7xxx aluminum alloy for recycling and manufacturing method

Abstract

A 7XXX series aluminum alloy suitable for recycling comprising, in % by weight, Zn: 5.0 - 7.0; Mg: 1.3 - 1.9; Cu: 2.2 - 2.5; Mn: 0.1 - 0.3; at least one element chosen from Cr and 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 in total, and the remainder being aluminum. This alloy can be used to manufacture a wrought product, the manufacturing method of which uses mixed 2XXX and 7XXX alloy scrap, comprising at least 10% by weight of 2XXX alloy scrap and at least 20% by weight of 7XXX alloy scrap.

Description

[0001] DESCRIPTION

[0002] Title: Recycling of 7XXX Aluminum Alloy and Manufacturing Process

[0003] technical field

[0004] 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.

[0005] Previous art

[0006] 7XXX series aluminum alloys are commonly used as wrought products for industrial applications such as transportation. These alloys offer the advantage of high mechanical properties and high toughness, which allows for a reduction in structural weight and thus lowers fuel consumption and greenhouse gas emissions.

[0007] Today, it is necessary to reduce greenhouse gas emissions during the production of these alloys. This reduction can be achieved by recycling aluminum alloy scraps and waste, thereby decreasing or even eliminating the use of primary aluminum produced by electrolysis and / or the addition of alloying elements.

[0008] Primary aluminum is produced by electrolysis. The best electrolysis plants, which use hydroelectric power, 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 made solely from scrap and waste is 0.5 tonnes of CO2 eq per plate. When a plate is produced using partially recycled materials, the mass of CO2 equivalent emitted can be estimated by linear interpolation between a plate produced using the aforementioned electrolysis process (0% recycling) and a plate made solely from 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 additive elements.

[0009] The aluminum industry strives to recycle its manufactured products in a closed loop whenever possible; that is, aluminum alloy scrap and waste are recycled to obtain the same alloy for which they were produced. This closed loop is integrated into the recycling loop for waste generated by manufacturers of aluminum products (or "pre-consumer scrap" in 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 final product manufacturing stages, where efforts are made to sort machining chips by alloy series, or even by alloy grade.It is also conceivable 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 aeronautics sector, where the industry seeks to recycle end-of-life aircraft.

[0010] In most aircraft, aluminum alloys account for up to 80% of the materials used. Aluminum alloys are particularly prevalent 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 typically consists of a 2XXX alloy skin and 7XXX alloy stiffeners. An aircraft wing generally comprises a 7XXX alloy upper skin, a 2XXX alloy lower skin, stiffeners that can be 7XXX and 2XXX alloys, and internal structural components (spars, ribs, etc.) generally made of 7XXX alloys.

[0011] The 2XXX series alloys are primarily used when damage tolerance and fracture strength are critical characteristics. LAA2024 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.

[0012] 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. UAA7075-T6 has been used since the 1940s due to its relatively high specific strength. However, this alloy's susceptibility to corrosion has led to its replacement by newer 7XXX series alloys in many applications. For example, TAA7475 has a higher yield strength and a better combination of corrosion resistance and toughness, making it an ideal replacement for TAA7075. Another high-performance alloy, TAA7050, is used, for example, in fuselage frames or for manufacturing wing skins.

[0013] Existing research aims to sort the components of aircraft structures made of 2XXX and 7XXX aluminum alloys in order 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 Laser-Induced Breakdown Spectroscopy (LIBS) technology. The sorting system includes 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.

[0014] EP1101830 discloses a process for manufacturing an intermediate product, such as a plate, billet or forging block, of 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. EP1101830 enables the recycling of machining scrap and chips into alloys of the 7XXX series.EP1101830 plans to use recycling products in 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%.

[0015] Therefore, there is 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.

[0016] Description of the invention

[0017] 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 be advantageous, for example, in the case of machining chips that may be tangled and difficult to separate. Even if they could be separated, the small size of the chips would reduce the efficiency and productivity of the sorting process.

[0018] A first object of the invention relates to an aluminum alloy 7xxx comprising in % by weight

[0019] Zn: 5.0 - 7.0, preferably 6.5 to 7.0

[0020] Mg: 1.3 - 1.9

[0021] Cu: 2.2 - 2.5

[0022] Mn: 0.1 - 0.3 at least one element chosen from Cr, Zr where the Cr content is 0.01 to 0.15 and the Zr content is 0.08 to 0.15, Ti: 0 - 0.15 Fe: 0 - 0.2

[0023] If: 0 - 0.1

[0024] Impurities < 0.05 each and < 0.15 total and the remainder aluminum.

