High strength al-mg-si alloy, extruded profile of the alloy, and a method for producing extruded profile

Abstract

The present disclosure relates to an extrudable AlMgSi alloy for high strength extruded parts especially suitable for use in vehicles, having the following composition, in percent by weight (wt.%); Mg: 0.85 – 1.15; Si: 0.60 – 0.75; Fe: 0.1 - 0.5; Cu: 0.25 - 0.60; Cr: 0.0 - 0.10; Mn: 0 - 0.15; Zn: <1.0; Ti: < 0.15; V: < 0.10; Zr: < 0.05; impurities equal to or less than 0.05 wt.% each and equal to or less than 0.15 wt.% in total, the remainder being Al, wherein the ratio Mg / Sieff is 1.3-2.5, Sieff = Si - (Fe+Mn+Cr) / 3 [wt.%]. The disclosure also describes a method for processing the AlMgSi alloy into extruded profiles, and high strength extruded profiles of the AlMgSi alloy, having yield stress of at least 320 MPa in a T6 condition.

Description

[0001] HIGH STRENGTH Al-Mg-Si ALLOY, EXTRUDED PROFILE OF THE ALLOY, AND A METHOD FOR PRODUCING EXTRUDED PROFILE

[0002] TECHNICAL FIELD

[0003] The present invention relates to high strength AA6XXX series alloys and a method for producing extruded profiles or extruded solid bars, which may be subjected to further forming processing to obtain extruded products with high strength and good mechanical properties obtained with high productivity efficiencies. The present invention also relates to extruded products of the high strength AA6XXX series alloys according to the present invention.

[0004] BACKGROUND ART

[0005] For automotive components based on extruded profiles 6XXX alloys have become the preferred choice due to the combination of mechanical properties, extrudability, corrosion resistance and recycling friendliness. However, for high strength 6XXX alloys extrudability becomes an issue, and for 6XXX alloys providing yield strength levels above 300 MPa the low extrudability significantly increases the cost. The reason for the reduced extrudability for the higher strength 6XXX alloys is a combination of more alloying elements in solid solution and dispersoid particles that contributes to increased deformation resistance and a lowering of the eutectic temperature caused by increased levels of alloying elements.

[0006] One way to improve extrudability and mechanical properties of 6XXX alloys is to use overheating where the billet is heated to a high temperature and then quenched to a normal billet temperature just before extrusion, as described in US patent No. 4,909,858. This is a process that today is being used by many automotive extruders, mainly to produce high and consistent mechanical properties. When it comes to increasing the extrudability the process works best for medium strength alloys and certain profile shapes. Here, a shift in the tearing mechanism from eutectic melting of MgjSi particles to solidus melting of the matrix gives a significant increase in the maximum possible extrusion speed before getting tearing in the profile surface. For higher alloyed 6XXX alloys the difference in temperature between the eutectic melting temperature of MgjSi and the solidus temperature becomes smaller and the gain in extrudability by a shift in tearing mechanism becomes smaller and eventually disappears completely. The increase of elements in solid solution for the overheated billets and thereby an increased deformation resistance outweighs the positive effect of the temperature difference between the eutectic and the solidus temperatures. Another possibility to increase the extrudability of high alloyed 6XXX alloys is to do the opposite of overheating, namely, to perform a soft annealing process of the billets where MgjSi particles are precipitated to reduce the amount of elements in solid solution, as described in applicants own patent application WO 2023 / 041557 Al. Most high strength 6XXX alloys have significant additions of Mn and possibly Cr and Zr to create dispersoid particles that retain a non-recrystallized fibrous grain structure in extruded profile. A high number of dispersoid particles is known to increase the deformation resistance and may therefore reduce the effect of the soft annealing process. In industrial production the gain of productivity must outweigh the extra cost of doing both a soft annealing of the billets and a separate solutionizing process for the extruded profiles.

[0007] Addition of Cu as an alloying element is also known to increase the strength of 6XXX aluminium alloys but high Cu content in the alloy is known to both increase the deformation resistance and reduce the eutectic temperature due to low-melting eutectic particles in the matrix which may cause tearing of the extruded profile. Hence, 6XXX alloys comprising high content of Cu are produced using very low extrusion speed in conventional extrusion processes.

[0008] Thus, there is a need for high strength extrusion aluminium alloys that can be effectively processed while producing extruded profiles with high and consistent mechanical properties.

[0009] SUMMARY OF INVENTION

[0010] An object of the present invention is to provide an extrudable high strength 6XXX aluminium alloy with high extrudability and suitable for producing extruded structural parts having high tensile strength, suitable to be used in vehicles. Another object of the invention is a method for producing the high strength extruded parts of the 6XXX aluminium alloy according to the disclosure.

[0011] These and other objects are achieved by the subject-matter of the appended independent claim(s).

[0012] The herein described extrudable AIMgSi alloy for high strength extruded parts suitable for use in vehicles, has the following composition, in percent by weight (wt.%);

[0013] Mg: 0.85 - 1.15;

[0014] Si: 0.60 - 0.75;

[0015] Fe: 0.1 - 0.5;

[0016] Cu: 0.25 - 0.60;

[0017] Cr: 0.0 - 0.10; Mn: 0 - 0.15;

[0018] Zn: <1.0;

[0019] Ti: < 0.15;

[0020] V: < 0.10;

[0021] Zr: < 0.05; impurities equal to or less than 0.05 wt.% each and equal to or less than 0.15 wt.% in total, the remainder being Al, wherein the ratio Mg / Sieff is 1.3-2.5, Sieff = Si - (Fe+Mn+Cr) / 3 [wt.%].

[0022] The aluminium alloy has considerable improved extrudability compared with other typical high strength 6XXX alloys used for high strength extruded profiles. In addition, the composition of the aluminium alloy according to the present disclosure leads to extruded profiles with high formability in W-temper, which obtains high mechanical strength in T6 condition, having yield stress, Rp0.2, at least 320 MPa. High extrudability and formability are important properties for high strength aluminium alloys since requirements for extruded parts, especially parts intended for use in vehicles, often need to meet strict dimensional tolerance limits. The present aluminium alloy may significantly reduce manufacturing costs and improve industrial process economy for a profile manufacturer.

