Recycled 7XXX aluminum alloy and manufacturing process

Abstract

Aluminum alloy of the 7XXX series suitable for recycling comprising in % by weight Zn: 5.0 – 7.0; Mg: 1.3 – 2.0; Cu: 2.0 – 3.0; Mn: 0.1 – 0.3; at least one element selected from Cr, Zr where the content of Cr is from 0.01 to 0.15 and the content of Zr is from 0.08 to 0.15; Ti: 0 – 0.15; Fe: 0 – 0.2; Si: 0 – 0.1; Impurities ≤ 0.05 each and ≤ 0.15 total and the remainder aluminum. This alloy can be used to manufacture a wrought product whose manufacturing process uses mixed scrap of 2XXX and 7XXX alloys, comprising at least 10% by weight of 2XXX alloy scrap and at least 20% by weight of 7XXX alloy scrap. Abbreviated figure: 1

Description

Title of the invention: Recycled 7XXX aluminum alloy and manufacturing process. Technical field

[0001] The invention relates to a 7XXX series aluminium alloy suitable for recycling and the use of this alloy to manufacture a wrought product using mixed 2XXX and 7XXX alloy waste. Previous art

[0002] 7XXX series aluminum alloys are commonly used as wrought products for industrial applications such as transportation. 7XXX series aluminum alloys offer the advantage of high mechanical properties and high toughness, which allows for a reduction in the weight of structures and thus a decrease in fuel consumption and greenhouse gas emissions.

[0003] It is now necessary to reduce greenhouse gas emissions during the production of these alloys. This reduction can be achieved by recycling aluminum alloy scrap and waste, thereby reducing or even eliminating the use of primary aluminum produced by electrolysis and / or the addition of alloying elements.

[0004] Primary aluminum is produced by electrolysis. The best electrolysis plants, which use hydroelectricity, have a carbon footprint of 4 tonnes of CO2 equivalent (CO2 eq) per tonne of foundry plate due to the use of carbon anodes. The typical carbon footprint for one tonne of electrolysis-produced aluminum foundry plate in Europe is 7 tonnes of CO2 eq. The carbon footprint of one tonne of foundry plate obtained using only scrap and waste is 0.5 t of CO2 eq per foundry plate. When a plate is produced using partially recycled materials, the mass of CO2 equivalent emitted can be estimated by linear interpolation between the aforementioned electrolysis plate (0% recycling) and a plate obtained using only scrap and waste (100% recycling).Recycling or recycling rate is the ratio between the weight of aluminum alloy scrap and waste used to make the plate and the weight of the plate, the remainder of the alloy being primary aluminum and / or additives.

[0005] The aluminum industry strives to recycle the products it manufactures in a closed loop whenever possible; that is, aluminum alloy scraps and waste are recycled to obtain the same alloy for which they were produced. This closed loop is integrated into the waste recycling loop. Produced by manufacturers of aluminum products (or "pre-consumer scrap" according to the dedicated Anglo-Saxon terminology). At all stages of semi-finished product manufacturing, scrap and waste are collected in skips for remelting. The same applies in the manufacturing stages of the final product, where efforts are made to sort machining chips by alloy series, or even by alloy grade. It is also possible to create such a closed loop within the so-called "post-consumer scrap" loop, according to Anglo-Saxon terminology, by implementing a recycling loop for the final product combined with sorting to separate and identify the constituent alloys at the end user's site. This is particularly the case in the aerospace sector, where the industry seeks to recycle end-of-life aircraft.

[0006] In most aircraft, aluminum alloys represent up to 80% of the materials used. Aluminum alloys are particularly used in structural applications; for example, the panels used for the entire outer fuselage, the upper and lower wing skins, wing spars, etc. The aeronautical structures of commercially available aircraft nearing the end of their service life are predominantly made of 7XXX and 2XXX series aluminum alloys. The fuselage generally consists of a 2XXX alloy skin and 7XXX alloy stiffeners. An aircraft wing generally consists of a 7XXX alloy upper skin, a 2XXX alloy lower skin, stiffeners that may be 7XXX and 2XXX alloys, and internal structural components (spars, ribs, etc.) generally made of 7XXX alloys.

[0007] The 2XXX series alloys are primarily used when damage tolerance and fracture strength are essential characteristics. AA2024 is one of the most commonly used aluminum alloys in fuselage structures due to its excellent damage tolerance in the T3 condition. Variants, such as the AA2524-T3 alloy, have been proposed for the manufacture of the Boeing 777. AA2224 and AA2324 offer increased strength and are used in the lower wing skin.