[0025] This alloy is particularly interesting because it allows for a wrought product with a good static-toughness compromise, while also being able to be manufactured from mixed waste of 2XXX and 7XXX alloys.

[0026] Preferably, the aluminum alloy comprises the following percentages by weight.

[0027] Zn: 5.0 - 7.0, preferably 6.5 to 7.0

[0028] Mg: 1.3 - 1.9

[0029] Cu: 2.2 - 2.5

[0030] Mn: 0.1 - 0.3

[0031] Cr: 0.01 - 0.15

[0032] Zr: 0.08 - 0.15

[0033] Ti: 0 - 0.15

[0034] Fe: 0 - 0.2

[0035] If: 0 - 0.1

[0036] Impurities < 0.05 each and < 0.15 total and the remainder aluminum.

[0037] Preferably, the Cu content is 2.2 to 2.4% by weight, preferably 2.2 to 2.3% 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.

[0038] Another object of the invention relates to a process for manufacturing a wrought product in aluminum alloy 7xxx. The manufacturing process includes 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 solidifying a rough form, a step of homogenizing the rough form, an optional reheating step, a step of hot wringing the homogenized rough form, an optional cold wringing step of the hot wrought product, a solution heating step, a quenching step, a stress-relieving step, and an artificial aging step.

[0039] 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 waste and at least 20% by weight of 7XXX alloy waste, preferably 15% to 40% by weight of 2XXX alloy waste, preferably 20% to 40%.

[0040] Preferably, the 2XXX alloy scrap includes AA2X24 alloy scrap. Preferably, less than 30% primary aluminum metal is added during the preparation of the liquid metal bath. 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% zinc by weight of chromium. Preferably, the scrap is introduced into the feedstock as shredded scrap, and / or turnings defined according to EN 12258-3, and / or in bowl form.

[0041] Figures

[0042] Figure 1 illustrates the R compromise p o,2 - KQ according to the data from example 1.

[0043] Detailed description of the invention

[0044] All aluminum alloys mentioned below are designated according to the rules and designations defined by The Aluminum Association in the Registration Record Series that it publishes regularly, unless otherwise stated.

[0045] The metallurgical states referred to are designated according to the European standard EN-515 (1993) unless otherwise stated.

[0046] All alloy compositions are provided as % by weight (weight %).

[0047] Unless otherwise stated, the static mechanical characteristics, in other words the breaking strength R m , the tensile yield strength R pThe 0.2 and 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 for K-ic. 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.

[0048] Unless otherwise stated, the definitions in standard EN 12258 (2012) apply.

[0049] The applicant realized that it is possible to offer a 7XXX alloy that can be obtained from a mixture of products for recycling into 7XXX series and 2XXX series alloys.

[0050] According to the invention, the 7XXX series aluminum alloy comprises, in weight percentages (weight %), Zn: 5.0 - 7.0; Mg: 1.3 - 1.9; Cu: 2.2 - 2.3; 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 aluminum.

[0051] The zinc content is 5.0 to 7.0% by weight. In one embodiment, the zinc content by weight is at least approximately 5.0% to obtain sufficient strength, and at most approximately 6.5% or at most approximately 6.75%. In one embodiment, the zinc content by weight is at least approximately 6.0% to obtain sufficient strength, and at most approximately 6.25%, 6.5%, 6.75%, or 7.0% to obtain the best compromise in terms of toughness and elongation. In one embodiment, the zinc content by weight is at least

[0052] 6.5%, and at most 6.75% or at most 7.0% in order to obtain the best compromise in terms of yield strength and toughness.

[0053] The Mg content is 1.3 to 1.9% by weight. In one embodiment, the Mg content by weight is at least approximately 1.3% to obtain sufficient strength, and at most approximately 1.6%, 1.7%, or 1.8%. In another embodiment, the Mg content by weight is at least approximately 1.4%, and at most approximately

[0054] 1.6% or at most approximately 1.7% or at most approximately 1.8% or at most approximately 1.9% in order to obtain the best compromise in terms of toughness and elongation. In one embodiment, the Mg content by weight is at least approximately 1.5%, and at most approximately

[0055] 1.7% or at most about 1.8% or at most about 1.9% in order to obtain the best compromise in terms of yield strength and toughness.

[0056] The Cu content is 2.2 to 2.5 by weight. In one embodiment, the Cu mass content is at least about 2.2% to obtain sufficient strength and at most about 2.4% or at most about 2.3% to limit susceptibility to hardening.

