CN117280059A - 6XXX alloy for high strength extruded products with high processability - Google Patents

Abstract

The present invention relates to an improved alloy for obtaining AA6 xxx-alloy extrudates having high strength (typically having an ultimate tensile strength of above 390 Mpa), high workability (especially high productivity), and high surface quality and high corrosion resistance. In particular, the alloy of the present invention comprises: in weight percent, 0.6 to 0.9 percent of Si, 0.55 to 0.76 percent of Mg, 0.65 to 0.9 percent of Cu, 0.4 to 0.7 percent of Mn, 0.05 to 0.2 percent of Cr, 0.10 to 0.19 percent of Zr, 0.05 to 0.5 percent of Fe, less than or equal to 1.0 percent of Zn, less than or equal to 0.10 percent of V, less than or equal to 0.10 percent of Ti, less than 0.05 percent of each of other elements and less than 0.15 percent in total, and the balance of aluminum. The extrudates of the present invention are advantageously used as automotive parts, such as crash boxes, bumpers, side bumpers or side beams.

Description

6XXX alloy for high strength extruded products with high processability

Technical Field

The invention relates to a6XXX series aluminum extrusion alloy, which is particularly suitable for the automobile industry.

Background

Aluminum alloys are used in various applications including automobiles in the form of extrudates. Among these alloys, the Cu-containing AA6 xxx-aluminum alloy series (e.g. AA 6013) are known to combine interesting chemical and mechanical properties such as strength, crashworthiness and even corrosion resistance. In addition to the above requirements, another requirement is that the aluminum alloy is easy to process and has high productivity, and no surface defects such as defects caused by preliminary melting or structural defects such as Peripheral Coarse Grains (PCG) which may occur during extrusion or in a subsequent heat treatment step.

Patent application WO 2015086116 discloses a manufacturing method for obtaining an extruded product made of a6xxx aluminium alloy, comprising the steps of: a) Homogenizing a billet cast from the aluminum alloy; b) Heating the homogenized cast billet; c) Extruding the billet through a die to form at least a solid or hollow extruded product; d) Quenching the extruded product to room temperature; e) Optionally stretching the extruded product to obtain a plastic deformation generally comprised between 0.5% and 5%; f) Aging the extruded product without any separate post-extrusion solution heat treatment of the extruded product between steps d) and f), characterized in that: i) The heating step b) is a solution heat treatment in which: b1 Heating the casting blank to a temperature between Ts-15 ℃ and Ts, wherein Ts is the solidus temperature of the aluminum alloy; b2 Cooling the casting blank to a value between 400 ℃ and 480 ℃ in average temperature of the casting blank, and simultaneously ensuring that the surface temperature of the casting blank is not lower than the temperature basically approaching 400 ℃; ii) extruding the cooled billet immediately (step c)), i.e. a few tens of seconds after the end of step b 2).

Patent application US2011155291 discloses a high strength aluminum alloy extrusion product comprising 0.6-1.2% Si, 0.8-1.3% Mg and 1.3-2.1% Cu while satisfying the following conditional expressions (1), (2), (3) and (4), 3% ++mg% ++cu% ++4% (1) Mg% ++si ++1.7xsi% (2) Mg% ++si ++2.7% (3) Cu%/2 ++mg ++/(Cu%/2) +/(Cu%/0.6% +/(Cu%/2) +0.4) and further comprising 0.04 to 0.35% Cr and 0.05% or less Mn impurity, the balance being aluminum and unavoidable impurities. The cross-section of the extruded product has a recrystallized microstructure with an average grain size of 500 μm or less.

Patent application WO 2018073389 discloses a method for optimizing the strength and energy absorption of a6XXX aluminum alloy extrusion for structural parts such as automobile bumpers, side bumpers, seat pedals, etc., in particular by thermomechanical aging (TMA) variation, comprising i) performing an artificial pre-aging treatment at a temperature T1 for a duration T1, the temperature T1 being selected to increase the yield strength of the extrusion by 5% to 20%, the temperature T1 typically being between 120 ℃ and 180 ℃, the duration T1 typically being between 1 and 100 hours, to obtain an artificial pre-aged extrusion; ii) plastically deforming the artificially pre-aged extrudate to obtain a deformed extrudate by 1% -80% >; iii) The deformed extrudate is subjected to a final artificial ageing treatment at a temperature T2 for a time T2, typically between 140 ℃ and 200 ℃, the time T2 typically being between 1 and 100 hours.

