7xxx forged product with improved compromise of tensile and toughness properties and method of making same

Abstract

The invention relates to a forged 7xxx aluminum alloy product comprising, in% by weight, Zn 6.7-7.4, Mg 1.35-1.75, Cu 1.85-2.35, Zr 0.04-0.14, Mn 0-0.5, Ti 0-0.15, V 0-0.15, Cr 0-0.25, Fe < = 0.05, Si < = 0.05, and Fe + Si < = 0.08, and subjected to artificial aging wherein the total equivalent aging time t (eq) at 155 DEG C is 24-45 hours, which can optimize the trade-off between tensile yield strength and toughness while improving low temperature fracture toughness and corrosion resistance in corrosive environments.

Description

Field of the Invention

[0001] The present invention relates to a method for manufacturing 7xxx aluminum forged products having an improved compromise between tensile and toughness properties, excellent low-temperature properties, and fatigue resistance in a corrosive environment, and more particularly to said manufacturing method and rolled products and their uses, especially designed for aerospace engineering and cryogenic applications. Background Art

[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 well known that in the process of manufacturing semi-finished products and structural components for aerospace structures, these various desired properties cannot be optimized simultaneously and independently of each other. When the chemical composition of the alloy or the parameters of the product manufacturing method are changed, some key properties may change in the opposite direction. This situation sometimes first appears in the properties commonly referred to as "static mechanical strength" (especially the ultimate tensile stress UTS and the tensile yield stress TYS), and secondly in the properties commonly referred to as "damage tolerance" (especially toughness and crack growth resistance). In addition, some other properties, such as fatigue resistance, corrosion resistance, formability, and elongation at break, are related to these properties in a complex and usually unpredictable manner. Therefore, optimizing all the properties of the material for mechanical structures (such as in the aerospace field) generally requires a compromise between several key parameters.

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

[0004] U.S. Patent 5,312,498 discloses a method for preparing an aluminum-based alloy product having improved exfoliation resistance and fracture toughness, said method comprising providing an aluminum-based 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-based alloy is processed, heat-treated, quenched, and aged to prepare a product having improved corrosion resistance and mechanical properties.

[0005] U.S. Patent 5,560,789 describes AA 7000 series alloys having high mechanical strength and their preparation methods. The alloys contain 7 to 13.5% Zn, 1 to 3.8% Mg, 0.6 to 2.7% Cu, 0 to 0.5% Mn, 0 to 0.4% Cr, 0 to 0.2% Zr by weight, with each of the other elements up to 0.05% and the total up to 0.15%, and the balance being Al.

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

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

[0008] U.S. Patent No. 6,972,110 teaches an alloy that preferably contains (by weight %) Zn: 7 - 9.5, Mg: 1.3 - 1.68, and Cu 1.3 - 1.9, and encourages maintaining Mg + Cu ≤ 3.5.

[0009] PCT Patent Application WO2004090183 discloses an alloy that essentially contains (by weight percentage): Zn: 6.0 - 9.5, Cu: 1.3 - 2.4, Mg: 1.5 - 2.6, Mn and Zr < 0.25, but for higher Zn contents, preferably 0.05 to 0.15, with other elements each less than 0.05 and the total less than 0.25, and the balance being aluminum, where (by weight percentage): 0.1[Cu] + 1.3 < [Mg] < 0.2[Cu] + 2.15, preferably 0.2[Cu] + 1.3 < [Mg] < 0.1[Cu] + 2.15.

[0010] US20050006010 discloses a method for preparing a high-strength Al-Zn-Cu-Mg alloy having improved fatigue crack growth resistance and high damage tolerance, the method comprising the steps of: casting an ingot having the following composition (in weight percentages): Zn 5.5-9.5, Cu 1.5-3.5, Mg 1.5-3.5, Mn < 0.25, Zr < 0.25, Cr < 0.10, Fe < 0.25, Si < 0.25, Ti < 0.10, Hf and / or V < 0.25, other elements each less than 0.05 and the total amount less than 0.15, with the balance being aluminum, homogenizing and / or preheating the ingot after casting, hot working the ingot, and optionally cold working it into a worked product having a thickness greater than 50 mm, solution heat treating, quenching the heat-treated product, and artificially aging the worked and heat-treated product, wherein the aging step comprises a first heat treatment at a temperature of 105°C to 135°C for more than 2 hours and less than 8 hours, and a second heat treatment at a temperature higher than 135°C but lower than 170°C for more than 5 hours and less than 15 hours.

[0011] EP 1544315 discloses a product, in particular a rolled, extruded or forged product, made of an AlZnCuMg alloy, the composition of which has the following weight percentages: Zn 6.7-7.3; Cu 1.9-2.5; Mg 1.0-2.0; Zr 0.07-0.13; Fe less than 0.15; Si less than 0.15; the total amount of other elements not more than 0.05% and at most 0.15%; and the balance being aluminum, wherein Mg / Cu < 1. The product is preferably treated by solution heat treatment, quenching, cold working and artificial aging.

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

[0013] U.S. Patent No. 8,673,209 discloses an aluminum alloy product having a thickness of about 4 inches or less and a method for preparing the same. When the product is solution heat treated, quenched, and artificially aged, and in parts made from the product, a combination of improved strength, fracture toughness, and corrosion resistance can be obtained. The alloy consists essentially of: about 6.8 to about 8.5 wt% Zn, about 1.5 to about 2.00 wt% Mg, about 1.75 to about 2.3 wt% Cu, about 0.05 to about 0.3 wt% Zr, less than about 0.1 wt% Mn, less than about 0.05 wt% Cr, with the balance being Al, incidental elements, and impurities.

[0014] WO2019 / 007817 relates to an extruded, rolled, and / or forged aluminum-based alloy product having a thickness of at least 25 mm, which contains (by weight%): Zn 6.70 - 7.40; Mg 1.50 - 1.80; Cu 2.20 - 2.60, where the ratio of Cu to Mg is at least 1.30; Zr 0.04 - 0.14; Mn 0 - 0.5; Ti 0 - 0.15; V 0 - 0.15; Cr 0 - 0.25; Fe 0 - 0.15; Si 0 - 0.15; impurities each ≤ 0.05 and the total amount ≤ 0.15.

[0015] EP2322677 discloses an aluminum alloy product suitable for manufacturing aerospace structural components (such as integral spars, ribs, and webs), such as sheets, forgings, and extrusions, which contains approximately: 6 to 10 wt% Zn; 1.2 to 1.9 wt% Mg; 1.2 to 2.2 wt% Cu, where Mg < (Cu + 0.3); and 0.05 to 0.4 wt% Zr, with the balance being Al, incidental elements, and impurities. Preferably, the alloy contains about 6.9 to 8.5 wt% Zn; 1.2 to 1.7 wt% Mg; 1.3 to 2 wt% Cu. The alloy provides a combination of improved strength and fracture toughness in thick gauges. When artificially aged according to the three-stage method of the preferred embodiment, the alloy also obtains excellent SCC performance, including in coastal conditions.