[0023] The present disclosure also relates to a method for manufacturing an extruded profile of an AIMgSi alloy according to the present disclosure. The method comprises the following steps: a) providing a billet of an aluminium alloy having the following composition, in percent by weight (wt.%);

[0024] Mg: 0.85 - 1.15;

[0025] Si: 0.60 - 0.75;

[0026] Fe: 0.1 - 0.5;

[0027] Cu: 0.25 - 0.60;

[0028] Cr: 0.0 - 0.10;

[0029] Mn: 0 - 0.15;

[0030] Zn: <1.0;

[0031] Ti: < 0.15;

[0032] V: < 0.10;

[0033] Zr: < 0.05; impurities equal to or less than 0.05 wt.% each and equal to or less than 0.15 wt.% in total, the remainder being Al, wherein the ratio Mg / Sieff is 1.3-2.5, Siefr = Si - (Fe+Mn+Cr) / 3 [wt.%]; b) homogenizing the cast billet at a temperature of 540-590 °C, for a period of up to 8 h; c) cooling from the homogenizing temperature to a soft annealing temperature of 350-450 °C, by using a cooling rate of at least 100°C / h; d) holding the extrusion billet at the soft annealing temperature for a period of 2-8 h, followed by cooling; e) preheating the extrusion billet; f) extruding the extrusion billet to an extruded profile, followed by air or water cooling; g) optionally stretching the extruded profile; h) optionally cutting the extruded profile into a pre-determined length; i) solution heat treating (SHT) the extruded profile at a temperature of 530-580 °C, followed by quenching; j) optionally cold deforming the SHT and quenched extruded profile; k) aging the extruded profile in a single, or multi-step aging process, said aging process comprising holding the extruded profile at a temperature of 160-220 °C for 1-24 hours.

[0034] By the method disclosed herein, comprising a soft annealing step, it is possible to extrude the present AIMgSi alloy, comprising high amounts of Cu, at significantly higher extrusion speeds compared with conventional production method, without experiencing tearing in the extruded profile. In addition, by using the present AIMgSi alloy and method disclosed herein extruded profiles in W-temper having excellent formability are obtained, which can be cold deformed to obtain final shape and accurate dimensions using low forces and efficient methods, while obtaining extruded products having a T6 temper above 320 MPa.

[0035] The present disclosure also relates to an extruded profile made of the AIMgSi alloy according to the present disclosure, and using the method disclosed herein, where the extruded profile has a recrystallized microstructure; and wherein the extruded profile has a tensile stress (Rp0.2) of at least 320 MPa in a T6 condition.

[0036] The present AIMgSi alloy and extruded parts made of the aluminium alloy according to the present disclosure, are suitable for structural parts in vehicles such as bumpers, wheel suspension parts, and spring links, and especially parts that are subjected to low cycle stress. Good low-cycle fatigue is a particularly important property of a spring link. The extruded parts made of the AIMgSi alloy according to the present disclosure and by the present disclosed method are particularly suitable for cold forming operations, such as mechanical calibration and hydroforming. Unless otherwise stated the AA6XXX series alloys as referred to herein refers to AIMgSi alloys as listed in the "International Alloy Designations and Chemical Composition Limits for Wrought Aluminum and Wrought Aluminum Alloys" published by The Aluminum Association (American National Standard, ANSI). References to 6XXX-series aluminium alloys refer to ISO alloy designations or European wrought alloy standards (CEN), which alloy and temper designation systems are basically identical with the ANSI system, as is generally known to the skilled person

[0037] BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1: SEM micrographs with identification of separate phases found in soft annealed 6061 alloys with 0.2 wt.% Cu (top picture (a)) and 0.5 wt.% Cu (bottom picture (b)), having composition as shown in Table 1.

[0039] Figure 2: Extrusion ram speed plotted against billet temperature for soft annealed and for homogenised only billets of a 6082 alloy, according to example 1. Black markers represent profiles with tearing, white markers represent good profiles whereas grey markers represent borderline profiles.

[0040] Figure 3: Extrusion ram speed plotted against billet temperature for soft annealed and for homogenised only billets of 6061 alloy with 0.2 wt.% Cu, according to example 1. Black markers represent profiles with tearing, white markers represent good profiles whereas grey markers represent borderline profiles.

[0041] Figure 4: Extrusion ram speed plotted against billet temperature for soft annealed billets of

[0042] 6061 alloy with 0.5 wt.% Cu, according to example 1. Black markers represent profiles with tearing, white markers represent good profiles whereas grey markers represent borderline profiles.

[0043] Figure 5: Tensile properties for 6061 alloys after separate solutionizing (SHT) at 550°C for 30 minutes followed by different ageing procedures. One set of samples of the 6061 with 0.2 wt.% Cu with 24 hours room temperature storage (natural aging) followed by 6 hours at 185°C, and two other sets of samples of the 6061 with 0.2 and 0.5 wt.% Cu with 5 minutes at room temperature storage (natural aging) and 6 hours at 175°C.

[0044] Figure 6: Tensile properties of four 6061 alloys with varying Cu content; 0, 0.1, 0.2 and 0.5 wt.% Cu, in W-temper vs. room temperature storage.

[0045] Figure 7. Micrographs of solutionized hollow extruded rectangular profiles with a seam weld in the middle of the area shown (dimensions 20x26 mm2and a wall thickness of 1.9 mm) of 6082 alloy (left) and alloy according to the present disclosure (right).

[0046] DETAILED DESCRIPTION

[0047] The invention will be described in more detail below with reference to exemplifying embodiments and the accompanying drawings. The invention is however not limited to the exemplifying embodiments discussed and / or shown in the drawings, but may be varied within the scope of the appended claims.

[0048] When ranges are disclosed in the present disclosure, such ranges include the end values of the range, unless explicitly disclosed otherwise. Similarly, if an open range is disclosed, the open range also includes the single end value of the open range, unless explicitly disclosed otherwise.

[0049] The herein described extrudable high strength alloy is based on 6061 alloy and has primarily been developed for extruded profiles for use in vehicles. Especially structural parts subjected to cyclic high loads, such as wheel suspension parts and spring links, however, the alloy is also well suited for other structural parts used in vehicles requiring high strength and good ductility, such as bumpers. It should however be noted that the extruded profile may also be used in other application. Moreover, the present disclosure is not limited to any specific geometrical configuration, i.e. cross-sectional shape, of the extruded profile. The geometrical configuration of the extruded profile may thus be adapted to the requirements for the intended use thereof. The extruded profile may for example be a solid profile or a hollow profile without departing from the present disclosure.