Patent application FR 2360684 A1 discloses an aluminium alloy product essentially containing, by weight, 0.4 to 1.2% Si,0.4 to 1.1% Mg, 0.2 to 0.8% Mn, 0.03 to 0.35% Fe, 0.1 to 0.6% Cu, the balance essentially aluminium. The alloy may be homogenized at 480 to 595 c, then processed into sheet or profile, then heat treated to form a solid solution, then cooled and aged to T4 temper, finally converted to a final product, and then strengthened by heating or aging to a T6 temper.

Patent application US2004084119 discloses a method for manufacturing high strength aluminum alloy extruded products suitable for use as structural materials for transportation equipment such as automobiles, railroad cars, and aircraft. The method comprises the following steps: extruding an aluminum alloy billet containing 0.5% to 1.5% Si, 0.9% to 1.6% Mg, 0.8% to 2.5% Cu while satisfying the following formulas (1), (2), (3) and (4), 3.ltoreq.Si% + Mg% + Cu%. Ltoreq.4 (1) Mg% <1.7x Si% (2) Mg% + Si%. Ltoreq.2.7 (3) Cu%/2.ltoreq.Mg%. Ltoreq.Cu%/2) +0.6 (4) and further containing 0.5% to 1.2% Mn, the balance being Al and unavoidable impurities, and forming it into a solid product by using a solid die or a hollow product by using a porous split extrusion die or a bridge type hole extrusion die, thereby obtaining a solid product or a hollow product having a fiber structure of 60% or more of the cross-sectional structural area of the product.

Patent application WO2016202810 discloses a manufacturing process for obtaining a6xxx series aluminium alloy solid extruded product comprising Si:0.3 to 1.7wt%; mg:0.1 to 1.4wt%; 0.1 to 0.8 wt.% Cu; zn:0.005-0.7 wt.%, of one or more dispersing elements selected from the group consisting of Mn 0.15-1 wt.%, cr 0.05-0.4 wt.% and Zr 0.05-0.25 wt.%, of iron (max 0.5 wt.%) of other elements (max 0.05 wt.%) and the balance aluminium, said extruded product having particularly high mechanical properties, its ultimate tensile strength being generally higher than 400MPa, preferably 430MPa, more preferably 450MPa, and without post-extrusion solution heat treatment operations. The invention also relates to a manufacturing method for obtaining a bumper system in which traction eyes are integrated, said traction eyes being made of said high mechanical properties aluminium alloy.

Patent application WO2019206826 discloses an extruded product made of a6xxx aluminium alloy comprising 0.40-0.80 wt.% Si,0.40-0.80 wt.% Mg,0.40-0.70 wt.% Cu, up to 0.4 wt.% Fe, up to 0.30 wt.% Mn, up to 0.2 wt.% Cr, up to 0.2 wt.% V, up to 0.14 wt.% Zr, up to 0.1 wt.% Ti, each up to 0.05 wt.% and totaling 0.15 wt.% of various impurities, the balance being aluminium, wherein the ratio Mg/free Si is 0.8 to 1.2, wherein free Si = Si-0.3 x (mn+fe), wherein Si, mg and Fe correspond to the weight percentage content of Si, mg and Fe in the 6xxx aluminium alloy, and to the corresponding extruded product, in particular having a tensile strength higher than 280MPa and excellent collision properties.

CN103131904 discloses an aluminum alloy material, which comprises the following components in percentage by mass: 0.8-1.3% Si,0.3-0.7% Cu,0.20-0.60% Mn,0.8-1.4% Mg,0.05-0.25% Cr,0.05-0.2% Zr, up to 0.5% Fe, up to 0.2% Zn, up to 0.1% Ti, the balance Al and impurities.

There is a need for an improved alloy to obtain AA6 xxx-alloy extrudates of high strength (typically having an ultimate tensile strength of greater than 390 MPa), high workability (especially high productivity), high surface quality and high corrosion resistance.

Disclosure of Invention

The invention relates to an extrusion profile comprising an aluminium-magnesium-silicon alloy, comprising in weight percent

Si 0.6% to 0.9%,

mg 0.55% to 0.76%,

0.65 to 0.9 percent of Cu,

mn 0.4% to 0.7%,

0.05 to 0.2 percent of Cr,

zr 0.10% to 0.19%,

0.05 to 0.5 percent of Fe,

Zn≤1.0％，

V≤0.10％，

Ti≤0.10％，

the other elements are each < 0.05% and total < 0.15%, the balance being aluminium.