[0008] The 7XXX series alloys are used in aeronautical components where high strength is the primary requirement, including upper wing skins, horizontal and vertical stabilizers, wing spars, and fuselage stiffeners. AA7075-T6 has been used since the 1940s due to its relatively high specific strength. However, the corrosion susceptibility of this alloy has led to its replacement by newer 7XXX series alloys in many applications. For example, LAA7475 has a higher yield strength and a better combination of corrosion resistance and toughness, making it an ideal replacement for LAA7075. Another high-performance alloy, AA7050, is used for example in fuselage frames or to manufacture wing coverings.

[0009] Work exists on sorting the components of aeronautical structures made of 2XXX and 7XXX aluminum alloys in such a way as to separate the constituent materials by alloy series, or even by grade. However, this type of sorting proves complex. EP3710812 (Boeing) discloses a sorting system for aircraft recycling based on LIBS (Laser-Induced Breakdown Spectroscopy) technology. The sorting system comprises a waste feed unit, a surface treatment unit, a material positioning unit, a LIBS analysis and detection unit, a transfer unit, and a sorting and recovery unit.

[0010] EPI 101830 discloses a process for manufacturing an intermediate product, such as a plate, billet or forging block, in a specified alloy of the 7XXX series, said specified alloy having a specified content of at least one first anti-recrystallizing element.The process is characterized by the supply of products for recycling, such as machining scrap and chips, comprising products for recycling into at least one second alloy of the 7XXX series having a target content of at least one second anti-recrystallizing element exceeding the maximum acceptable content in said specified alloy; the production of a batch of liquid metal of specified grade, in whole or in part, from said products for recycling, said production including refining to reduce the content of said second anti-recrystallizing element to a value below the maximum acceptable content in said specified alloy; and the formation of said product by casting said liquid metal of specified grade. EPI 101830 enables the recycling of machining scrap and chips into alloys of the 7XXX series.EPI 101830 plans to use recycling products made of alloys other than those of the 7XXX series, typically alloys of the 2XXX series such as 2024. Such recycling products can also be used in the process according to the invention, provided that the proportion of 2XXX alloys is low, namely less than about 20%, and preferably less than 10%.

[0011] There is therefore a need to develop a recycling solution for scrap and waste made up of a mixture of 7XXX and 2XXX series alloys with a large quantity of 2XXX alloy. Description of the invention

[0012] The present invention proposes a recycling method for alloy mixtures containing both 2XXX and 7XXX alloys without the need for prior sorting. This solution can prove advantageous, for example, in the case of machining chips that may be tangled and difficult to separate. from the others. And even if they could be separated, the small size of the chips would reduce the efficiency and productivity of the sorting.

[0013] A first object of the invention relates to an aluminum alloy 7xxx comprising, in % by weight, Zn: 5.0 - 7.0, Mg: 1.3-2.0, Cu: 2.0 - 3.0, Mn: 0.1-0.3 at least one element chosen from Cr, Zr where the Cr content is from 0.01 to 0.15 and the Zr content is from 0.08 to 0.15, Ti: 0-0.15 Fe: 0 - 0.2 If :0-0.1 Impurities < 0.05 each and < 0.15 total and the remainder aluminum.

[0014] This alloy is particularly interesting because it allows a wrought product to be obtained with a good static-toughness compromise while being able to be manufactured from mixed waste of 2XXX and 7XXX alloys.

[0015] Preferably, the aluminum alloy comprises in % by weight Zn: 5.0 - 7.0 Mg: 1.3-2.0 Cu: 2.0 - 3.0 Mn: 0.1-0.3 Cr: 0.01-0.15 Zr: 0.08-0.15 Ti: 0-0.15 Fe: 0 - 0.2 Si: 0-0.1 Impurities < 0.05 each and < 0.15 total and the remainder aluminum.

[0016] Preferably, the Cu content is 2.1 to 2.8% by weight, preferably 2.2 to 2.5% by weight. Preferably, the Mg content is 1.4 to 1.8% by weight, preferably 1.5 to 1.7% by weight. Preferably, the Mn content is 0.10 to 0.30% by weight. Preferably, the Cr content is 0.05 to 0.15% by weight, preferably 0.06 to 0.15% by weight.

[0017] Another object of the invention relates to a method for manufacturing a wrought product made of aluminum alloy 7xxx. The manufacturing method comprises a step of preparing a charge, a step of melting the charge and then processing it to obtain a bath of liquid metal having a composition according to the first object of the invention, a step of pouring the bath of liquid metal and solidification of a raw form, a homogenization step of the raw form, an optional reheating step, a hot forging step of the homogenized raw form, an optional cold forging step of the hot forged product, a solution treatment step, a quenching step, a stress-relieving step, and an artificial aging step.