[0050] The present disclosure provides an extrudable AIMgSi alloy for high strength extruded parts, especially suitable for use in vehicles, having the following composition, in percent by weight (wt.%);

[0051] Mg 0.85 - 1.15,

[0052] Si 0.60 - 0.75, Fe 0.1 - 0.5,

[0053] Cu 0.25 - 0.60,

[0054] Cr 0.0 - 0.10,

[0055] Mn 0 - 0.15,

[0056] Zn <1.0,

[0057] Ti < 0.15,

[0058] V < 0.10,

[0059] Zr < 0.05, impurities equal to or less than 0.05 wt.% each and equal to or less than 0.15 wt.% in total, the remainder being Al. The ratio Mg / Sieff being 1.3-2.5, where Siefr = Si - (Fe+Mn+Cr) / 3 [wt.%]

[0060] In the following, the importance of the different elements of the alloy composition will be briefly discussed. All percentages for the chemical composition are given in weight-% (wt.%), unless explicitly stated otherwise. Any preferred upper and / or lower limits given herein for the individual elements of the composition can be freely combined within the broadest limits of the respective elements in the composition as specified above, unless explicitly disclosed otherwise.

[0061] Magnesium (Mg): 0.85-1.15 wt.%.

[0062] Mg combines with Si to form Mg2Si particles which are important to obtain desired mechanical strength. Mg is therefore an essential element of the herein described aluminum alloy. A high Mg content is positive for ductility, and in addition allows to increase the Si content and still have a Mg / Si ratio that ensures high ductility and high extrudability. Preferably, Mg is present from 0.85 to 1.05 wt.%.

[0063] Silicon (Si): 0.60-0.75 wt.%.

[0064] Silicon is an important element of the herein described aluminum alloy since it, as described above, combines with Mg to form Mg2Si particles which in turn contribute to precipitation hardening. In order to obtain sufficient mechanical strength after aging, the herein described aluminum alloy therefore comprises at least 0.60% of Si. The amount of Si is preferably from 0.65 to 0.75 wt.%, or from 0.65 to 0.72 wt.%, to maximize strength while being adapted to the preferred Mg content.

[0065] The amount of Mg tied up in Mg2Si-particles leads to a reduced amount of Mg in solid solution, and this especially contributes to a reduced deformation resistance of the alloy. Si in solid solution has a much lower impact on the deformation resistance of the alloy. With a balanced content of Mg and Si to form Mg2Si-particles the melting temperature is determined by the binary eutectic temperature between aluminium matrix plus Mg2Si-particles, which is around 595°C (quasi-binary section according to H.W.L. Phillips in "Annotated Equilibrium Diagrams of Some Aluminium Alloy Systems", Institute of Metals, 1959). If the aluminium matrix contains excess Si in solid solution the eutectic temperature will gradually decrease. If the excess Si is high enough to form Si-particles together with Mg2Si-particles the ternary eutectic temperature between aluminium matrix plus Mg2Si-particles plus Si-particles will drop to about 555°C. Thus, to maximize the melting temperature and thereby maximizing the extrusion speed it is an advantage to have composition close to the balanced content of Mg and Si to form Mg2Si-particles. Therefore, the ratio Mg / Sieff should be in the range from 1.3 to 2.5, preferably in the range 1.4-2.2, or even more preferably in the range 1.6-2.1, to avoid ternary eutectic, but to promote a binary eutectic of Mg2Si and Al that melts at high temperatures, preferably at around a temperature of 590-595 °C.

[0066] Sieff = Si - (Fe+Mn+Cr) / 3 [wt.%].

[0067] Copper (Cu): 0.25-0.60 wt.%.

[0068] Copper contributes significantly to add strength to the material after aging, and is therefore an essential element in the present alloy. The Cu may be in solid solution in the billet, in which case there will probably be a gradual decrease in the Al - Mg2Si eutectic temperature with increasing Cu content. If AI2Cu particles are formed, the melting temperature of a binary eutectic of Al and AI2Cu is approximately 548°C. If these particles are present together with Si particles, a ternary eutectic of Al, AI2CU and Si may form, which has a melting temperature of about 525°C. If Q-phase (AI5Cu2Mg8Si6) particles are formed in the material, there could be a quaternary peritectic reaction, which takes place at a temperature around 529 °C;

[0069] AI5Cu2MggSi6 + Al ~ Liq. + Mg2Si + Si

[0070] Low melting reactions like these taking place will typically lead to a dramatic drop of the extrusion speed. FIG. 1 shows SEM (Scanning Electron Microscopy) micrographs of alloys with 0.2 wt.% Cu (a) and 0.5wt.% Cu (b), respectively, according to example 1 below. The micrographs show that there were Q-phase particles present in both of the examples of billets processed by the method disclosed herein and as described in the below example, i.e. having been subjected to a soft annealing step. Surprisingly, tests have shown that soft annealed billets with a Cu content as high as at least 0.51 wt.% did not cause any tearing due to low melting Cu containing particles, even at high extrusion speed. It is believed that this behavior is because of the small size of the Q-phase particles and the volume fraction of these particles in the extrusion billet. There may be some dissolving of the Q- phase particles due to the deformation heating during extrusion, however the extent of melting is too low to cause any tearing in the profile. The content of Cu is preferably from 0.30 to 0.55 wt.%, or even more preferably from 0.32 to 0.55 wt.%. In a high-Cu embodiment the Cu content may be more than 0.35 wt.%, or at least 0.40 wt.%. High copper content leads to high mechanical strength of the extruded profile after aging treatment.

[0071] Manganese (Mn): 0-0.15 wt.%.

[0072] Mn is a dispersoid forming element which increases the deformation resistance of the alloy. The dispersoid particles containing Mn inhibits recrystallization and may add some strength of the material. However, in the present alloy it is desired to have a recrystallized microstructure, and the added strength by Mn is minor. It is therefore preferred that the amount Mn is kept below 0.10 wt.% to limit the amount of dispersoid particles in the alloy, or even below 0.08 wt.%. However, in order to provide a recycling friendly alloy, the amount of Mn may be from 0.05-0.10 wt.%.

[0073] Chromium (Cr): 0.0-0.10 wt.%.

[0074] Cr is also a dispersoid forming element and compared with Mn, Cr forms a much higher density of dispersoids per weight percent added compared with Mn. Hence, a high addition of Cr would increase the deformation resistance in the alloy, which is why the maximum amount is 0.10 wt.%. Dispersoid particles containing Cr also affects the recrystallization resistance of the alloy. It is desired to keep the number of dispersoids low enough such that the extruded profile obtains a fully recrystallized grain structure, however, the number of dispersoids should be sufficiently high to avoid grain growth and to keep a fine grain structure in the extruded profile. Therefore, the amount of Cr should preferably be kept in the range between 0.03 and 0.09 wt.%.

[0075] Iron (Fe): 0.1-0.5 wt.%.

