Ultra high strength 6xxx alloys enabled by the suppression of natural ageing effect

Abstract

The invention concerns manufacturing process for obtaining extrusions made from a 6xxx aluminium alloy, comprising the following successive steps, casting a billet comprising, in weight %, Si 0.4 - 1.2, Mg 0.4 -1.0, Cu 0.02 - 1.1, Fe 0.15 - 0.55, Sn 0.04 - 0.15, Zn ≤ 0.50, V ≤ 0,20, Ti ≤ 0,20, one or more of Cr ≤ 0.25, Zr ≤ 0.20 and Mn ≤ 0.80, other elements < 0.05 each and < 0.15 total, rest aluminium ; homogenizing the billet ; re-heating the homogenized cast billet ; extruding said re-heated billet through a die ; quenching said extrusion down to room temperature ; applying a controlled cold deformation step ; natural ageing said extrusion during between 0.8h and 10h ; artificial ageing said naturally aged extrusion. The invention concerns also an extruded profile made from a 6xxx aluminium alloy comprising in weight %, Si 0.4 - 1.2, Mg 0.4 -1.0, Cu 0.02 - 1.1, Fe 0.15 - 0.55, Sn 0.04 - 0.15, Zn ≤ 0.50, V ≤ 0,20, Ti ≤ 0,20, one or more of Cr ≤ 0.25, Zr ≤ 0.20 and Mn ≤ 0.80, other elements < 0.05 each and < 0.15 total, rest aluminium and the use of such extruded profile as automotive component.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a 6XXX series aluminium extrusion alloy, particularly useful for the automotive industry.BACKGROUND OF THE INVENTION

[0002] Aluminium alloys are used in the form of extrusions for various applications including automotive usages. 6xxx extruded products are usually used after the steps of extrusion, solutioning and quenching and artificial ageing. However, between the end of cooling and artificial ageing, the extruded product is often stored a certain period of time, called period of natural ageing (NA) or floor ageing for manufacturing purposes. 6xxx alloys suffer from the "negative effect of natural ageing", that is, 6xxx alloys extruded products tend to lose their mechanical properties, measured after final ageing, very rapidly depending on the natural ageing applied. Depending on the duration of this period of natural ageing, it has a negative effect on the mechanical properties of the extruded products after artificial ageing.

[0003] The patent application CN116516218 discloses high-strength and floor ageing effect 6xxx aluminum alloy and a preparation method thereof. 6xxx aluminum alloy with high strength and floor ageing effect, is consisting of the following components in terms of mass percentage: Mg: 0.70-1.20%; Si: 0.80-1.30%; Cu: ≤0.50%; Mn: ≤0.60%; Cr: ≤0.30%; Zr: ≤0.20%; Sn: 0.05-0.20%; Fe: ≤0.35%; other unavoidable impurity elements, the rest is Al; and the Mg / Si ratio is 0.70-1.00.

[0004] The patent application CN113373331 discloses an aluminum alloy with low extrusion deformation resistance and sufficient strength of the finished product, which is suitable for the production of automobile battery tray products. The aluminium alloy has the following weight percentages: Si: 0.7%-0.8%, Fe: ≤0.15%, Cu: 0.03%-0.08%, Mn: 0.08%-0.13%, Mg: 0.6%-0.7 %, Cr: ≤0.05%, Zn: ≤0.05%, Sn: 0.05%-0.10%, Ti: ≤0.03%, single impurity ≤0.05%, total impurities ≤0.15%, the balance is Al.

[0005] The patent application EP3390678 discloses a new high strength 6xxx aluminum alloys and methods of manufacturing these alloys. These 6xxx alloys have the following composition: 0.001 - 0.25 wt. % Cr, 0.4 - 2.0 wt. % Cu, 0.10 - 0.30 wt. % Fe, 0.5 - 2.0 wt. % Mg, 0.005 - 0.40 wt. % Mn, 0.5 - 1.5 wt. % Si, up to 0.15 wt. % Ti, up to 4.0 wt. % Zn, up to 0.2 wt. % Zr, up to 0.2 wt. % Sc, up to 0.25 wt. % Sn, up to 0.1 wt. % Ni, up to 0.15 wt. % impurities, remainder aluminum.

