CORROSION RESISTANCE POWDERCOATED RECYCLE FRIENDLY

ALUMINUM SOFT ALLOYS FIELD OF THE INVENTION

The present invention relates to a reliable high extrusion rate production method for recycle friendly aluminum soft alloy of the type 6060X, which besides A1 ,Mg and Si contains important amounts of Cu , Zn , Fe and Mn as alloying elements, followed by an pretreatment with an alkaline or acid etching of at least 1,0 preferably 2 gram/m2 yielding powdercoated aluminum profiles with a very high corrosion resistance after powder coating for the most common conversion (Ti, Ti,Zr, preanodisation, etc ) - powdercoating systems available in the market. BACKGROUND TO THE INVENTION

Aluminum soft alloys are typically used for the production of components with a high surface quality for use in decorative applications, by shaping the alloy into a wide variety of forms using extrusion. Aluminum soft alloys are further suitable for use in a wide variety of non- structural, non-critical applications such as architectural applications, extrusions like frames for windows and doors, curtainwalls, storefronts, skylight architectural applications, doors, shop fittings, irrigation tubing, sports equipment, non- structural applications in aircraft industry, road transport, rail transport etc. house buildings and other buildings. Aluminum soft alloys offer good corrosion resistance, good machinability, good weldability, good formability and acceptable strength. They are heat treatable and may be artificially aged. In many applications, after extrusion, the aluminum soft alloy is subjected to etching and anodization. Aluminum soft alloys may also be subjected to powder coating or to any other suitable surface treatment. Components or parts made of aluminum soft alloys typically take the shape of sheets or plates, wires, rods, bars, extrusions, structural shapes, tubing, pipe, forgings, foil, etc. Main alloying elements contained in aluminum soft alloys may include Mg, Fe, Si, Cu, Mn, Cr, Zn, Ti. The most common aluminum soft alloy in Europe is the 6060 alloy, which contains Mg and Si as alloying elements and has a minimal tensile strength of 215 MPa. Tensile strength and other mechanical properties to which these 6060 soft alloys must respond are described in Extrusion Norm (EN) EN 755-1 and EN 755-2.

Products made of 6060 aluminum soft alloys nowadays require strict control of the alloy composition, in particular in relation to the presence of traces alloying elements. This imposes the incorporation of high amounts of primary aluminum into the recycled aluminum in the practical production of aluminum alloys, as removing elements from an alloy composition is complicated, expensive and time consuming and risks to increase the costs of the use of recycled aluminum to a level which makes it unattractive.

An EN AW 6060 aluminum alloy which responds to the European EN 573-3 in relation to its composition, may typically contain the following alloying elements in the indicated concentrations (in wt. % with respect to the weight of the alloy composition): Cu < 0.10 Zn < 0.15 Mn < 0.10 0.10 < Fe < 0.30 0.35 < Mg < 0.60 0.30 < Si < 0.60

An EN AW 6063 aluminum alloy which responds to the European norm in relation to its composition, may typically contain the following impurities in the indicated concentrations (in wt. % with respect to the weight of the alloy composition): Cu < 0.10 Zn < 0.10 Mn < 0.10 Fe < 0.35 0.45 < Mg < 0.60 0.20 < Si < 0.60 In practice, commercially available 6060R and 6063R (R = Restricted ) primary alloys contain the following elements in the indicated concentrations (in wt. % with respect to the weight of the alloy composition) :

Cu < 0.02 Zn < 0.02 Mn < 0.04 0.16 < Fe < 0.22

0.45 < Mg and Si < 0.50 for 215 MPa alloys 0.50 < Mg and Si < 0.55 for 245 MPa alloys.

The concentration of Fe in soft alloys of these types is restricted to a maximum of 0.22 wt.% , preferably below 0,19 wt. % , because of its negative impact on extrusion rate or speed and negative impact on the surface quality of extruded products due to the presence of heavy pick-ups at higher iron levels. The concentration of Mn is generally restricted to a maximum of 0.04 wt. % , preferably below 0,01 wt. % , because Mn is known to interfere in aluminum re-crystallization during extrusion, and to give rise to the formation of large grains with an irregular shape and/or a fiber structure and a dull surface after anodization. The presence of too high amounts of Mn has further been found to increase the cooling speed and the formation of large Mg2Si precipitates, which have an adverse effect on the mechanical properties of the extruded product. The concentration of Cu is generally restricted to a maximum of 0.02 wt.% , preferably below 0,01 wt. % to minimize the risk to the occurrence of corrosion problems, which may deteriorate the surface quality and give rise to colour or gloss problems after anodizing. Cu is also known to have a negative impact on extrusion speed. The concentration of Zn is generally restricted to a maximum of 0.02 wt.% , preferably below 0,01 % , in view of its negative impact on the anodization behavior of the soft alloys, due to preferential grain etching.