[0016] None of these documents disclose the beneficial effects of the following combination, that is, combining an aluminum alloy containing Zn 6.65 - 7.45 wt%, Mg 1.35 - 1.75 wt%, Cu 1.85 - 2.35 wt%, Zr 0.04 - 0.14 wt%, Mn 0 - 0.5 wt%, Ti 0 - 0.15 wt%, V 0 - 0.15 wt%, Cr 0 - 0.25 wt%, Fe ≤ 0.05 wt%, Si ≤ 0.05 wt% and Fe + Si ≤ 0.08 wt% with the following artificial aging, where the equivalent aging time t(eq) at 155 °C is 24 hours to 45 hours, which can optimize the compromise between tensile yield strength and toughness, while improving low-temperature fracture toughness and fatigue resistance in a corrosive environment. Summary of the Invention

[0017] The present invention relates to a method for manufacturing high-strength 7xxx aluminum forging products, which provides an improved compromise between tensile yield strength and toughness by controlling the composition (especially the amounts of Fe and Si) and the manufacturing parameters (especially the artificial aging conditions), while improving the low-temperature fracture toughness and fatigue resistance in a corrosive environment. The present invention also relates to a rolled 7xxx product obtainable by the method of the present invention.

[0018] According to the present invention, the term "low-temperature temperature" is defined to include temperatures significantly below room temperature and typically below -100 °C (173 K). Thus, the temperatures at which hydrogen (-253 °C / 20 K), oxygen (-183 °C / 90 K), and nitrogen (-196 °C / 77 K) become liquid at atmospheric pressure are considered low-temperature temperatures. For the purpose of experimental evaluation, the temperature of -196 °C / 77 K is considered a low-temperature temperature. Room temperature is defined according to its common usage and includes temperatures from about 20 °C to about 25 °C. For the purpose of experimental evaluation, a temperature of 22 °C is considered room temperature.

[0019] The present invention relates to a method for manufacturing a forged 7xxx aluminum-based alloy product, the method comprising the steps of:

[0020] a) Preparing a molten alloy metal bath comprising, in weight percent (wt.%)

[0021] Zn 6.65 - 7.45

[0022] Mg 1.35 - 1.75

[0023] Cu 1.85 - 2.35

[0024] Zr 0.04 - 0.14

[0025] Mn 0 - 0.5

[0026] Ti 0 - 0.15, preferably 0.02 to 0.06 wt.%,

[0027] V 0 - 0.15

[0028] Cr 0 - 0.25

[0029] Fe ≤ 0.05

[0030] Si ≤ 0.05

[0031] Fe + Si ≤ 0.08,

[0032] Each of the other impurities < 0.05 and the total amount < 0.15, the balance being aluminum.

[0033] b) Cast the molten alloy metal to obtain a slab or billet;

[0034] c) Homogenize the ingot or billet to obtain a homogenized ingot or billet;

[0035] d) Hot-work the homogenized slab or billet to obtain a forged product with a final thickness of at least 25 mm, preferably 25 mm to 200 mm, such as an extruded, rolled, and / or forged product;

[0036] e) Solution heat treat and quench the forged product to obtain a quenched forged product;

[0037] f) Stress relieve the quenched forged product to obtain a stress-relieved forged product;

[0038] g) Artificial age the stress-relieved forged product, wherein the total equivalent aging time t(eq) at 155 °C is 24 hours to 45 hours, preferably 24 hours to 34 hours, and even more preferably 26 hours to 30 hours,

[0039] The total equivalent time t(eq) at 155 °C is defined by the following formula:

[0040]

[0041] where T is the instantaneous temperature in Kelvin during the aging process, Tref is the reference temperature selected at 155 °C (428 K), and t(eq) is in hours.

[0042] The method is advantageously carried out using a molten alloy bath in which the Zn content is 6.90 to 7.30% by weight (wt.%), and even more preferably 6.90 to 7.25%.

[0043] The method is advantageously carried out using a molten alloy bath in which the Cu content is 1.95 to 2.35% by weight (wt.%), and even more preferably 2.00 to 2.35%.

[0044] Preferably, the molten alloy metal bath comprises, in weight % (wt. %), Zn 6.90 - 7.30, Mg 1.35 - 1.75, Cu 1.95 - 2.35, Zr 0.04 - 0.14, Mn 0 - 0.5, Ti 0 - 0.15, V 0 - 0.15, Cr 0 - 0.25, Fe ≤ 0.05, Si ≤ 0.05% and Fe + Si ≤ 0.08%, and other impurities each < 0.05 and in total < 0.15, with the balance being aluminum. Even more preferably, the molten alloy metal bath comprises, in weight % (wt. %), Zn 6.90 - 7.25, Mg 1.35 - 1.75, Cu 2.00 - 2.35, Zr 0.04 - 0.14, Mn 0 - 0.5, Ti 0 - 0.15, V 0 - 0.15, Cr 0 - 0.25, Fe ≤ 0.05, Si ≤ 0.05% and Fe + Si ≤ 0.08%, and other impurities each < 0.05 and in total < 0.15, with the balance being aluminum.

[0045] The method advantageously uses a molten alloy bath comprising Si ≤ 0.03 wt.% and Fe ≤ 0.05 wt.%. Preferably, the total content of Fe + Si is ≤ 0.07 wt.%, even more preferably ≤ 0.06 wt.%. Preferably, the total content of Fe + Si is ≥ 0.03 wt.%, even more preferably ≥ 0.04 wt.%.

[0046] The present invention relates to a rolled product having a thickness t (in millimeters) of at least 25 mm, preferably 25 mm to 200 mm, the rolled product comprising, in weight % (wt. %)

[0047] Zn 6.65 - 7.45

[0048] Mg 1.35 - 1.75

[0049] Cu 1.85 - 2.35

[0050] Zr 0.04 - 0.14

[0051] Mn 0 - 0.5

[0052] Ti 0 - 0.15

[0053] V 0 - 0.15

[0054] Cr 0 - 0.25

[0055] Fe ≤ 0.05

[0056] Si ≤ 0.05

[0057] Fe + Si ≤ 0.08

[0058] The content of other impurities is each <0.05 and the total amount is <0.15, and the rest is aluminum.

[0059] And the toughness K at room temperature measured in MPa·√m according to ASTM standard E399 (2020) 1c (L - T) is higher than -0.25*t + 65 MPa√m, preferably higher than -0.25*t + 68 MPa√m, and even more preferably -0.25*t + 72 MPa√m.