[0006] The patent application CN114703407 discloses high-performance Al-Mg-Si-Cu-Sn aluminum alloy. The alloy consists of the following components: Mg: 0.1-1.0%, Si: 0.3-1.2%, Cu: 0.1-0.6 %, Sn: 0.01-0.2%, unavoidable impurities ≤0.02%, the balance is Al.

[0007] There is a need to maintain the strength potential of 6xxx aluminium alloys in artificial ageing (AA) after extrusion, without losing strength the first hours after extrusion due to NA.SUMMARY OF THE INVENTION

[0008] A first object of the invention is a manufacturing process for obtaining extrusions made from a 6xxx aluminium alloy, comprising the following successive steps: a) Casting a billet comprising, in weight %, Si 0.4 - 1.2, Mg 0.4 - 1.0, Cu 0.02 -1.1, Fe 0.15 - 0.55, Sn 0.04 - 0.15, Zn ≤ 0.50, V ≤ 0.20, Ti ≤ 0.20, one or more of Cr ≤ 0.25, Zr ≤ 0.20 and Mn≤ 0.80, other elements < 0.05 each and < 0.15 total, rest aluminium; b) Homogenizing the billet; c) Re-heating the homogenized cast billet; d) Extruding said re-heated billet through a die; e) Quenching said extrusion down to room temperature; f) Applying a controlled cold deformation step; g) Natural ageing said extrusion for between 0.8h and 10h; h) Artificial ageing said naturally aged extrusion.

[0009] A second object of the invention is an extruded profile made from a 6xxx aluminium alloy comprising in wt.%, Si 0.4 - 1.2, Mg 0.4 - 1.0, Cu 0.02 - 1.1, Fe 0.15 - 0.55, Sn 0.04-0.15, Zn ≤ 0.50, V ≤ 0.20, Ti ≤ 0.20, one or more of Cr ≤ 0.25, Zr ≤ 0.20 and Mn≤ 0.80, other elements < 0.05 each and < 0.15 total, rest aluminium.

[0010] A third object of the invention is the use of an extruded profile as an automotive component such as a crash box, a bumper, a side impact beam or a side sill, structural and non-structural parts of battery box.DESCRIPTION OF THE INVENTION

[0011] All aluminium alloys referred to in the following are designated using the rules and designations defined by the Aluminium Association in Registration Record Series that it publishes regularly, unless mentioned otherwise.

[0012] Metallurgical tempers referred to are designated using the European standard EN-515. Static tensile mechanical characteristics, in other words, the ultimate tensile strength Rm (or UTS), the tensile yield strength at 0.2% plastic elongation Rp0,2 (or TYS), and elongation A% (or E%), are determined by a tensile test according to NF EN ISO 6892-1.

[0013] A first object of the invention is a manufacturing process for obtaining extrusions made from a 6xxx aluminium alloy, comprising the following successive steps: a) Casting a billet comprising, in weight %, Si 0.4 - 1.2, Mg 0.4 - 1.0, Cu 0.02 - 1.1, Fe 0.15 - 0.55, Sn 0.04-0.15, Zn ≤ 0.50, V ≤ 0.20, Ti ≤ 0.20, one or more of Cr ≤ 0.25, Zr ≤ 0.20 and Mn≤ 0.80, other elements < 0.05 each and < 0.15 total, rest aluminium; b) Homogenizing the billet; c) Re-heating the homogenized cast billet; d) Extruding said re-heated billet through a die; e) Quenching said extrusion down to room temperature; f) Applying a controlled cold deformation step; g) Natural ageing said extrusion for between 0.8h and 10h; h) Artificial ageing said naturally aged extrusion.

