aged by the three-step method of the preferred embodiment, this alloy also achieves excellent stress corrosion cracking performance, including under seacoast conditions.

[0016] None of these documents discloses the advantages of combining aluminum alloys containing, by weight, 6.65 to 7.45 Zn, 1.35 to 1.75 Mg, 1.85 to 2.35 Cu, 0.04 to 0.14 Zr, 0 to 0.5 Mn, 0 to 0.15 Ti, 0 to 0.15 V, 0 to 0.25 Cr, 0.05% or less Fe, and 0.05% or less Si, with Fe+Si being 0.08% or less, and artificially aged at 155°C for an equivalent aging time t(eq) of 24 to 45 hours, thereby optimizing the compromise between tensile yield strength and toughness, and improving cryogenic fracture toughness and fatigue resistance in corrosive environments. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] U.S. Patent No. 5,312,498 [Patent Document 2] U.S. Patent No. 5,560,789 [Patent Document 3] U.S. Patent No. 5,865,911 [Patent Document 4] U.S. Patent No. 6,027,582 [Patent Document 5] U.S. Patent No. 6,972,110 [Patent Document 6] International Publication No. 2004 / 090183 [Patent Document 7] US Patent Application Publication No. 2005 / 0006010 [Patent Document 8] European Patent No. 1544315 [Patent Document 9] U.S. Patent No. 8,277,580 [Patent Document 10] U.S. Patent No. 8,673,209 [Patent Document 11] International Publication No. 2019 / 007817 [Patent Document 12] European Patent No. 2322677 Summary of the Invention [Problem to be solved by the invention]

[0018] The present invention relates to a method for producing high-strength wrought 7xxx aluminum products that, by controlling the composition, particularly the amounts of Fe and Si, and the processing parameters, particularly the artificial aging conditions, provide an improved compromise between tensile yield strength and toughness, as well as improved cryogenic fracture toughness and fatigue resistance in corrosive environments. The present invention also relates to rolled 7xxx products obtainable by the method of the present invention. [Means for solving the problem]

[0019] The term "cryogenic temperature" is defined in accordance with the present invention to include temperatures significantly below room temperature, typically temperatures below -100°C (173K). Thus, temperatures at which hydrogen (-253°C / 20K), oxygen (-183°C / 90K), and nitrogen (-196°C / 77K) become liquid at atmospheric pressure are included as cryogenic temperatures. For experimental evaluation, a temperature of -196°C / 77K is considered cryogenic. Room temperature is defined according to its common usage and includes temperatures from about 20°C to about 25°C. For experimental evaluation, a temperature of 22°C is considered room temperature.

[0020] The present invention provides a) in weight percent (wt.%), 6.65~7.45 Zn 1.35~1.75 Mg 1.85~2.35 Cu 0.04 to 0.14 Zr 0 to 0.5 Mn 0 to 0.15, preferably 0.02 to 0.06 wt. % Ti, V from 0 to 0.15 0~0.25Cr Fe below 0.05 Si below 0.05 Fe+Si less than 0.08, Other impurities, each less than 0.05 and total less than 0.15, balance aluminum; preparing a molten alloy metal bath comprising: b) casting the molten alloy metal to obtain a slab or billet; c) homogenizing the ingot or billet to obtain a homogenized ingot or billet; d) hot working the homogenized slab or billet to obtain a wrought product such as an extruded, rolled and / or forged product having a final thickness of at least 25 mm, preferably between 25 and 200 mm; e) solution heat treating and quenching the wrought material to obtain a quenched wrought material; f) stress relieving the quenched wrought material to obtain a stress-relieved wrought material; g) in the step of artificially aging the stress-relieved wrought material, the total equivalent aging time t(eq) at 155°C is 24 to 45 hours, preferably 24 to 34 hours, and even more preferably 26 to 30 hours; The total equivalent time t(eq) at 155°C is calculated using the formula:

number

[0021] The method is advantageously carried out using a molten alloy bath with a Zn content in weight percent (wt.%) between 6.90 and 7.30, even more preferably between 6.90 and 7.25.

[0022] The method is advantageously carried out using a molten alloy bath having a Cu content in weight percent (wt.%) between 1.95 and 2.35, even more preferably between 2.00 and 2.35.

[0023] Preferably, the molten alloy metal bath contains, in weight percent (wt.%), 6.90-7.30 Zn, 1.35-1.75 Mg, 1.95-2.35 Cu, 0.04-0.14 Zr, 0-0.5 Mn, 0-0.15 Ti, 0-0.15 V, 0-0.25 Cr, 0.05% or less Fe, 0.05% or less Si, where Fe+Si is 0.08%, and other impurities each less than 0.05 and total less than 0.15, the balance being aluminum. Even more preferably, the molten alloy metal bath contains, in weight percent (wt.%), 6.90-7.25 Zn, 1.35-1.75 Mg, 2.00-2.35 Cu, 0.04-0.14 Zr, 0-0.5 Mn, 0-0.15 Ti, 0-0.15 V, 0-0.25 Cr, not more than 0.05 Fe, not more than 0.05 Si, where Fe+Si is not more than 0.08%, and other impurities each less than 0.05 and total less than 0.15, the balance being Aluminum.

[0024] The method is advantageously carried out using a molten alloy bath containing not more than 0.03% by weight of Si and not more than 0.05% by weight of Fe. Preferably, the sum of the Fe+Si contents is not more than 0.07% by weight, even more preferably not more than 0.06% by weight. Preferably, the sum of the Fe+Si contents is not less than 0.03% by weight, even more preferably not less than 0.04% by weight.

[0025] The present invention comprises, in weight percent (wt.%): 6.65~7.45 Zn 1.35~1.75 Mg 1.85~2.35 Cu 0.04 to 0.14 Zr 0 to 0.5 Mn Ti 0~0.15 V from 0 to 0.15 0~0.25Cr Fe below 0.05 Si below 0.05 Fe+Si below 0.08 In a rolled product having a thickness t in millimeters of at least 25 mm, preferably 25 to 200 mm, containing other impurities each less than 0.05 and a total of less than 0.15, the remainder being aluminum, Toughness K in MPa.√m at room temperature measured according to ASTM standard E399(2020) 1c (LT) is -0.25 * t+65MPa.√ higher, preferably -0.25 * Higher than t+68MPa.√, and even more preferably -0.25 * For rolled products higher than t+72MPa.√.