[0018] The feed preparation step is characterized in that the feed used to form the liquid metal bath comprises at least 10% by weight of 2XXX alloy scrap and at least 20% by weight of 7XXX alloy scrap, preferably 15% to 40% by weight of 2XXX alloy scrap, preferably 20% to 40%.

[0019] Preferably, the 2XXX alloy scrap includes AA2X24 alloy scrap. Preferably, during the preparation of the liquid metal bath, less than 30% primary aluminum metal is added. The primary aluminum metal is unalloyed aluminum with an aluminum content of at least 99.60% by weight. Preferably, the 7XXX alloy scrap includes 7XXX alloy scrap containing more than 0.10% chromium by weight of chromium, and / or 7XXX alloy scrap containing more than 0.05% chromium by weight of chromium. Preferably, the scrap is introduced into the feedstock in the form of shredded scrap, and / or turnings defined according to EN 12258-3, and / or in the form of a bowl. Figures

[0020] Fig. 1 illustrates the Rp0j2 - KQ compromise based on the data from Example 1. Detailed description of the invention

[0021] All aluminium alloys mentioned below are designated according to the rules and designations defined by The Aluminium Association in Registration Record Series which it publishes regularly, unless otherwise stated.

[0022] The metallurgical states referred to are designated according to the European standard EN-515 (1993) unless otherwise stated.

[0023] All alloy compositions are provided as % by weight (weight %).

[0024] Unless otherwise specified, the static mechanical properties, in other words the tensile strength Rm, the tensile yield strength Rp0>2, and the elongation at break A%, are determined by a tensile test according to EN 10002-1 or NF EN ISO 6892-1. The location and orientation of the parts are defined by EN 485-1. The stress intensity factor (Kq) is determined according to ASTM E 399-23. ASTM E 399 provides the criteria for determining whether Kq is a valid value of Kic. For a given specimen geometry, KQ values ​​obtained for different materials are comparable provided that the yield strengths of the materials are of the same order of magnitude.

[0025] Unless otherwise specified, the definitions in standard EN 12258 (2012) apply.

[0026] The applicant realized that it is possible to propose a 7XXX alloy that can be obtained from a mixture of products for recycling into alloys of the 7XXX series and the 2XXX series.

[0027] According to the invention, the 7XXX series aluminium alloy comprises in weight percentage (weight %) Zn: 5.0 - 7.0; Mg: 1.3 - 2.0; Cu: 2.0 - 3.0; Mn: 0.1 - 0.3; at least one of the elements selected from Cr, Zr where the content of Cr is from 0.01 to 0.15 and the content of Zr is from 0.08 to 0.15; Ti: 0 - 0.15; Fe: 0 - 0.2; Si: 0 - 0.1; impurities < 0.05 each and < 0.15 total and the remainder aluminium.

[0028] The Zn content is from 5.0 to 7.0% by weight. In one embodiment, the Zn mass content is at least approximately 5.0%, and at most approximately 6.5%, or at most approximately 6.75%, or at most approximately 7.0%. In another embodiment, the Zn mass content is at least approximately 6.0%, and at most approximately 6.25%, or at most approximately 6.5%, or at most approximately 6.75%, or at most approximately 7.0%.

[0029] The Mg content is from 1.3 to 2.0% by weight. In one embodiment, the Mg content by mass is at least approximately 1.3%, and at most approximately 1.6%, 1.7%, 1.8%, or 1.9%. In another embodiment, the Mg content by mass is at least approximately 1.4%, and at most approximately 1.6%, 1.7%, 1.8%, or 1.9%. In another embodiment, the Mg content by mass is at least approximately 1.5%, and at most approximately 1.7%, 1.8%, 1.9%, or 2.0%.

[0030] The Cu content is from 2.0 to 3.0 by weight. In one embodiment, the Cu mass content is at least approximately 2.1%, and at most approximately 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3.0%. In one embodiment, the Cu mass content is at least approximately 2.2%, and at most approximately 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, or 3.0%.

[0031] The 7XXX aluminum alloy according to the invention simultaneously comprises the presence of Mn and the presence of Zr and / or Cr. Each of these elements allows the formation of dispersoids that are particularly useful for controlling the grain size of the final product. The dispersoids are small precipitates, with a typical average size of 0.05 to 0.3 µm. The dispersoids contribute to controlling recrystallization that can occur during manufacturing. The simultaneous presence of Mn and Zr and / or Cr proves particularly advantageous in offering such a composition because it provides greater tolerance to waste mixtures composed of 7XXX series alloys and 2XXX series alloys. In particular, in the case where the waste mixture includes a 2XXX alloy containing Mn, for example a 2X24 type alloy because this alloy contains Mn.