[0014] According to the invention, the manufacturing process for obtaining extrusions made from an alloy of the composition disclosed in step a) allows to obtain an extrusion whose mechanical strength potential is maintained, in particular there is no loss of strength in the first few hours following step f). The addition of Sn maintains the properties of the 6xxx alloys and prevents the effects of natural aging and its negative impact on mechanical properties.

[0015] The homogenization temperature of step b) is preferably from 500°C to 600°C and more preferably from 530°C to 590°C, and even more preferably from 540°C to 580°C.

[0016] In one embodiment of the invention, the homogenizing comprises two steps treatment, wherein the temperature of the second step is higher than the temperature of the first step. Preferably, the homogenizing two steps treatment b) consists in a first step at a temperature from 500°C to 560°C, preferably from 510°C to 550°C and more preferably from 515°C to 545°C during at most 10 hours, preferably at most 8 hours and even more preferably at most 6 hours, and a second step at a temperature between 540°C and 590°C, preferably from 545°C to 580°C and more preferably from 550°C to 570°C for between 8 and 18 hours, preferably between 10 and 16 hours.

[0017] After the homogenizing of step b) the homogenized cast billet is cooled to room temperature.

[0018] In one embodiment, for the manufacture of extrusions, the re-heating step before extrusion consists in a pre-heating of the homogenized cast billet, between 400°C and 530°C during a period of less than 1 hour, before performing subsequently the extrusion step d).

[0019] In another embodiment, for the manufacture of extrusions, the re-heating step c) comprises re-heating at a temperature between Ts-60°C and Ts, wherein Ts is the solidus temperature of the said aluminium alloy, and quenching until the billet mean temperature reaches a value between 400°C and 480°C in its center while ensuring that the billet surface never goes below a temperature of substantially 400°C. In the scope of this embodiment, the extrusion of step d) is performed immediately after the step of quenching. Immediately corresponds typically to a time period between 1 second to 2 minutes. This time period has to be limited to avoid that the surface temperature of the billet goes below 400°C. Quenching step is preferably performed by water spraying. Extrusion is carried out at an extrusion rate from 5 m / min to 15 m / min with preferably an entry temperature of the head of the billet from 450°C to 500°C and an entry temperature of the foot of the billet from 400°C to 450°C to obtain an extruded profile. The head of the billet is the first part to be extruded and the foot of the billet is the last part to be extruded.

[0020] After extrusion the extruded profile is quenched in step e). Quenching can be realized with strong air flow or preferably with a water spray, a water bath and or more preferably through a standing wave.

[0021] In one embodiment, the extruding step d) allows to form a solid or hollow extrusion.

[0022] After extrusion a controlled cold deformation or stretching is applied in a step f). The purpose of such stretching is to have a stress-relief and straight extrusion, according to the deformation it underwent during step e). The extrusion is stretched, which induces a plastic deformation, preferably of at least 0.1 % and preferentially of at least 0.5 % and preferably of at most 4%, more preferably of at most 2% and even more preferably of at most 1%.

[0023] The extrusion is then naturally aged for between 0.8 to 10 hours. Natural ageing corresponds to properties changes at room temperature after quenching. It may start immediately after quenching or after an incubation period. Preferably, natural ageing period is for between 1 and 9 hours, more preferably between 2 and 8 hours, even more preferably between 3 and 7 hours and even more and more preferably between 4 and 7 hours.

[0024] Finally, the extrusion is artificially final aged in step h). In one embodiment, the extrusion is aged to a T6 temper. In a preferred embodiment, the ageing temperature is from 160°C to 180°C for a duration from 5 to 2 hours. In another embodiment, the extrusion is overaged to a T7 temper.

[0025] In one embodiment an artificial preaging step is done after the natural ageing step g) and before the final artificial ageing step h), at a temperature between for 120°C and 200°C for a duration from 0.5 to 12 hours.