[0060] Advantageously, the composition of the rolled product contains 6.90 to 7.30 wt.% of Zn, even more preferably 6.90 to 7.25 wt.%.

[0061] Advantageously, the composition of the rolled product contains 1.95 to 2.35 wt.% of Cu, even more preferably 2.00 to 2.35 wt.%.

[0062] Preferably, the composition of the rolled product contains 6.90 - 7.30 wt.% of Zn, 1.35 - 1.75 wt.% of Mg, 1.95 - 2.35 wt.% of Cu, 0.04 - 0.14 wt.% of Zr, 0 - 0.5 wt.% of Mn, 0 - 0.15 wt.% of Ti, 0 - 0.15 wt.% of V, 0 - 0.25 wt.% of Cr, Fe ≤ 0.05 wt.%, Si ≤ 0.05 wt.% and Fe + Si ≤ 0.08 wt.%, and the content of other impurities is each <0.05 and the total amount is <0.15, and the rest is aluminum. More preferably, the composition of the rolled product contains 6.90 - 7.25 wt.% of Zn, 1.35 - 1.75 wt.% of Mg, 2.00 - 2.35 wt.% of Cu, 0.04 - 0.14 wt.% of Zr, 0 - 0.5 wt.% of Mn, 0 - 0.15 wt.% of Ti, 0 - 0.15 wt.% of V, 0 - 0.25 wt.% of Cr, Fe ≤ 0.05 wt.%, Si ≤ 0.05 wt.% and Fe + Si ≤ 0.08 wt.%, and the content of other impurities is each <0.05 and the total amount is <0.15, and the rest is aluminum.

[0063] In a preferred embodiment, both the fracture toughness and elongation of the rolled product of the present invention show a surprisingly small decrease when cooled from room temperature to liquid nitrogen temperature. The rolled product of the present invention shows that the toughness K1c(T - L) at a low temperature of about -196 °C measured in MPa·√m according to ASTM standard E399 2020 is reduced by less than 10%, preferably less than 8%, and more preferably less than 7% compared with K1c(T - L) measured at room temperature according to ASTM standard E399 - 2020.

[0064] Preferably, the rolled product of the present invention shows that the toughness K1c(T-L) in MPa·√m at a low temperature of about -196 °C measured according to ASTM standard E399-2020 is higher than -0.15*t + 45 MPa·√m, preferably higher than -0.15*t + 49 MPa·√m, and even more preferably higher than -0.15*t + 55 MPa, where t is the thickness of the rolled product in mm.

[0065] In a preferred embodiment, the thickness of the rolled product is 70 mm to 160 mm, preferably 70 mm to 102 mm.

[0066] Preferably, the rolled product contains Si ≤ 0.03 wt% and Fe ≤ 0.05 wt%. Preferably, the total content of Fe + Si in the rolled product is ≤ 0.07 wt%, and even more preferably ≤ 0.06 wt%. Preferably, the total content of Fe + Si in the rolled product is ≥ 0.03 wt%, and even more preferably ≥ 0.04 wt%. Preferably, the total content of Fe + Si in the rolled product is 0.03 wt% to 0.08 wt%, preferably 0.03 wt% to 0.07 wt%, and even more preferably 0.03 wt% to 0.06 wt%.

[0067] Preferably, the Zn content in the rolled product by weight is 7.10 to 7.25 wt%.

[0068] Preferably, the Ti content in the rolled product in wt.% (wt.%) is ≤ 0.06, preferably 0.02 to 0.06, and even more preferably 0.03 to 0.05.

[0069] The rolled product of the present invention or the product obtained by the method of the present invention is advantageously used as or incorporated into structural members for building aircraft or spacecraft. It can be used as ribs, spars, and / or frames.

[0070] In another advantageous embodiment, the rolled product of the present invention or the product obtained by the method of the present invention is advantageously used for manufacturing mechanical parts for gas compression at low temperatures below -100 °C, especially for hydrogen or oxygen or nitrogen or methane or natural gas compression, such as pistons, impellers.

[0071] In another advantageous embodiment, the rolled product of the present invention or the product obtained by the method of the present invention is advantageously used for manufacturing cryogenic storage tanks or stationary inland storage tanks or transport storage tanks for liquefied gases (such as liquid hydrogen or liquid oxygen or liquid nitrogen or liquid methane or liquid natural gas). Description of the Drawings

[0072] Figure 1 ​​Figure 1 Shows the toughness K at low temperatures 1c (T-L) variation with sheet thickness.

[0073] Figure 2 Figure 2 Shows the trade-off between the tensile yield strength in the rolling direction (L) and the toughness in the L-T direction measured at medium thickness at room temperature (RT).

[0074] Figure 3 Figure 3 Shows the variation of the TYS and toughness K 1c (T-L) trade-off in the rolling direction at room temperature and low temperatures.

[0075] Figure 4 Figure 4 Shows the toughness K at room temperature for different compositions 1c (L-T) variation with the total amount of Fe+Si.

[0076] Figure 5 Figure 5 Shows the toughness K at room temperature under different artificial aging conditions 1c (L-T) variation with the total amount of Fe+Si.

[0077] Figure 6 Figure 6 Shows the toughness K 1c (L-T) variation with sheet thickness.

[0078] Figure 7 Figure 7 Shows the fatigue crack growth rate (L-T) of the reference product under normal ambient air humidity conditions and humid air conditions.

[0079] Figure 8 Figure 8 Shows the fatigue crack growth rate (L-T) of the product of the present invention under normal ambient air humidity conditions and humid air conditions. Detailed Description of the Invention

[0080] Unless otherwise specified, all descriptions of the chemical composition of the alloy are expressed as weight percentages based on the total weight of the alloy. The alloy naming conforms to the regulations of The Aluminium Association known to those skilled in the art.

[0081] ​​​​​​​​​​​​​​The definition of the state is specified in NF EN 515 (2017). Unless otherwise mentioned, the static mechanical properties, namely the ultimate tensile strength UTS, the tensile yield stress TYS, and the elongation at break E, are determined by a tensile test according to the standard ASTM B557, in which the sampling position and its direction are defined. Unless otherwise specified, the definitions of standard EN 12258 apply. The fracture toughness K is determined according to ASTM standard E399 - 2020 1C Materials with a thickness up to 102 mm (4 inches) are tested at t / 2, and materials with a thickness greater than 102 mm (4 inches) are tested at t / 4. For S - L, all samples are tested at t / 2. Unless otherwise specified, the width W of the C(T) specimen is 101.6 mm (4 inches), and B = 50.8 mm (2 inches).