[0032] Most of the 7XXX series alloys registered by the Aluminium Association for applications where a compromise between static strength and toughness is required contain a single element of the type Mn, Cr, or Zr in a minimum quantity. A minimum quantity indicates that the presence of this element is mandatory. This is the case, for example, with alloys AA7050, AA7040, and AA7010, which contain Zr, or alloys AA7060, AA7X75, and AA7349, which contain Cr. It should be noted that only alloys AA7005 and AA7020 have a composition that includes the mandatory presence of Mn, Cr, and Zr. These alloys, however, differ from the invention by a very low Cu content, which limits the yield strength, preventing a sufficient compromise between static strength and toughness for an aeronautical structural application.

[0033] Preferably, the 7XXX aluminum alloy according to the invention simultaneously comprises the presence of Mn, Cr and Zr.

[0034] The alloy according to the invention is particularly advantageous to produce from recycled products of the 7XXX and 2XXX series alloys if the 7XXX alloy waste contains more than 0.10% chromium by weight of chromium, and / or if the 7XXX alloy waste contains more than 0.05% zirconium by weight of zirconium. Advantageously, the 7XXX alloy waste containing chromium includes AA7X49, AA7060, AA7064, AA7X75, or AA7X78 alloy waste. Advantageously, the 7XXX alloy waste containing zirconium includes AA7010, AA7X40, AA7X50, AA7X55, AA7056, AA7160, AA7065, AA7X81, and AA7X85 alloy waste. Advantageously, 2XXX alloy waste includes AA2X24 type alloy waste. AA2X24 type alloys are AA2024, AA2024A, AA2124, AA2224, AA2224A, AA2324, AA2424, AA2524, AA2624, AA2724, AA2824.

[0035] The Mn content is from 0.1 to 0.3% by weight. Preferably, the Mn content is from 0.10 to 0.30% by weight. In one embodiment, the Mn mass content is at least approximately 0.10%, and at most approximately 0.20%, or at most approximately 0.22%, or at most approximately 0.24%, or at most approximately 0.26%, or at most approximately 0.28%, or at most approximately 0.30%. In another embodiment, the Mn mass content is at least approximately 0.14%, and at most approximately 0.20%, or at most approximately 0.22%, or at most approximately 0.24%, or at most approximately 0.26%, or at most approximately 0.28%, or at most approximately 0.30%. In one embodiment, the mass content of Mn is at least approximately 0.16%, and at most approximately 0.20%, or at most approximately 0.22%, or at most approximately 0.24%, or at most approximately 0.26%, or at most approximately 0.28%, or at most approximately 0.30%. In one embodiment, the mass content of Mn is at least approximately 0.18%, and at most approximately 0.20%, or at most approximately 0.22%, or at most approximately 0.18%. plus approximately 0.24% or at most approximately 0.26% or at most approximately 0.28% or at most approximately 0.30%.

[0036] The Zr content is preferably from 0.08 to 0.15% by weight. Preferably, the Zr content is from 0.09 to 0.12% by weight. In one embodiment, the Zr mass content is at least approximately 0.08%, and at most approximately 0.12% or at most approximately 0.14%. In another embodiment, the Zr mass content is at least approximately 0.10%, and at most approximately 0.12% or at most approximately 0.14%.

[0037] The Cr content is preferably from 0.01 to 0.15% by weight. Preferably, the Cr content is from 0.05 to 0.15% by weight, preferably from 0.06 to 0.15% by weight. In one embodiment, the Cr content by mass is at least approximately 0.01%, and at most approximately 0.03%, or at most approximately 0.05%, or at most approximately 0.07%, or at most approximately 0.08%, or at most approximately 0.11%, or at most approximately 0.13%, or at most approximately 0.15%. In one embodiment, the Cr content by mass is at least approximately 0.05%, and at most approximately 0.07%, or at most approximately 0.09%, or at most approximately 0.11%, or at most approximately 0.13%, or at most approximately 0.15%. In one embodiment, the mass content of Cr is at least approximately 0.06%, and at most approximately 0.09%, or at most approximately 0.11%, or at most approximately 0.13%, or at most approximately 0.15%. In another embodiment, the mass content of Cr is at least approximately 0.08%, and at most approximately 0.11%, or at most approximately 0.13%, or at most approximately 0.15%.In one embodiment, the mass content of Cr is at least about 0.10%, and at most about 0.13% or at most about 0.15%.