Another object of the present invention is a process for preparing an extrusion profile according to the invention comprising the following successive steps

(a) A cast billet comprising, in weight percent

Si 0.6% to 0.9%,

mg 0.55% to 0.76%,

0.65 to 0.9 percent of Cu,

mn 0.4% to 0.7%,

0.05 to 0.2 percent of Cr,

zr 0.10% to 0.19%,

0.05 to 0.5 percent of Fe,

Zn≤1.0％，

V≤0.10％，

Ti≤0.10％，

each of the other elements is less than 0.05 percent and less than 0.15 percent in total, the balance being aluminum,

(b) The blank is homogenized and the blank is homogenized,

(c) The homogenized blank is cooled to room temperature,

(d) Solution heat treating the homogenized billet at a temperature of 500 ℃ to 560 ℃ for 150 seconds to 500 seconds and quenching to a temperature of 300 ℃ to 500 ℃, or directly reheating the homogenized billet to a temperature of 300 ℃ to 500 ℃ without a solution step,

(e) Extruding the heat-treated and quenched or reheated billet at an extrusion rate of 5m/mn to 15m/mn to obtain an extruded profile,

(f) Quenching, stretching and aging the extruded profile.

A further object of the invention is the use of the extruded profile according to the invention as a vehicle part, such as a crash box, a bumper, a side bumper or a side sill.

Drawings

Fig. 1: microstructure of the alloy A4 (fig. 1 a) or A6 (fig. 1 b) extrudates.

Fig. 2: calculation lines for the same ultimate tensile strength (MPa) under the rheological stress/solidus temperature coordinate system.

Detailed Description

Unless otherwise indicated, all aluminum alloys mentioned below employ the rules and designations defined by the aluminum association (The Aluminum Association, inc.) in its periodic publication of registration records series (Registration Record Series).

The metallurgical states mentioned all use the European EN-515 standard.

The static tensile mechanical properties, namely ultimate tensile strength Rm (or UTS), tensile yield strength Rp0,2 (or YTS) at 0.2% plastic elongation and elongation A% (or E%), are determined by a tensile test according to NF EN ISO 6892-1.

According to the present invention, the improved aluminum-magnesium-silicon alloy can obtain a high strength extrusion while having high workability. By high processability is meant, in particular, a high extrusion rate while maintaining a good microstructure in which no incipient melting occurs and the thickness of the peripheral coarse grain layer is limited. This is achieved mainly by low rheological stresses and high solidus temperatures.

According to the invention, the extruded profile comprises the following components (in weight percent): 0.6 to 0.9% of Si, 0.55 to 0.76% of Mg, 0.65 to 0.9% of Cu, 0.4 to 0.7% of Mn, 0.05 to 0.2% of Cr, 0.10 to 0.19% of Zr, 0.05 to 0.5% of Fe, less than or equal to 1.0% of Zn, less than or equal to 0.10% of V, less than or equal to 0.10% of Ti, less than 0.05% of each of other elements and less than 0.15% in total, and the balance of aluminum.

The Si, cu and Mg contents are carefully adjusted in order to obtain the desired strength, rheological stress and solidus temperature characteristics.

The Si content is preferably at least 0.70 wt%, more preferably at least 0.75 wt%. The Si content is preferably at most 0.90 wt%, more preferably at most 0.85 wt%. The Mg content is preferably at least 0.58 wt.%, more preferably at least 0.62 wt.%. The Mg content is preferably at most 0.75 wt.%, preferably at most 0.74 wt.%, more preferably at most 0.72 wt.%. The Cu content is preferably at least 0.70 wt.%, more preferably at least 0.75 wt.%. The Cu content is preferably at most 0.90 wt.%, more preferably at most 0.85 wt.%. In a preferred embodiment, the Cu content is 0.75 to 0.85 wt.%.

The sum of Si, cu and Mg is preferably controlled. In one embodiment, the sum of si+mg+cu is at least 2.0 wt%, more preferably at least 2.15 wt%, and/or at most 2.4 wt%, more preferably at most 2.35 wt%, even more preferably at most 2.33 wt%.