Beside these mentioned problems there is a big fear in the market to use soft alloys with higher amount of these elements, and then in particular higher concentrations of Zn and Cu. Cu should be absolutely lower as 0.02 wt% , seen the fact that all known aluminum copper wrought alloys ( 2XXX ) have severe corrosion problems . The reason of these restrictions dates from 1990, in this period a lot of Russian aluminum entered in the western European market with higher trace elements , like Cu, Zn and Fe. In this period there were a lot of claims in the building market with filiform corrosion. Research at the University of Gent, Professor Defrancq, showed a clear relation between these trace elements and the occurrence of filiform corrosion. From that period on, 6060R alloys were used with restricted trace elements and narrow tolerances on chemical composition were used as described above. After introducing these restricted 6060R soft alloys the problem filiform corrosion disappeared completely.

The increasing demand for aluminum-based products and increasing globalization of the aluminum industry have contributed to an increasing aluminum alloy consumption. In view thereof, and in view of the remarkable ability of aluminum and its alloys to be repeatedly recycled with a minimum risk to product integrity loss and material loss through oxidation, a further increasing demand for the use of recycled aluminum is to be expected in future. Not only will the use of recycled aluminum permit to save on the exploitation of virgin aluminum sources, significant energy savings as well as emission reductions may be realized when compared to primary aluminum production. European estimates suggest that the mass of solid waste generated per ton of recycled aluminum is about 95% lower than that for primary metal. Therefore, the secondary aluminum stream of recycled aluminum has been identified as an attractive source for the production of aluminum alloys.

Recycled aluminum may originate from a variety of alloys, which in turn may originate from a fairly wide variety of applications. Recycled aluminum may for example originate from cast products typically made from 4XXX- alloys which usually have a high Si content, from rolling products typically made from 5XXX - alloys which usually contain rather high percentage of Mg, from extruded profiles made from other alloys such as 2XXX-alloys with a high Cu content, from 3XXX-alloys with a high Mn content or from 7XXX-alloys which usually containing high percentage of Mg and Zn. Often, at the end of their life cycle, these products are collected all together and usually a detailed sorting of different aluminum alloys is not carried out. Recycling may therefore lead to higher levels of certain elements in the recycled aluminum, such as Mg , Si ,Zn, Cu, Fe, Mn, etc. Furthermore, upon recycling of demolished products which contain aluminum parts, like parts taken from buildings or vehicles, the recycled parts may show increased levels of Fe, Mn, Cu and Zn. As a consequence these elements risk to end up in applications which make use of recycled aluminum, even when employing performant sorting techniques.

Following European REACH legislation in 2017, it is no longer allowed to use a stable Cr ⁶⁺ conversion layer for powdercoating , requiring nowadays a strict control of the alloy composition, in particular in relation to the presence of traces alloying elements Fe, Mn, Zn and Cu . This imposes the incorporation of high amounts of primary aluminum into the recycled aluminum in the practical production of aluminum alloys, as removing elements from an alloy composition is complicated, expensive and time consuming and risks to increase the costs of the use of recycled aluminum to a level which makes it unattractive. Further in 2018 and 2019 some cases of filiform corrosion with such primary aluminum diluted recycled aluminum were observed in the market. The real cause of the return of filiform corrosion is not clear but as a consequence the use of recycled aluminum is under severe pressure.

It is an object of the present invention to provide a method for producing extruded soft alloys coping with the presence of higher concentrations of these elements and the absence of the forbidden Cr 6+ conversion layer without scarifying the corrosion behavior in particular the filiform corrosion.

SUMMARY OF THE INVENTION

The different aspects of the present invention can be summarized in accordance with the following numbered embodiments.

1. A method for manufacturing a pretreated extruded 6060X type aluminum soft alloy (10) comprising besides Mg and Si, in an amount between 0,2 and 0,6 wt% of total weight also Fe, Mn, Zn and Cu as alloying elements each independently present in an amount of about and between 0,015 and 0,35 wt% of total weight; said method comprising; i. heating said 6060X type aluminum soft alloy to be extruded to a softening temperature; ii. forcing the thus softened 6060X type aluminum alloy (2) through the die opening (33) of an extrusion die (3) with a ram speed of at least 7 mm/s; iii. collecting the extruded 6060X type aluminum soft alloy (10) that emerges from the die opening (33) through the die exit (23); iv. inerting the extruded 6060X type aluminum soft alloy (10) at the position where the extruded aluminum soft alloy (10) emerges from the die opening (33) with the flow of an inert gas (15), in particular liquid nitrogen; v. maintaining the extruded 6060X type aluminum soft alloy (10) at the position where it emerges from the die and after the inertization at a temperature in the range of 500 - 600°C; in particular in the range of 550°C up to 595°C; and characterized in that the method further comprises the step of vi. subjecting the inertized extruded 6060X type aluminum soft alloy to an etching pretreatment with an alkaline or acid of at least 1,0 preferably 2 gram / m ² followed by an acid desmutting to avoid enrichment of Cu, Zn, Mn left on the surface in case of alkaline etching; to yield the pretreated extruded 6060X type aluminum soft alloy (10).

