Extruded profile of an aluminium alloy and method for producing an extruded profile

Abstract

An extruded profile, suitable for building and construction applications, made of an aluminum alloy having the following composition, in percent by weight (wt.-%): Si 0.20 – 0.38, Mg 0.20 – 0.38, Fe 0.10 – 0.30, Mn 0.02 – 0.10, Cu equal to or less than 0.10, Zn equal to or less than 0.15, Cr equal to or less than 0.05, Ti equal to or less than 0.10, impurities equal to or less than 0.05 wt.-% each and equal to or less than 0.15 wt.-% in total, the reminder being Al.

Description

[0001] EXTRUDED PROFILE OF AN ALUMINIUM ALLOY AND METHOD FOR PRODUCING AN EXTRUDED PROFILE

[0002] TECHNICAL FIELD

[0003] The present disclosure relates in general to an extruded profile made of an aluminum alloy. The present disclosure further relates in general to a method for producing such an extruded profile, and to the use thereof.

[0004] BACKGROUND

[0005] Aluminum based materials are frequently used within the building and construction industry today. One reason therefore is the high strength-to-weight ratios that may be achieved, which in turn e.g., enables reducing the load on a building's supporting structure. Aluminum based materials may also enable improved energy efficiency in buildings due to being heat reflective, rather than energy absorbing. Furthermore, aluminum based materials have a high natural resistance to corrosion, thereby enabling a long service life. These materials may also, if desired, be anodized or painted to further improve corrosion resistance and / or obtain a desired aesthetic appearance. Aluminum based materials also have the advantage of being fully recyclable an infinite number of times without deterioration in the achievable properties resulting from such recycling.

[0006] Examples of applications within the building and construction industry for aluminum metal based materials include building profiles, facades, roofing, door and window frames, railings, ladders, etc. In some of these applications, extruded profiles of the aluminum metal based material are used. The most frequently used aluminum metal based materials for extruded profiles for building and construction applications with modest strength requirements include EN AW 6063 and EN AW 6060. In applications requiring higher strength, EN AW 6106 or even EN AW 6082 may typically be used.

[0007] Although aluminum metal based materials constitute an environmentally friendly choice of material, e.g., for providing long service life and being fully recyclable as mentioned above, there are continuous efforts to further reduce the environmental impact of such products. This could for example be achieved by reducing the wall thickness of a product, such as an extruded profile. A reduced wall thickness may be directly translated into corresponding reduction of the carbon dioxide footprint for each component produced from the material. This must however be balanced against the required (or desired) properties of the product. Furthermore, for a profile manufacturer, it is important that such a reduction of the wall thickness of the profile does not lead to any substantial increase in the manufacturing costs.

[0008] SUMMARY

[0009] The object of the present invention is to enable a reduced environmental impact for an extruded profile intended to be used in building and construction applications.

[0010] The object is achieved by the subject-matter of the appended independent claim(s).

[0011] The herein described extruded profile is made of an aluminum alloy having the following composition, in percent by weight (wt.-%):

[0012] Si 0.20 - 0.38,

[0013] Mg 0.20 - 0.38,

[0014] Fe 0.10 - 0.30,

[0015] Mn 0.02 - 0.10,

[0016] Cu equal to or less than 0.10,

[0017] Zn equal to or less than 0.15,

[0018] Cr equal to or less than 0.05,

[0019] Ti equal to or less than 0.10, impurities equal to or less than 0.05 wt.-% each, and equal to or less than 0.15 wt.-% in total, and the reminder being Al.

[0020] The composition of the aluminum alloy of the extruded profile leads to a considerable improvement in extrudability compared to e.g., EN AW 6060, which is an alloy considered to have a high extrudability. The improved extrudability of the herein described aluminum alloy facilitates reducing the wall thickness of the profile, and thereby also enables a reduced carbon dioxide footprint and hence reduced environmental impact.

[0021] Furthermore, the composition of the aluminum alloy of the extruded profile leads to an improved surface quality, in terms of surface roughness and severeness of die lines, of the profile in the as- extruded condition compared to e.g., EN AW 6060. Thereby, less etching is needed to remove material from the surface of the extruded profile to obtain a desired surface quality / appearance after subsequent surface treatment, such as anodization. A reduction of material to be removed from the surface of the extruded profile in turn enables a reduction of the sludge generated during etching and that need to be processed using various chemicals. This in turn also leads to a reduction of the environmental impact.

[0022] These improvements in the environmental impact are achieved without leading to any substantial increase in the manufacturing costs. In fact, the improved extrudability enables a higher productivity and thereby improved process economy for a profile manufacturer.

[0023] Moreover, the extruded profile may be subjected to various surface treatment processes, such as anodizing or painting, with a resulting high quality surface finish. In fact, it is possible to achieve a surface finish at least as good as the surface finish of e.g., EN AW 6060. Thereby, it is also possible to meet the customers' expectations in terms of aesthetic appearance of the surface of the extruded profile.