[0026] Advantageously, the composition of the rolled product comprises a Zn content in weight percent (wt.%) between 6.90 and 7.30, even more preferably between 6.90 and 7.25.

[0027] Advantageously, the composition of the rolled product comprises a Cu content in weight percent (wt.%) between 1.95 and 2.35, even more preferably between 2.00 and 2.35.

[0028] Preferably, the composition of the rolled product is, in weight percent (wt.%), 6.90-7.30 Zn, 1.35-1.75 Mg, 1.95-2.35 Cu, 0.04-0.14 Zr, 0-0.5 Mn, 0-0.15 Ti, 0-0.15 V, 0-0.25 Cr, 0.05 or less Fe, 0.05 or less Si, where Fe+Si is 0.08% or less, and other impurities each less than 0.05 and total less than 0.15, the balance being aluminum. More preferably, the composition of the rolled product is, in weight percent (wt.%), 6.90-7.25 Zn, 1.35-1.75 Mg, 2.00-2.35 Cu, 0.04-0.14 Zr, 0-0.5 Mn, 0-0.15 Ti, 0-0.15 V, 0-0.25 Cr, 0.05 or less Fe, 0.05 or less Si, where Fe+Si is 0.08% or less, and other impurities each less than 0.05 and total less than 0.15, the balance being aluminum.

[0029] In a preferred embodiment, the rolled product according to the invention exhibits a surprisingly small decrease in both fracture toughness and elongation from room temperature down to liquid nitrogen temperature. The rolled product according to the invention exhibits a toughness K1c(TL) in MPa.√m at cryogenic temperatures of about -196°C, measured according to ASTM standard E399-2020, that decreases by less than 10%, preferably less than 8%, more preferably less than 7%, compared to K1c(TL) in MPa.√m measured according to ASTM standard E399-2020 at room temperature.

[0030] Preferably, the rolled product according to the present invention has a hardness of -0.15 * t+45MPa.√m or higher, preferably -0.15 * t+49MPa.√m or higher, and even more preferably -0.15 * denotes the toughness K1c(TL) in MPa.√m at cryogenic temperatures of about -196°C, measured according to ASTM standard E399-2020, higher than t + 55 MPa.√m, where t is the thickness of the rolled product in mm.

[0031] In a preferred embodiment, the rolled product has a thickness of 70 to 160 mm, preferably 70 to 102 mm.

[0032] Preferably, the rolled product contains 0.03 wt% or less Si and 0.05 wt% or less Fe. Preferably, the rolled product contains a total Fe+Si content of 0.07 wt% or less, even more preferably 0.06 wt% or less. Preferably, the rolled product contains a total Fe+Si content of 0.03 wt% or more, even more preferably 0.04 wt% or more. Preferably, the rolled product contains a total Fe+Si content of 0.03-0.08 wt%, preferably 0.03-0.07 wt%, even more preferably 0.03-0.06 wt%.

[0033] Preferably, the rolled product contains a Zn content by weight of 7.10 to 7.25 wt.%.

[0034] Preferably, the rolled product comprises a Ti content in weight percent (wt.%) less than or equal to 0.06, preferably between 0.02 and 0.06, even more preferably between 0.03 and 0.05.

[0035] The rolled product according to the invention or the product obtained by the method according to the invention is advantageously used as or integrated into structural elements for the construction of aircraft or spacecraft: it can be used as wing ribs, spars and / or frames.

[0036] In another advantageous embodiment, the rolled product according to the invention or the product obtained by the method according to the invention is advantageously used to manufacture machine parts such as pistons, impellers, etc. for gas compression, in particular for hydrogen or oxygen or nitrogen or methane or natural gas compression, at cryogenic temperatures below -100°C.

[0037] In another advantageous embodiment, the rolled product according to the invention or the product obtained by the method according to the invention is advantageously used to manufacture cryogenic tanks or stationary inland storage tanks or transport storage tanks for liquid gases, such as liquid hydrogen or liquid oxygen or liquid nitrogen or liquid methane or liquid natural gas. [Brief explanation of the drawings]

[0038] [Figure 1] This shows the change in toughness K1c(TL) at cryogenic temperatures with respect to plate thickness. [Figure 2] It represents a compromise at room temperature (RT) between tensile yield strength in the rolling direction (L) and LT toughness, measured at mid-thickness. [Figure 3] The trade-off between TYS and toughness K1c(TL) in the rolling direction is shown at room temperature and cryogenic temperatures. [Figure 4] The change in room temperature toughness K1c(LT) versus the sum of Fe and Si for various compositions is shown. [Figure 5]The change in room temperature toughness K1c(LT) versus the sum of Fe and Si is shown for different artificial aging conditions. [Figure 6] This shows the change in toughness K1c(LT) relative to plate thickness. [Figure 7] The fatigue crack growth rate (LT) for the reference product is shown under normal ambient atmospheric humidity conditions and humid atmospheric conditions. [Figure 8] 1 shows the fatigue crack growth rate (LT) for products according to the present invention under normal ambient atmospheric humidity conditions and humid atmospheric conditions. DETAILED DESCRIPTION OF THE INVENTION

[0039] [Detailed explanation] Unless otherwise indicated, all designations relating to alloy chemical composition are expressed as weight mass percentages based on the total weight of the alloy. Alloy designations conform to Aluminum Association conventions known to those skilled in the art.