[0082] For extrusion, the thickness of the extruded product is defined according to the standard NF EN 2066 (2002). The cross - section is divided into elementary rectangles with dimensions A and B; A is always the maximum dimension of the elementary rectangle, and B is considered the thickness of the elementary rectangle.

[0083] 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 particularly important for the structural performance and are typically specified or subjected to structural calculations. These are typically components that, once broken, may seriously endanger the safety of the mechanical structure, its users, or third parties. In the case of an aircraft, the structural members include fuselage members (such as fuselage skin), stringers, bulkheads, ring frames, wing components (such as wing skin, stringers or stiffeners, ribs, spars), empennage (such as horizontal and vertical stabilizers), floor beams, seat rails, and doors.

[0084] When used in this specification, the symbol * means multiply.

[0085] When used in this specification, the term "about" means a value with a tolerance of + / - 5% of the displayed value.

[0086] The method of the present invention includes different steps.

[0087] The first step aims to prepare a molten alloy metal pool, which contains or advantageously consists essentially of: Zn 6.65 - 7.45 wt.%, Mg 1.35 - 1.75 wt.%, Cu 1.85 - 2.35 wt.%, Zr 0.04 - 0.14 wt.%, Mn 0 - 0.5 wt.%, Ti 0 - 0.15 wt.%, V 0 - 0.15 wt.%, Cr 0 - 0.25 wt.%, Fe ≤ 0.05 wt.%, Si ≤ 0.05 wt.% and Fe + Si ≤ 0.08 wt.%, and other impurities each < 0.05 wt.% and the total < 0.15 wt.%, with the balance being aluminum.

[0088] Preferably, the molten alloy metal bath comprises or advantageously consists essentially of: Zn 6.90 - 7.30, Mg 1.35 - 1.75, Cu 1.95 - 2.35, Zr 0.04 - 0.14, Mn 0 - 0.5, Ti 0 - 0.15, V 0 - 0.15, Cr 0 - 0.25, Fe ≤ 0.05, Si ≤ 0.05% and Fe + Si ≤ 0.08%, in weight percent (wt.%), and other impurities each < 0.05 and total < 0.15, the balance being aluminum.

[0089] Even more preferably, the molten alloy metal bath comprises or advantageously consists essentially of: Zn 6.90 - 7.25, Mg 1.35 - 1.75, Cu 2.00 - 2.35, Zr 0.04 - 0.14, Mn 0 - 0.5, Ti 0 - 0.15, V 0 - 0.15, Cr 0 - 0.25, Fe ≤ 0.05, Si ≤ 0.05% and Fe + Si ≤ 0.08%, in weight percent (wt.%), and other impurities each < 0.05 and total < 0.15, the balance being aluminum.

[0090] Then, the molten alloy metal is cast to obtain a slab or a billet. The slab of the present invention is a parallelepiped; it can also be referred to as an "ingot".

[0091] Then, the slab or billet is homogenized. In a preferred embodiment, the homogenization is preferably carried out at a temperature of about 450 °C to about 510 °C for generally 5 to 30 hours in at least one step, or preferably at a temperature of about 470 °C to 500 °C for 8 to 20 hours, or even more preferably at a temperature of 470 °C to 490 °C for 8 to 20 hours.

[0092] The homogenized slab or billet is hot - worked to obtain a forged product with 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, even more preferably about 70 mm to about 102 mm. The forged product is a rolled product or an extruded product or a forged product. The forged product can be directly obtained by forging a billet or an ingot or from a rolled product (e.g., first rolled then forged) or from an extruded product (e.g., first extruded then forged). In one embodiment, the homogenized slab is hot - rolled to obtain a rolled product with 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, even more preferably about 75 mm to about 102 mm or about 70 mm to about 80 mm. The hot - rolling is preferably carried out in one or more stages, wherein the inlet temperature is preferably about 380 °C to about 460 °C, and preferably about 400 °C to about 450 °C.

[0093] The forged product (such as a rolled product or an extruded product and / or a forged product) is solution heat treated to obtain a solution heat treated forged product, preferably at a temperature of 460 °C to about 510 °C or preferably about 470 °C to 500 °C or even more preferably 470 °C to 490 °C for 1 to 10 hours typically according to the thickness.

[0094] Then, the solution heat treated forged product is quenched to obtain a quenched forged product, preferably in water at room temperature.

[0095] Then, the quenched forged product is stress relieved to obtain a stress relieved forged product. Stress relief is obtained by controlled tension or compression, where the permanent plastic deformation is preferably less than 5%, and preferably 1 to 4%, more preferably 2 to 3%.

[0096] Then, the stress relieved forged product is artificially aged, where the total equivalent aging time t(eq) at 155 °C is 24 hours to 45 hours, preferably 24 hours to 34 hours, even more preferably 26 hours to 30 hours.

[0097] The total equivalent time t(eq) at 155 °C is defined by the following formula:

[0098]

[0099] where T is the instantaneous temperature in °K during the aging process, Tref is the reference temperature selected at 155 °C (428 K), and t(eq) is expressed in hours.

[0100] The total equivalent time t(eq) at 155 °C is defined by the following formula:

[0101]

[0102] where T is the instantaneous temperature in Kelvin during the aging process, Tref is the reference temperature selected at 155 °C (428 K), and t(eq) is expressed in hours.

[0103] This expression involves the integral of the function exp(-16000 / T) with respect to time t, where T is the instantaneous temperature in Kelvin. The integral can be calculated using numerical integration. Methods of numerical integration are described, for example, in "Numerical Recipes - The Art of Scientific Computing - Third Edition" by Press W.H. et al., published by Cambridge University Press in 2007. This book describes different numerical methods for integrating functions (paragraph 4). A simple method that can be used to calculate the equivalent time is the trapezoidal rule (see paragraph 4.1.1, formula 4.1.3).

[0104] In some cases, the integral can be calculated analytically, for example when the aging is considered as a step at a constant temperature.

[0105] If the aging is defined by a single step at temperature T1 (in Kelvin) for a duration t1 (in hours), then the equivalent time (in hours) at 155 °C (428 K) can be written in the following form:

[0106] t(eq) = t1 * exp(-16000 / T1 + 16000 / 428)

[0107] If the aging is defined by two steps (for example: a first step at temperature T1 for a duration t1, and a second step at temperature T2 for a duration t2), then the equivalent time at 155 °C (428 K) for each step can be calculated using the same principle.

[0108] t(eq) = t1 * exp(-16000 / T1 + 16000 / 428) + t2 * exp(-16000 / T2 + 16000 / 428)

[0109] If the aging is defined by two steps and there is a controlled heating gradient between the two steps, then the two steps defined as above can be considered and the corresponding equivalent time can be calculated by numerically integrating the heating gradient.