[0024] The chemical composition of the aluminum alloy of the extruded profile leads to a reduction of the obtainable strength of extruded profile compared to extruded profiles of EN AW 6063 and EN AW 6060. However, the extruded profiles offered by profile manufacturers today often have a higher mechanical strength than actually needed by the customer. Thus, the herein described extruded profile may advantageously be used for applications where the currently offered extruded profiles are above the requirements in mechanical properties.

[0025] The present disclosure also relates to a method for producing an extruded profile. The method comprises the following steps:

[0026] (a) providing a billet of an aluminum alloy having the following composition, in percent by weight (wt.-%):

[0027] Si 0.20 - 0.38,

[0028] Mg 0.20 - 0.38,

[0029] Fe 0.10 - 0.30,

[0030] Mn 0.02 - 0.10,

[0031] Cu equal to or less than 0.10,

[0032] Zn equal to or less than 0.15,

[0033] Cr equal to or less than 0.05, Ti equal to or less than 0.10, impurities equal to or less than 0.05 wt.-% each and equal to or less than 0.15 wt.-% in total, the reminder being Al;

[0034] (b) homogenizing the billet at a temperature of 480 - 620 °C for 1 - 5 hours, followed by cooling to room temperature;

[0035] (c) preheating the billet to a billet temperature of 440 - 530 °C, preferably 460 - 500 °C;

[0036] (d) extruding the preheated billet to an extruded profile, followed by air or water cooling;

[0037] (e) optionally stretching the extruded profile;

[0038] (f) optionally solution heat treating the extruded profile, followed by quenching;

[0039] (g) aging the extruded profile in a single or multi-step aging process, said aging process comprising holding at a peak temperature of 160 - 200 °C for 1 - 100 hours; and

[0040] (h) optionally subjecting the extruded profile to a surface treatment, such as anodization or painting.

[0041] BRIEF DESCRIPTION OF DRAWINGS

[0042] Fig. 1 represents a graph showing the contents of Mg and Si, respectively, of the experimental alloys in relation to the Mg-Si range of the aluminum alloy according to the present disclosure,

[0043] Fig. 2 illustrates a part of the cross section of the extruded profile according to the experimental tests,

[0044] Fig. 3 illustrates a graph of extrusion pressure, determined at different measurements points as the extrusion proceed, for the experimental alloys,

[0045] Fig. 4 illustrates theoretical relative extrudability of the experimental alloys Alloy 1 - 5 compared to Alloy A,

[0046] Fig. 5 illustrates digital images of measurement area of the respective profiles illustrating the die lines (bottom), and the corresponding recorded depth profiles (top), Fig. 6 illustrates surface roughness, Ra, of the experimental alloys in the as-extruded condition,

[0047] Fig. 7 illustrates a graph showing hardness ( H V) as a function of aging time for the experimental alloys when aged at 185 °C,

[0048] Fig. 8a illustrates yield strength, Rp0.2, of the experimental alloys after aging according to two different procedures,

[0049] Fig. 8b illustrates tensile strength, Rm, of the experimental alloys after aging according to the two different procedures, and

[0050] Fig. 8c illustrates elongation of the experimental alloys after aging according to the two different procedures.

[0051] DETAILED DESCRIPTION

[0052] 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.

[0053] 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.

[0054] The herein described extruded profile has primarily been developed for use in building and construction applications, such as building profiles, door and / or window frames (including sliding frames), railings, etc. . It should however be noted that the extruded profile may also be used in other applications, in particular when it is desired to reduce the environmental impact and only low or modest strength is required. Examples of other applications for the herein described extruded profile include profiles for weather protection, frames for solar panels and decorative trims e.g., for the interior of vehicles, but are not limited thereto. 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.

[0055] The present disclosure provides an extruded profile of an aluminum based alloy, said aluminum based alloy having a composition comprising, in percent by weight (wt.-%):

[0056] Si 0.20 - 0.38,

[0057] Mg 0.20 - 0.38,

[0058] Fe 0.10 - 0.30,

[0059] Mn 0.02 - 0.10,

[0060] Cu equal to or less than 0.10,

[0061] Zn equal to or less than 0.15,

[0062] Cr equal to or less than 0.05,

[0063] Ti equal to or less than 0.10, impurities equal to or less than 0.05 wt.-% each, and equal to or less than 0.15 wt.-% in total, the reminder constituting Al.

[0064] 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.

[0065] Silicon (Si): 0.20-0.38 wt.-%.

[0066] Silicon is an important element of the herein described aluminum alloy since it combines with Mg to form dispersed 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 0.20% of Si. Preferably, Si is present in an amount of equal to or more than 0.22%, or even equal to or more than 0.24%.

[0067] However, the amount of Si also affects the extrudability of the aluminum alloy. To obtain an improved extrudability compared to previously known aluminum alloys for building and construction applications so as to thereby facilitate reducing the wall thickness of the extruded profile, the herein described aluminum alloy therefore comprises at most 0.38% of Si. Preferably, Si is present in an amount of equal to or less than 0.36%.