[0040] The definitions of the tempers are given in NF EN515(2017). Unless otherwise stated, the static mechanical properties, i.e., ultimate tensile strength UTS, tensile yield stress TYS and elongation at break E, are determined by tensile tests according to the ASTM B557 standard, the locations of specimens taken and their orientation are defined in ASTM B557. Unless otherwise specified, the definitions of the EN12258 standard apply. Fracture toughness K 1C is determined in accordance with ASTM standard E399-2020. Materials are tested at t / 2 up to a maximum thickness of 102 mm (4 in.) and at t / 4 for thicknesses greater than 102 mm (4 in.). For SL, all specimens are tested at t / 2. Unless otherwise specified, C(T) specimens have widths W = 101.6 mm (4 in.) and B = 50.8 mm (2 in.).

[0041] For extrusions, the thickness of the extruded product is defined according to the NF EN 2066 (2002) standard: the cross section is divided into a basic rectangle of dimensions A and B, A is always the largest dimension of the basic rectangle and B is considered to be the thickness of the basic rectangle.

[0042] The term "structural member" is a term well known in the art and refers to a component used in a mechanical structure whose static and / or dynamic mechanical properties are critical to structural performance and for which structural calculations are usually specified or performed. These are typically components whose failure could pose a significant risk to the safety of the mechanical structure, its users, or third parties. In the case of an aircraft, structural members include fuselage (e.g., fuselage skin), longerons, bulkheads, circumferential frames, wing components (e.g., wing skins, longerons or stiffeners, wing ribs, wing spars), tail (e.g., horizontal and vertical stabilizers), floor beams, seat tracks, and door members.

[0043] symbol * As used herein, means multiplication.

[0044] The term "about" as used herein means a value with a tolerance of ±5% of the stated value.

[0045] The method of the present invention comprises various steps.

[0046] The first step aims to prepare a molten alloy metal bath comprising, or advantageously consisting essentially of, in weight percent (wt.%) 6.65-7.45 Zn, 1.35-1.75 Mg, 1.85-2.35 Cu, 0.04-0.14 Zr, 0-0.5 Mn, 0-0.15 Ti, 0-0.15 V, 0-0.25 Cr, not more than 0.05 Fe, not more than 0.05% Si, where Fe+Si is not more than 0.08%, and other impurities each less than 0.05 and total less than 0.15, the balance being aluminum.

[0047] Preferably, the molten alloy metal bath comprises, or advantageously consists essentially of, in weight percent (wt.%) 6.90-7.30 Zn, 1.35-1.75 Mg, 1.95-2.35 Cu, 0.04-0.14 Zr, 0-0.5 Mn, 0-0.15 Ti, 0-0.15 V, 0-0.25 Cr, not more than 0.05 Fe, not more than 0.05 Si, with Fe+Si not more than 0.08%, and other impurities each less than 0.05 and total less than 0.15, the balance being Aluminium.

[0048] Even more preferably, the molten alloy metal bath comprises, or advantageously consists essentially of, in weight percent (wt.%) 6.90-7.25 Zn, 1.35-1.75 Mg, 2.00-2.35 Cu, 0.04-0.14 Zr, 0-0.5 Mn, 0-0.15 Ti, 0-0.15 V, 0-0.25 Cr, not more than 0.05 Fe, not more than 0.05 Si, with Fe+Si not more than 0.08%, and other impurities each less than 0.05 and total less than 0.15, the balance being Aluminium.

[0049] The molten alloy metal is then cast into a slab or billet. The slab according to the present invention is a parallelepiped and may also be called an "ingot."

[0050] The slab or billet is then homogenized. In one preferred embodiment, homogenization is preferably carried out in at least one step at a temperature of about 450°C to about 510°C for typically 5 to 30 hours, or preferably at a temperature of about 470°C to about 500°C for 8 to 20 hours, and even more preferably at a temperature of 470°C to 490°C for 8 to 20 hours.

[0051] The homogenized slab or billet is hot worked to obtain a wrought product having a final thickness of at least 25 mm, preferably about 25 mm to about 200 mm, more preferably about 70 mm to about 160 mm, and even more preferably about 70 mm to about 102 mm. The wrought product is a rolled product, an extruded product, or a forged product. The forged product can be obtained directly by forging a billet or ingot, or can be obtained from a rolled product (e.g., first rolled and then forged), or from an extruded product (e.g., first extruded and then forged). In one embodiment, the homogenized slab is hot rolled to obtain a rolled product having a final thickness of at least 25 mm, preferably about 25 mm to about 200 mm, more preferably about 70 mm to about 160 mm, and even more preferably about 75 mm to about 102 mm or about 70 mm to about 80 mm. Hot rolling is preferably carried out in one or more stages, preferably at an inlet temperature of about 380°C to about 460°C, more preferably about 400°C to about 450°C.

[0052] The wrought material (e.g., rolled or extruded and / or forged product) is solution heat treated, preferably at a temperature of from 460°C to about 510°C, or more preferably from about 470°C to about 500°C, or even more preferably from 470°C to 490°C, typically for 1 to 10 hours depending on the thickness, to obtain a solution heat treated wrought material.

[0053] The solution heat treated wrought material is then quenched, preferably in water at room temperature, to obtain a quenched wrought material.

[0054] The quenched wrought material is then stress relieved to obtain a stress relieved wrought material, where stress relief is achieved by controlled stretching or compression with a permanent plastic deformation of preferably less than 5%, more preferably 1-4%, more preferably 2-3%.

[0055] The stress relieved wrought material is then artificially aged for a total equivalent ageing time t(eq) at 155°C of 24 to 45 hours, preferably 24 to 34 hours, and even more preferably 26 to 30 hours.

[0056] The total equivalent time t(eq) at 155°C is calculated using the formula:

number

[0057] The total equivalent time t(eq) at 155°C is calculated using the formula:

number

[0058] This formula involves the integral of the function exp(-16000 / T) with respect to time t, where T is the instantaneous temperature in Kelvin. This integral can be calculated using numerical integration. Methods for numerical integration are described, for example, in "Numerical Recipes - The Art of Scientific Computing - Third Edition" by Press WH et al., published by Cambridge University Press in 2007. This book describes various numerical methods for integrating functions (paragraph 4). One simple method that can be used to calculate the equivalent time is the trapezoidal rule (see paragraph 4.1.1, equation 4.1.3).