[0026] In a particular embodiment, the final ageing step comprises: i) an artificial pre-ageing treatment with a duration t1 at a temperature T1 said temperature T1 being typically between 120°C and 200°C and said duration t1 being typically between 0.5 and 100 hours, preferably between 0.5 and 12 hours, and even more preferably between 1 and 12 hours to obtain an artificially preaged extrusion, ii) a plastic deformation of said artificially preaged extrusion between 1% and 80% to obtain a deformed extrusion, iii) a final artificial ageing treatment of said deformed extrusion with a duration t2 at a temperature T2, said temperature T2 being typically between 140°C and 200°C and said the duration t2 being typically between 1 and 100 hours.

[0027] Said plastic deformation of step ii) is preferably obtained by stretching, or by in any others techniques such as hydro forming or pressing or stamping or bending or roll bending or stretch bending or rotary stretch bending or pulse magnetic forming or flow forming or forging or rolling or drawing or deep drawing or impact or inverse extrusion or punching or blanking. Said plastic deformation is preferentially performed at room temperature. In one preferred embodiment, said plastic deformation is applied uniformly on the said artificially preaged extrusion. In one other embodiment, said plastic deformation is applied locally on the said artificially preaged extrusion,

[0028] Another object of the invention is an extruded profile made from a 6xxx aluminium alloy comprising in wt.%, Si 0.4 - 1.2, Mg 0.4 - 1.0, Cu 0.02 - 1.1, Fe 0.15 - 0.55, Sn 0.04-0.15, Zn ≤ 0.50, V ≤ 0.20, Ti ≤ 0.20 one or more of Cr ≤ 0.25, Zr ≤ 0.20 and Mn≤ 0.80, other elements < 0.05 each and < 0.15 total, rest aluminium.

[0029] According to the invention, an improved 6xxx aluminium alloy allows to conserve the same mechanical properties throughout the natural ageing process, lasting up to 10 hours after extrusion. Natural ageing can have a very negative effect on extruded profiles, and the longer the natural ageing period, the greater the decrease in mechanical properties.

[0030] Si, Cu and Mg content are carefully adjusted in order to obtain the desired properties of strength, flow stress and the convenient solidus temperature.

[0031] In one embodiment, an extruded profile of the invention is made from an aluminium alloy comprising Cr ≤ 0.18 wt.%, Zr ≤ 0.16 wt.% and Mn≤ 0.57wt.%.

[0032] In another embodiment, an extruded profile of the invention is made from an aluminium alloy comprising Si 0.4 - 1.0 wt.%, Mg 0.4 - 0.9 wt.%, preferably Mg 0.4 - 0.83 wt.%, Cu 0.02 - 0.9 wt.%, preferably Cu 0.02 - 0.85 wt.%.

[0033] In another embodiment, an extruded profile of the invention is made from an aluminium alloy comprising Si 0.4 - 0.9 wt.%, Mg 0.4 - 1.0 wt.%, Cu 0.02 - 1.1 wt.%, Fe 0.15 - 0.55 wt.%, Mn 0.05 - 0.57 wt.%, Cr 0.06 - 0.15 wt.%, and Zr 0.05 - 0.15 wt.%.

[0034] In another preferred embodiment an extruded profile of the invention is made from an aluminium alloy comprising Si 0.4 - 0.9 wt.%, Mg 0.4 - 0.83 wt.%, Cu 0.02 - 0.85, wt.%, Mn 0.05 - 0.60 wt.%, Cr 0.06 - 0.15 wt.%, Zr 0.05 - 0.15 wt.%, Fe 0.15 - 0.55 wt.%, Sn 0.04 - 0.08 wt.%, Zn ≤ 0,50 wt.%, V ≤ 0.10 wt.%, Ti ≤ 0.10 wt.%, other elements ≤0.05 each and ≤0.15 total, rest aluminium.

[0035] In an embodiment, the content of Si is at least 0.4% in weight, or is at least 0.5%, or is at least 0.6%, or is at least 0.7%, or is at least 0.8%, or is at least 0.9%, or is at least 1.0%, or is at least 1.1%, and / or is at most 1.2%, or is at most 1.1%, or is at most 1.0%, or is at most 0.9%, or is at most 0.8%, or is at most 0.7%, or is at most 0.6%, or is at most 0.5%.