[0076] Iron is typically an impurity element that comes from sources like the aluminium oxide, the production process and from scrap metal. Allowing up to 0.5 wt.% Fe allows more post-consumer scrap additions to the alloy, which is desired from a sustainability perspective as it reduces the carbon footprint of the aluminium alloy. A high content of Fe may reduce the corrosion properties of the alloy, and in some embodiments, the preferred amount of Fe is therefore between 0.15 and 0.40 wt.%, or between 0.20 and 0.35 wt.%. Titanium (Ti): less than 0.15 wt.%

[0077] Ti is normally added as a grain refiner in combination with boron (B) or carbon (C) forming TiBz or TiCxparticles. These particles act as nucleation sites for aluminium crystals and are contributing to a fine grain size of the alloy during casting. The Ti content for obtaining grain refinement is typically up to 0.05 wt.%, such as 0.005 to 0.03 wt.%. Ti is a peritectic element and additions up to about 0.15% will remain in solid solution. Due to the peritectic behaviour the Ti is segregated towards the centre of the grains during casting and may form Ti-enriched bands in the extrusion direction of the extruded profile. It is believed that such Ti-enriched bands slow down the diffusion rate of Mg and Si towards grain boundaries at elevated temperatures, which allows slower cooling rates from extrusion temperature, without compromising ductility and strength of the material. Ti also has a positive effect on the corrosion properties of the material. The minimum concentration of Ti is preferably 0.005 wt%. The content of Ti should be less than 0.15 wt% to avoid precipitation of primary AUTi particles in the peritectic reaction. Preferably the Ti content should be less than 0.12 wt% in order to reduce the negative effect on extrudability.

[0078] Vanadium (V): less than 0.10 wt.%.

[0079] V is also a peritectic element and behaves similarly as Ti, forming V-enriched bands along the extrusion direction in the extruded profile. The amount of V is kept less than 0.10 wt.% to reduce the negative effect on the extrudability.

[0080] Zinc (Zn): less than 1.0 wt.%.

[0081] Zn may be present in an amount up to 1.0 wt.%, which allows addition of post-consumer scrap to the alloy. Zn does not significantly affect the extrudability of the material, although at a high amount of Zn there might be a slight reduction of the extrudability of the alloy.

[0082] Zirconium (Zr) less than 0.05 wt.%

[0083] Zr may be present in an amount of less than 0.05 wt.%. Zr is a dispersoid forming element and its content should be limited to less than 0.05 wt.% to reduce negative effect on the extrudability.

[0084] The present disclosure also relates to a method for producing an extruded profile of the alloy according to the disclosure. The method comprises the following steps: a) providing a billet of an aluminium alloy having the following composition, in percent by weight (wt.%);

[0085] Mg: 0.85 - 1.15; Si: 0.60 - 0.75;

[0086] Fe: 0.1 - 0.5;

[0087] Cu: 0.25 - 0.60;

[0088] Cr: 0.0 - 0.10;

[0089] Mn: 0 - 0.15;

[0090] Zn: <1.0;

[0091] Ti: < 0.15;

[0092] V: < 0.10;

[0093] Zr: < 0.05; impurities equal to or less than 0.05 wt.% each and equal to or less than 0.15 wt.% in total, and the remainder being Al, wherein the ratio Mg / Sieff is 1.3-2.5, Sieff = Si - (Fe+Mn+Cr) / 3 [wt.%]; b) homogenizing the cast billet at a temperature of 540-590 °C, for a period of up to 8 h; c) cooling from the homogenizing temperature to a soft annealing temperature of 350-450 °C, by using a cooling rate of at least 100 °C / h; d) holding the extrusion billet at the soft annealing temperature for a period of 2-8 h, followed by cooling; e) preheating the extrusion billet; f) extruding the extrusion billet to an extruded profile, followed by air or water cooling; g) optionally stretching the extruded profile; h) optionally cutting the extruded profile into a pre-determined length; i) solution heat treating (SHT) the extruded profile at a temperature of 530-580 °C, followed by quenching; j) optionally cold deforming the SHT and quenched extruded profile; k) aging the extruded profile in a single, or multi-step aging process, said aging process comprising holding the extruded profile at a temperature of 160-220 °C for 1-24 hours.

[0094] The alloy composition in step a) may be varied within the ranges for the alloying elements as stated above for the aluminium alloy according to the present disclosure.

[0095] The obtainable extrusion speed with an extrusion billet of a 6XXX alloy is not only affected by the deformation resistance of the material but also by the melting temperature of the material since melting reactions in most cases are the reason for getting tearing in an extruded profile. A highly alloyed 6XXX material will in most cases have some MgjSi-particles present in the material, in addition to at least Mn and Cr containing dispersoid particles. During extrusion there will be a sharp increase in the temperature due to the deformation of the material when it is pushed through an extrusion die, and if the extrusion speed is too high there will be a melting reaction with tearing of the profile as the result. Mg in solid solution has a strong effect on the deformation resistance whereas Si has a minor effect on the deformation resistance. By keeping a low preheating temperature of the billet, it is possible to retain the Mg2Si particles during extrusion and reduce the deformation resistance. Even though the mechanism for tearing is eutectic melting of Mg2Si particles, which is lower than solidus melting of the aluminium matrix, the large reduction in the deformation resistance can in some cases give a dramatic increase in the maximum extrusion speed, such as up to 200 % speed increase, before tearing of the extruded profile. Hence, to obtain maximum extrusion speed for soft annealed material it is important to have a material that has the lowest possible deformation resistance and the highest possible eutectic melting temperature. For a high strength 6XXX alloy the highest melting temperature is obtained for a material that is balanced with respect to Mg2Si.

[0096] With a balanced content of Mg and Si to form Mg2Si-particles the melting temperature is, as explained above, determined by the binary eutectic temperature between aluminium matrix plus Mg2Si-particles, which is around 595°C. If the aluminium matrix contains excess Si in solid solution the eutectic temperature will gradually decrease. If the excess Si is high enough to form Si-particles together with Mg2Si-particles the ternary eutectic temperature between aluminium matrix plus Mg2Si-particles plus Si-particles will drop to about 555°C. Thus, to maximize the melting temperature and thereby maximizing the extrusion speed it is an advantage to have composition close to the balanced content of Mg and Si to form Mg2Si-particles. For this reason, the ratio Mg / Sieff should be in the range from 1.3 to 2.5, preferably in the range 1.4-2.2, or even more preferably in the range 1.6- 2.1, to avoid ternary eutectic, but to promote a binary eutectic of Mg2Si and Al that melts at high temperatures, preferably at a temperature of 590-595 °C. Sieff = Si - (Fe+Mn+Cr) / 3 [wt.%]. The alloy according to the present disclosure has low amounts of both Mn and Cr, thus contributing only minor to the deformation resistance.