[0059] In some cases, for example when aging is considered as a step at constant temperature, the integral can be calculated analytically.

[0060] If ageing is defined by a single step of temperature T1 in Kelvin and duration t1 in hours, then the equivalent time in hours at 155°C (428K) is:

number

[0061] If ageing is defined in two stages (e.g., a first stage at temperature T1 for duration t1, and a second stage at temperature T2 for duration t2), the equivalent time at 155°C (428K) can be calculated for each stage using the same principle.

number

[0062] If the ageing is defined by two stages with a controlled heating ramp between the two stages, the corresponding equivalent time can be calculated considering the two stages as already defined above and integrating the heating ramp by numerical integration.

[0063] The total equivalent ageing time t(eq) at 155°C is at least 24 hours, preferably at least 25 or 26 hours, or even more preferably at least 27 hours. The total equivalent ageing time t(eq) at 155°C is less than 45 hours, preferably less than 40 hours, less than 39 hours, less than 38 hours, less than 37 hours, less than 36 hours, less than 35 hours, less than 34 hours, less than 33 hours, less than 32 hours, less than 31 hours, or even more preferably less than 30 hours. Any combination of minimum and maximum values ​​listed above will provide the best compromise between toughness and yield strength at ambient and cryogenic temperatures.

[0064] The ageing treatment is advantageously carried out in two stages, the first stage being at a temperature of 100 to 150°C, preferably 110 to 130°C, for 3 to 20 hours, preferably 3 to 10 hours, and the second stage being at a temperature of 140 to 180°C, preferably 140 to 170°C, for 6 to 90 hours, preferably 150 to 165°C, for 9 to 50 hours.

[0065] The specific composition of the product of the invention, in particular the content of Fe and Si of 0.08% by weight or less, in combination with a properly designed artificial aging treatment makes it possible to obtain products with a better compromise between tensile yield strength and toughness at ambient and cryogenic temperatures, in particular between tensile yield strength in the rolling direction (L direction) and toughness in the LT direction at ambient temperature.

[0066] The alloy according to the present invention contains 6.65-7.45 wt% Zn. To obtain sufficient strength, a minimum Zn content of 6.65 wt%, preferably 6.90 wt%, more preferably 7.0 wt%, and even more preferably 7.10 wt% is required, however, to obtain the required balance of properties, particularly toughness and elongation, Zn should not exceed 7.45 wt%, preferably 7.30 wt%, and more preferably 7.25 wt%.

[0067] The alloy according to the present invention contains 1.35-1.75 wt% Mg. To obtain sufficient strength, a minimum Mg content of 1.35 wt%, preferably 1.40 wt% or 1.50 wt% or even 1.60 wt% is required. However, to obtain the required balance of properties, especially toughness and elongation, the Mg content should not exceed 1.75 wt%, preferably 1.70 wt%.

[0068] The alloy according to the present invention contains 1.85-2.35 wt% Cu. To obtain sufficient strength, a minimum Cu content of 1.85 wt%, preferably 1.95 wt%, more preferably 2.0 wt%, or even more preferably 2.1 wt% is required. However, to avoid quench sensitivity, Cu should not exceed 2.35 wt%, preferably 2.30 wt%, or even more preferably 2.25 wt%.

[0069] The alloys of the present invention further contain 0.04-0.14 wt.% Zr, which is typically used for grain size control. The Zr content should preferably comprise at least about 0.07 wt.%, preferably about 0.09 wt.%, to limit recrystallization, but advantageously should remain below about 0.12 wt.% to reduce problems during casting.

[0070] Titanium can typically be added up to 0.15 wt. % during casting to limit the as-cast grain size, if desired. Ti can be combined with either boron or carbon. The present invention is typically applicable to up to about 0.06 wt. % or about 0.05 wt. % Ti. In a preferred embodiment of the present invention, the Ti content is about 0.02 wt. % to about 0.06 wt. %, preferably about 0.03 wt. % to about 0.05 wt. %.

[0071] Manganese additions up to 0.5 wt. % are possible but are preferably avoided and generally kept below about 0.05 wt. %, preferably below about 0.04 wt. %, and more preferably below about 0.03 wt. %.

[0072] Up to 0.15 wt. % vanadium can be added, but is preferably avoided and generally kept below about 0.05 wt. %, preferably below about 0.04 wt. %, and more preferably below about 0.03 wt. %.

[0073] Additions of up to 0.25 wt. % chromium are possible but are preferably avoided and generally kept below about 0.05 wt. %, preferably below about 0.04 wt. %, and more preferably below about 0.03 wt. %.

[0074] The present alloy may contain iron and silicon, which affect fracture toughness properties. It has been observed that to achieve a better compromise between tensile yield strength and toughness, a small (less than 10%) decrease in fracture toughness at cryogenic temperatures, and little increase in fatigue crack growth rate under humid conditions compared to fatigue under ambient laboratory conditions, the iron and silicon content (e.g., Fe + Si content) should not exceed about 0.08 wt.%, preferably about 0.07 wt.%, more preferably 0.06 wt.%, and even more preferably 0.05 wt.%. The inventors have found that a selected composition and an Fe + Si content of 0.08 wt.% or less, combined with a properly designed aging treatment with a total equivalent aging time, t(eq), of 24 to 45 hours at 155°C, can achieve significant improvements in tensile yield strength and toughness compromise, cryogenic toughness and elongation, and fatigue crack growth rate under humid conditions.

[0075] The inventors have found that a satisfactory compromise can be obtained with an Fe+Si content of more than 0.03 wt.%, or even more than 0.04 wt.%, or even more than 0.05 wt.%.