[0068] Magnesium (Mg): 0.20-0.38 wt.-%.

[0069] As described above, 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. In order to obtain sufficient mechanical strength after aging, the aluminum alloy comprises at least 0.20% of Mg. Preferably, Mg is present in an amount of equal to or more than 0.22%, or even equal to or more than 0.24%.

[0070] However, the extrudability of the aluminum alloy decreases with increasing amount of Mg. To obtain an improved extrudability compared to previously known aluminum alloys for building and construction applications, the herein described aluminum alloy therefore comprises at most 0.38% of Mg. Preferably, Mg is present in an amount of equal to or less than 0.36%.

[0071] Preferably, Mg and Si may be present in the aluminum alloy in an amount such that Equation 1 is fulfilled. Thereby, the extrudability of the aluminum alloy may be even further improved.

[0072] [wt. — % Mg] < 0.48 — 0.48 * [wt. — % Si] Eq. l

[0073] Iron (Fe): 0.10 - 0.30 wt.-%

[0074] Iron is an element which may facilitate anodization of the extruded profile. Furthermore, reducing the iron content to lower than 0.10 wt.-% would require replacing a high amount of recycled scrap with primary aluminum in the raw material used for producing the aluminum alloy, which in turn would considerably increase the CO2footprint as well as increase the cost of the raw material. Therefore, the herein described aluminum alloy comprises at least 0.10% of Fe. Preferably, the Fe is present in an amount of equal to or higher than 0.15%, or even equal to or higher than 0.18%.

[0075] Increasing the amount of Fe typically facilities obtaining a matte surface appearance, typically sought for in building and construction applications, after possible anodization. However, a too high content of Fe may lead to a reduction of the extrudability as well as a reduction of the surface quality in the as-extruded condition. Therefore, the herein described aluminum alloy comprises at most 0.30% of Fe. Preferably, Fe may be present in an amount of equal to or less than 0.26% or even equal to or less than 0.24%.

[0076] Preferably, Fe and Si may be present in the aluminum alloy in an amount such that Equation 2 is fulfilled. Thereby, the quality of the surface of the profile in the as-extruded condition may be improved, which in turn results in less etching needed before a possible surface treatment, such as anodization or painting.

[0077] [wt. —% Fe] / [wt. —% Si] > 0.55 Eq. 2 to or less than 0.10 wt.-%

[0078] Copper is not an essential element of the herein described aluminum alloy, but may be present in amounts of up to maximally 0.10% without negatively affecting the desired properties. For example, a too high Cu content may risk leading a reduction of the corrosion resistance, to an unfavorable response during etching, and / or undesirable increase in gloss of an anodized surface of the extruded profile. Preferably, Cu may be present in an amount of equal to or lower than 0.05 %.

[0079] Copper is however an element that may contribute to solid solution strengthening and thereby increase the mechanical properties. nese (Mn): 0.02 - 0.10 wt.-%

[0080] A small addition of Mn may have the advantageous effect of reducing the stability of P-AIFeSi and thereby facilitate transformation thereof to a-AIFeSi during homogenization. This may in turn improve the quality of the surface in the as-extruded condition. A reduction of P-AIFeSi may also be beneficial for the finish of an anodized surface as said phase has a tendency to be embedded in the anodized surface layer, which is not desired. Therefore, the herein described aluminum alloy advantageously comprise equal to or more than 0.02% of Mn. Preferably, Mn is present in an amount of equal to or more than 0.03%. However, a too high content of Mn may lead to formation of undesired dispersoids. The Mn content of the herein described aluminum alloy is therefore limited to maximally 0.10%. Preferably, Mn may be present in amounts equal to or less than 0.08%.

[0081] Zink (Zn): equal to or less than 0.15 wt.-%

[0082] Zink is not an essential element of the herein described aluminum alloy, but may be present in amounts of up to 0.15% without negatively affecting the desired properties. If present, Zn may for example contribute to strength by solid solution strengthening. Preferably, Zn is present in amounts equal to or lower than 0.10%, or even equal to or lower than 0.05%.

[0083] Chromium (Cr): equal to or less than 0.05 wt.-%

[0084] Chromium is not an essential element of the herein described aluminum alloy. However, Cr may be present in amounts up to 0.05%, if desired, without deteriorating the desired properties. Small additions of Cr may for example have the advantageous effect of facilitating to achieve a matte appearance of an anodized surface of the extruded profile. Preferably, Cr may be present in amounts of equal to or less than 0.03%.

[0085] Titanium (Ti): equal to or less than 0.10 wt.-%

[0086] Titanium is not an essential element of the herein described aluminum alloy, but may be present in amounts of up to 0.10%. Titanium may for example be added for the purpose of acting as a grain refiner, if desired. Preferably, Ti is present in an amount of equal to or less than 0.05%, or equal to or less than 0.04%.