Mn, cr and Zr are added in particular in order to control the microstructure of the extrusion profile. The microstructure of the extrudate is preferably substantially unrecrystallized. By substantially unrecrystallized microstructure is meant that the proportion of recrystallized grains in the wall thickness of the extrudate is less than 35%, preferably less than 30%, more preferably less than 20%. Advantageously, the peripheral coarse grains of each side wall have a thickness of at most 400 μm, preferably at most 250 μm, preferably at most 200 μm. Peripheral Coarse Grains (PCGs) are a layer of recrystallized grains on the surface of the extrusion profile. It is measured in place on the extrusion and typically does not include an angular region and a weld zone.

The Mn content is preferably at least 0.40 wt.%, more preferably at least 0.45 wt.%. The Mn content is preferably at most 0.65 wt%, more preferably at most 0.55 wt%. The Cr content is preferably at least 0.06 wt.%, more preferably at least 0.07 wt.%. The Cr content is preferably at most 0.18 wt.%, more preferably at most 0.12 wt.%. The Zr content is preferably at least 0.11 wt.%, more preferably at least 0.12 wt.%. The Zr content is preferably at most 0.18% by weight, more preferably at most 0.16% by weight. The Zn content is at most 1.0 wt%, preferably at most 0.8 wt%, or at most 0.7 wt%, or at most 0.6 wt%, or at most 0.5 wt%, or at most 0.4 wt%, or at most 0.3 wt%, or at most 0.2 wt%, or even at most 0.1 wt%. The inventors have found that the alloys of the present invention can withstand such Zn levels without adversely affecting their properties, which is advantageous for recycling.

The content of V is at most 0.10 wt.%, preferably at most 0.05 wt.%, or even at most 0.03 wt.%.

Ti is preferably added to control the grain structure of the casting. In one embodiment, the Ti content is 0.01 to 0.07 wt%, preferably 0.01 to 0.05 wt%.

The Fe content is at least 0.05 wt.% and at most 0.5 wt.%. The Fe content is preferably at least 0.10 wt.%, more preferably at least 0.15 wt.%. The Fe content is preferably at most 0.40 wt%, more preferably at most 0.30 wt%. The inventors have found that the alloy of the present invention can withstand such Fe contents without adversely affecting its properties, which is advantageous for recycling.

The content of other elements is less than 0.05 wt% each and totalLess than 0.15 wt%. Other elements are usually unavoidable impurities or incidental elements added in very small amounts, e.g. boron, which can usually be present as TiB ₂ Is added together with titanium.

Preferably, the composition is adjusted such that the solidus temperature calculated using standard thermodynamic databases is from 580 ℃ to 610 ℃, preferably from 585 ℃ to 600 ℃, more preferably from 588 ℃ to 595 ℃, even more preferably from 589 ℃ to 594 ℃. With this relatively high solidus temperature, it is possible to increase the extrusion rate without the risk of incipient melting.

Preferably, the ingredients and homogenization are adjusted to improve processability to a strain rate of 0.14s at 480 DEG C ^-1 The rheological stress measured at this time is not more than 35MPa, preferably not more than 32MPa. In particular, extrusion rates of 5 to 15m/mn (preferably 6 to 12 m/mn) can be obtained with the alloy of the invention without the occurrence of microscopic defects such as incipient melting or thick PCG.

Preferably, the extrusion profile according to the invention has a longitudinal ultimate tensile strength in the T6 state of at least 390MPa, preferably at least 400MPa.

In particular, the inventors have found that with the alloy of the invention, a preferred solidus temperature of 588 ℃ to 595 ℃ can be obtained simultaneously, at 480 ℃ and a strain rate of 0.14s ^-1 Preferably a rheological stress of at most 35MPa, a longitudinal ultimate tensile strength of at least 390MPa in the T6 state, a more preferably a solidus temperature of 589 ℃ to 594 ℃, a strain rate of 0.14s at 480 ℃ and a tensile strength of at least 35MPa ^-1 More preferred rheological stresses of at most 32MPa are measured, and the longitudinal ultimate tensile strength of the extrudate in the T6 state is at least 400MPa.

The process for preparing an extrusion profile according to the invention comprises the following successive steps: casting an alloy billet, homogenizing the billet, cooling the homogenized billet to room temperature, solution heat treating and quenching or simply reheating the homogenized billet, extruding, quenching, stretching and ageing treatment according to the invention.