2. The method according to embodiment 1, further comprising the step of; vii. installation of a Ti, Zr , Ti/Zr or preferably an p re anodisation layer of at least 4 pm on the etched inertized extruded 6060X type aluminum soft alloy, to yield the pretreated extruded 6060X type aluminum soft alloy (10). 3. The method for manufacturing an extruded 6060X aluminum soft alloy (10) according to embodiments 1 or 2; wherein the aluminum soft alloy is a 6060 or 6063 type aluminum soft alloy.

4. The method according to any one of embodiments 1 to 3, wherein the 6060X type aluminum soft alloy contains following alloying elements (in wt. % ) : i. Si 0,20 - 0,60; preferably 0,40 - 0,50 ; ii. Mg 0,20 - 0,60; preferably 0,35 - 0,45; iii. Mn 0,015 - 0.15 ; preferably 0,03 -0,10; iv. Cu 0,015 - 0.25 ; preferably 0,03 - 0,10 v. Zn 0,015- 0.15 ; preferably 0,03 -0,10; vi. Fe 0,18 - 0,35 ; preferably 0,20 - 0,30 vii. Others up to 0,03 and in total 0,15 balance Al.

5. A method according to any of the preceding embodiments , wherein the temperature of the extruded 6060X type aluminum soft alloy (10) at the position where it emerges from the die is maintained in the range 550 - 595 °C. 6. A method according to any one of the preceding embodiments , wherein the inert gas is nitrogen.

7. The method according to any one of the preceding embodiments wherein the inert gas (15) is forced through holes or slots in the immediate neighborhood of the die exit (23).

8. The method according to any one of the preceding embodiments wherein the softened aluminum alloy (2) is forced through the die opening (33) with a ramspeed of at least 7 mm/s; preferably from about 7 mm/s up to about 12 mm/s; in particular at a ram speed of about 8 mm/s. 9. The method according to any one of the preceding embodiments wherein the extruded aluminum soft alloy (10) has a minimal tensile strength of 215 MPa.

The method according to any one of the preceding embodiments wherein the dies at the profile forming area (bearings) have a compound layer of at least 2 to 5 pm; and a diffusion layer of at least 0,15 mm; preferably a diffusion layer of about 0,30 mm

11. A device for manufacturing an extruded 6060X type aluminum soft alloy (100) according to the method of any one of the preceding embodiments, wherein the device comprises; a. a container (8) for a preheated softened aluminum soft alloy (2), b. a pusher or ram (9) for pushing the softened alloy from the container through a die opening (33) for extruding the alloy into a desired shape, c. a supply of an inert gas (15) at a position where the extruded part emerges from the die exit (23), and characterized in that it comprises d. a device (6) for measuring the temperature of the extruded aluminum soft alloy (10), preferably an infrared camera, at the position where it emerges from the die, and in that the device is configured to maintain the extruded aluminum soft alloy at the position where it emerges from the die in the range of 500 - 600 ° C; in particular in the range of 550°C up to 595°C.

12. The device according to embodiment 11, comprising a heating element (11) for maintaining the container (8) at an elevated temperature, i.e. at a temperature to maintain the aluminum soft alloy (2) as a softened aluminum soft alloy (2).

13. The device according to embodiments 11 or 12 , wherein the device for manufacturing an extruded aluminum soft alloy (100) comprises an inert gas supply device (5) to supply said inert gas (15). 14. The device according to any one of embodiments 11 to 13 comprising holes or slots in the immediate neighborhood of the die exit (23 ) to supply the inert gas (15) at the position where the extruded part emerges from the die opening (33).

15. The device according to embodiment 14, wherein the slots or holes are present in the die support parts (13) and / or the die backers (12).

16. The device according to any one of embodiments 11 to 15, wherein the dies at the at the profile forming area (bearings) have a compound layer of at least 2 to 5 pm; and a diffusion layer of at least 0,15 mm; preferably a diffusion layer of about 0,30 mm

17. A pretreated extruded 6060X type aluminum soft alloy (10) obtained by the method according to any one of embodiments 1 to 11, wherein said aluminum soft alloy contains following alloying elements (in wt. % ) : i. Si 0,20 - 0,60; preferably 0,40 - 0,50 ; ii. Mg 0,20 - 0,60; preferably 0,35 - 0,45; iii. Mn 0,015 - 0.15 ; preferably 0,03 - 0,10; iv. Cu 0,015 - 0.25 ; preferably 0,03 - 0,10; v. Zn 0,015 - 0.15 ; preferably 0,03 - 0,10; vi. Fe 0,18 - 0,35 ; preferably 0,20 - 0,30 vii. Others up to 0,03 and in total 0,15 balance Al.

18. The pretreated extruded aluminum soft alloy (10) according to embodiment 17 having a minimal tensile strength of 215 MPa.