[0076] In one embodiment of the present invention, the iron and silicon content (e.g., Fe + Si content) is 0.03-0.08 wt%, preferably 0.03-0.07 wt%, more preferably 0.03-0.06 wt%, and even more preferably 0.03-0.05 wt%. In another embodiment, the alloy may have an iron and silicon content (e.g., Fe + Si content) of 0.04-0.08 wt%, preferably 0.04-0.07 wt%, more preferably 0.04-0.06 wt%, and even more preferably 0.04-0.05 wt%. In another embodiment, the alloy may have an iron and silicon content (e.g., Fe + Si content) of 0.05-0.08 wt%, preferably 0.05-0.07 wt%, and more preferably 0.05-0.06 wt%.

[0077] The alloy may contain up to 0.05 wt.%, preferably up to 0.03 wt.% Si. The alloy may contain up to 0.05 wt.%, preferably up to 0.03 wt.% Fe.

[0078] The alloy may contain incidental impurities. The term "incidental impurities" refers to relatively small amounts of other elements, less than 0.05% or less than 0.01% by weight, totaling less than 0.15% by weight of the total weight of the 7xxx aluminum alloy product. Incidental impurities may be present without departing from the scope of the present invention.

[0079] The term "comprising" shall be interpreted to mean that no additional elements other than those recited are intentionally added to provide the novel and essential characteristics of the present invention. It is nevertheless understood that trace amounts of such elements may be present in the final alloy product due to impurities and / or leaching from contact with manufacturing equipment. However, it is understood that the mere addition of any such elements in amounts that do not otherwise affect the combination of properties desired and achieved herein should not / cannot circumvent the scope of the present invention.

[0080] The present invention is particularly interesting for rolled products having a thickness of at least 25 mm, preferably between 25 and 200 mm, more preferably between 70 and 200 mm, or between 70 and 160 mm, even more preferably between 70 and 102 mm.

[0081] A rolled product according to the invention having a thickness of at least 25 mm, preferably between 25 mm and 200 mm, more preferably between 70 mm and 200 mm, or between 70 mm and 160 mm, even more preferably between 70 mm and 102 mm, advantageously has the following properties:

[0082] At least -0.25 * t+65MPa.√m, more preferably at least -0.25 * t+68MPa.√m, and even more preferably at least -0.25 *t+72MPa.√m, K in the LT direction at room temperature measured according to ASTM E399-2020 1C toughness, where t is the thickness of the rolled product in mm.

[0083] Preferably, the rolled product advantageously has a yield strength in the rolling direction L of at least 450 MPa. Preferably, a yield strength in the transverse direction LT of at least 410 MPa, even more preferably at least 420 MPa.

[0084] In a preferred embodiment, the rolled product according to the invention exhibits a surprisingly small decrease in both fracture toughness and elongation from room temperature down to liquid nitrogen temperature. The rolled product according to the invention exhibits a toughness K1c(TL) in MPa.√m at cryogenic temperatures of about -196°C, measured according to ASTM standard E399 2020, that is reduced by less than 10%, preferably less than 8%, more preferably less than 7%, compared to K1c(TL) in MPa.√m measured at room temperature according to ASTM standard E399-2020.

[0085] Preferably, the rolled product according to the present invention has a hardness of -0.15 * t+45MPa.√m or higher, preferably -0.15 * t+49MPa.√m or higher, and even more preferably -0.15 * denotes the toughness K1c(TL) in MPa.√m at cryogenic temperatures of about -196°C, measured according to ASTM standard E399-2020, higher than t + 55 MPa.√m, where t is the thickness of the rolled product in mm.

[0086] The rolled product according to the invention or the product obtained by the method according to the invention is advantageously used as or integrated into structural elements for the construction of aircraft or spacecraft.

[0087] In one advantageous embodiment, the product according to the invention is used for wing ribs, spars, and frames. In one embodiment of the invention, the rolled product according to the invention is welded with other rolled products to form wing ribs, spars, and frames. In another embodiment, the rolled product according to the invention or a product obtained by the method according to the invention is advantageously used in structural components for use at cryogenic temperatures, typically cryogenic tanks. Among other cryogenic uses, the rolled product according to the invention or a product obtained by the method according to the invention is advantageous for manufacturing machine parts such as pistons and impellers for gas compression at cryogenic temperatures, in particular for compressing hydrogen, oxygen, nitrogen, methane, or natural gas. In one embodiment, the rolled product according to the invention or a product obtained by the method according to the invention is used for manufacturing stationary inland storage tanks or transport storage tanks for liquid gases, such as liquid hydrogen, liquid oxygen, liquid nitrogen, liquid methane, or liquid natural gas. Transport storage tanks are mobile tanks, such as tanks used in cars, trucks, lorries, trains, ships, aircraft, and rockets when the liquid gas is used as fuel, or tanks used in trucks, lorries, trains, and ships for transporting liquid gases. [Example]

[0088] Two ingots were cast using two compositions, A and B, according to the present invention. The ingots were homogenized, hot rolled to thicknesses of 76.2 mm (A1) and 152.4 mm (B3), and then solution heat treated, stretched, and final aged according to the method of the present invention. Chemical and processing information for these two lots is shown in Tables 1 and 2, respectively.

[0089] [Table 1]

[0090] [Table 2]

[0091] Tensile and K IC Tests were performed both at room temperature (22°C) and at cryogenic temperatures, specifically at liquid nitrogen temperature (-196°C). Tensile tests were performed according to ASTM B557. Samples were taken at mid-thickness (t / 2) and quarter-thickness (t / 4). Tensile tests were performed in the transverse (LT) and transverse (ST) directions.

[0092] [Table 3]

[0093] [Table 4]

[0094] [Table 5]

[0095] An increase in yield strength has been observed between cryogenic and ambient temperatures, with the increase being over 12% in the ST direction and over 18% in the LT direction.

[0096] K 1C Tests were performed according to ASTM E399 using C(T) specimens in either TL or SL orientation.

[0097] [Table 6]

[0098] A slight decrease in toughness is observed between cryogenic and ambient temperatures. This decrease increases with plate gauge. 1c For (TL), it is less than 7%, and for 76.2 mm in this direction, it is even less than 4%, 1c For (SL) it is less than 15%, and at 76.2 mm in this direction it is even less than 10.5%.