[0087] Impurities

[0088] The aluminum alloy may further comprise normally occurring impurities. Such impurities may be present as a result of the raw material used (such as the composition of recycled scrap used for producing the aluminum alloy) or may be a result of the process for producing the aluminum alloy, without departing from the present disclosure. The total content of impurities in the aluminum alloy is however limited to maximally 0.15 wt.-% to reduce the risk for deterioration of desired properties. Moreover, each impurity element is only allowed to be present in an amount of maximally 0.05 wt.- %. Examples of impurity elements include Ca, Sn, Sb, Pb, Zr and B, but are not limited thereto.

[0089] Method for producing the extruded profile

[0090] The extruded profile according to the present disclosure may be produced by providing a billet of the above described aluminum alloy. This may for example be made by DC casting of a melt having the above described composition.

[0091] The billet is thereafter subjected to a homogenization. The purpose of the homogenization is to reduce microsegregations and dissolve Mg2Si formed during casting, to thereby facilitate the subsequent extrusion. The homogenization also serves the purpose of transforming as much as possible of the plate-like -phase AIFeSi particles, formed during casting, to the more rounded a- phase of AIFeSi. This is because -AIFeSi is associated with poor hot workability due to the shape thereof as well as being brittle, and therefore has an adverse effect on the extrudability. Homogenization may be performed at a temperature of 480- 620 °C for 1 - 5 hours. Suitably, homogenization may be performed at a temperature of 540 - 600 °C, preferably 560 - 590 °C, for 1 - 5 hours, preferably 2 - 4 hours. The billet is thereafter cooled to room temperature. Said cooling could for example be made with an average cooling rate of 300 - 500 °C / h. It should however be noted that lower cooling rates are also possible, such as about 1 °C / min, since any Mg2Si precipitated during cooling will be relatively small and well distributed, and can easily be dissolved during subsequent processing steps. Higher average cooling rates than 500 °C / h are also possible, but not necessary, and can thus be avoided for reasons of process economy.

[0092] After homogenization, the billet is preheated to a billet temperature of 420 - 530°C, preferably 460- 500 °C, and thereafter subjected to extrusion in a conventional extrusion press to obtain an extruded profile of a desired cross-section. The extruded profile is thereafter cooled, which can be made by air or water cooling. At least in case of profiles with thin-walled cross-sections, such as wall thicknesses of about 2 mm or less, it is not necessary to use any forced cooling, although this may be used, if desired. A sufficient amount of Mg and Si will still remain in solid solution to achieve the desired response during subsequent aging. The extruded profile may be a solid profile or a hollow profile depending on the intended use thereof. To reduce the environmental impact, the extruded profile may suitably be a thin-walled extruded profile. The thickest wall portion of the cross section of the profile may for example have a thickness of equal to or less than 1.5 mm, or even equal to or less than 1.3 mm. In fact, the high extrudability of the herein described aluminum alloy enables producing profiles having a wall thickness of equal to or lower than 1.0 mm without any specific measures taken.

[0093] The extruded profile of the above described aluminum alloy generally has a fully recrystallized grain structure. The low content of dispersoid forming elements, Mn and Cr, in the aluminium alloy promotes a recrystallized grain structure.

[0094] After extrusion, the extruded profile may suitably be straightened in accordance with conventional processes therefore. Such straightening may for example be made by stretching the extruded profile. Stretching may for example be performed so as to cause a plastic deformation of the extruded profile of up to 5%, e.g., 1 - 5 %, but is not limited thereto.

[0095] The extruded profile may be stored in the as-extruded (and optionally stretched) condition at for example room temperature before subsequent processing steps, if desired or needed for practical reasons. Such storing may typically lead to natural aging for aluminum alloys belonging to the 6xxx series. In general, clustering of Mg and Si occurs during natural aging of 6xxx aluminum alloys, which in turn may lead to an increase in the mechanical strength of the extruded profile. Said increase in the mechanical strength may have an adverse effect on the increase in strength during subsequent artificial aging for highly alloyed 6xxx aluminum alloys. However, in view of the low content of Mg and Si of the herein described alloy, it is believed that there will not be any adverse effect of possible natural aging on subsequent artificial aging. Instead, natural aging may have a positive effect on the mechanical properties. Thus, the herein described method may also comprise a step of natural aging, for example for 1 - 100 hours (such as 2 - 48 hours).

[0096] Although not necessary, the extruded profile may, prior to artificial aging, be subjected to a solution heat treatment, if desired. Solution heat treatment may for example be performed at a temperature of 460 - 580 °C for 20 minutes - 2 hours. Preferably, solution heat treatment may be performed at a temperature of 540 - 560 °C for 0.5 - 1 hours. To take full advantage of a possible solution heat treatment, cooling from the solution heat treatment temperature may suitably be made by forced cooling, e.g. by forced air cooling or water quenching. The extruded profile is thereafter subjected to artificial aging, which may be performed in a single step process or a multi-step aging process (such as a dual-step process). The aging process may suitably comprise at least a step of holding the extruded profile at a peak temperature of 160 - 220 °C for 1 - 100 hours. A peak temperature is here intended to mean the highest temperature at which the extruded profile is aged.