[0110] The total equivalent aging time t(eq) at 155 °C is at least 24 hours, preferably at least 25 hours or 26 hours, or even more preferably at least 27 hours. The total equivalent aging time t(eq) at 155 °C is less than 45 hours, preferably less than 40 hours, 39 hours, 38 hours, 37 hours, 36 hours, 35 hours, 34 hours, 33 hours, 32 hours, 31 hours, or even more preferably less than 30 hours. Any combination of the above minimum and maximum values can achieve the best compromise between toughness and yield strength at ambient temperature and low temperature.

[0111] The aging treatment is advantageously carried out in two steps, where the first step is carried out 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 step is carried out at a temperature of 140 to 180 °C, preferably 140 to 170 °C, for 6 to 90 hours, preferably at a temperature of 150 to 165 °C for 9 to 50 hours.

[0112] The product of the present invention has its specific composition, in particular the Fe and Si contents are ≤ 0.08 wt%, and when combined with a properly designed artificial aging treatment, a product with a better compromise between the tensile yield strength and toughness at ambient temperature and low temperature can be obtained, especially a better compromise between the tensile yield strength in the rolling direction (L direction) and the toughness in the L-T direction at ambient temperature.

[0113] The alloy of the present invention contains 6.65 to 7.45 wt% of Zn. To obtain sufficient strength, the minimum required Zn content is 6.65 wt%, preferably 6.90 wt%, more preferably 7.0 wt%, even more preferably 7.10 wt%; however, to obtain a balance of the desired properties (especially toughness and elongation), Zn should not exceed 7.45 wt%, preferably 7.30 wt%, more preferably 7.25 wt%.

[0114] The alloy of the present invention contains 1.35 to 1.75 wt% of Mg. To obtain sufficient strength, the minimum required Mg content is 1.35 wt%, and preferably 1.40 wt% or 1.50 wt%, or even 1.60 wt%. However, to obtain a balance of the desired properties (especially toughness and elongation), the Mg content should not exceed 1.75 wt%, and preferably 1.70 wt%.

[0115] The alloy of the present invention contains 1.85 to 2.35 wt% of Cu. To obtain sufficient strength, the minimum required Cu content is 1.85 wt%, preferably 1.95, more preferably 2.0 wt%, or even more preferably 2.1 wt%. However, to avoid quench sensitivity, Cu should not exceed 2.35 wt%, and preferably 2.30%, or even more preferably 2.25 wt%.

[0116] The alloy of the present invention further contains 0.04 to 0.14 wt% of Zr, which is generally used for grain size control. To limit recrystallization, the Zr content should preferably be at least about 0.07 wt%, and preferably about 0.09 wt%, but to reduce problems during the casting process, it should be advantageously kept below about 0.12 wt%.

[0117] To limit the as-cast grain size, titanium can generally be added up to 0.15 wt% during casting, if desired. Ti can be combined with boron or carbon. The present invention generally can accommodate up to about 0.06 wt% or about 0.05 wt% of Ti. In a preferred embodiment of the present invention, the Ti content is from about 0.02 wt% to about 0.06 wt%, and preferably from about 0.03 wt% to about 0.05 wt%.

[0118] Up to 0.5 wt% of manganese can be added, but addition 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%.

[0119] Up to 0.15 wt% of vanadium can be added, but addition 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%.

[0120] Up to 0.25 wt% of chromium can be added, but addition 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%.

[0121] The alloys of the present invention can contain iron and silicon which affect the fracture toughness properties. It has been observed that 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% in order to obtain a better compromise between tensile yield strength and toughness, a small decrease in fracture toughness at low temperatures (less than 10%), and little increase in the fatigue crack growth rate under high humidity conditions compared to fatigue under ambient laboratory conditions. The inventors have found that for the selected compositions and an Fe + Si content below 0.08 wt%, when combined with a properly designed aging treatment (where the total equivalent aging time t(eq) at 155 °C is from 24 hours to 45 hours), a significant improvement in the tensile yield strength - toughness compromise, toughness and elongation at low temperatures, and fatigue crack rate under high humidity conditions can be obtained.

[0122] The inventors have found that a satisfactory compromise can be obtained even if the Fe + Si content is higher than 0.03 wt%, or higher than 0.04 wt% or higher than 0.05 wt%.

[0123] In one embodiment of the present invention, the iron and silicon content (e.g., Fe + Si content) is from 0.03% to 0.08% by weight, preferably from 0.03% to 0.07% by weight, more preferably from 0.03% to 0.06% by weight, and even more preferably from 0.03% to 0.05% by weight. In another embodiment, the alloy of the present invention may contain an iron and silicon content (e.g., Fe + Si content) of from 0.04% to 0.08% by weight, preferably from 0.04% to 0.07% by weight, more preferably from 0.04% to 0.06% by weight, and even more preferably from 0.04% to 0.05% by weight. In another embodiment, the alloy of the present invention may contain an iron and silicon content (e.g., Fe + Si content) of from 0.05% to 0.08% by weight, preferably from 0.05% to 0.07% by weight, more preferably from 0.05% to 0.06% by weight.

[0124] The alloy of the present invention may include up to 0.05% by weight of Si, preferably up to 0.03% by weight. The alloy of the present invention may include up to 0.05% by weight of Fe, preferably up to 0.03% by weight.

[0125] The alloy of the present invention may include incidental impurities. The term "incidental impurities" may include relatively small amounts of other elements less than 0.05% by weight or less than 0.01% by weight, and the total amount is 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.

[0126] The term "comprising" should be construed to mean that no other elements are intended to be added except for the elements recited to provide the novelty and basic characteristics of the present invention. However, it should be understood that due to impurities and / or leaching resulting from contact with manufacturing equipment, trace amounts of these elements may enter the final alloy product. However, it should be understood that the scope of the present invention should not / cannot be circumvented by merely adding any such elements, as long as the amount does not affect the combination of properties desired and obtained herein.

[0127] The present invention is particularly suitable for rolled products, especially those having a thickness of at least 25 mm, preferably 25 mm to 200 mm, more preferably 70 mm to 200 mm, or 70 mm to 160 mm, and even more preferably 70 mm to 102 mm.

[0128] According to the present invention, a rolled product having a thickness of at least 25 mm, preferably 25 mm to 200 mm, more preferably 70 mm to 200 mm or 70 to 160 mm, and even more preferably 70 mm to 102 mm advantageously has the following properties:

[0129] K in the L-T direction at room temperature measured according to ASTM E399-2020 1CThe toughness is at least -0.25*t + 65 MPa·√m, more preferably at least -0.25*t + 68 MPa·√m, and even more preferably at least -0.25*t + 72 MPa·√m, where t is the thickness of the rolled product in mm.