[0097] In the homogenizing step the extrusion billets are heated to a temperature above the solvus temperature of the alloy. A typical homogenization temperature according to the present method lies in the range 540-590 °C. A typical time of the homogenization step (b) may be up to 8 hours, and at least 1 hour. In a standard, traditional process the extrusion billets are cooled from the homogenization temperature down to room temperature at a cooling rate typically between 200 and 500°C / hour. According to the present method, a soft annealing step (step d) follows the homogenizing process, and the purpose of the soft annealing step is to reduce the deformation resistance of the extrusion billet. Reduction of the deformation resistance is achieved by precipitating a large volume fraction of Mg2Si-particles. The amount of Mg tied up in the Mg2Si- particles leads to a reduced amount of Mg in solid solution, and this especially contributes to the reduced deformation resistance.

[0098] The cooling from the homogenization temperature to the soft annealing temperature can be performed at different cooling rates. A slow cooling rate, such as 5-50 °C per hour may lead to relatively large Mg2Si-particles in the aluminium matrix, while a faster cooling rate of about 100 °C to 500 °C per hour would give a more saturated matrix of Mg2Si-particles having much smaller average particle size. A high number of small Mg2Si-particles is more effective in draining the aluminium matrix from Mg atoms than fewer and larger Mg2Si-particles. In addition, small Mg2Si-particles are dissolved much faster in the downstream solutionizing step. Therefore, it is preferred to use a cooling rate of at least 100 °C per hour, and more preferred at least 200 °C per hour, from the homogenizing temperature to the soft annealing temperature (in step c). The holding time at the soft annealing temperature of between 350 and 450 °C (step d) should be between 2-8 hours to ensure that as much Mg as possible has been drained from the aluminium matrix. The soft annealing treatment time should be restricted to the time necessary to extract the Mg from the matrix as extending the time may lead to unwanted growth of the Mg2Si-particles. The cooling from the soft annealing temperature to room temperature should preferably be fast, such as 200-500 °C per hour to ensure that small average particle size of the Mg2Si-particles is kept in the material.

[0099] The preheating temperature of the soft annealed billet in the preheating step e) should preferably be to the same temperature as the hold temperature of the soft annealing step (d); suitable preheating temperature in step (e) may therefore be from 350 to 450 °C. The relatively low preheating temperature is beneficial since it allows more deformation heating caused by the press force, and this allows much higher extrusion speed compared with traditional extrusion with billets that have not been subjected to the soft annealing treatment.

[0100] The extruded profile may be a hollow profile with one or more voids, or a solid profile, or a profile having a complex cross-sectional shape. The extruded profile is cooled by air or water cooling after the extrusion die exit. It is not critical to quench the extruded profiles as the profiles are subjected to solution heat treatment (SHT) before the aging. Since the extruded profile does not require quenching out of the extrusion press, the front and back ends can be used in further manufacturing processes, thus less production scrap is produces compared with extrusions that needs to be quenched directly after the extrusion press. In addition, a slower cooling may be advantageous for quench sensitive alloys.

[0101] The extruded profile may optionally be stretched (step g) for straightening and stress relief of the extruded profile, according to known methods.

[0102] After extrusion the profiles will typically be cut to shorter lengths and heated (solution heat treated, SHT, also denoted solutionizing) to a temperature above the solvus temperature to dissolve the Mg2Si-particles that were formed during the cooling and soft annealing process following the homogenizing process. The choice of temperature in the solutionizing process (step i) should be selected to minimize the necessary time at the SHT temperature. If the SHT temperature is exactly or close to the solvus temperature the time for dissolving all the Mg2Si-particles would be very long. At a higher temperature above the solvus the dissolution of the Mg2Si-particles is much faster, the upper temperature limit is the solidus temperature of the alloy. Smaller Mg2Si-particle sizes are also beneficial as it contributes to considerably reduce the SHT time. The SHT temperature in step (i) should be kept between 530 and 580 °C, preferably the SHT temperature is above 545 °C, or above 555 °C, or above 560 °C for achieving faster dissolution of Mg2Si-particles. Any Cu containing phases will typically dissolve at lower temperatures than the Mg2Si-particles.

[0103] Following the SHT the extruded profiles are quenched (step i). The quenching is preferably done by water quenching or water spraying. In some embodiments cut lengths of the extruded profiles may be quenched in a vertical or substantially vertical direction by submerging the whole length of the extruded profile into a quenching bath. By "vertically quenching" it is meant that the extruded profile may typically be oriented in a vertical direction, i.e. with its longitudinal direction oriented vertically, while being submerged in the quenching bath. Such vertical quenching is particularly advantageous for hollow profiles having at least two hollow voids as it enables fast cooling across the entire profile cross-section. The duration of the submergence of the profile is preferably less than 30 seconds, typically 10-15 seconds or less. The vertical quenching may be performed by a robotic arm.

[0104] The SHT and quenched extruded profile in W-temper is soft and formable with low spring-back within a relatively short time after the quenching. Due to these properties any forming operations are advantageously done on the extruded profile in the W-temper within a short time after the quenching operation. Such forming may include cold deformation such as stretching to straighten the profile, mechanical calibration of the extruded profile to obtain accurate dimensions within tolerance limits, hydroforming and / or bending to obtain predetermined shape, or other cold work deformation operation known in the art. Due to the softness and low spring-back force of the W- temper material such cold forming operations requires only low forces.

[0105] The alloy according to the present disclosure ages naturally and spontaneously after the SHT, therefore the hardness of the SHT and quenched profile increases relatively steeply after a short time of natural aging, when the SHT and quenched profile is stored at room temperature. Also, the elongation is affected by the natural aging. FIG. 6 shows the development of yield stress, Rp0.2, and elongation, Ag, for SHT and quenched profiles of 6061 test alloys with 0.0, 0.1, 0.2 and 0.5 wt.% Cu, respectively, stored at room temperature (W-temper). It is seen that all alloy variants have a very low yield stress of below or around 60 MPa the first approx. 10 minutes in room temperature storage, after which time the yield stress increases steeply. Surprisingly, the alloy comprising 0.5 wt.% Cu retains a low yield stress for a longer time at room temperature storage compared with the other alloys having lower amounts or no Cu, before the yield stress increases sharply and becomes higher than the other alloys in the diagram. Looking at the elongation it is seen that the material is very ductile the first minutes, between about 20-22 % (the first elongation value for the alloy comprising 0.2 wt.% Cu seems to be wrong as it differs significantly from the other alloys) after room temperature storage while the elongation diminishes, before increasing slightly and stabilizing around 19-20.5 %. Therefore, the storage time period of the SHT and quenched extruded profile should be kept short before subjecting the extruded profile to cold forming processes, such as mechanical calibration, hydroforming, bending or other cold forming. The SHT and quenched extruded profile in W-temper used in the cold forming operations preferably has a tensile stress of maximum 100 MPa, more preferred maximum 80 MPa. The cold forming operations (step j) are preferably performed within 4 hours after the quenching in step i), preferably within maximum 1-2 hours, or most preferred within 20 minutes after the quenching (step i).