19. The pretreated extruded aluminum soft alloy (10) according to embodiments 17 or 18, wherein the direct surface defects are less or equal to 3,0%, in particular less or equal to 2,5%. 0. The pretreated extruded aluminum soft alloy (10) according to any one of embodiments 17 to 19, wherein the indirect defects are less or equal to 4,0%, in particular less or equal to 3,5%. 21. A powder coated extruded aluminum soft alloy obtained by powder coating a pretreated extruded aluminum soft alloy (10) according to any one of embodiments 17 to 19.

22. The powder coated extruded aluminum soft alloy according to embodiment 21 having an A rating in either of the filiform corrosion test (FFC) or the Acetic Acid Salt Spray test (AASS).

BRIEF DESCRIPTION OF THE DRAWINGS

With specific reference now to the figures, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the different embodiments of the present invention only. They are presented in the cause of providing what is believed to be the most useful and readily description of the principles and conceptual aspects of the invention. In this regard no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention. The description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.

Fig. 1: Typical Mg and Si contents of aluminum soft (6060X, 6060 6063), medium 6005 A, 6101) and hard alloys (6061, 6082).

Fig. 2: Schematic cross sectional view of a device for manufacturing an extruded aluminum soft alloy (100) using the method according to the invention.

Fig. 3A: Schematic cross-sectional view of an extruded fa9ade profile, indicating where the temperature was measured and maintained at 595°C, in this instance close to the hottest point of the profile (Shaded zone), (dashed area is hot spot (hottest area of the profile)) Fig. 3B: Schematic cross-sectional view of an extruded window profile, indicating where the temperature was measured and maintained at 550°C, in this instance more distant from the hottest point of the profile (Shaded zone) (dashed area is hot spot (hottest area of the profile))

DETAILED DESCRIPTION OF THE INVENTION

The recyclefriendly soft alloys typical contains alloying elements in the below examplified ranges, with especially the trace element at the higher end of the tolerance field (in wt. % with respect to the weight of the alloy composition) when compared to the Restricted alloys {supra):

Trace alloying elements Mn 0,015 - 0,15 Cu 0,015 - 0,25 Zn 0,015 - 0,25 Fe 0,18 - 0,35 Main alloying elements Si 0,40 - 0,60 Mg 0,25 - 0,45

Others up to 0,03 and in total 0,15 and balance A1

The first big deviation in trace alloying elements is iron. Due to recycling these values can be far above 0,22 wt . % and as a result we expect a very negative impact on the extrusion rate. It is also known if Iron is in alpha condition ( round form ) and not in beta condition ( needle ) the negative impact on extrusion speed is neglectable. As known from WO 98 / 42884 Publication date 1 October 1998. It is recommended that Mn is optimal 0,04 - 0,07 wt % to achieve optimal beta -alpha conversion during the homogenisation process to avoid tearing or reduction in extrusion rate during extrusion. At these Mn values the negative impact of Fe is of minor importance. The second big deviation in trace alloying elements is Zn . Due recycling these values are far above 0,02 and as result there is a negative impact on anodisation behavior due to preferential grain etching. As know from US 3594133 Publication date 20/7/1971 it is recommended that Cu = 0,97 Zn to avoid PGE during alkaline etching. Recent research has confirmed this theory WO2017 /093304 A1 Publication date 8/6/2017. However higher levels of Cu can result in filiform corrosion of coated profiles

As a result all these additional alloying elements in recycle friendly soft alloys gives a higher amount of surface problems during extrusion and as a result a lower extrusion rate and a lower reliable extrusion process when compared with in practice available primary soft alloys . Most known surface defects are for example pick-up ( hard inclusions in the extrudate ) , cracking or tearing ( disruptions in the extrudate ) , rough surface ( scratches in the extrudate with Rt higer as 9 pm ), and filiform corrosion.

Today all methods to evaluate surface quality are based on controls of the press operator at the exit of the die. To produce high quality surfaces is a very complex and difficult process. In case of bad surface quality operator will reduce extrusion speed or lower billet temperature. Very often the problem is not solved, and production is stopped. Often the reason is not clear, and several restarts are necessary.

One of the parameters controlled by the press operator is the temperature of the extruded aluminum part that has left the extrusion die. This temperature control is absolute necessary seen the fact that due to the higher concentrations of trace elements there are a lot of intermetallic particles in these recyclefriendly alloys , in particular low melting particles , that can cause incipient melting and may lead to a strong drop in extrusion speed. Measurement of the temperature of the extruded aluminum part that has left the extrusion die is rather complex. Mechanical contact temperature measurements are very cumbersome and not possible without damaging the profile. Theoretical calculations of the temperature by energy input of the process by finite elements, such as the CADEX system of SMS, are not reliable and were no success. Infrared measurements without contact are very difficult due the high emissivity of the aluminums, although there has been a lot progress the last years which made this new and innovative solution possible. Further you need to find the hottest point (hot spot) of the profile which is very often in the interior of the profile where it is impossible to measure. That is the main reason that today it is still the operator who is responsible for the settings of the most important press parameters.

All these problems have as result that industry hesitates to use recycle friendly aluminum alloys if high surface quality is needed.