[0130] Preferably, the rolled product advantageously has a yield strength of at least 450 MPa in the rolling direction L. Preferably, the yield strength in the transverse direction LT is at least 410 MPa, even more preferably at least 420 MPa.

[0131] In a preferred embodiment, both the fracture toughness and the elongation of the rolled product of the present invention show a surprisingly small decrease when cooled from room temperature to liquid nitrogen temperature. The rolled product of the present invention shows that the toughness K1c(T-L) in MPa·√m at a low temperature of about -196 °C measured according to ASTM standard E399-2020 is less than 10%, preferably less than 8%, and even more preferably less than 7% lower than the K1c(T-L) in MPa·√m measured at room temperature according to ASTM standard E399-2020.

[0132] Preferably, the rolled product of the present invention shows that the toughness K1c(T-L) in MPa·√m at a low temperature of about -196 °C measured according to ASTM standard E399-2020 is higher than -0.15*t + 45 MPa·√m, preferably higher than -0.15*t + 49 MPa·√m, and even more preferably higher than -0.15*t + 55 MPa, where t is the thickness of the rolled product in mm.

[0133] The rolled product of the present invention or a product obtained by the method of the present invention is advantageously used as or incorporated into structural members for constructing aircraft or spacecraft.

[0134] In a preferred embodiment, the products of the present invention are used for wing ribs, spars and frames. In an embodiment of the present invention, the rolled products of the present invention are welded to other rolled products to form wing ribs, spars and frames. In another embodiment, the rolled products of the present invention or the products obtained by the method of the present invention are advantageously used for structural members used at cryogenic temperatures, typically cryogenic storage tanks. In applications at cryogenic temperatures, the rolled products of the present invention or the products obtained by the method of the present invention are advantageous for manufacturing mechanical parts for gas compression at cryogenic temperatures, especially for hydrogen or oxygen or nitrogen or methane or natural gas compression, such as pistons or impellers. In one embodiment, the rolled products of the present invention or the products obtained by the method of the present invention are used to manufacture stationary inland storage tanks or transport storage tanks for liquefied gases (such as liquid hydrogen or liquid oxygen or liquid nitrogen or liquid methane or liquid natural gas). A transport storage tank is a movable storage tank, for example, when the liquefied gas is used as fuel, a storage tank for an automobile or a truck or a van or a train or a ship or an aircraft or a rocket, or a storage tank for a truck or a van or a train or a ship to transport the liquefied gas.

[0135] Examples

[0136] Example 1

[0137] According to the present invention, two ingots are cast using two compositions A and B. The ingots are homogenized and hot rolled to a thickness of 76.2 mm (A1) and 152.4 mm (B3), and then solution heat treated, stretched and finally aged according to the method of the present invention. The chemical and process information for these two batches is shown in Tables 1 and 2 respectively.

[0138] [Table 1]

[0139] (wt%) Si Fe Cu Mn Mg Zn Zr Ti Si + Fe A 0.02 0.03 2.15 - 1.65 7.21 0.10 0.03 0.05 B 0.02 0.04 2.10 - 1.64 7.05 0.10 0.03 0.06

[0140] [Table 2]

[0141]

[0142] Stretching and K IC The tests are carried out at room temperature (22 °C) and at cryogenic temperatures (precisely, at liquid nitrogen temperature (-196 °C)). The tensile tests are carried out according to ASTM B557. Samples are taken at the mid-thickness (t / 2) and at the quarter-thickness (t / 4). The tensile tests are carried out in the transverse direction (LT) and the short transverse direction (ST).

[0143] [Table 3]

[0144]

[0145] [Table 4]

[0146]

[0147] [Table 5]

[0148]

[0149]

[0150] Between the low temperature and the ambient temperature, an increase in the yield strength was observed. The increase was more than 12% in the ST direction and more than 18% in the LT direction.

[0151] K was measured in the T-L or S-L direction using a C(T) specimen in accordance with ASTM E399 1C test.

[0152] [Table 6]

[0153]

[0154] *Kq

[0155] Between the low temperature and the ambient temperature, a slight decrease in toughness was observed. The decrease increased with the plate thickness, and the decrease in K 1c (T-L) remained less than 7%, and even less than 4% at 76.2 mm in this orientation, and the decrease in K 1c (S-L) remained less than 15%, and even less than 10.5% at 76.2 mm in this orientation.

[0156] Figure 1 Shows the toughness K 1c (T-L) as a function of the plate thickness at low temperature. It can be observed that the toughness K1c(T-L) in MPa.√m of specimens A1 and B1 at a low temperature of about -196 °C is higher than -15*t + 45 MPa.√m, preferably higher than -0.15*t + 49 MPa.√m, and even more preferably higher than -0.15*t + 55 MPa, where t is the thickness of the product in mm.

[0157] Example 2

[0158] Ingots of four aluminum alloys C, D, E, and F were cast, homogenized, and hot-rolled to thicknesses of 75 mm (C1), 69.9 mm (D1), 76 mm (E1 and F1), respectively, and then solution heat-treated, stretched, and finally aged. The chemical and process information for these four batches 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 in WO2019 / 007817, respectively. The chemical and process information for these reference samples is listed in the following table. The composition of alloy F is the composition of the present invention, but sample F1 was subjected to a shorter artificial aging, and excellent TYS(L)-K 1c (L-T) compromise could not be obtained.

[0159] [Table 7]

[0160]

[0161] [Table 8]

[0162]

[0163] The tensile strength and toughness of C1, E1, and F1 were taken from the prior art. For comparison, sample A1 was tested similarly at t / 2 for comparison.

[0164] [Table 9]

[0165]

[0166] The yield strength of sheet D1 was tested in the LT direction, and the K1C test was carried out using a C(T) specimen according to ASTM E399, and samples were taken at t / 2. The properties obtained were compared with those of sheet A1 of Example 1 of the present invention.

[0167] [Table 10]

[0168]

[0169] [Table 11]

[0170]

[0171] Figure 2 The compromise between the tensile yield strength in the rolling direction (L) and the toughness in the L-T direction measured at the quarter thickness and the mid-thickness of sheets A1 and C1 at room temperature (RT) is shown. The significantly better compromise between the toughness and yield strength of A1 is attributed to the low content of Fe+Si and the optimized aging.

[0172] Figure 3Shows the trade-off between the tensile yield strength in the transverse direction (LT) and the toughness of T-L measured at room temperature and at the liquid nitrogen temperature of -196 °C. It can be observed that the toughness of the A1 sheet decreases less than that of the D1 sheet. This is attributed to the chemical composition, especially the lower Fe+Si content.