[0106] The cold deformation may comprise mechanical calibration of a hollow extruded profile in W- temper to achieve tight dimensional tolerances. The mechanical calibration may be a hydrocalibration. The hydro-calibration method uses a liquid, preferably water, trapped inside as a mandrel in a hollow profile when compressing the profile from the outside using a die tool which is configured to define the external shape or boundary of the final shape of the extruded profile. The extruded profile is plastically deformed into the desired shape by using a pressing tool that may move the die tool, leading to an increase of the internal pressure in the hollow chamber containing the entrapped liquid. In combination with the extruded profile made of the alloy according to the present disclosure in the W-temper the low yield stress and spring back of the material will require only low forces, and it would be possible to achieve extremely good dimensional tolerances. Other mechanical calibration method known in the field may also be used for obtaining dimensional tolerances, e.g. by using mandrel inserts.

[0107] The cold deformation may include hydroforming operation. Hydroforming may be used as an alternative to machining to correct or adjust the exterior shape of a hollow extruded profile, and to obtain tight tolerance products. A hydroforming process may include placing the extruded profile in a tool that has a shape (of the tool's internal walls) corresponding to the desired external shape of the profile, filling the hollows with a liquid, typically water, closing both ends of the profile with closing devices, and applying a high pressure trough the closing devices. The profile walls are expanded towards the tooling internal surfaces by the high pressure, and the extruded profile is plastically deformed and shaped by the tooling walls. In conventional hydroforming process large forces are required to expand the extruded profile and to keep the tooling in position during the forming process. Another challenge may be to obtain precise dimension of material having large spring-back force. The present extruded profile in W-temper is highly suitable for hydroforming since the material has very low tensile stress, and low spring-back, as described above.

[0108] The aging (step k) of the extruded profile is done by a single, or multi-step aging process, where the aging comprises holding the extruded profile at a temperature of 160-220 °C for 1-24 hours, obtaining a T6 temper having yield strength above 320 MPa. Preferably the aging in step I) comprises holding the extruded profile at a temperature of 180-200 °C for 2-10 hours to obtain a yield stress (Rp0.2) of above 340 MPa in a T6 condition. It is preferred that the aging step is performed within 2- 4 hours after the solution heat treatment and quenching, and any cold forming operations since storage in room temperature may negatively influence the maximum obtainable mechanical strength of the material in T6 condition. Preferably, the aging step is performed within 20-60 minutes after the SHT and quench step. Performing the aging step within the indicated time may add significant strength to the extruded product in T6 condition.

[0109] By the method disclosed herein, it is possible to extrude the present high strength alloy having a high content of Cu at significantly higher extrusion speeds than with conventional method, without experiencing tearing in the extruded profile. In addition, by the present alloy and method extruded profiles in W-temper are highly formable and can be cold formed to obtain final shape and dimensions at low forces, while obtaining extruded products having a T6 temper above 320 MPa.

[0110] The extruded profile made by method according to the present disclosure obtains a fully recrystallized grain structure. High extrusion speeds promote small grain size in the extruded material, and the extruded profile according to the present disclosure has a recrystallized, fine grained structure, that is stable in the SHT process. The bulk average grain size (diameter) in the extruded profile is preferably less than 150 pm, or more preferably less than 100 pm.

[0111] The extruded profile in W-temper, directly after SHT and quenching has high formability and low yield stress, having a Rp0.2 less than 100 MPa, and more preferably less than 80 MPa. The yield stress increases significantly when the extruded profile is stored at room temperature, as shown in FIG. 6. The excellent formability of extruded profile according to the present disclosure, in a W- temper condition, makes the extruded profiles very suitable for use in hydroforming processes. Preferably, the hydroforming takes place at maximum 4 hours after the SHT and quenching of the extruded profile, for the same reasons as discussed above.

[0112] The extruded profile of the present disclosure obtains a yield stress in a T6 condition of at least 320 MPa, preferably at least 340 MPa. The aged profile has a high ductility, which together with the high tensile strength provides important low cycle fatigue properties, important for e.g. spring link parts. Recrystallized hollow profiles of the present disclosure have more isotropic mechanical characteristics, compared with a typical high strength extruded profile having a fibrous grain structure in in the extrusion direction. The more isotropic mechanical characteristics seem to be favorable in ductility issues, meaning a high capacity to accumulate plastic strain which is the case in very low cycle fatigue.

[0113] Corrosion tests for testing intergranular corrosion properties according to ISO 11846:1995 Method B, wherein samples of the parts are immersed in acidic liquid for 24 hours and cross sections are investigated in a light optical microscope to find the deepest attacks, have shown that the average of the three deepest corrosion attacks were 192 pm. Many OEMs sets a maximum limit of 300 pm for intergranular corrosion, hence the present extruded profile of the alloy disclosed herein has good corrosion properties. EXAMPLE 1

[0114] Lab extrusion trials were conducted in an 800 tons laboratory extrusion press with a 4" (100 mm) diameter container. One 6082 alloy and two 6061 based alloys comprising different amounts of Cu (0.2 wt.% and 0.5 wt.%) were cast as 95 mm diameter logs in a laboratory DC casting machine. The 6061-0.2Cu alloy is included in the example as a comparing alloy, as its composition lies outside the claimed Cu range.

[0115] Table 1.

[0116] Some of the billets were soft annealed by a slow cooling from the homogenising temperature of 550°C down to 350°C and held there for 8 hours, according to the method of the present disclosure. Other billets of the same alloys were homogenised at 550°C and cooled rapidly down to room temperature, according to conventional processes. The section used was a round bar of 09 mm with two 1. Oxl.O mm2ribs giving a reduction ratio of approximately 120:1. The billets were heated in an induction coil to the pre-set temperature at a rate of approximately 100°C / min. The extrusion started approximately 1 minute after heating the billet. FIGs. 2, 3 and 4 show the results from extrusion of these variants. The billets were preheated to different temperatures and extruded at different ram speeds. Each extruded profile was visually inspected, and the markers were chosen according to the appearance of the profile. A profile with tearing resulted in a black marker, whereas a good profile resulted in a white marker. Borderline profiles were plotted with a grey maker. Soft annealed samples are marked with triangles ("Soft") and the homogenized only samples are marked with squares ("Hom").