By making use of this last generation infrared contactless temperature measurement equipment and measuring the temperature at a easy to measure zone and determining the correlation between this zone and the hottest zone of the profile ( hot spot ) it has been found to be able to produce profiles from 6060X type aluminum soft alloys having very high alloying elements and trace elements, with very high extrusion rate and high surface quality. (See Extrusion Test runs ).

Using the method of the instant application, independent of the pretreatment solutions used in industry prior to aluminum coating, surface problems like filiform corrosion were resolved for such pretreated extruded recyclefriendly 6060X type aluminum soft alloys coping with the presence of higher concentrations of trace elements and the absence of the forbidden Cr 6+ conversion layer.

To achieve such an excellent surface quality and to permit producing parts with desired high extrusion rate or speed, the process of the present invention comprises the steps of creating an inert atmosphere at the die exit and of monitoring the and maintaining the temperature of the extruded aluminum at the exit of the die in a temperature range of between 500 and 600°C, preferably between 550 and 595°C, followed by an etching pretreatment with an alkaline or acid. Surprisingly, using said conditions, only a low-grade etching of at least 1,0 preferably 2 gram / mm ² is already sufficient to obtain an aluminum soft alloy with excellent surface qualities and free from surface problems like filiform corrosion upon powder coating. The present invention relates to a process for producing an extruded part, wherein an amount of an aluminum recyclefriendly 6060X alloy having a composition as described herein before, is heated to a softening temperature which is below the melting temperature of the aluminum soft alloy with the purpose of softening the alloy, after which the softened alloy is forced through an extrusion die at an extrusion temperature until it exits the extrusion die at an extrusion die outlet so that an extruded alloy part is produced. The process of the present invention is amongst others characterized in that the extruded alloy part is contacted with a flow of an inert gas at the position where it exits the die, and in maintaining the temperature at the die exit within the herein prescribed range.

The inert gas used in the process of the present invention may be any inert gas considered suitable by the skilled person, for example nitrogen, helium, argon etc or mixtures of two or more hereof. More preferably use is made of liquid nitrogen seen the massive expansion of liquid nitrogen when it comes in contact with the extrudate.

Contacting of the extruded alloy with an inert gas flow has the effect that the surface of the extruded part leaving the die is rendered inert while still hot. Contacting the extruded alloy with a flow of an inert gas as it leaves the extrusion die, permits minimizing the risk to unwanted oxidation of the extruded alloy which still has a high temperature. A further improvement of this invention is to force the flow of the inert gas as close as possible to the exit by drilling holes or slots in the support plate of the die and to force the inert gas in the immediate neighborhood of the die exit. By this technique the consumption of this expensive gas could be reduced strongly. Introducing the inert gas as close as possible to the exit also assist in controlling the temperature of the extrudate in having a cooling effect on the extrudate. It has been observed that the presence of the the further elements like Fe, Mn, Zn and Cu in recyclefriendly 6060X aluminum soft alloys has an impact on the solidus temperature of the extrudate. The solidus temperature is the temperature were first liquid fase is observed in the material, and in the recyclefriendly 6060X aluminum soft alloys this temperature is reduced. Close to the solidus temperature the material cannot withstand against shearforces active at the die and starts to crack. Recyclefriendly aluminium alloy start to crack much earlier due their lower solidustemperature . Injecting the inert gas the immediate neighborhood of the die exit, will result in a local cooling effect, and prevent cracks otherwise caused by the lower solidustemperature of the recyclefriendly 6060X aluminum soft alloys.

The present invention permits producing products from aluminum alloys with the conventional mechanical properties required by the intended applications for example the building or construction industry regardless of the presence of otherwise unwanted elements like Fe, Mn, Zn and Cu which are assumed to adversely affect the visual quality and extrusion speed. By strict controlling the temperature of the extruded part at the exit of the die, extruded parts with a desired surface quality and desired mechanical properties may be produced. Thereby the high extrusion speeds conventionally used in the art may be maintained, regardless of the presence of high trace alloying elements in the aluminum soft alloy composition of this invention. The obtained surface quality of these aluminum soft alloys which may contain recycled aluminum, having a chemical composition as described above and executed with production methods as described above is completely within the norms as described in Qualanod (2017) and Qualicoat (2013).

As further detailed hereinafter, in a preferred embodiment the die surfaces at the profileforming area's (bearing) should comprise a compound or white layer (such as a gas nitride dies with a nitride layer or CrN coated dies with a Cr-N hard coat) of minimal 5 pm, preferably of about 8 pm with a diffusion layer of about 0,15 to about 0,30 mm. Further parameters that could have an influence on the surface quality of the extruded alloy are the billet quality, and the Temperature Time Treatment (TTT) after extrusion.