[0036] In a preferred embodiment the content of Si is from 0.4% to 1.0% and preferably from 0.4% to 0.9% in weight.

[0037] In an embodiment, the content of Mg is at least 0.40% in weight, or is at least 0.45%, or is at least 0.50%, or is at least 0.55%, or is at least 0.60%, or is at least 0.65%, or is at least 0.70%, or is at least 0.75%, and / or is at most 0.83%, or is at most 0.78%, or is at most 0.73%, or is at most 0.68%, or is at most 0.63%, or is at most 0.58%, or is at most 0.53%, or is at most 0.48%.

[0038] In a preferred embodiment the content of Mg is from 0.4% to 0.9% and preferably from 0.4% to 0.83% in weight.

[0039] In an embodiment, the content of Cu is at least 0.1% in weight, or is at least 0.2%, or is at least 0.3%, or is at least 0.4%, or is at least 0.5%, or is at least 0.6%, or is at least 0.7%, and / or is at most 0.9%, or is at most 0.8%, or is at most 0.7%, or is at most 0.6%, or is at most 0.5%, or is at most 0.4%, or is at most 0.3%, or is at most 0.2%.

[0040] In a preferred embodiment the content of Cu is from 0.02% to 0.9% and preferably from 0.02% to 0.85% in weight.

[0041] Mn, Cr and / or Zr are added in particular to control the microstructure of the extruded profile. According to the amount of Mn, Cr and Zr, the microstructure of the extruded profile is recrystallized or essentially unrecrystallized. By essentially unrecrystallized microstructure it is meant that the proportion of recrystallized grains is less than 35 %, preferentially less than 30 % and preferably less than 20% through the thickness of the walls the extruded profile. Advantageously, the peripheral coarse grain is, per wall side, at most 400 µm thick, preferably at most 250 µm thick and most preferably at most 200 µm thick. The peripheral coarse grain (PCG) is a layer of recrystallized grains on the surface of the extruded profile. It is measured in appropriate location of the extruded profile, usually excluding angles and welding zones.

[0042] In an embodiment, the content of Cr is at least 0,01% in weight, or is at least 0,02%, or is at least 0,03%, or is at least 0,04%, or is at least 0,05%, or is at least 0,06%, or is at least 0,07%, or is at least 0,08%, or is at least 0,09%, or is at least 0,10%, or is at least 0,11%, or is at least 0,12%, or is at least 0,13%, or is at least 0,14%, or is at least 0,15%, and / or is at most 0,25%, or is at most 0,24%, or is at most 0,23%, or is at most 0,22%, or is at most 0,21%, or is at most 0,20%, or is at most 0,19%, or is at most 0,18%, or is at most 0,17%, or is at most 0,16%, or is at most 0,15%, or is at most 0,14%, or is at most 0,13%, or is at most 0,12%, or is at most 0,11%, or is at most 0,10%.

[0043] In a preferred embodiment the content of Cr is from 0.01 % to 0.25 % and preferably from 0.06 % to 0.15 % in weight.

[0044] In an embodiment, the content of Zr is at least 0,01% in weight, or is at least 0,02%, or is at least 0,03%, or is at least 0,04%, or is at least 0,05%, or is at least 0,06%, or is at least 0,07%, or is at least 0,08%, or is at least 0,09%, or is at least 0,10%, and / or is at most 0,20%, or is at most 0,19%, or is at most 0,18%, or is at most 0,17%, or is at most 0,16%, or is at most 0,15%, or is at most 0,14%, or is at most 0,13%, or is at most 0,12%, or is at most 0,11%, or is at most 0,10%.

[0045] In a preferred embodiment the content of Zr is from 0.01 % to 0.20 % and preferably from 0.05 % to 0.15 % in weight.