[0038] The Ti content is from 0 to 0.15% by weight. In one embodiment, the Ti mass content is at least approximately 0.02%, and at most approximately 0.08%, or at most approximately 0.10%, or at most approximately 0.13%, or at most approximately 0.15%. In another embodiment, the Ti mass content is at least approximately 0.025%, and at most approximately 0.08%, or at most approximately 0.10%, or at most approximately 0.13%, or at most approximately 0.15%.

[0039] It is preferable to limit the content of unavoidable impurities in the alloy so as to achieve the most favorable damage tolerance properties. Unavoidable impurities include iron and silicon, with a content of 0.2% or less by weight for iron and 0.1% or less by weight for silicon. Preferably, the iron content is 0.20%, 0.15%, 0.12%, 0.10%, or 0.08% or less by weight. In a preferred embodiment of the invention, the iron content is 0.05 to 0.20%, 0.05 to 0.15%, 0.05 to 0.12%, 0.05 to 0.10%, or 0.03 to 0.15%. In a preferred embodiment according to the invention, the silicon content is 0 to 0.10% or 0 to 0.08% or 0.03 to 0.10% or 0.03 to 0.08% or 0.04 to 0.08%.

[0040] The other elements considered as impurities have a content less than or equal to 0.05% by weight each and 0.15% by weight in total. The remainder is aluminum.

[0041] According to a preferred mode, the 7XXX series aluminum alloy comprises in weight percentage (weight %) Zn: 5.0 - 7.0; Mg: 1.3 - 2.0; Cu: 2.0 - 3.0; Mn: 0.1 - 0.3; Cr: 0.01 - 0.15; Zr: 0.08 - 0.15; Ti: 0 - 0.15; Fe: 0 - 0.2; Si: 0 - 0.1; Impurities < 0.05 each and < 0.15 total and the remainder aluminum.

[0042] The aluminum alloy according to the invention has the advantage of being able to be produced from a mixture of waste alloys of the 7XXX series and the 2XXX series, preferably without having to add a significant amount of primary aluminum metal.

[0043] The aluminum alloy according to the invention is used to manufacture wrought products. Preferably, the wrought products are manufactured according to a well-known process comprising a step of preparing a charge consisting of aluminum alloys in solid and optionally liquid form, a step of melting the charge and then processing to obtain a bath of liquid metal having a composition according to the invention, a step of pouring the bath of liquid metal and solidifying a rough shape, a homogenization step, an optional reheating step, a hot forming step, optionally a cold forming step, a solution heating step, a quenching step, a stress-relieving step, and an artificial aging step.

[0044] The molten metal bath is produced from a feedstock. The ingredients introduced into the furnace to produce the molten metal bath are called the "feedstock." The feedstock thus corresponds to the constituent ingredients used to produce the aluminum alloy. Examples of these ingredients include alloy scrap, alloying elements, and primary aluminum metal. The ingredients may be in solid or liquid form (for example, residual molten metal from a previous casting remaining in the furnace). Alloying elements are intentionally added. "Primary aluminum metal" is defined as unalloyed aluminum with an aluminum content of at least 99.60% by weight.

[0045] The industrial practice of processing plants generally consists of manufacturing products from a specific alloy using primary aluminum metal that has been alloyed to the required grade by adding specific alloying elements, and / or from large scraps and chips of the specific alloy to be cast, originating from the plant's own production, such as slab peel flakes or rolling rejects. This industrial practice ensures a high degree of control over the specific alloys, which helps to avoid, in particular, random variations in the composition of the products obtained.

[0046] The inventors found that, thanks to the composition of the aluminum alloy according to the invention, which simultaneously contains manganese (Mn) and at least one element from chromium (Cr) and zinc (Zr), it was no longer necessary to use scrap metal corresponding to the alloy to be cast, and that it was possible to use in the feedstock a mixture of 2XXX alloy scrap and 7XXX alloy scrap. In particular, they were able to determine that the feedstock used to cast the alloy according to the invention can contain at least 10% by weight of 2XXX alloy scrap and at least 20% by weight of 7XXX alloy scrap. Preferably, the mixture of 2XXX alloy waste and 7XXX alloy waste comprises at least 15% by weight of 2XXX alloy waste, or 20% by weight of 2XXX alloy waste, or 25% by weight of 2XXX alloy waste, or 30% by weight of 2XXX alloy waste.Preferably, the mixture of 2XXX alloy waste and 7XXX alloy waste comprises at least 25% by weight of 7XXX alloy waste, or at least 30% by weight of 7XXX alloy waste, or even at least 40% by weight of 7XXX alloy waste.