The billet preferably has an iron beta -alpha conversion of at least 90%, and is free from hard particle inclusions, such as AI2O3, TiB, FeiCb , AI2O3, S1O2, etc, with a maximum particle size of 50 pm. To ensure small precipitates below 1 pm after aging the TTT after extrusion preferably comprises a single or two step aging protocol, comprising a cooling speed of about 3°C / sec and maintaining the extruded profile at a temperature of about 160 to about 180°C for at least 8h; in one embodiment at about 175°C for about 8 hours; in another embodiment at about 165°C for about 12 hours. Together with the aforementioned control of the temperature with an inert atmosphere at the die exit these TTT after extrusion treatments result in an extruded 6060X type aluminum soft alloy with a minimal tensile strength of 215 N/mm ² with hardening percipitates which are smaller than 1 pm.

Expressed differently, in a preferred embodiment the method of the present allows through;

Strict Temperature control at the exit of the extrusion press after an inert atmosphere;

The aforementioned TTT after extrusion process; and in particular when nitrided dies are used, to produce defect free surfaces after extrusion and etching pretreatment; even when

6060X alloy composition with higher amount trace elements Fe , Mn, Cu and Zn, are being used

As further detailed in the examples hereinafter, proper pretreatment of the thus obtained 6060X soft alloy, such as a state of art acid etching or alkaline etching ( at least 1,0 or preferably 2 gram/m2 ) , and in case of alkaline etching followed by a standard acid desmutting to avoid enrichments of Zn, Cu,Mn on the surface. This etching step of the inertized extruded alloy, is preferably followed by deposition of a good stable conversion layer on Ti , Zr , Ti / Zr base or an anodisation layer of at least 4 pm is also used. As final step a single or two layered powdercoating (very popular in the Netherlands) is placed of typical 70 pm. After these all of these standard and popular pretreatments for powdercaoting only Rate A results for FFC (FiliForm Corrosion test , a special developed test to see how resilient an powder coated aluminium profiles are against filiform corrosion or filamentous corrosion after powdercoating.) and AASS tests (Acetic Acid Salt Spray test : a general test developed to test corrosion behavior of powder coated aluminium profiles (very popular in automotive ) are obtained.

The present invention is further provides a device 100 for manufacturing an of an aluminum recyclefriendly soft alloy having a composition as described above 10. A preferred embodiment of a device suitable for producing an extruded part of an aluminum soft alloy obtainable using the method as described above, is shown in figure

2. The device comprises a container 8, with container liners 7 in which the aluminum alloy or billet 2 to be extruded is pushed in. Often the container 8 will be heated to maintain the temperature of the aluminum soft alloy or billet 2 at a desired level. The aluminum soft alloy or billet has been heated to softening temperature by a billet furnace. The device comprises also a forwarding system 1 for forwarding the softened aluminum alloy or billet 2 from the container into, through and out of an extrusion die

3. Forwarding systems used in this type of devices are generally known to the skilled person and usually comprise a hydraulic system with a hydraulic press 50. As pressure is applied, the billet 2 is crushed against the die 3, becoming shorter and wider until its expansion is restricted by full contact with the container liner walls 7 wherein the billet

2 is contained. Then, as the pressure increases, the soft (but still solid) metal 2 has no place to go and begins to squeeze through the shaped orifice or die opening 33 of the die

3 to emerge on the other side from the die exit 23 as a fully formed profile 10. The front part of the hydraulic system will usually comprise a ram 9 or a pusher, which forces the aluminum alloy or billet 2 through the die opening 33 into die cavity 43.

The extrusion die 3 comprises a die opening 33 in the shape of the part 10 to be extruded. The extrusion die 3 may also comprise a die cavity 43 delimited by die backers 12 and die support parts 13. Depending on billet size and die opening 33, a continuous extrusion as much as +/- 50 meter may be produced with each stroke of the press. The newly-formed extruded part 10 is supported on a runout conveyor or table 4 as it leaves the die 3.

As close as possible to the die opening 33 of the extrusion die 3, preferably within the die cavity 43 delimited by the die backers 12 and die support parts 13 of the extrusion die 3, an inert gas 15 is supplied from an inert gas supply 5 in such a way that the extruded aluminum alloy part 10 which emerges from the die opening 33 is contacted by or surrounded by an inert gas 15 to create an inert atmosphere in the die cavity 43, at least at the position where the freshly extruded still hot aluminum alloy leaves the extrusion die 3. Suitable inert gases are well known to the skilled person and include nitrogen, helium, argon etc, but preferably nitrogen is used. More preferably use is made of a nitrogen flow obtained from the expansion of liquid nitrogen, as besides providing an inert atmosphere a cooling effect may be achieved as well. In an alternative embodiment use can be made of CO2 gas which originates from the expansion of solid CO2. The skilled person will be capable of adapting the inert gas flow so that a desired inertisation and if possible cooling is achieved at the position where the aluminum alloy emerges from die opening 33. This way, the risk to unwanted oxidation of the extruded metal alloy may be reduced, and extruded aluminum parts may be obtained the surface quality of which may be improved. Thereto, the device of this invention also comprises a device 5 for supplying an inert gas to die opening 33. This may be achieved in several ways, for example by an inert gas supply at the position of the die opening 33. In an alternative embodiment, inert gas may be supplied along holes or slots in the support plate 13 and/or die backers 12 present behind the die opening (33) of the die 3 , towards and into the die exit 23.