[0057] 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. They form during homogenization. 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 scrap mixtures composed of 7XXX series alloys and 2XXX series alloys. In particular, this is especially true when the scrap mixture includes a 2XXX alloy containing Mn, for example, a 2X24 type alloy, as this alloy contains Mn.

[0058] Most of the 7XXX series alloys registered by the Aluminum 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 aeronautical structural applications.

[0059] Preferably, the 7XXX aluminum alloy according to the invention simultaneously comprises the presence of Mn, Cr and Zr.

[0060] 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 (Cr), and / or if the 7XXX alloy waste contains more than 0.05% chromium by weight of zinc (Zr). Advantageously, the 7XXX alloy waste containing Cr includes AA7X49, AA7060, AA7064, AA7X75, or AA7X78 alloy waste. Advantageously, the 7XXX alloy waste containing Zr includes AA7010, AA7X40, AA7X50, AA7X55, AA7056, AA7160, AA7065, AA7X81, and AA7X85 alloy waste. Advantageously, the 2XXX alloy waste includes AA2X24 alloy waste. AA2X24 type alloys are AA2024, AA2024A, AA2124, AA2224, AA2224A, AA2324, AA2424, AA2524, AA2624, AA2724, AA2824.

[0061] The Mn content is 0.1 to 0.3% by weight. Preferably, the Mn content is 0.10 to 0.30% by weight. In one embodiment, the Mn content by weight is at least approximately 0.10%, and at most approximately 0.20%, 0.22%, 0.24%, 0.26%, 0.28%, or 0.30%. In another embodiment, the Mn content by weight is at least approximately 0.14%, and at most approximately 0.20%, 0.22%, 0.24%, 0.26%, 0.28%, or 0.30%. In one embodiment, the weight content of Mn is at least about 0.16%, and at most about 0.20% or at most about 0.22% or at most about 0.24% or at most about 0.26% or at most about 0.28% or at most about 0.30%.In one embodiment, the weight content of Mn is at least about 0.18%, and at most about 0.20% or at most about 0.22% or at most about 0.24% or at most about 0.26% or at most about 0.28% or at most about 0.30%.

[0062] 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 content by weight is at least approximately 0.08%, and at most approximately 0.12% or at most approximately 0.14%. In another embodiment, the Zr content by weight is at least approximately 0.10%, and at most approximately 0.12% or at most approximately 0.14%.

[0063] 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 weight 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 weight 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 weight 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 weight 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 weight content of Cr is at least about 0.10%, and at most about 0.13% or at most about 0.15%.

[0064] The Ti content is from 0 to 0.15% by weight. Titanium is advantageously present at a content of at least approximately 0.02% by weight in order to control the grain size of the casting grain. In one embodiment, the Ti content by weight is therefore 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 content by weight 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%. In yet another embodiment, the Ti content by weight is at least 0.02%, or even 0.05%, and at most 0.15%, or at most 0.13%, or at most 0.10%.

[0065] It is preferable to limit the content of unavoidable impurities in the alloy 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%.

[0066] The other elements considered as impurities have a content of less than or equal to 0.05% by weight each and 0.15% by weight in total. The remainder is aluminum.

[0067] According to a preferred mode, the 7XXX series aluminum alloy comprises in weight percentage (weight %) Zn: 5.0 - 7.0; Mg: 1.3 - 1.9; Cu: 2.2-2.5; 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.

[0068] The aluminum alloy according to the invention has the advantage of being able to be produced from a mixture of scrap alloys from the 7XXX and 2XXX series, preferably without having to add a significant amount of primary aluminum metal. The aluminum alloy according to the invention is used to manufacture wrought products.Preferably, 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 it 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 it into a rough form, 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. The bath of liquid metal is produced from a charge. The ingredients introduced into the furnace used to produce the bath of liquid metal are called the "charge." The charge thus corresponds to the constituent ingredients used to produce the aluminum alloy.Ingredients include alloy scrap, alloying elements, and primary aluminum metal. These ingredients can be in solid or liquid form (for example, leftover molten metal from a previous casting remaining in the furnace). Alloying elements are intentionally added. Primary aluminum metal is unalloyed aluminum with an aluminum content of at least 99.60% by weight.

[0069] The industrial practice in processing plants generally consists of manufacturing products from specific alloys 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 plate trimmings 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 resulting products.

[0070] The inventors discovered 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 desired alloy and that it was possible to use a mixture of 2XXX alloy and 7XXX alloy scrap metal in the casting. In particular, they were able to determine that the casting material used for the alloy according to the invention can contain at least 10% by weight of 2XXX alloy scrap metal and at least 20% by weight of 7XXX alloy scrap metal. 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.