[0097] In case of a multi-step aging process (such as a dual-step aging process), the aging process may suitably comprise a first aging step of holding the extruded profile at a lower temperature than the peak temperature; suitably at 100 - 160 °C, or preferably at 120 - 160 °C. The first aging step may suitably be performed prior to the step at which the extruded profile is held at peak temperature, and may be performed primarily to achieve a desired nucleation of Mg2Si precipitates. Such a first aging step may for example be performed for 0.5 - 3 hours, preferably 1-2 hours. In case of a multi- step aging process, the extruded profile is typically not cooled between the individual steps of the process.

[0098] The upper limit of the duration of 100 hours for the aging step at which the extruded profile is held at peak temperature is not a critical upper limit of the duration of the aging, but is primarily selected for reasons of process economy. It should here be noted that a lower peak aging temperature typically requires a longer duration, and vice versa, to achieve a similar aging response in terms of increase in mechanical strength. Moreover, aging may be performed to an under-aged condition or to a peak aged condition, depending on the desired mechanical strength. Preferably, aging of the extruded profile may be performed, in a single or multi-step aging process, said aging process comprising holding at a peak temperature of 180 - 195 °C for at least 5 hours. A peak aged condition may for example be achieved by aging at a peak temperature of 185 - 190 °C for 10 - 25 hours.

[0099] Depending on the intended use thereof, the extruded profile may be subjected to a surface treatment for the purpose of obtaining a desired aesthetic appearance and / or further improve the corrosion resistance. Examples of such surface treatments include anodization and painting. Irrespectively of whether the extruded profile should be anodized or painted, the extruded profile may after artificial aging be subjected to etching for the purpose of removing minor surface imperfections and exposing the metal surface. Such etching may be performed in accordance with previously known methods therefore, and the etchant may be caustic or acid.

[0100] Anodization may be performed in accordance with previously known methods therefore. For example, anodization may be performed using a sulfuric acid electrolyte. Anodization may suitably be performed to a thickness of the anodic surface layer of 8 - 12 pm, although other thicknesses are also possible. If desired, the anodized surface may be subjected to coloring using an appropriate dye penetrating the pores of the anodized surface layer. Irrespectively of whether additional coloring has been performed, the extruded profile may after anodization be sealed as known in the art. This may for example be performed using nickel acetate.

[0101] Properties

[0102] As well understood by a person skilled in the art, the properties of the herein described extruded profile will depend on the condition of the extruded profile. Here, a distinction is made between as- extruded condition and various aged conditions.

[0103] The composition of the herein described aluminum alloy enables obtaining an extruded profile having a surface roughness, Ra, of less than 0.42 pm in the as-extruded condition (i.e. without any etching of the surface being performed). Surface roughness may be determined in accordance with ISO 3274:1996, BFW probe arm A 10-45-2 / 90°.

[0104] Furthermore, the herein described aluminum alloy enables obtaining an extruded profile having a tensile strength, Rm, of 100 - 180 MPa and a yield strength, Rp0.2, of 80 - 150 MPa, when the extruded profile is in peak aged condition. Furthermore, the elongation, A50, may in said condition be 4.5 - 8.5 %. Tensile strength, yield strength and elongation may be determined in accordance with ISO 6982-1, with the tensile load being applied in the extrusion direction.

[0105] Moreover, when in the peak aged condition, the extruded profile may obtain a hardness, determined in accordance with ISO 6507-1, of 40 - 65 HV.

[0106] The extruded profile may also be aged to an underaged condition, if desired. For example, aging at 190 °C for 2 hours may result in tensile strength, Rm, of 90 - 120 MPa, a yield strength, Rp0.2, of 40 - 70 MPa, and an elongation, A50, of 14-20%.

[0107] As previously described, the herein described extruded profile may also be subjected to for example anodization or painting after aging. Such processes do not affect the mechanical strength of the extruded profile, and the mechanical strength achieved during aging will therefore be maintained also after the extruded profile has been anodized or painted. Anodization of the extruded profile to a thickness of the anodic surface layer of 8 - 12 pm may result in a mean specular gloss, determined according to ISO 7668, at 60° of 8.5 - 11.5 GU. The thickness of the anodic surface layer may be determined through examination of cross section using microscopy according to ISO 1463.

[0108] Experimental tests

[0109] A plurality of experimental alloys were produced by remelting of billets of an EN AW 6060 alloy followed by alloying of the respective melts to arrive at different chemical compositions. Melting was performed in a resistance furnace with a capacity of 500 kg. The melts were, after alloying, cast into billets of 203 mm diameter through direct -chill (DC) casting.

[0110] The compositions of the experimental alloys, as determined through optical emission spectroscopy (OES) analysis, are specified in Table 1. Alloy A constitutes a reference alloy whose composition was selected to target the composition of a commercially available aluminum alloy known to have high extrudability.

[0111] Figure 1 represents a graph showing the contents of Mg and Si, respectively, of the experimental alloys in relation to the Mg-Si range of 0.20-0.38 wt.-% Mg and 0.20-0.38% Si of the aluminum alloy according to the present disclosure.