As mentioned before, and attributing to the inertisation of the environment at the position where the aluminum alloy emerges from the die opening 33, in a preferred embodiment the die surfaces at the profile forming area (bearings) should comprising a compound or white layer (such as a gas nitrided dies or CrN coated dies yielding repectively a nitride layer or Cr-N hard coating) of minimal 5 pm, preferably of about 8 pm with a diffusion layer of about 0,15 to about 0,30 mm. Depending on the nature and composition of the alloy, the extruded part 10 may be cooled after it has left the die 3, either by natural cooling in the environment or through the use of air or water quenches, to ensure that the desired metallurgical properties are obtained after aging.

The device of this invention may further preferably comprise a temperature sensor 6 for measuring the temperature of the extruded part 10 which has left the extrusion die 3 and ascertaining that the temperature of the extruded part is maintained in the range of between 500 and 600°C; in particular between 550°C and 595°C. For measuring the temperature, various devices known to the skilled person may be used, for example an infrared camera. After having been subjected the extrusion process, the extruded part is transferred to a cooling table for the Temperature Time Treatment (TTT) after extrusion treatment.

The present invention further relates to a device for producing an extruded part of an aluminum soft alloy composition as described above, wherein the device may comprises an art known heating device 11 (such as a heating coil surrounding the container) for heating the container and maintaining the typically preheated and softened aluminum soft alloy at its elevated temperature, a pusher for pushing the softened alloy into an extrusion die for extruding the alloy into a desired shape, a device for supplying an inert gas at the exit of the die, a device for measuring the temperature of the extruded part which has left the extrusion die, and controlling the temperature of the extruded part in the range of between 500 and 600°C; in particular between 550°C and 595°C.

EXAMPLES Extrusion Test Runs

The below table (Table 1) provides a comparison between extrusion testruns of a series of tested alloys (Table 1A) including a primary classic aluminum soft alloy (Alloy 1) with two typical recyclefriendly soft alloys (Alloy 2 & 3) used in the method according to the invention. For each material two testrun conditions (Table IB) were compared, respectively applying on the one hand temperature control according to the method of the present invention and on the other hand omitting this temperature control during the extrusion process. Three parameters were monitored during these runs. Two of them relating to surface problems causing the production to stop either immediately (Direct Surface Problems) or before the target volume for surface problems is reached (Indirect Surface Problems). The last parameter is the average ram speed that can be maintained without affecting the quality of the extruded aluminum soft alloy.

These test runs show that for the classic alloys the need of temperature control for an experienced operator is not really necessary. These alloys have a broad stable process window showing an acceptable ram speed of at least 8 mm/sec, with a small number of surface problems irrespective of the operational conditions being used. Table 1A - Composition of tested Alloys

Extrusion Conditions

Billets were pressed through a die cavity as schematically shown in Figure 2, comprising dies (3) having a Nitride layer with the following characteristics; - a compound layer or white layer of min 5 pm, preferably 8 pm; and - a diffusion layer of 0,15 mm preferably 0,30 mm.

In these experiments’ temperature measurement of the extruded profiles is always done at the same place at the top of the profile where a stable temperature measurement is possible. In these tests the AMETEK Land's SPOT AL EQS pyrometer and SPOT actuator were used. Set temperatures (max exit temperature) was 595°C Fig 3 A - close to hot spot and Set temperature (max exit temperature ) was 550°C - far from hot spot , as indicated in Fig. 3B.

The maximal exit temperature of the extruded profiles was determined after shrouding with liquid nitrogen at 1 m from die exit (Max. Ex. Temp. )

Table IB - Extrusion testrun results

Contrary to the classic alloys with low concentrations of trace elements, where temperature control at the die exit are apparently not required, for the recyclefriendly soft alloys (Alloy 2 & 3) the contrary ram speed reduces with more than 10% and stops caused by surface problems more than double. For these recyclefriendly soft alloys the process window is small, showing a clear effect of the temperature on each of the aforementioned parameters as evident from the following table (Table 1C). In a series of test runs the extrusion was done under an inert atmosphere and only the set temperature was changed, respectively processing either 15°C below the set temperature or 15°C above the set temperature. At the lower temperatures there is a clear impact on the ram speed, but at the higher temperatures there is a dramatic increase in both the direct and the indirect surface problems. It follows from the foregoing experiments that for the recyclefriendly alloys a good temperature control is absolutely recommended to achieve good results. To a certain extend, this requirement of a good temperature control can be explained by the difference in Solidustemperature between the classic alloy 1 and the recyclefriendly alloys 2 and 3 (Table 2).