[0046] In an embodiment, the content of Mn is at least 0,05% in weight, or is at least 0,10%, or is at least 0,15%, and / or is at most 0,80%, or is at most 0,75%, or is at most 0,70%, or is at most 0,65%, or is at most 0,60%, or is at most 0,55%, or is at most 0,50%, or is at most 0,45%, or is at most 0,40%. In a preferred embodiment the content of Mn is from 0.05 % to 0.80 % and preferably from 0.05 % to 0.60 % in weight.

[0047] In an embodiment, the content of Sn is at least 0.04% in weight, or is at least 0.05%, or is at least 0.06%, or is at least 0.07%, or is at least 0.08%, or is at least 0.09%, or is at least 0.10%, or is at least 0.11%, or is at least 0.12%, or is at least 0.13%, or is at least 0.14%, and / or is at most 0.15%, or is at most 0.14%, or is at most 0.13%, or is at most 0.12%, or is at most 0.11%, or is at most 0.10%, or is at most 0.09%, or is at most 0.08%, or is at most 0.07%, or is at most 0.06%, or is at most 0.05%. In a preferred embodiment, the Sn content is from 0.04 to 0.08 in weight. Although they are not bound by any specific theory, the present inventors believe that the addition Sn can suppress the effect of natural ageing (NA) on the mechanical properties of the final aged extruded profile for the first hours after extrusion through the Sn-vacancies binding. As a result of the Sn addition, vacancy-assisted solute diffusion will retard and NA will slow down.

[0048] In an embodiment, the content of Fe is at least 0.15% in weight, or is at least 0.20%, or is at least 0.25%, or is at least 0.30%, or is at least 0.35%, or is at least 0.40%, or is at least 0.45%, or is at least 0.50%, and / or is at most 0.55%, or is at most 0.50%, or is at most 0.45%, or is at most 0.40%, or is at most 0.35%, or is at most 0.30%, or is at most 0.25%, or is at most 0.20%. In a preferred embodiment, the Fe content is from 0.15 to 0.35 wt.% in weight.

[0049] The Zn content is at most 0.50 wt.% in weight, preferably at most 0.40 wt.% or at most 0.30 wt.% or at most 0.20 wt.% or at most 0.10 wt.% or even at most 0.05 wt.%.

[0050] The V content is at least 0.01% in weight, or is at least 0.015%, or is at least 0.02%, and / or is at most 0.20%, or is at most 0.15%, or is at most 0.10%, or is at most 0.05%, or is at most 0.03%.

[0051] Ti is preferably added to control the as-cast grain structure at a content lower than 0,20 wt.%. In an embodiment the Ti content is from 0.01 wt.% to 0.07 wt.% and preferably from 0.01 wt.% to 0.05 wt.%.

[0052] The content of other elements is less than 0.05 wt.% each and less than 0.15 wt.% total. The other elements are typically unavoidable impurities or incidental elements added in very small quantity such as boron which can be typically added together with Ti in the form of TiB 2 .

[0053] Preferably, the composition is adjusted so that the calculated solidus temperature using standard thermodynamic database is from 580°C to 610°C, preferably from 585°C to 600°C and more preferably from 588°C to 595°C, and even more preferably from 589°C to 594°C. With this relatively high solidus temperature it is possible to increase extrusion rate without having the risk of incipient melting.

[0054] The extruded profile may be use as an automotive component such as a crash box, a bumper, a side impact beam or a side sill, structural and non-structural parts of battery box.EXAMPLE Example 1

[0055] A billet has been cast with two compositions A et B listed in Table 1. Then the billet was homogenized at a temperature of around 520°C for 5 hours and 560°C for 12 hours. The homogenized cast billet was re-heated between 470°C and 490°C and introduced into the container of the extrusion press. The extrusion was then quenched down to room temperature with a cooling device (water standing wave). Then a controlled cold deformation up to 1% was applied to obtain a straight extruded profile. Table 1: Chemical composition in weight %SiFeMgCuMnNiCrZrTiVZnSnAlloy A0.830.190.760.210.53<0.010.100.140.030.020.02-Alloy B0.870.190.800.220.55<0.010.090.130.030.010.020.04

[0056] Alloy A is a comparative example and Alloy B is according to the invention.