[0071] In a preferred embodiment, the charge comprises 10% to 40%, preferably 15% to 40% by weight, of 2XXX alloy scrap, preferably a 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.

[0072] In a preferred embodiment, the feed comprises 7XXX alloy scrap from 20% to 80% by weight. In another 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 yet 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%.

[0073] Preferably, the 7XXX alloy waste comprises 7XXX alloy waste containing Cr in a content exceeding 0.10 wt%, and 7XXX alloy waste containing Zr in a content exceeding 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 exceeding 0.10% include AA7049, AA7349, AA7060, AA7064, AA7X75, and AA7X78. Examples of alloys containing Zr in a content exceeding 0.05% include AA7010, AA7X40, AA7X50, AA7X55, AA7056, AA7160, AA7065, AA7X81, and AA7X85.

[0074] 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 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 to rectify the composition and / or remove certain metallic and non-metallic impurities. The waste can also be pre-introduced into a rotary furnace for remelting and 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.

[0075] Once the charge is prepared, it is then melted, and the alloy is produced. During production, alloying elements may be added, in particular, alloying elements containing zinc or any other necessary elements such as copper, magnesium, manganese, chromium, and zinc. Preferably, less than 30%, and preferably less than 20%, of primary aluminum metal is added during production. 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).

[0076] The ability to utilize 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.

[0077] The solidification of a molten metal bath into a rough form is preferably carried out by vertical semi-continuous casting (direct chill casting or DC casting, according to Anglo-Saxon terminology). This rough form can be a plate or a billet.

[0078] 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.

[0079] This homogenized rough form is hot-forged, optionally cold-forged, to obtain a wrought product. This wrought product can be a rolled product, an extruded product, or a forged product. The forged product can 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 another 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.

[0080] The wrought product is dissolved and quenched in a liquid at room temperature. The dissolution temperature is preferably between 460°C and 520°C, and more preferably between 460°C and 490°C. The dissolution time is at least 15 minutes, typically 30 minutes to 2 hours. The wrought product is then stress-relieved. Stress-relieving can be achieved by tensioning with a plastic deformation of 1% to 7%.

[0081] 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 here can be delivered to customers in a specific Tx state, for example, T6 or T7. The artificial aging process, also called tempering, allows the product to reach a specific yield strength (R). p o.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.

[0082] Examples

[0083] Example 1

[0084] Two ingots were cast according to two compositions A and B (Table 1), each measuring 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.

[0085] [Table 1] - Composition by weight %

[0086] 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 originates from a recycling loop of 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 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.

[0087] For 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. Furthermore, 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 practical for manufacturing an alloy such as AA7050, unlike the alloy according to the invention, which allows for this.

[0088] [Table 2] - Composition by weight %

[0089] The ingots were then homogenized for approximately 24 hours at 480°C, and subsequently machined into parallelepipeds measuring 500 mm x 180 mm x 60 mm before being hot-rolled. The machined ingots were reheated to approximately 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 room 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, breaking load, 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). [Table 3] - Mechanical properties.

[0090] It is observed that the sheets produced according to the composition of the invention offer a better compromise R p o.2 (TL) - KQ (TL) than the reference sheet metal.

Claims

DEMANDS 1. 7xxx aluminum alloy comprising in % by weight Zn: 5.0 - 7.0, preferably 6.5 to 7.0 Mg: 1.3-1.9 Cu: 2.2 - 2.5 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 Other impurities < 0.05 each and < 0.15 total and the remainder aluminum.

2. Aluminum alloy 7xxx according to claim 1 comprising in % by weight Zn: 5.0 - 7.0 Mg: 1.3 - 1.9 Cu: 2.2 - 2.5 Mn: 0.1 - 0.3 Cr: 0.01 -0.15 Zr: 0.08-0.15 Ti: 0-0.15 Fe: 0-0.2 If: 0-0.1 Impurities < 0.05 each and < 0.15 total and the remainder aluminum.

3. Aluminium alloy 7xxx according to claim 1 or 2 in which the Cu content is 2.2 to 2.4% by weight, preferably 2.2 to 2.3% by weight.

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

5. Aluminium alloy 7xxx according to any one of claims 1 to 4 in which the Mn content is from 0.10 to 0.30% by weight.

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 process 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 bath of liquid metal having a composition according to one of claims 1 to 6, a step of pouring the bath of liquid metal 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 bath of liquid metal 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. Manufacturing process according to claim 7 characterized in that the 2XXX alloy waste comprises AA2X24 alloy waste.

9. A method for 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. 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. 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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