[0099] Figure 1 shows the toughness K at cryogenic temperatures as a function of plate thickness. 1c The change in TL (T) is shown. The A1 and B1 specimens show a change in TL (T) at a cryogenic temperature of about -196°C. * t+45MPa.√m or higher, preferably -0.15 * t+49MPa.√m or higher, and even more preferably -0.15 * It can be observed that the toughness K1c(TL) in MPa.√m is higher than t + 55 MPa.√m, where t is the thickness of the product in mm. [Example]

[0100] Four ingots of aluminum alloys C, D, E, and F were cast, homogenized, and hot rolled to thicknesses of 75 mm (C1), 69.9 mm (D1), and 76 mm (E1 and F1), respectively, followed by solution heat treatment, stretching, and final aging. Chemical and process information for these four lots is shown in Tables 8 and 9, respectively. Alloy C corresponds to alloy P of Example 3 described in EP 1 544 315, alloy D represents AA7050, and alloys E and F correspond to alloys E and C of Example 1 of WO 2019 / 007817, respectively. Chemical and process information for these reference samples is shown in the table below. Alloy F has a composition according to the present invention, but sample F1 is made of TYS(L) and K. 1c (LT) are treated with shorter artificial aging times which does not allow to obtain a good compromise.

[0101] [Table 7]

[0102] [Table 8]

[0103] The tensile strength and toughness of C1, E1, F1 are taken from the prior art. For comparison purposes, sample A1 was also tested at t / 2 and compared.

[0104] [Table 9]

[0105] The yield strength of the D1 plate was tested in the LT direction, and the K1C test was carried out using C(T) specimens taken at t / 2 according to ASTM E 399. The obtained properties were compared with the A1 plate of the invention according to Example 1.

[0106] [Table 10]

[0107] [Table 11]

[0108] Figure 2 shows the compromise between the tensile yield strength in the rolling direction (L) and the toughness in the LT direction at room temperature (RT) measured at quarter thickness and mid-thickness for the A1 and C1 plates, respectively. The significant improvement in the compromise between toughness and yield strength for A1 is due to the low Fe+Si content and optimized aging.

[0109] Figure 3 shows the compromise between transverse (LT) tensile yield strength and TL toughness measured at room temperature and at the liquid nitrogen temperature of -196 °C. It can be observed that the A1 plate shows less loss of toughness than the D1 plate. This is due to the chemical composition, especially the lower Fe+Si content. [Example]

[0110] Various ingots of compositions A, C, G, H, J, K and M were cast and deformed, and the respective composition and process details are given in Tables 14 and 15. All these castings were deformed into plates of thickness ranging from 70 to 102 mm.

[0111] Alloys C, G and H correspond to prior art alloys, while J, K and M are compositions according to the invention. Alloy A is the same as in Example 1.

[0112] Two types of aging conditions were evaluated: a total equivalent time at 155°C of greater than 24 hours ("a") according to the present invention, and a total equivalent time at 155°C of 23 hours or less ("b") for comparison. Tensile tests and toughness measurements were performed at room temperature. The results are shown in Table 16. The properties of Alloy A shown in Example 2 are also listed in Table 14.

[0113] [Table 12]

[0114] [Table 13]

[0115] [Table 14]

[0116] 4 to 6 show the data in Table 14.

[0117] In Figures 4 to 6, samples with compositions according to the invention and processed according to the invention are represented by solid diamonds (A1-a, J1-A, K2-a). Samples with compositions according to the invention but processed differently are represented by hollow diamonds (M2-b). Triangle symbols are used to represent compositions that differ from the invention by an Fe + Si content greater than 0.08 wt% (C1-a and C1-b). Round circle symbols are used to represent compositions that differ from the invention by the main alloying element (G2-a, H2-a). The triangle or round circle symbols are either hollow if the process differs from the invention, i.e., the equivalent time at 155°C is 23 hours or less, or are accompanied by solid symbols if the process is according to the invention.

[0118] Figure 4 shows the K for products artificially aged for a total equivalent time at 155°C over 24 hours. 1c The effect of Fe+Si content on toughness (LT) is shown in Fig. 1. In all cases, for the thickness range of about 70 mm to about 102 mm, decreasing the amount of Fe+Si resulted in a significant decrease in toughness (K). 1c It is observed that this allows the (LT) to improve. However, this tendency is more pronounced in samples A1-a, J1-a, and K2-a, which have been processed according to the present invention and artificially aged for a total equivalent time of 24 to 45 hours at 155 °C, and which have a composition with an Fe + Si content of 0.08 wt% or less.

[0119] For samples having the composition according to the invention and having the main elements according to the invention except for the Fe, Si and / or (Fe + Si) content (samples A1-a, J1-A, K2-A and C1-a), which have been artificially aged according to the invention, the slope Δ1 is 1c Sample C1-a was aged for an equivalent time of 24.4 hours at 155°C and exhibited a lower toughness K 1c (LT). We attribute this behavior to its Fe+Si content.

[0120] For samples artificially aged according to the invention (H2-a and G2-a) whose composition deviates from the invention but whose Fe, Si and / or (Fe+Si) content is in accordance with the invention, the slope Δ2 is the slope of the main alloying elements, K 1c This is representative of the effect on LT. The slope Δ2 is lower than the slope Δ1. We attribute this behavior to the composition selection, particularly the synergistic effect of the Zn and Mg contents on the one hand and the Fe+Si contents on the other.

[0121] Figure 5 shows the relationship between the Fe+Si content and the K 1cThe arrows M2-b to K2-a (ΔT1) and C1-b to C1-a (ΔT2) represent the effect of the total equivalent time at 155°C for the same Fe+Si content for the compositions according to the invention and for the compositions according to the prior art, respectively. It is clearly observed that increasing the total equivalent time at 155°C of ageing makes it possible to increase the toughness. However, this tendency is more pronounced for compositions according to the invention with an Fe+Si content of 0.08 wt.% or less (arrow ΔT1).