The homogenization temperature is preferably 510 ℃ to 600 ℃, more preferably 530 ℃ to 590 ℃, even more preferably 540 ℃ to 580 ℃, even more preferably 560 ℃ to 580 ℃.

The method of the invention for heat treating homogenized billets prior to extrusion has two main embodiments. In a first embodiment, the homogenized billet is solution heat treated at a temperature of 500 ℃ to 560 ℃ for 150 seconds to 500 seconds and then quenched to a temperature of 300 ℃ to 500 ℃. In a first embodiment, the homogenized billet is preferably solution heat treated at a temperature of 530 ℃ to 560 ℃ for 150 seconds to 500 seconds and then quenched to a temperature of 330 ℃ to 500 ℃. Within the scope of the present invention, the temperature of the blank is understood to be the average surface temperature of the blank. Notably, the temperature after quenching refers to the temperature after stabilization: during and shortly after quenching, the surface temperature of the blank may be locally below 300 ℃. In a second embodiment, the homogenized billet is directly reheated to 300 ℃ to 500 ℃, preferably 330 ℃ to 500 ℃, without the need for a solid solution step. The first embodiment generally gives higher strength extrudates than the second embodiment. Preferably, the heat treatment of the homogenized billet is performed in such a way that the temperature difference between one end (head) and the other end (bottom) of the billet is at least 30 ℃, preferably at least 50 ℃, more preferably at least 70 ℃ before extrusion.

Extrusion was performed as follows: the extrusion rate is 5m/mn to 15m/mn, the inlet temperature of the billet head is preferably 400 ℃ to 500 ℃, and the inlet temperature of the billet bottom is 330 ℃ to 450 ℃ to obtain an extruded profile. The head of the billet is the first extruded part and the bottom of the billet is the last extruded part. With the present invention, the processability is improved, in particular the extrusion rate is preferably at least 7m/mn, preferably at least 8m/mn, more preferably at least 10m/mn, without any defects such as incipient melting or PCG overabundance.

In one embodiment, the extrusion profile of the present invention is made from a billet homogenized at a homogenization temperature of 530 ℃ to 580 ℃ and extruded at an extrusion rate of at least 7m/mn.

After extrusion, the extrudate is quenched. Quenching may be achieved by a strong gas flow or preferably water spray, and/or more preferably by standing waves. The extruded profile is then stretched to produce a plastic deformation, preferably of at least 0.1%, preferably at least 0.5%, preferably at most 4%, more preferably at most 2%, even more preferably at most 1%. Finally, aging the extruded profile. The extrudate is preferably aged to a T6 state. In a preferred embodiment, the ageing treatment temperature is 160 to 180 ℃ and the duration is 5 to 20 hours. In another embodiment, the extrudate is overaged to a T7 state.

The extruded profile of the present invention can be used as automotive parts such as crash boxes, bumpers, side impact beams, battery housings or side beams, and the like.

Examples

The billets of the composition shown in table 1 were already cast. Alloys A2 and A4 are in accordance with the invention.

The components in Table 1 are in weight percent.

The A1 billet was homogenized at 550 ℃. The billets A6, A7 and A8 were homogenized at 555 ℃. All other billets were homogenized at 575 ℃. After the billet was cooled to room temperature, solution and quenching were performed before extrusion. The blank is heated to 530 ℃ and held at this temperature for at least 2 minutes, and then subjected to a water quench treatment to stabilize the temperature to approximately 480 ℃ but not less than 350 ℃.

The billet is then extruded at an extrusion outlet temperature of 560 ℃ or higher without surface defects. Extruded is a hollow profile with a wall thickness of 1.8 mm.

Subsequently, the extrudate is cooled to room temperature, preferably using water quenching, to fully evaluate the mechanical properties and ductility of the alloy.

The extrudate is then stretched to produce 0.5% to 1.0% plastic deformation, followed by aging to achieve maximum strength. The extrudate was finally aged at 170 ℃ to peak strength (T6 temper).

The extrudates made from alloys A1, A2 and A4 have a substantially unrecrystallized microstructure with a PCG thickness of about 150 μm per wall, so that the proportion of recrystallized grains is below 20%. Figure 1a shows a cross section of an extrusion made according to the invention with a PCG thickness of about 150 μm. The extrudates made from alloys A7 and A8 had a substantially unrecrystallized microstructure with PCG thickness of about 135 μm and 90 μm, respectively, per sidewall. The extrudates made from alloys A3 and A5 had a recrystallized microstructure. As shown in fig. 1b, the extrudate made of alloy A6 has a PCG microstructure of about 500 μm thickness per sidewall.