[0112] Table 1. Chemical composition of experimental alloys, balance consisting of Al

[0113] * Comparative, outside of claimed scope

[0114] The obtained billets were subjected to homogenization at a soaking temperature of 585 °C for two hours, followed by cooling at a cooling rate of about 400 °C / h. The homogenized billets were thereafter machined down to a billet diameter of 178 mm and a billet length of 662 mm before extrusion.

[0115] Extrusion of the experimental alloys was performed into a solid profile 1 having a cross section as partly shown in Figure 2. The parts of the profile that are not shown in the figure relates to details, such as various flanges, that are specific to an example of an intended final product. These details of the cross sectional shape of the profile have no significance for the tests described below and have therefore been omitted for clarity and brevity. The cross section of the profile 1 may be described as comprising two straight leg portions 2, 4 connected by means of a curved portion 3. The wall thickness t of each of the leg portions 2, 4 is 1.25 mm. The leg portions 2, 4 are oriented at an angle a of 96.5° relative each other. The curved portion has essentially the same wall thickness as the leg portions 2, 4.

[0116] The billet temperature used for the extrusion was 480 °C and the extrusion speed was set to 41 m / min. The profiles were cooled in air after extrusion. The same die was used for all experimental alloys. Alloy A was extruded first, followed by the billets of the other experimental alloys in their numerical order.

[0117] Figure 3 illustrates a graph of the extrusion pressure, determined at different measurement points as the extrusion proceed, for the experimental alloys. A lower extrusion pressure means a higher extrudability, as illustrated by the arrow in Figure 3. It can be seen from the results that Alloy 1 has a slightly better extrudability than Alloy A, and that each of the Alloys 2-5 demonstrates even higher extrudability. The highest extrudability was achieved for Alloys 3-5. These experimental alloys all fulfill the criterion given by Equation 1 described above. The criterion of Equation 1 is schematically represented in Figure 1 by the dashed line.

[0118] The extrudability of the experimental alloys can also be compared through theoretical calculations based on their respective compositions. Models that may be used for such calculations are described for example in Ole Runar Myhr , Rune 0sthus , Anders Nesse and Trond Furu, “Modeling of Recrystallization, Quench Sensitivity and Surface Tearing of Gxxx-Series Alloys", ET2022 conference, 2022, and in Mads Iddberg, Ole Runar Myhr, Anders Nesse, and Trond Furu, "A modelling framework for rapid evaluation of speed limitations during extrusion of aluminium profiles", Aluminium 2000 conference, 2023. Figure 4 illustrates relative extrudability of Alloys 1- 5 in relation to Alloy A, determined through theoretical calculations performed using the PRO3™ software, which is a digital twin developed by Norsk Hydro. For the results shown in Figure 4, the relative extrudability for the material was calculated by comparing the maximum extrudability of a 9 mm cylindrical profile from a 100 mm billet for each experimental alloy. The calculations were also based on the experimental alloys having been homogenized at 585 °C for 2 hours followed by industrial cooling in air.

[0119] It should here be noted that theoretical extrudability may be calculated using different models, and based on different assumptions, and can therefore give different results. However, by comparing the theoretical extrudability of different alloys with the theoretical extrudability of a reference alloy (here Alloy A), the same trend will be seen irrespectively of the model used for determining theoretical extrudability. Therefore, the result present in Figure 4 shall merely be regarded as a way of theoretically comparing the extrudability of the different experimental alloys.

[0120] Evaluation of surface quality after extrusion

[0121] After extrusion, samples were taken from leg portion 2 (see Fig. 2) of the profiles of each of the experimental alloys and investigated with respect to the quality of the surface of the profiles in the as-extruded condition. More specifically, surface roughness was determined in accordance with ISO 3274:1996, BFW probe arm A 10-45-2- / 90°. Furthermore, the MHAR surface measuring device MarSurf M 400 with drive unit SD26 was used to examine severeness of die lines by recording depth profiles over a linear distance of 45 mm, transversal to the extrusion direction.

[0122] The surface quality for the profile of Alloy A was found to be consistent with what was expected based on previous experiences from the commercially available aluminum alloy whose composition was targeted, and is in general considered to be a good surface quality for the intended application. The profiles of each of Alloys 1-5 were however found to possess even better surface quality in the as-extruded condition.

[0123] Figure 5 illustrates images, taken by a digital camera, of the area in which the measurement was made (bottom) showing the die lines, and the corresponding recorded depth profiles (top) before filtering of the background. It can be seen from Figure 5 that the severeness of the die lines is considerably reduced for Alloys 2-5 compared to Alloy A and Alloy 1. In contrast to Alloy A and Alloy 1, each of the Alloys 2-5 fulfill the criterion of Equation 2 as described above. Without being bound by theory, it is believed that the ratio of Fe to Si may affect the composition and / or morphology of iron containing precipitates, which in turn may affect the severeness of the die lines formed during extrusion. The best results were obtained for Alloys 3-5, as can be seen from the figure.