[0047] In a preferred embodiment, the filler comprises 10% to 40%, preferably 15% to 40% by weight, of 2XXX alloy scrap, preferably further 20% to 40%, or 25% to 40%, or 30% to 40%. According to a preferred embodiment, the 2XXX alloy scrap is AA2X24 alloy scrap. AA2X24 alloy scrap comprises scrap of AA2024, AA2024A, AA2124, AA2224, AA2224A, AA2324, AA2424, AA2524, AA2624, AA2724, AA2824 alloys, or a combination thereof.

[0048] In a preferred embodiment, the feed comprises 7XXX alloy scrap from 20% to 80% by weight. In one embodiment, the feed comprises 7XXX alloy scrap in % by weight of at least approximately 20%, and at most approximately 30%, or at most approximately 40%, or at most approximately 50%, or at most approximately 60%, or at most approximately 70%, or at most approximately 80%. In another embodiment, the feed comprises 7XXX alloy scrap in % by weight of at least approximately 40%, and at most approximately 60%, or at most approximately 70%, or at most approximately 80%.

[0049] Preferably, the 7XXX alloy waste comprises 7XXX alloy waste containing Cr in a content greater than 0.10 wt%, and 7XXX alloy waste containing Zr in a content greater than 0.05 wt%. This mixture is particularly advantageous when the alloy according to the invention simultaneously contains Mn, Cr, and Zr. Examples of 7XXX alloys containing Cr in a content greater than 0.10% include AA7049, AA7349, AA7060, AA7064, AA7X75, and AA7X78. Examples of alloys containing Zr in a content greater than 0.05% include AA7010, AA7X40, AA7X50, AA7X55, AA7056, AA7160, AA7065, AA7X81, and AA7X85.

[0050] The waste from both 7XXX and 2XXX alloys used to make the charge can be in the form of shredded scrap and / or turnings and / or in the form of a boll and / or in liquid form. Shredded scrap, as defined by EN 12258-3, refers to offcuts or trimmings from sheet metal resulting from cutting, shearing, or other similar operations. Turnings, as defined by EN 12258-3, refer to grains, chips, or shavings produced by machining or other operations. In another embodiment, the waste can originate from the recycling of aeronautical structures. The waste can be in divided and / or compacted form. A boll is a remelting ingot, preferably in monolithic form.According to the invention, waste from both 7XXX and 2XXX alloys in the form of shredded scrap and / or turnings can be remelted into bowls; it may optionally have undergone certain metallurgical treatments aimed at rectifying the composition and / or removing certain metallic and non-metallic impurities. The waste can also be pre-introduced into a rotary furnace for remelting, then cast into bowls. The bowls are then used to constitute the feedstock. Another envisaged embodiment is to use the molten metal in the rotary furnace without solidifying it, and introduce it directly into the furnace feeding the casting.

[0051] Once the charge has been prepared, it is then melted, and the alloy is produced. During the production of alloying elements, in particular alloying elements containing Zn or any other necessary elements such as Cu, Mg, Mn, Cr, Zr may be added.

[0052] Preferably, during processing, less than 30% primary aluminum metal, and preferably less than 20% primary aluminum metal, is added. The primary aluminum metal is unalloyed aluminum with an aluminum content of at least 99.60% by weight. This primary aluminum metal is generally obtained by electrolysis. It may be designated P0406, P0610, or P1020 according to the rules and designations defined by The Aluminum Association in “International Designations and Chemical Composition Limits for Unalloyed Aluminum” (revised January 2018).

[0053] The possibility of using unsorted 7XXX and 2XXX alloy waste, along with a low proportion of primary aluminum metal, makes the process economically attractive. This process reduces the amount of CO2 equivalent emitted per ton of product manufactured due to the high recycling rate and the low use of primary aluminum metal.

[0054] The step of solidifying a bath of liquid metal into a rough form is preferably carried out by vertical semi-continuous casting (direct chill casting or DC casting according to Anglo-Saxon terminology). Said rough form can be a plate or a billet.

[0055] The raw form is then homogenized at a homogenization temperature of 440 to 520 °C, preferably above 460 °C, followed by cooling either to a hot forging start temperature of 380 to 460 °C, or to a temperature below the hot forging start temperature. In the latter case, the homogenized plate is reheated to reach a hot forging start temperature of 380 to 460 °C.