[0057] The extrusion was then stored at room temperature for times ranging from 0.5h to 12h, corresponding to a natural ageing (NA) from 0.5h to 12h.

[0058] Then, all extruded profiles were submitted to final ageing, 12h at 170°C.

[0059] Tensile properties of extruded profiles made from Alloys A and B after several natural ageing times were characterized after the final artificial ageing. Table 2: Tensile Yield Strength (MPa) of extruded profiles made from Alloys A and B as a function of naturel ageingTensile Yield Strength (MPa) NA timeExtruded profile made from Alloy A Extruded profile made from Alloy B 0.5h3553562h3443543h3363494h3303505h3253496h3233497h3303428h3293399h33133910h33133811h33233112h329331

[0060] Thus, it can be seen that between 0.8h and 10h of natural ageing, the addition of Sn provides higher mechanical properties after final ageing. The addition of Sn reduces the negative impact on the mechanical properties of natural ageing. Indeed, the addition of Sn can resolve the negative effect of natural ageing by allowing a more feasible process window where artificial ageing or a short stabilization treatment can be done to ensure to preserve the hardening potential of the alloy.Example 2

[0061] The same A and B alloys were used to produce extruded profiles A and B using the same process described above. However, after the natural ageing and before the final ageing step, an intermediate pre-ageing step was added. The extruded profiles were pre-aged 0.5h at 170°C.

[0062] After one week, the extruded profiles were finally aged 12h at 170°C.

[0063] Tensile properties of extruded profiles made from Alloys A and B after 6h natural ageing time were characterized just after the final ageing. Table 3: Tensile Yield Strength (MPa) of extruded profiles made from Alloys A and B after pre-ageing and final ageing to T6 performed after 6h of natural ageingTensile Yield Strength (MPa) NA timeExtruded profile made from Alloy A Extruded profile made from Alloy B 6h325348

[0064] Therefore, the addition of Sn reduces the effects of natural ageing on mechanical properties. Thus, the addition of Sn coupled with pre-ageing allows to maintain the mechanical properties of the alloy even after one week.Example 3

[0065] The same A and B alloys were used to produce extruded profiles A and B using the same process described in example 1. However, after the natural ageing, a thermomechanical ageing step (TMA) was added, in which the extruded profiles were pre-aged 8h at 140°C, stretched at 4% and final-aged 8h at a temperature of 170°C.

[0066] Tensile properties of extruded profiles made from Alloys A and B after 0.5h and 6h natural ageing times were characterized just after the final ageing. Table 4: Tensile Yield Strength (MPa) of extruded profiles made from Alloys A and B after thermomechanical ageing performed after 0.5h or after 6h of natural ageingTensile Yield Strength (MPa) NA aging timeExtruded profile made from Alloy A Extruded profile made from Alloy B 0.5h3933926h373384

[0067] Therefore, the addition of Sn and the thermomechanical ageing reduce the effects of natural ageing on mechanical properties, particularly when natural ageing is high. Indeed, we can see that between 0.5h and 6h, the alloy with Sn maintains its mechanical properties, whereas the difference between 0.5h and 6h of natural aging has a more significant impact on the alloy without Sn.

Claims

1. A manufacturing process for obtaining extrusions made from a 6xxx aluminium alloy, comprising the following successive steps: a) Casting a billet comprising, in weight %, Si 0.4 - 1.2, Mg 0.4 - 1.0, Cu 0.02 - 1.1, Fe 0.15 - 0.55, Sn 0.04-0.15, Zn ≤ 0.50, V ≤ 0,20, Ti ≤ 0,20, one or more of Cr ≤ 0.25, Zr ≤ 0.20 and Mn ≤ 0.80, other elements < 0.05 each and < 0.15 total, rest aluminium; b) Homogenizing the billet; c) Re-heating the homogenized cast billet; d) Extruding said re-heated billet through a die; e) Quenching said extrusion down to room temperature; f) Applying a controlled cold deformation step; g) Natural ageing said extrusion during between 0.8h and 10h; h) Artificial ageing said naturally aged extrusion.