[0173] Example 3

[0174] Cast and transform different ingots (compositions A, C, G, H, J, K, M); the details of the corresponding compositions and processes are listed in Tables 14 and 15. All these castings were transformed into sheets with a thickness of 70 to 102 mm.

[0175] Alloys C, G, H correspond to prior art alloys, and J, K, M are the compositions of the present invention. Alloy A is similar to that in Example 1.

[0176] Two aging conditions were evaluated, corresponding to the total equivalent time at 155 °C above 24 h ("a") of the present invention and the total equivalent time at 155 °C below 23 h ("b") for comparison. Tensile tests and toughness measurements were carried out at room temperature. The results are shown in Table 16. The properties of Alloy A shown in Example 2 are also shown in Table 14.

[0177] [Table 12]

[0178]

[0179] [Table 13]

[0180]

[0181]

[0182] [Table 14]

[0183]

[0184] Figures 4 to 6 Shows the data in Table 14.

[0185] At Figures 4 to 6Among them, the samples with the composition of the present invention and processed according to the present invention are represented by black diamonds (A1-a, J1-A, K2-a). The samples with the composition of the present invention but processed in a different manner are represented by hollow diamonds (M2-b). The triangular symbols are used to represent the compositions (C1-a and C1-b) that are different from the present invention in that the Fe+Si content is greater than 0.08% by weight. The circular symbols are used to represent the compositions (G2-a, H2-a) in which the main alloying elements are different from the present invention. If the process is different from the present invention, that is, the equivalent time at 155 °C is less than 23 hours, the triangular or circular symbols are hollow, or, if the process is the process of the present invention, they are solid symbols.

[0186] Figure 4 Shows the effect of Fe+Si content on K 1c (L-T) in artificially aged products with a total equivalent time higher than 24 h at 155 °C. For a thickness range of about 70 mm to about 102 mm, it can be observed that in all cases, reducing the amount of Fe+Si can improve the toughness K 1c (L-T). However, for the samples A1-a, J1-a, K2-a processed according to the present invention, artificially aged at 155 °C for a total equivalent time of 24 hours to 45 hours and having a composition with a particularly Fe+Si content less than or equal to 0.08% by weight, this trend is more obvious.

[0187] For the samples with the composition of the present invention and artificially aged according to the present invention and the samples with the main elements other than Fe, Si and / or (Fe+Si) content of the present invention and artificially aged according to the present invention (samples A1-a, J1-A, K2-A and C1-a), the slope Δ1 represents the effect of (Fe+Si) on K 1c L-T. The sample C1-a aged at 155 °C for an equivalent time of 24.4 h shows lower toughness K 1c (L-T). The inventors attribute this characteristic to its Fe+Si content.

[0188] For the samples (H2-a and G2-a) with a composition outside the scope of the present invention but having the Fe, Si and / or (Fe+Si) content of the present invention and artificially aged according to the present invention, the slope Δ2 represents the effect of the main alloying elements on K 1c L-T. The slope Δ2 is less than the slope Δ1. The inventors attribute this characteristic to the synergistic effect of the composition selection, especially the Zn and Mg contents and the Fe+Si content.

[0189] Figure 5 Shows the effect of Fe+Si content on K 1c(L-T) influence. The arrow from M2-b to K2-a (ΔT1) and the arrow from C1-b to C1-a (ΔT2) respectively represent the influence of the total equivalent time at 155 °C on the composition of the present invention or the prior art under the same Fe+Si content. It can be clearly observed that extending the total equivalent time of aging at 155 °C can improve toughness. However, for the composition of the present invention with an Fe+Si content lower than 0.08 wt%, this trend is more obvious (arrow ΔT1).

[0190] The toughness K1c (L-T) of samples A1-a, J1-a, and K2-a with a thickness of 75 mm to 102 mm is 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 thickness of the sheet in mm ( Figure 6 ).

[0191] Although the Fe+Si content is lower than 0.08%, the toughness K1c (L-T) of samples M2-b, K2-a, and H2-a is lower than that of the samples of the present invention. The inventor attributes this characteristic to the composition and / or the failure to meet the artificial aging conditions with a total equivalent time of 24 h to 45 h at 155 °C.

[0192] Example 4

[0193] The fatigue crack growth rate of the B3 sheet described in Example 1 was evaluated and compared with the reference product O3 with a similar thickness of 152.4 mm (6 inches). Alloys O and B are alloys of the present invention (Table 15), where the Fe+Si content is lower than 0.08 wt%. The O3 sheet was processed in a similar manner to the B3 sheet, except that the artificial aging condition was an equivalent aging time of 19.9 h at 155 °C (Table 16).

[0194] [Table 15]

[0195]

[0196] [Table 16]

[0197]

[0198] The fatigue crack growth rate was evaluated according to ASTM E647. The specimen orientation was L-T. The standard compact tension (i.e., C(T)) specimen size was used for the test. The size B of all test specimens was 7.6 mm (0.3 inches), and W was 50.8 mm (2 inches). The FCGR test procedure was generally carried out according to ASTM E647, and the specific requirements were as follows: (1) stress ratio 0.1, and f = 10 Hz; (2) pre-cracking was carried out under a constant load amplitude, and the initial ΔK reached ΔK at the end of pre-crackingi The value of 10 MPa*√m. After pre-cracking, tests are carried out under the same load as the pre-cracking, at a constant load amplitude. The tests are carried out at room temperature.

[0199] Two relative humidity (RH) conditions of two kinds of plates are evaluated: one is under normal ambient air humidity conditions (27 - 32% humidity, referred to as "standard air"), and the other is under humid air conditions (92 - 93% humidity, referred to as "humid air").

[0200] Figure 7 and Figure 8 respectively disclose the variation of the fatigue crack growth rate of plates O3 and B3 with environmental conditions.

[0201] It can be observed that the products (B3, Figure 8 ) with the selected composition of the present invention and aged at 155°C for an equivalent time higher than 24 h show similar fatigue crack growth rates regardless of the relative humidity considered. The products (O3, Figure 7 ) aged at 155°C for an equivalent time lower than 23 h show a significant dependence on humidity.