Table 1C - of tested alloys during production under different conditions of Temperature Control

Table 2 . Solidustemperature of tested alloys. Solidustemperatuur ( °C )

Filiform Corrosion Test - Test 1

For soft aluminum alloys high concentrations of traces of alloying elements like Cu are not recommended. For example in certain countries Cu concentrations above 0,02 are sort of forbidden and etching rates below 2,0 gram/m ² are not allowed following specifications of qualicoat in particular for seaside quality. It is generally accepted that these criteria regarding the presence of the trace alloying elements and the amount of etching rates is necessary to prevent filiform corrosion of soft aluminum alloys.

The extruded profiles obtained using the aforementioned exemplified extrusion method according to the invention were tested for their filiform corrosion resistance. The most common pretreatments in the market were used and tested, namely;

• Alkaline / Acid etch - Alkaline etching (minimum 1 gram/m ² ), Acid desmutting (HNO ₃ soluton) and as conversion an alficoat Ti - conversion layer (Alufmisch);

• Alkaline / Acid etch with high etching rates (50 - 70 gram/m ² ) and as conversion preanodisation 4 - 10 pm (Preano); and

• Double Acid etch with etch rate 2 gram/m ² and as conversion layer precoat Ti - Zr conversion layer (Precoat)

Table 3 : Pretreated Soft aluminum alloy samples tested The thus pretreated materials (summarized in Table 3 above) were subsequently exposed in triplicate to the filiform corrosion test (FFC) (Qualicoat, modified ISO 4623- 2), briefly;

The samples were scratched in 2 directions length 10 or 2x5 cm; - HC1 (37%, 1.19 g/cm ³ ) is dripped along the scratches during ± 1 min;

Acid is removed with a piece of cloth;

After lh at Room Temperature the samples were applied in a controlled Climate chamber and exposed to a humidity at 82% ± 5% and a temperature of 40°C ± 2°C using the following test cycle.

Time of 1 test cycle : lOOOh Number of test hours : ~t000

Pretreatment of the samples : Exposed after scratch application and HCI treatment

Application of a scratch : 2 scratches on each sample {w: 1mm, erf, QC FFC test) Relevant test surface : Plate surface, excl. edges Angle of exposure : Horizontal position Test program ; Specific Type of evaluation : Only final evaluations

Surprisingly, and as summarized in Table 4 below, even with a low rate of etching, even recycle alloys with high concentrations of alloy trace elements all pass the filiform corrosion test and receive the highest rating A.

Table 4 : Filiform Corrosion Test Results Acetic Acid Salt Spray Test - Test 2

To confirm the observed corrosion resistance for the extruded recycle friendly 6060X soft alloys obtained using the extrusion method according to the invention, a further test has been performed on a further series of Test Alloys with even higher Cu concentrations (Table 5)

Table 5 - Compositions of Alloys tested

Extrusion conditions

Extrusion conditions were the same as above, briefly billets were pressed with an average ram speed of 8 mm/sec through a die cavity as schematically shown in Figure 2, comprising dies (3) having a Nitride layer with the following characteristics; - a compound layer or white layer of min 5 pm, preferably 8 pm; and - a diffusion layer of 0,15 mm preferably 0,30 mm. In these experiments’ temperature measurement of the extruded profiles is always done at the same place at the top of the profile where a stable temperature measurement is possible. In these tests the AMETEK Land's SPOT AL EQS pyrometer and SPOT actuator were used. Set temperatures at these locations were 550°C in case of window profile and 595°C in case of a facade profile. See Fig. 3 A and 3 B

Temperature Time Treatment after extusion to ensure small percipitates after aging: Max.Ex.Temp. always above 500 ° C Coolingspeed 3 ° C /sec Aging 8h at 175 ° C

Pretreatments

Pretreatment conditions were the same as above

Corrosion Tests

Besides the filiform corrosion test (FFC) (same as above), the pretreated materials were also exposed in triplicate to the Acetic Acid Salt Spray test (AASS), a general test developed to test corrosion behavior of materials after powdercoating (very popular in automotive). In this test sample specimens are placed in an enclosed chamber and exposed to a continuous indirect spray of salt water solution, prepared in accordance with the requirements of the test standard (ASTM G85 Annex 1) and acidified (pH 3.1- 3.3) by the addition of acetic acid. This spray is set to fall-out on to the specimens at a rate of 1-2 ml/80 cm ² /hour, in a chamber temperature of 35 °C.

Test Results

Hereinafter the results are summarized for the different pretreatment methods and both the FCC and the AASS test wherein a rate A indicates that all three samples pass the test.

All tested samples received an A rating both in the FCC test as in the AASS test.

All tested samples received an A rating both in the FCC test as in the AASS test.

All tested samples received an A rating both in the FCC test as in the AASS test.

This further test confirms that the 6060X alloys as defined herein and extruded using the method according to the invention, results in extruded profiles with a high corrosion resistance, even in the absence of the forbidden Cr 6+ conversion layer.

It also is important to mention that in all above tests the final powder coating was executed with two different types of powdercoatings , Interpon Akzo Noble and Axalta, and that no significant difference were observed during all corrosion tests between both powdercoatingss, indicating that the positive effect on surface problems is independent of the powder coating used, and dictated by the extrusion and pretreatment method used.