[0056] This homogenized rough form is hot-forged, optionally cold-forged, to obtain a wrought product. This wrought product may be a rolled product, an extruded product, or a forged product. The forged product may be obtained directly by forging a forging blank or from the rolled product (for example, first rolled and then forged), or from the extruded product (for example, first extruded and then forged). In one embodiment, the homogenized rough form is a homogenized plate that is hot-rolled to obtain a rolled product. In one embodiment, the homogenized plate is hot-rolled, optionally cold-rolled, to obtain a rolled product with a final thickness of at least 6 mm, preferably from about 25 mm to about 100 mm.Hot rolling is preferably carried out in one or more stages with an inlet temperature preferably between about 380 °C and about 460 °C and preferably between about 400 °C and about 450 °C.

[0057] The wrought product is dissolved and quenched in a liquid at ambient temperature. The dissolution temperature is preferably from 460 °C to 520 °C, and more preferably from 460 °C to 490 °C. The dissolution time is at least 15 minutes, typically from 30 minutes to 2 hours. The wrought product is then stress-relieved. Stress-relieving can be carried out by tension with a plastic deformation of 1% to 7%.

[0058] The mechanical properties of the final product can be controlled by various artificial aging conditions depending on the intended use. The aluminum alloy product described herein can be delivered to customers in a Tx state, for example, a T6 state or a T7 state. The artificial aging step, also called tempering, allows the product to reach a yield strength level Rpo.2 and optimizes other desirable alloy properties, such as toughness or corrosion resistance. The artificial aging step can be carried out at a suitable temperature, for example, from approximately 100 °C to approximately 200 °C. The artificial aging step can be carried out in one or more stages. Typically, a first stage at approximately 120 °C, followed by a stage at a temperature of 150 °C to 180 °C. The duration of each stage typically varies from 2 to 20 hours. Examples

[0059] Example 1

[0060] Two ingots were cast according to two compositions A and B (Table 1) with dimensions 1330 mm x 200 mm x 80 mm. Alloy A corresponds to a typical reference composition of an AA7050 alloy. Alloy B corresponds to a composition according to the invention.

[0061] [Table 1] - Composition by weight % Si% Fe % Cu % Mn% Mg % Cr % Zn % Ti % Zr % A 0.06 0.08 2.1 <0.04 2.1 <0.05 6.2 0.03 0.10 B 0.06 0.08 2.3 0.20 1.6 0.11 6.9 0.03 0.11

[0062] Alloy B can be obtained according to the preferred process of the invention. A waste mixture comprising 7XXX and 2XXX alloys is used in the feedstock. The mixture in question originates from a recycling loop from machining companies serving the aerospace industry. The waste is in the form of turnings, in divided format. Before being used to produce the alloy, a portion of the mixture was remelted in order to analyze its average composition. This is shown in Table 2. Based on the respective alloying element contents, the inventors believe that this waste consists of AA7050, AA7075, and AA2024 alloys in a weight proportion of approximately 30% AA7050, 30% AA7075, and 40% AA2024. We therefore have a waste mixture consisting of approximately 60% by weight of 7XXX waste and 40% by weight of the 2XXX waste mixture. To produce alloy B, approximately 22% of primary aluminum metal of type P0406, containing a minimum of 99%.85% aluminum was added along with Cr, Zr and Zn alloying elements to obtain the composition of alloy B. Thus, the filler used to obtain alloy B comprises approximately 22% primary aluminum metal, 47% 7XXX alloy scrap and 31% 2XXX alloy.

[0063] By way of comparison, the constituent filler of alloy A can be obtained from the same waste mixture as that used for alloy B. However, to obtain alloy A, it is necessary to dilute it by adding 65% primary aluminum metal of type P0406. Thus, the filler used to obtain alloy A comprises approximately 85% primary aluminum metal, 6% 7XXX alloy waste, and 9% 2XXX alloy. In addition, alloying elements of Zr, Cu, Mg, and Zn were added to obtain the composition of alloy A. Due to this significant addition of primary aluminum metal, the use of unsorted 2XXX-7XXX waste is not advantageous for manufacturing an alloy such as alloy AA7050, unlike the alloy according to the invention, which allows for this.