[0124] Figure 6 illustrates surface roughness, Ra, of the experimental alloys in the as-extruded condition. As evident from the figure, the surface roughness of Alloys 1-5 is considerably lower than the surface roughness of Alloy A.

[0125] To verify that the improved surface quality of the profiles of Alloys 1-5 was not simply a result of being extruded after Alloy A using the same die, an already available billet of the above mentioned commercially available aluminum alloy was also extruded after the experimental alloys. The commercially available aluminum alloy was subjected to the same processing conditions with regard to homogenization and extrusion as described above. The resulting surface quality was only slightly better than the surface quality of the profile of Alloy A. More specifically, the surface roughness, Ra, was about 0.45 pm, which may be compared with about 0.46 pm for Alloy A and less than 0.40 pm for Alloys 1-5. Moreover, the depth profile, demonstrating the severeness of the die lines, was similar to that of Alloy A.

[0126] Aging trials

[0127] Laboratory aging trials were performed to investigate the aging time dependence on material hardness. Before aging, the extruded profiles of the experimental alloys were solution heat treated for 30 minutes at 545 °C, followed by water quenching. Aging was performed according to a dual step (i.e. a multi-step) aging procedure comprising a first step of holding at 130 °C for 1 hour followed by a second step of holding at a peak temperature of 185 °C. The hardness was determined in accordance with ISO 6507-1.

[0128] The result is shown in Figure 7, which illustrates a graph showing the hardness ( HV) as a function of aging time at peak temperature in hours. It can be clearly seen from the graph that longer aging times are needed in order to reach peak hardness for Alloys 2-5 compared to Alloy A and Alloy 1. Moreover, the peak hardness is considerably lower for Alloys 2-5 compared to Alloy A. The differences in material hardness between the different experimental alloys is primarily a consequence of the differences in Mg and Si content of the experimental alloys. Tensile testing

[0129] The extruded profiles were subjected to two different dual step aging procedures, here denominated DSA190 and DSA185, respectively. According to the DSA190 procedure, the extruded profiles were, after storing at room temperature for about 2 hours, subjected to a first aging step at a temperature of 130 °C for 30 minutes followed by a second aging step at a peak temperature 190 °C for 2 hours in a full scale production furnace. Said aging procedure may be expected to lead to a substantially peak aged condition for Alloy A, whereas at least Alloys 2-5 may be expected to be underaged, based on the results shown in Figure 7.

[0130] According to the DSA185 procedure, the extruded profiles were, after a solution heat treatment for 30 minutes at 545 °C followed by water quenching, subjected to a first aging step comprising holding at 130 °C for 1 hour followed by holding at a peak temperature of 185 °C to achieve a peak aged condition. DSA185 was performed in a laboratory furnace. The aging time for the different experimental alloys was chosen based on the result shown in Figure 7, i.e. the duration needed to arrive at peak hardness.

[0131] Samples for tensile testing were thereafter taken from the aged profiles. Tensile testing was performed in accordance with ISO 6982-1, with the tensile load being in the extrusion direction. The result is specified in Table 2, and also shown in Figures 8a-8c.

[0132] Table 2. Tensile properties after aging Surface appearance after anodization

[0133] The extruded profiles were, after aging according to procedure DSA190 described above, etched using a caustic etchant and thereafter subjected to anodization using a sulfuric acid electrolyte followed by conventional sealing (no coloring of the anodized surface layer was made). The duration of the anodization was selected to target a thickness of the resulting oxide layer of 10 pm, which is a common thickness for anodized aluminum profiles for building and construction applications.

[0134] Evaluation of surface anodic coating and surface appearance after anodization was made according to EN ISO 7599. More specifically, oxide thickness was determined through examination of cross section using microscopy in accordance with ISO 1463. Specular gloss was determined in accordance with ISO 7668.

[0135] Table 3 lists the results of the oxide thickness measurements, and Table 4 lists the results of the specular gloss measurements.

[0136] Table 3. Oxide thickness

[0137] Table 4. Gloss at 60° measurement angle Overall, a good surface appearance, similar to that of the reference Alloy A, was seen for all of Alloys 1-5. This demonstrates that it is possible to meet the customers' expectations for building and construction applications in terms of anodized surface appearance despite the change in chemical composition of the alloy of the extruded profile compared to the conventional EN AW 6060 alloys.

Claims

CLAIMS1. An extruded profile made of an aluminum alloy having the following composition, in percent by weight (wt.-%):Si 0.20 - 0.38,Mg 0.20 - 0.38,Fe 0.10 - 0.30,Mn 0.02 - 0.10,Cu equal to or less than 0.10,Zn equal to or less than 0.15,Cr equal to or less than 0.05,Ti equal to or less than 0.10, impurities equal to or less than 0.05 wt.-% each and equal to or less than 0.15 wt.-% in total, the reminder being Al.

2. The extruded profile according to claim 1, wherein the aluminum alloy comprises equal to or more than 0.22 wt.-% of Si; preferably equal to or more than 0.24 wt.-% of Si.