Claims

1. A method for manufacturing a forged 7xxx aluminum-based alloy product, the method comprising the following steps: a) Prepare a molten alloy metal bath, which contains, by weight % (wt. %), Zn 6.65 - 7.45 Mg 1.35 - 1.75 Cu 1.85 - 2.35 Zr 0.04-0.14 Mn 0 - 0.5 Ti 0 - 0.15, preferably 0.02 to 0.06 wt.%, V 0-0.15 Cr 0-0.25 Fe ≤ 0.05 Si ≤ 0.05 Fe + Si ≤ 0.08, other impurities each < 0.05 and the total amount < 0.15, with the balance being aluminum; b) Cast the molten alloy metal to obtain a slab or billet; c) Homogenize the ingot or billet to obtain a homogenized ingot or billet; d) Hot-work the homogenized slab or billet to obtain a forged product with a final thickness of at least 25 mm, such as an extruded, rolled, and / or forged product; e) Solution heat-treat and quench the forged product to obtain a quenched forged product; f) Stress-relieve the quenched forged product to obtain a stress-relieved forged product; g) Artificial age the stress-relieved forged product, wherein the total equivalent aging time t(eq) at 155 °C is 24 hours to 45 hours, The total equivalent time t(eq) at 155 °C is defined by the following formula: where T is the instantaneous temperature in Kelvin during the aging process, Tref is the reference temperature selected at 155 °C (428 K), and t(eq) is expressed in hours.

2. The method for manufacturing a forged 7xxx aluminum-based alloy product according to claim 1, wherein the Zn content is 6.90 to 7.30 by weight % (wt. %).

3. The method for manufacturing a forged 7xxx aluminum-based alloy product according to claim 1, wherein the Zn content is 6.90 to 7.25 by weight % (wt. %).

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

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

6. The method for manufacturing a forged 7xxx aluminum-based alloy product according to claim 1, wherein the molten alloy metal bath contains, by weight % (wt. %), Zn 6.90 - 7.30 Mg 1.35 - 1.75 Cu 1.95 - 2.35 Zr 0.04-0.14 Mn 0 - 0.5 Ti 0 - 0.15, preferably 0.02 to 0.06 wt.%, V 0-0.15 Cr 0-0.25 Fe ≤ 0.05 Si ≤ 0.05 Fe + Si ≤ 0.08, other impurities each < 0.05 and the total amount < 0.15, with the balance being aluminum.

7. The method for manufacturing a forged 7xxx aluminum-based alloy product according to claim 1, wherein the molten alloy metal bath contains, by weight % (wt. %), Zn 6.90 - 7.25 Mg 1.35 - 1.75 Cu 2.00 - 2.35 Zr 0.04-0.14 Mn 0 - 0.5 Ti 0 - 0.15, preferably 0.02 to 0.06 wt.%, V 0-0.15 Cr 0-0.25 Fe ≤ 0.05 Si ≤ 0.05 Fe + Si ≤ 0.08, Other impurities are each < 0.05 and the total amount is < 0.15, the balance being aluminum.

8. The method for manufacturing a forged 7xxx aluminum-based alloy product according to any one of claims 1 to 7, wherein Si ≤ 0.03 wt.% and Fe ≤ 0.05 wt.%.

9. The method for manufacturing a forged 7xxx aluminum-based alloy product according to any one of claims 1 to 8, wherein the Fe + Si content is ≤ 0.07 wt.%, preferably ≤ 0.06 wt.%.

10. The method for manufacturing a forged 7xxx aluminum-based alloy product according to any one of claims 1 to 9, wherein the Fe + Si content is ≥ 0.03 wt.%, preferably ≥ 0.04 wt.%.

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

12. The method for manufacturing a forged 7xxx aluminum-based alloy product according to any one of claims 1 to 11, wherein the aging treatment is carried out in two steps, wherein the first step is carried out 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 step is carried out at a temperature of 140 to 180 °C, preferably 140 to 170 °C, for 6 to 90 hours, preferably at a temperature of 150 to 165 °C for 9 to 50 hours.

13. A rolled product having a thickness t in millimeters of at least 25 mm, preferably 25 mm to 200 mm, the rolled product comprising (by weight%) Zn 6.65 - 7.45 Mg 1.35 - 1.75 Cu 1.85 - 2.35 Zr 0.04-0.14 Mn 0 - 0.5 Ti 0 - 0.15 V 0-0.15 Cr 0-0.25 Fe ≤ 0.05 Si ≤ 0.05 Fe + Si ≤ 0.08 Other impurities are each < 0.05 and the total amount is < 0.15, the balance being aluminum, And the toughness K in MPa·√m measured at room temperature at mid-thickness according to ASTM standard E399-2020 1c (L-T) is higher than -0.25*t + 65 MPa·√m, preferably higher than -0.25*t + 68 MPa·√m, even more preferably -0.25*t + 72 MPa·√m, where t is the thickness of the rolled product in mm.

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

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

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. 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. The rolled product according to claim 13, which comprises (by weight%) Zn 6.90 - 7.30 Mg 1.35 - 1.75 Cu 1.95 - 2.35 Zr 0.04-0.14 Mn 0 - 0.5 Ti 0 - 0.15, preferably 0.02 to 0.06 wt.%, V 0-0.15 Cr 0-0.25 Fe ≤ 0.05 Si ≤ 0.05 Fe + Si ≤ 0.08, Other impurities are each <0.05 and the total amount is <0.15, and the balance is aluminum.

19. The rolled product according to claim 13, comprising (in wt.%) Zn 6.90 - 7.25 Mg 1.35 - 1.75 Cu 2.00 - 2.35 Zr 0.04-0.14 Mn 0 - 0.5 Ti 0 - 0.15, preferably 0.02 to 0.06 wt.%, V 0-0.15 Cr 0-0.25 Fe ≤ 0.05 Si ≤ 0.05 Fe + Si ≤ 0.08, Other impurities are each <0.05 and the total amount is <0.15, and the balance is aluminum.

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

21. The rolled product according to any one of claims 13 or 20, wherein the toughness K1c(T - L) in MPa.√m at a cryogenic temperature of about -196 °C measured according to ASTM standard E399 - 2020 is higher than -0.15*t + 45 MPa.√m, preferably higher than -0.15*t + 49 MPa.√m, and even more preferably higher than -0.15*t + 55 MPa, where t is the thickness of the rolled product in mm.

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

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

24. The rolled product according to any one of claims 13 to 23, wherein the Fe + Si content is 0.03 wt.% to 0.07 wt.%, preferably 0.03 wt.% to 0.06 wt.%.

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

26. The rolled product according to any one of claims 13 to 25, wherein the Ti content is ≤ 0.06 in wt.%, preferably 0.02 to 0.06, and even more preferably 0.03 to 0.

05.

27. Use of the 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 structural members suitable for building aircraft - such as wing ribs, spars, and frames.

28. Use of the 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 mechanical parts for gas compression at cryogenic temperatures - in particular for mechanical parts for hydrogen or oxygen or nitrogen or methane or natural gas compression, such as pistons or impellers.

29. Use of the 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 storage tanks or stationary inland storage tanks or transport storage tanks for liquefied gases - such as liquid hydrogen or liquid oxygen or liquid nitrogen or liquid methane or liquid natural gas.

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