[0122] Samples A1-a, J1-a and K2-a with thicknesses between 75 and 102 mm exhibit toughness K1c(LT) higher than −0.25t+65 MPa.√m, preferably higher than −0.25t+68 MPa.√m, and even more preferably higher than −0.25t+72 MPa.√m, where t is the plate thickness in mm (Fig. 6).

[0123] Samples M2-b, K2-a and H2-a, despite having an Fe+Si content less than 0.08%, show lower toughness K1c(LT) than the samples according to the invention. We attribute this behavior to the composition and / or artificial ageing conditions, which do not meet the total equivalent time of 24-45 hours at 155°C. [Example]

[0124] The fatigue crack growth rate of the B3 plates mentioned in Example 1 was evaluated and compared to a reference product O3 of similar thickness, 152.4 mm (6 inches). Alloys O and B are according to the present invention (Table 15) and contain Fe+Si contents of 0.08 wt. % or less. The O3 plates were processed similarly to the B3 plates, except that the artificial aging conditions indicate an equivalent aging time of 19.9 hours at 155°C (Table 16).

[0125] [Table 15]

[0126] [Table 16]

[0127] Fatigue crack growth rates were evaluated according to ASTM E647. The coupon orientation was LT. Standard compact tension, or C(T), coupon dimensions were used for testing. Dimensions B was 7.6 mm (0.3 in.) and W was 50.8 mm (2 in.) for all test coupons. The FCGR test procedure conforms to ASTM E647, and its specific requirements are generally as follows: (1) stress ratio 0.1 and f = 10 Hz; (2) pre-crack was performed under a constant load amplitude, with ΔK at the start and ΔK at the end of the pre-crack. i =10MPa * The value of √m is reached. After pre-cracking, the test is carried out under the same load as pre-cracking but with a constant load amplitude. The test is carried out at room temperature.

[0128] For both plates, two relative humidity (RH) conditions were evaluated: normal ambient atmospheric humidity conditions (27-32% humidity, referred to as "standard atmosphere") and humid atmospheric conditions (92-93% humidity, referred to as "humid atmosphere").

[0129] Figures 7 and 8 show the variation of fatigue crack growth rate with environmental conditions for plates O3 and B3, respectively.

[0130] It is observed that products with compositions selected according to the invention and aged for equivalent times at 155°C of more than 24 hours (B3, Figure 8) exhibit similar fatigue crack growth rates regardless of the relative humidity considered. Products aged for equivalent times at 155°C of 23 hours or less (O3, Figure 7) show a significant dependence on humidity.

Claims

1. a) in weight percent (wt. %), 6.65 to 7.45 Zn 1.35 to 1.75 Mg Cu 1.85 to 2.35 0.04 to 0.14 Zr Mn of 0 to 0.5 0 to 0.15, preferably 0.02 to 0.06 wt. % Ti, V between 0 and 0.15 0 to 0.25 Cr Fe below 0.05 Si of 0.05 or less Fe+Si not greater than 0.08; Other impurities each less than 0.05 and total less than 0.15, balance aluminum; preparing a bath of molten alloy metal comprising: b) casting the molten alloy metal to obtain a slab or billet; c) homogenizing the ingot or billet to obtain a homogenized ingot or billet; d) hot working the homogenized slab or billet to obtain a wrought product, such as an extruded, rolled and / or forged product, having a final thickness of at least 25 mm; e) solution heat treating and quenching the wrought material to obtain a quenched wrought material; f) stress relieving the quenched wrought material to obtain a stress-relieved wrought material; g) in the step of artificially aging the stress-relieved wrought material, the total equivalent aging time t(eq) at 155°C is 24 to 45 hours; The total equivalent time t(eq) at 155°C is calculated by the formula: [Equation 1] is defined by where T is the instantaneous temperature in Kelvin during aging, and T ｒｅｆ is the reference temperature selected at 155°C (428K) and t(eq) is expressed in time units, A method for producing a 7xxx aluminum-based alloy wrought material, comprising:

2. The method for producing a 7xxx aluminum-based alloy wrought material according to claim 1, wherein the Zn content is 6.90 to 7.30 wt.%.

3. The method for producing a 7xxx aluminum-based alloy wrought material according to claim 1, wherein the Zn content is 6.90 to 7.25 wt. %.

4. The method for producing a 7xxx aluminum-based alloy wrought material according to any one of claims 1 to 3, wherein the Cu content is 1.95 to 2.35 by weight percent (wt.%).

5. The method for producing a 7xxx aluminum-based alloy wrought material according to any one of claims 1 to 3, wherein the Cu content is 2.00 to 2.35 by weight percent (wt.%).

6. The bath of molten alloy metal is in weight percent (wt. %): Zn 6.90-7.30 1.35 to 1.75 Mg Cu 1.95 to 2.35 0.04 to 0.14 Zr Mn of 0 to 0.5 0 to 0.15, preferably 0.02 to 0.06 wt. % Ti, V between 0 and 0.15 0 to 0.25 Cr Fe below 0.05 Si of 0.05 or less Fe+Si not greater than 0.08; Other impurities each less than 0.05 and total less than 0.15, balance aluminum; 2. The method of claim 1 for producing a 7xxx aluminum-based alloy wrought product, comprising:

7. The bath of molten alloy metal is in weight percent (wt. %): 6.90 to 7.25 Zn 1.35 to 1.75 Mg Cu 2.00 to 2.35 0.04 to 0.14 Zr Mn of 0 to 0.5 0 to 0.15, preferably 0.02 to 0.06 wt. % Ti, V between 0 and 0.15 0 to 0.25 Cr Fe below 0.05 Si of 0.05 or less Fe+Si not greater than 0.08; Other impurities each less than 0.05 and total less than 0.15, balance aluminum; 2. The method of claim 1 for producing a 7xxx aluminum-based alloy wrought product, comprising:

8. 8. A method for producing a 7xxx aluminum-based alloy wrought material according to any one of claims 1 to 7, wherein Si is 0.03 wt% or less and Fe is 0.05 wt% or less.