[0064] [Table 2] - Composition by weight % Si % Fe % Cu % Mn % Mg % Cr % Zn % Ti % Zr % Waste mixture 7X XX-2XXX 0.08 0.10 3.0 0.3 2.1 0.07 3.5 0.04 0.03

[0065] The ingots were then homogenized for approximately 24 hours at 480 °C, and subsequently machined into parallelepiped shapes measuring 500 mm x 180 mm x 60 mm before being hot-rolled. The machined ingots were reheated to an approximate temperature of 430 °C and then hot-rolled in the casting direction to a final thickness of 20 mm. The rolled sheets were then solution-treated at 480 °C for 1 hour, quenched in water at ambient temperature, and then subjected to tensile stress with a permanent deformation of approximately 2%. Each sheet was then tempered. In the case of alloy B, part of the sheet underwent a two-step tempering process of 6 h at 120 °C + 10 h at 165 °C and another part underwent a two-step tempering process of 6 h at 120 °C + 15 h at 165 °C. The sheets thus treated were then tested to measure the yield strength, tensile strength, elongation and toughness (Table 3).Tensile test specimens were taken at mid-thickness in the TL orientation relative to the rolling / casting direction. Toughness test specimens were also taken at mid-thickness and tested in the TL direction. The toughness test specimens used were CT10 specimens (thickness B = 10 mm, width W = 24 mm according to the nomenclature of ASTM E399).

[0066] [Table 2] - Mechanical properties Ref Income Rp0.2 Rm A% Kq MPa Mpa % (MPa.'Vm) TL TL TL TL A 6h-120°C + 20h-165°C 457 528 13.2 29.4 B 6h-120°C + 10h-165°C 480 539 12.1 33.1 6h-120°C + 15h-165°C 445 515 12.2 35.0

[0067] It is observed that the sheets produced according to the composition of the invention present a better compromise Rpo.2 (TL) - Kq (TL) than the reference sheet.

Claims

Demands

1. Aluminium alloy 7xxx comprising in % by weight Zn: 5.0 - 7.0 Mg: 1.3-2.0 Cu: 2.0 - 3.0 Mn: 0.1-0.3 at least one element selected from Cr, Zr where the content of Cr is from 0.01 to 0.15 and the content of Zr is from 0.08 to 0.15 Ti: 0-0.15 Fe: 0 - 0.2 Si: 0-0.1 Other impurities < 0.05 each and < 0.15 total and the remainder aluminium.

2. Aluminium alloy 7xxx according to claim 1 comprising in % by weight Zn: 5.0 - 7.0 Mg: 1.3-2.0 Cu: 2.0 - 3.0 Mn: 0.1-0.3 Cr: 0.01 -0.15 Zr: 0.08-0.15 Ti: 0-0.15 Fe: 0 - 0.2 Si: 0-0.1 Impurities < 0.05 each and < 0.15 total and the remainder aluminium.

3. Aluminium alloy 7xxx according to claim 1 or 2 wherein the Cu content is 2.1 to 2.8% by weight, preferably 2.2 to 2.5% by weight.

4. Aluminium alloy 7xxx according to claim 1 to 3 wherein the Mg content is 1.4 to 1.8 wt%, preferably 1.5 to 1.7 wt%.

5. Aluminium alloy 7xxx according to any one of claims 1 to 4 wherein the Mn content is from 0.10 to 0.30 wt%.

6. Aluminium alloy 7xxx according to any one of claims 1 to 5 wherein the Cr content is from 0.05 to 0.15% by weight, preferably from 0.06 to 0.15% by weight.

7. A method for manufacturing a wrought product of aluminum alloy 7xxx comprising a step of preparing a feed, a step of melting the feed and then processing to obtain a liquid metal bath having a composition according to any one of claims 1 to 6, a step of pouring the liquid metal bath and solidifying a rough form, a step of homogenizing the rough form, an optional reheating step, a hot wringing step of the homogenized rough form, an optional cold wringing step of the hot wrought product, a solution treatment step, a quenching step, a stress-relieving step, and an artificial aging step, characterized in that the feed used to constitute the liquid metal bath comprises at least 10% by weight of 2XXX alloy scrap and at least 20% by weight of 7XXX alloy scrap, preferably from 15% to 40% by weight of 2XXX alloy scrap.

8. A manufacturing process according to claim 7 characterized in that the 2XXX alloy waste comprises AA2X24 alloy waste.

9. A method of manufacturing a product according to claim 7 or 8 characterized in that during the preparation of the liquid metal bath less than 30% of primary aluminum metal is added, wherein the primary aluminum metal is unalloyed aluminum with an aluminum content of at least 99.60% by weight.

10. A manufacturing process according to any one of claims 7 to 9 characterized in that the 7XXX alloy waste comprises 7XXX alloy waste comprising Cr in a content greater than 0.10% by weight, and / or 7XXX alloy waste comprising Zr in a content greater than 0.05% by weight.

11. A manufacturing process according to any one of claims 6 to 9 characterized in that the waste is introduced into the feed in the form of shredded scrap and / or turnings defined according to standard EN 12258-3 and / or in the form of a bowl and / or in liquid form.

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