[0117] For the soft annealed 6082 billets tearing in the profile occurred a lower extrusion speed than for homogenised billets (FIG. 2). Due to the high amounts of Mn and Cr in the 6082 alloy the deformation resistance was high. Also, a 6082 alloy typically has 0.6-0.7 wt% Mg and the effect of reducing the Mg content in solid solution by soft annealing will therefore be moderate. Moreover, soft annealing at temperatures in range 350-450°C will precipitate both MgjSi particles as well as Si particles due to the low Mg / Si ratio in a 6082 alloy. In the extrusion process these particles will form a ternary eutectic together with aluminium that will melt at 555-559°C, according to AIMgSi phase diagrams known in the literature. In contrast to the 6082 reference alloy, the extrusion speeds obtained for the soft annealed billets of the 6061 alloy with 0.2 wt% Cu were much higher than for the homogenised only billets. The reason is a combination of different effects; low amount of Mn and Cr that give a minor contribution to the deformation resistance; an initial high Mg content in the alloy and in solid solution was significantly reduced by the soft annealing to grow Mg2Si particles; with balanced Mg / Si ratio ternary eutectic was not formed but a binary eutectic of Mg2Si and aluminium that melts in the range to 590-595°C if the alloy is Quasi-Binary. Since the profiles had to be separately solutionized after extrusion it was not necessary to get the Mg2Si particles dissolved during extrusion. For the homogenised billets, the preheating temperature needed to be in the range of 470-500°C to get most of the Mg and Si in solid solution, whereas for the soft annealed billets that had a low deformation resistance only the available pressure limited the billet temperature. These combined effects gave an increase in maximum extrusion speed of approximately 200% for the soft annealed billets with 0.20 wt% Cu assuming a billet preheating temperature of 480°C for the homogenised billets and 420°C for the soft annealed billets.

[0118] For the 6061 alloy with 0.5 wt% Cu only soft annealed billets were tested. It is however believed that the combined effects as discussed for the 6061 alloy with 0.2 wt% Cu are also present with the alloy comprising 0.5 wt.% Cu, and there is a significant increase in extrusion speed due to the soft annealing. The extrusion speeds and results achieved for the alloy comprising 0.5 wt.% Cu was very surprising. It was especially surprising that soft annealed 6061 billets with a Cu content of 0.5 wt% did not cause any tearing due to low melting Cu containing particles. Without wishing to be bound by the theory it is thought that the reason why the Q-phase particles (AI5Cu2Mg8Si6) did not create problems with tearing probably had to do with the sizes and the volume fraction of these particles, ref. FIG. 1 (a) and (b) showing SEM micrographs with identification of separate phases found in the soft annealed 6061 alloys with 0.2 wt% Cu (top picture) and 0.5 wt% Cu (bottom picture). The particles may dissolve due to the deformation heating during extrusion before reaching the die exit, or the amount of melting may be too low to cause any tearing in the profile.

[0119] Mechanical properties of the 6061 alloy variants with 0.2 and 0.5 wt.% Cu respectively were tested on a hollow extruded rectangular profile with dimensions 20x26 mm2and a wall thickness of 1.9 mm. The profiles were solutionized at 550°C for 30 minutes total time (including heating) followed by quenching in water. Ageing was performed in two different ways:

[0120] • Room temperature storage for 24 hours and 200°C per hour heating rate to 185°C and hold at this temperature for 6 hours (alloy with 0.2 wt.% Cu only). • 5 minutes room temperature storage prior to putting the samples in an oven set at a temperature of 175°C and 6 hours hold at this temperature.

[0121] The separate solutionizing gave attractive properties for the 6061 based alloys, typically higher than obtained after extrusion and no separate solutionizing prior to ageing. From FIG. 5 one clearly sees the positive effect of short storage time between solutionizing and ageing. Although 175°C for 6 hours seemed to give a slightly underaged condition, the difference in ultimate tensile stress, Rm, was around 30 MPa and the difference in yield stress, Rp0.2 was approximately 20 MPa. The 6061 alloy with 0.5 wt.% Cu due to the larger difference between Rp0.2 and Rm, seemed to be more underaged but still showed an increase in Rp0.2 and Rm of 15-20 MPa.

[0122] EXAMPLE 2

[0123] Industrial scale trials were performed on an existing production program currently using a 6082 alloy. The existing industrial program already used separate solutionizing on 6082 profiles to achieve necessary formability and mechanical properties, and the technology could therefore be easily implemented for the AIMgSi alloys according to the present disclosure.

[0124] Apart from the low extrudability of 6082 alloys, another problem in a process involving separate solutionizing of profiles from these alloys is to avoid a thick coarse grained recrystallized surface layer and recrystallization in the seam weld area. A high amount of dispersoid forming elements like Mn and Cr and correct choice of homogenising parameters are good starting points, but also extrusion speed and the times and temperatures in the separate solutionizing process are very important factors.

[0125] With the AIMgSi alloy according to the present disclosure the amount of dispersoid forming elements were low and the extrusion speeds were high, giving a fully recrystallized and fine-grained structure in the extruded profile. To test the stability of the grain structure in extruded profiles of the AIMgSi alloy according to the present disclosure, samples were solutionized at 570°C for 2 hours and did not show any signs of grain growth. This proved that a recrystallized structure was much more robust with respect to further grain growth and a stop in an industrial forming line of up to 2 hours will not cause a problem. Grain structures of solutionized 6082 profile and solutionized profile of the alloy according to the present disclosure, at 550°C for 30 minutes can be seen in Figure 7 (6082 alloy to the left, alloy according to present disclosure to the right). The profiles were extruded in a 12" extrusion press and manufactured into a spring link - Rear Lower Control Arm (RLCA). The wall thicknesses of the extrusion varied between 3 and 8 mm. With the alloy according to the present disclosure it was possible to extrude 150-200% faster than with the 6082 alloy currently used in the industrial process.

[0126] Another benefit with the AIMgSi alloy according to the disclosure was the profile quenching at the exit of the extrusion press. Since it was going to be separately solutionized afterwards it was not necessary to make a fast cooling of the profiles to get good mechanical properties, only to get it cooled enough before being stretched. For profiles that are not going to be separately solutionized they will typically have to be water quenched out of the press. In that case the material between the die exit and the start of the quench typically must be scrapped. With the AIMgSi alloy according to the present disclosure one can probably save about one meter of the back end of the profile as good material.

[0127] Cut lengths of the extruded profiles of the alloy according to the present disclosure were loaded to the forming line for the existing spring link production with 6082 profiles. Except for adjusting the solutionizing temperature up by 10-15°C nothing else was changed. The separate solutionized profiles were then quenched vertically in a water tank and formed to a spring link before being aged to a T6 condition. Mechanical properties were measured on formed and aged spring link parts and can be seen in Table 2.