9. 9. A method for producing a wrought 7xxx aluminium-based alloy product according to any one of claims 1 to 8, wherein the Fe+Si content is not more than 0.07% by weight, preferably not more than 0.06% by weight.

10. 10. A method for producing a wrought 7xxx aluminum-based alloy material according to any one of claims 1 to 9, wherein the Fe+Si content is at least 0.03 wt.%, preferably at least 0.04 wt.%.

11. A method for producing a wrought 7xxx aluminum-based alloy material according to any one of claims 1 to 10, wherein the total equivalent ageing time t(eq) at 155°C is 24 to 34 hours, preferably 26 to 30 hours.

12. A method for producing a wrought 7xxx aluminum-based alloy product according to any one of claims 1 to 11, wherein the ageing treatment is carried out in two stages, the first stage being at a temperature of 100 to 150°C, preferably 110 to 130°C, for 3 to 20 hours, preferably 3 to 10 hours, and the second stage being at a temperature of 140 to 180°C, preferably 140 to 170°C, for 6 to 90 hours, preferably 150 to 165°C, for 9 to 50 hours.

13. In weight percent, 6.65 to 7.45 Zn 1.35 to 1.75 Mg Cu 1.85 to 2.35 0.04 to 0.14 Zr Mn of 0 to 0.5 Ti 0 to 0.15 V between 0 and 0.15 0 to 0.25 Cr Fe below 0.05 Si of 0.05 or less Fe+Si less than 0.08 In a rolled product having a thickness t in millimeters of at least 25 mm, preferably 25 to 200 mm, containing other impurities each less than 0.05 and less than 0.15 in total, the remainder being aluminum, Toughness K in MPa.√m measured at the center of the thickness at room temperature according to ASTM standard E399-2020 １ｃ (L-T) is -0.25 ＊ t+65 MPa. √m, preferably −0.25 ＊ t+68 MPa.√m, and even more preferably −0.25 ＊ t + 72 MPa.√m, where t is the thickness of the rolled product in mm.

14. 14. The rolled product of claim 13, wherein the Zn content is in the range of 6.90 to 7.30 weight percent (wt. %).

15. 15. The rolled product of claim 14, wherein the Zn content is in the range of 6.90 to 7.25 weight percent (wt. %).

16. 16. The rolled product according to any one of claims 13 to 15, wherein the Cu content is 1.95 to 2.35 in weight percent (wt. %).

17. 17. The rolled product according to any one of claims 13 to 16, wherein the Cu content is 2.00 to 2.35 in weight percent (wt. %).

18. In weight percent, Zn 6.90-7.30 1.35 to 1.75 Mg Cu 1.95 to 2.35 0.04 to 0.14 Zr Mn of 0 to 0.5 0 to 0.15, preferably 0.02 to 0.06 wt. % Ti, V between 0 and 0.15 0 to 0.25 Cr Fe below 0.05 Si of 0.05 or less Fe+Si not greater than 0.08; Other impurities each less than 0.05 and total less than 0.15, balance aluminum; The rolled product of claim 13, comprising:

19. In weight percent, 6.90 to 7.25 Zn 1.35 to 1.75 Mg Cu 2.00 to 2.35 0.04 to 0.14 Zr Mn of 0 to 0.5 0 to 0.15, preferably 0.02 to 0.06 wt. % Ti, V between 0 and 0.15 0 to 0.25 Cr Fe below 0.05 Si of 0.05 or less Fe+Si not greater than 0.08; Other impurities each less than 0.05 and total less than 0.15, balance aluminum; The rolled product of claim 13, comprising:

20. Toughness K in MPa.√m at cryogenic temperatures of approximately -196°C, measured according to ASTM standard E399 2020 １ｃ (T-L) is the K in MPa √m measured at room temperature according to ASTM standard E399-2020 １ｃ 20. The rolled product according to any one of claims 13 to 19, wherein the thickness is reduced by less than 10%, preferably less than 8%, more preferably less than 7% compared to (T-L).

21. The toughness K1c(TL) in MPa.√m at a cryogenic temperature of approximately -196°C, measured in accordance with ASTM standard E399-2020, is -0.15 ＊ t+45 MPa. √m, preferably -0.15 ＊ t+49 MPa.√m, and even more preferably −0.15 ＊ 21. A rolled product according to any one of claims 13 to 20, having a compressive strength higher than t + 55 MPa.√m, where t is the thickness of the rolled product in mm.

22. A rolled product according to any one of claims 13 to 21, having a thickness of 70 to 160 mm, preferably 70 to 102 mm.

23. 23. The rolled product according to any one of claims 13 to 22, wherein Si is 0.03 wt% or less and Fe is 0.05 wt% or less.

24. 24. Rolled product according to any one of claims 13 to 23, wherein the Fe+Si content is between 0.03 and 0.07% by weight, preferably between 0.03 and 0.06% by weight.

25. 25. The rolled product according to any one of claims 13 to 24, wherein the Zn content is in the range of 7.10 to 7.25 weight percent (wt. %).

26. 26. The rolled product according to any one of claims 13 to 25, wherein the Ti content is less than or equal to 0.06, preferably between 0.02 and 0.06, and even more preferably between 0.03 and 0.05, in weight percent (wt. %).

27. 27. Use of a product according to any one of claims 13 to 26 or obtainable by a method according to any one of claims 1 to 12, for manufacturing structural components suitable for the construction of aircraft, such as wing ribs, spars and frames.

28. Use of a product according to any one of claims 13 to 26 or obtainable by the method according to any one of claims 1 to 12 for manufacturing machine parts such as pistons or impellers for gas compression at cryogenic temperatures, in particular for hydrogen or oxygen or nitrogen or methane or natural gas compression.

29. 27. Use of a product according to any one of claims 13 to 26 or obtainable by the method according to any one of claims 1 to 12, for manufacturing cryogenic tanks or stationary inland storage tanks or transport storage tanks for liquid gases such as liquid hydrogen or liquid oxygen or liquid nitrogen or liquid methane or liquid natural gas.

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