2. A manufacturing process according to claim 1, wherein in the step b) the temperature is between 500°C to 600°C.

3. A manufacturing process according to claim 1, wherein in the step b) comprises two step treatment, wherein the temperature of the second step is higher than the temperature of the first step.

4. A manufacturing process according to claim 3, wherein in the step b) the first step is at a temperature between 500°C and 560°C during at most 10 hours, and the second step is at a temperature between 540°C and 590°C during between 8 and 18 hours.

5. A manufacturing process according to any claims 1 to 4, wherein step c) comprises re-heating at a temperature between Ts-60°C and Ts, wherein Ts is the solidus temperature of the said aluminium alloy, and quenching until the billet mean temperature reaches a value between 400°C and 480°C in its center while ensuring that the billet surface never goes below a temperature of substantially 400°C.

6. A manufacturing process according to any claims 1 to 5, wherein step h) is: i) an artificial pre-ageing treatment with a duration t1 at a temperature T1 said temperature T1 being typically between 120°C and 200°C and said duration t1 being typically between 1 and 100 hours, to obtain an artificially preaged extrusion, ii) a plastic deformation of said artificially preaged extrusion between 1% and 80% to obtain a deformed extrusion, iii) a final artificial ageing treatment of said deformed extrusion with a duration t2 at a temperature T2, said temperature T2 being typically between 140°C and 200°C and said the duration t2 being typically between 1 and 100 hours.

7. A manufacturing process according to claim 6 wherein plastic deformation step ii) is obtained by stretching or hydroforming or pressing or stamping or bending or roll bending or stretch bending or rotary stretch bending or pulse magnetic forming or flow forming or forging or rolling or drawing or deep drawing or impact or inverse extrusion or punching or blanking.

8. A manufacturing process according claim 6, wherein the pre-ageing step i) is provided during 0.5h to 12h.

9. An extruded profile made from a 6xxx aluminium alloy comprising in wt.%, Si 0.4 -1.2, Mg 0.4 - 1.0, Cu 0.02 - 1.1, Fe 0.15 - 0.55, Sn 0.04-0.15, Zn ≤ 0.50, V ≤ 0.20, Ti ≤ 0.20, one or more of Cr ≤ 0.25, Zr ≤ 0.20 and Mn≤ 0.80, other elements < 0.05 each and < 0.15 total, rest aluminium.

10. An extruded profile according to claim 9 wherein Sn 0.04-0.08 wt.%.

11. An extruded profile according to any of claims 9 to 10 wherein Si 0.4 - 0.9 wt.%, Mg 0.4 - 1.0 wt.%, Cu 0.02 - 1.1 wt.%, Fe 0.15 - 0.55 wt.%, and wherein Mn 0.05 - 0.57 wt.%, Cr 0.06 - 0.15 wt.%, Zr 0.05 - 0.15 wt.%.

12. An extruded profile according to any of claim 9 to 11 wherein the alloy comprises in wt.%, Si 0.4 - 0.9, Mg 0.4-0.83, Cu 0.02 - 0.85, Mn 0.05 - 0.60, Cr 0.06 - 0.15 Zr 0.05 - 0.15 Fe 0.15 - 0.55, Sn 0.04 - 0.08, Zn ≤ 0,50, V ≤ 0.10, Ti ≤ 0.10, other elements ≤0.05 each and ≤0.15 total, rest aluminium.

13. An extruded profile according to any claims 9 to 12 wherein the solidus temperature of the alloy is from 580°C to 610°C, preferably from 585°C to 600°C and more preferably from 588°C to 595°C and even more preferably from 589°C to 594°C.

14. Use of an extruded profile according to anyone of claims 9 to 13 as an automotive component such as a crash box, a bumper, a side impact beam or a side sill, structural and non-structural parts of battery box.

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