3. The extruded profile according to any one of claims 1 or 2, wherein the aluminum alloy comprises equal to or less than 0.36 wt.-% of Si.

4. The extruded profile according to any one of the preceding claims, wherein the aluminum alloy comprises equal to or more than 0.22 wt.-% of Mg; preferably equal to or more than 0.24 wt.-% of Mg.

5. The extruded profile according to any one of the preceding claims, wherein the aluminum alloy comprises equal to or less than 0.36 wt.-% of Mg.

6. The extruded profile according to any one of the preceding claims, wherein the aluminum alloy comprises equal to or more than 0.15 wt.-% of Fe; preferably equal to or more than 0.18 wt.-%.

7. The extruded profile according to any of the preceding claims, wherein the aluminum alloy comprises equal to or less than 0.26 wt.-% of Fe; preferably equal to or less than 0.24 wt.-% of Fe.

8. The extruded profile according to any of the preceding claims, wherein the aluminum alloy comprises equal to or more than 0.03 wt.-% of Mn.

9. The extruded profile according to any one of the preceding claims, wherein the composition of the aluminum alloy fulfills the criterion given by Equation 1:[wt. — % Mg] < 0.48 — 0.48 * [wt. — % Si] Eq.

110. The extruded profile according to any one of the preceding claims, wherein the composition of the aluminum alloy fulfills the criterion given by Equation 2:[wt. -% Fe] / [wt. -% Si] > 0.55 Eq.

211. The extruded profile according to any one of the preceding claims, wherein a thickest wall portion of the extruded profile has a wall thickness of equal to or less than 1.5 mm; preferably a wall thickness of equal to or less than 1.3 mm.

12. The extruded profile according to any one of the preceding claims, having a surface roughness of less than 0.42 pm, determined in accordance with ISO 3274:1996 with BFW probe arm A 10-45-2 / 90°, when in as-extruded condition.

13. The extruded profile according to any one of the preceding claims, having, when in peak aged condition, a tensile strength, Rm, of 100 - 180 MPa and a yield strength, Rp0.2, of 80 - 150 MPa, as determined in accordance with ISO 6982-1.

14. The extruded profile according to any one of the preceding claims, comprising a surface anodic coating, preferably wherein the surface anodic coating has a mean thickness of 8 - 12 pm as determined through examination of cross section using microscopy according to ISO 1463.

15. The extruded profile according to claim 14, wherein the surface of the extruded profile has a mean specular gloss, determined according to ISO 7668, at 60° of 8.5 - 11.5 GU.

16. Method for producing an extruded profile, the method comprising the following steps:(a) providing a billet of an aluminum alloy having the following composition, in percent by weight (wt.-%):Si 0.20 - 0.38,Mg 0.20 - 0.38,Fe 0.10 - 0.30,Mn 0.02 - 0.10,Cu equal to or less than 0.10,Zn equal to or less than 0.15,Cr equal to or less than 0.05,Ti equal to or less than 0.10, impurities equal to or less than 0.05 wt.-% each and equal to or less than 0.15 wt.-% in total, the reminder being Al;(b) homogenizing the billet at a temperature of 480 - 620 °C for 1 - 5 hours, followed by cooling to room temperature;(c) preheating the billet to a billet temperature of 420 - 530 °C, preferably 460 - 500 °C;(d) extruding the preheated billet to an extruded profile, followed by air or water cooling;(e) optionally stretching the extruded profile;(f) optionally solution heat treating the extruded profile;(g) aging the extruded profile in a single or multi-step aging process, said aging process comprising holding the extruded profile at a peak temperature of 160 - 220 °C for 1 - 100 hours; and(h) optionally subjecting the extruded profile to a surface treatment, such as anodization or painting.

17. The method according to claim 16, wherein step (d) comprises extruding the preheated billet to an extruded profile in which a thickest portion of the extruded profile has a wall thickness of equal to or less than 1.5 mm, or equal to or less than 1.3 mm.

18. The method according to any one of claims 16 and 17, wherein step (g) comprises aging the extruded profile in a single or multi-step aging process, said aging process comprising holding at a peak temperature of 180 - 195 °C for at least 5 hours.

19. The method according to any one of claims 16 to 18, wherein step (f) comprises solution heat treating the extruded profile at a temperature of 460 - 580 °C for 20 minutes - 2 hours followed by forced cooling.

20. The method according to any one of claims 16 to 19, wherein step (b) comprises homogenizing the billet at a temperature of 560 - 590 °C for 2 - 4 hours, followed by cooling to room temperature; optionally wherein said cooling is performed with an average cooling rate of 300 - 500 °C / h.

21. The method according to any one of claims 16 to 20, wherein step (e) comprises stretching the extruded profile to cause a plastic deformation of the extruded profile of up to 5%, preferably 1 - 5 % plastic deformation.

22. Use of the extruded profile according to any one of claims 1 to 15 in building and construction applications, such as for producing a building profile, a door or window frame, a railing, or a ladder, or for producing a frame for a solar panel.

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