[0128] Table 2.

[0129] The 6082 material in production showed slightly higher strength and elongation values. However, the minimum strength requirement for the spring link is a yield stress, Rp0.2, of 320 MPa, and the material from the alloy according to the present disclosure met this limit with a good margin. The Z value, which is the reduction of area in percentage and is related to the true fracture strain of the material, was slightly better for the material produced according to the present disclosure. Where Ao is the initial cross-sectional gauge area of the tensile sample, and A is the cross-sectional area of the fracture. High ductility of the material is particularly important for the low cycle fatigue properties of a spring link, which typically is the design criteria for such a part. The part should withstand repeated deformations caused by the wheel of a vehicle hitting a big hole or the curb side of the road.

[0130] The spring links with mechanical properties shown in Table 2, were tested in the same component test rig as the 6082 spring links in serial production. For the 6082 spring links the average number of cycles before failure was 93.000 cycles whereas the spring links produced of the alloys and method according to the present disclosure lasted 122.000 cycles before failure. This was even after being corrosion tested in neutral salt spray in accordance with ISO 9227 for 720 hours before being fatigue tested. This was not done on the serial production parts made from 6082.

Claims

CLAIMS1. An extrudable AIMgSi alloy for high strength extruded parts suitable for use in vehicles, having the following composition, in percent by weight (wt.%);Mg: 0.85 - 1.15;Si: 0.60 - 0.75;Fe: 0.1 - 0.5;Cu: 0.25 - 0.60;Cr: 0.0 - 0.10;Mn: 0 - 0.15;Zn: <1.0;Ti: < 0.15;V: < 0.10;Zr: < 0.05; impurities equal to or less than 0.05 wt.% each and equal to or less than 0.15 wt.% in total, the remainder being Al, wherein the ratio Mg / Sieff is 1.3-2.5, Sieff = Si - (Fe+Mn+Cr) / 3 [wt.%].

2. The extrudable alloy according to claim 1, wherein the ratio Mg / Sieff is 1.4-2.2; or 1.6-2.1.

3. The extrudable alloy according to any one of claims 1-2, wherein the amount of Mg is 0.85-1.05 wt.%.

4. The extrudable alloy according to any one of claims 1-3, wherein the amount of Si is 0.65- 0.75 wt%; or 0.65-0.72 wt.%.

5. The extrudable alloy according to any one of claims 1-4, wherein the amount of Cu is 0.30- 0.55 wt.%; or 0.32-0.55 wt.%.

6. The extrudable alloy according to any one of claims 1-5, wherein the amount of Fe is 0.15- 0.40 wt.%; or 0.20-0.35 wt.%.

7. The extrudable alloy according to any one of claims 1-6, wherein the amount of Mn is less than 0.10 wt.%; or less than 0.08 wt.%.

8. The extrudable alloy according to any one of claims 1-7, wherein the amount of Cr is 0.03-0.09 wt.%.

9. A method for producing an extruded profile of an AIMgSi alloy according to any one of claims 1-8, the method comprising the following steps: a) providing an extrusion billet of an aluminium alloy having the following composition, in percent by weight (wt.%);Mg: 0.85 - 1.15;Si: 0.60 - 0.75;Fe: 0.1 - 0.5;Cu: 0.25 - 0.60;Cr: 0.0 - 0.10;Mn: 0 - 0.15;Zn: <1.0;Ti: < 0.15;V: < 0.10;Zr: < 0.05; impurities equal to or less than 0.05 wt.% each and equal to or less than 0.15 wt.% in total, the remainder being Al, wherein the ratio Mg / Sieff is 1.3-2.5, Sieff = Si - (Fe+Mn+Cr) / 3 [wt.%]; b) homogenizing the extrusion billet at a temperature of 540-590 °C, for a period of up to 8 h; c) cooling the extrusion billet from the homogenizing temperature to a soft annealing temperature of 350-450 °C, by using a cooling rate of at least 100 °C / h; d) holding the extrusion billet at the soft annealing temperature for a period of 2-8 h, followed by cooling; e) preheating the extrusion billet; f) extruding the extrusion billet to an extruded profile, followed by air or water cooling; g) optionally stretching the extruded profile; h) optionally cutting the extruded profile into a pre-determined length; i) solution heat treating (SHT) the extruded profile at a temperature of 530-580 °C, followed by quenching; j) optionally cold deforming the SHT and quenched extruded profile; k) aging the extruded profile in a single, or multi-step aging process, said aging process comprising holding the extruded profile at a temperature of 160-220 °C for 1-24 hours.

10. The method according to claim 9, wherein the quenching in step i) comprises vertically quenching the extruded profile into a quenching bath.

11. The method according to any one of claims 9-10, wherein the cold deforming step j) is performed maximum 4 hours after the quenching in step i).

12. The method according to any one of claims 9-11, wherein the cold deforming step j) includes one or more of stretching, mechanical calibrating or hydroforming.

13. The method according to any one of claims 9-12, wherein the aging in step k) comprises holding the extruded profile at a temperature of 180-200 °C for 2-10 hours.

14. The method according to any one of claims 9-13, wherein the aging step k) is performed within 2-4 hours after the SHT and quenching step i).

15. An extruded profile made of an aluminium alloy having the following composition, in percent by weight (wt.%);Mg: 0.85 - 1.15;Si: 0.60 - 0.75;Fe: 0.1 - 0.5;Cu: 0.25 - 0.60;Cr: 0.0 - 0.10;Mn: 0 - 0.15;Zn: <1.0;Ti: < 0.15;V: < 0.10;Zr: < 0.05; impurities equal to or less than 0.05 wt.% each and equal to or less than 0.15 wt.% in total, the remainder being Al, wherein the ratio Mg / Sieff is 1.3-2.5, Sieff = Si - (Fe+Mn+Cr) / 3 [wt.%]; where the extruded profile has a fully recrystallized grain structure with an average grain size diameter of less than 150 pm; and wherein the extruded profile has a yield stress (Rp0.2) of at least 320 MPa in a T6 condition.

16. The extruded profile according to claim 15, where the extruded profile in W-temper has a yield stress, Rp0.2, less than 100 MPa.

17. The extruded profile according to any one of claims 15-16, where the extruded profile is used as a structural part in vehicles, such as a spring link part, wheel suspension part or a bumper.

18. Use of the method according to any one of claims 9-14, to manufacture a structural part for use in vehicles, such as a spring link part, wheel suspension part or a bumper.

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