The parallel rheological stresses of each alloy raw material (i.e. billet) were measured by performing a thermal compression test at 480 ℃. Strain rate used in compression test was 0.14s ^-1 . Rheological stress is directly related to processability, as the lower the rheological stress, the less extrusion resistance and the higher the possible extrusion rate for a given device. At the same time, the extrusion rate may be limited by the maximum temperature that can be tolerated by the extrusion. The mechanical properties and rheological stresses are provided in table 2.

TABLE 2

Table 2: mechanical properties and rheological stress

Based on the data obtained, the inventors have established a model to predict the rheological stress and mechanical strength of the alloy of the invention from the solidus temperature and to convert the alloy of the invention into an extruded profile by the method of this example. The simulation results are shown in FIG. 2. The use of the alloys according to the invention makes it possible to achieve a very favourable balance between workability and strength, in particular at calculated solidus temperatures of 588 ℃ to 595 ℃, and at 480 ℃ and strain rates of 0.14s at the same time ^-1 Rheological stress of at most 35MPa measured at that time, and ultimate tensile strength in the T6 stateAn extrudate having a degree of at least 400MPa and being free of microscopic defects such as incipient melting or thick PCG.

Claims (10)

1. An extrusion comprising an aluminium-magnesium-silicon alloy comprising in weight percent

Si 0.6% to 0.9%,

mg 0.55% to 0.76%,

0.65 to 0.9 percent of Cu,

mn 0.4% to 0.7%,

0.05 to 0.2 percent of Cr,

zr 0.10% to 0.19%,

0.05 to 0.5 percent of Fe,

Zn≤1.0％，

V≤0.10％，

Ti≤0.10％，

the other elements are each < 0.05% and total < 0.15%, the balance being aluminium.

2. The extrusion of claim 1 wherein the copper content is 0.75 to 0.85 weight percent.

3. The extrusion of claim 1 or 2, wherein the microstructure is substantially unrecrystallized.

4. The extrusion of claim 4 wherein the peripheral coarse grains of each sidewall are up to 400 μm thick.

5. The extruded profile of any one of claims 1 to 4, wherein the solidus temperature of the alloy is from 580 ℃ to 610 ℃, preferably from 585 ℃ to 600 ℃, more preferably from 588 ℃ to 595 ℃, even more preferably from 589 ℃ to 594 ℃.

6. The extrusion profile of any one of claims 1 to 5 having a strain rate of 0.14s at 480 ℃ ^-1 The rheological stress measured at this time is at most 35MPa, preferably at most 32MPa.

7. The extrusion profile according to any one of claims 1 to 6, wherein the extrusion profile is in a T6 state and has a longitudinal ultimate tensile strength of at least 390MPa, preferably at least 400MPa.

8. A process for preparing an extrusion profile according to any one of claims 1 to 7, comprising the following successive steps

(a) A cast billet comprising, in weight percent,

si 0.6% to 0.9%,

mg 0.55% to 0.76%,

0.65 to 0.9 percent of Cu,

mn 0.4% to 0.7%,

0.05 to 0.2 percent of Cr,

zr 0.10% to 0.19%,

0.05 to 0.5 percent of Fe,

Zn≤1.0％，

V≤0.10％，

Ti≤0.10％，

each of the other elements is less than 0.05 percent and less than 0.15 percent in total, the balance being aluminum,

(b) The blank is homogenized and the blank is homogenized,

(c) The homogenized blank is cooled to room temperature,

(d) Solution heat treating the homogenized billet at a temperature of 500 ℃ to 560 ℃ for 150 seconds to 500 seconds and quenching to a temperature of 300 ℃ to 500 ℃, or directly reheating the homogenized billet to a temperature of 300 ℃ to 500 ℃ without a solution step,

(e) Extruding the heat-treated and quenched or reheated billet at an extrusion rate of 5m/mn to 15m/mn to obtain an extruded profile,

(f) Quenching, stretching and aging the extruded profile.

9. The process for preparing an extrusion profile according to claim 8, wherein the homogenization temperature is from 530 ℃ to 580 ℃ and the extrusion rate is at least 7m/mn.

10. Use of the extrusion according to any of claims 1 to 7 as a vehicle part, such as a crash box, a bumper, a side bumper or a side sill.