EP3129517A1

EP3129517A1 - Method for the manufacturing of products with anodized high gloss surfaces from extruded profiles of al-mg-si or al-mg-si cu extrusion alloys

Info

Publication number: EP3129517A1
Application number: EP15769522.2A
Authority: EP
Inventors: Ulf Tundal; Oddvin Reiso
Original assignee: Norsk Hydro ASA
Current assignee: Norsk Hydro ASA
Priority date: 2014-03-27
Filing date: 2015-03-24
Publication date: 2017-02-15
Anticipated expiration: 2035-03-24
Also published as: EP3129517A4; EP3129517B1; WO2015147648A1; US20170009322A1

Abstract

Method for the manufacturing of products with anodized high gloss surfaces from extruded profiles of Ai-Mg-Si or AS-Mg-Si-Cu, where the alloys initially are cast to extrusion billet(s), containing in wt.% Si: 0,25-1,00 Mg: 0,25-1,00 Fe: 0,00-0,15 Cu: 0,00-0,30 Mn: 0,00 -- 0,20 Cr: 0,00-0,10 Zr: 0,00 -0,10 Sc: 0.00 -0,10 Zn: 0,00-0,10 Ti: 0,00-0,05., and Including incidental impurities and balance A.L a) where the billet is homogenised at a holding temperature between 480°C and 620°C and soaked at this temperature for 0-12 hours, where after the billet is subjected to cooling from the homogenisation temperature at. a rate of 150°C/h or faster, b) the billet is preheated to a temperature between 400 and 540°C and extruded preferably to a solid shape profile and cooled rapidly down to room temperature, c) optionally artificially ageing the profile, d) deforming the profile more than 10% by a cold roiling operation, whereafter e) the profile is flash annealed with a heating time of maximum two minutes to a temperature of between 450 ~ 530 °C for not more than 5 minutes and subsequently quenched, and f) optionally the profile after flash annealing is further subjected to a cold deforming operation to remove residua! stresses from cooling and adjusting dimensional tolerances, and g) the profile is finally aged.

Description

^" et od for the manufacturing of products ith anod&e high glo s surfaces

from extruded profiles of AF g-SI or Ah g-ShCu extrusion llo s"

The present Invention relates to a method for the manufacturing of products with anodteed high gloss surfaces from extruded profiles of Ai-Mg-Si or AhlV¾~Si-Cu alloys.

The oxide layer AI2O.3} formed during anodizing is build up y dissolving the outer layer of the aluminium. For each 3 μηι of oxide layer formed 2 pm of the aluminium is dissolved, Since the oxide layer is bulkier than the aluminium the total thickness will then Increase by 1 pm. in order to obtain high gloss of an anodlzed aluminium product it Is Important to keep the amount of constituent particles with a diameter larger than approximately 0.3 pm (S, ernick, R. Pinner and P.O. Sheasby, The Surface Treatment and Finishing of Aluminium and its Alloys, ASM INTERNATIONAL, FINISHING PUBLICATIONS LTD, Fifth Edition Vol 1 , 1987, p. 143} at a low level since these particles will be embedded In the anodi ed layer and cause a reduction in the gloss. The most Important factor to achieve this is to keep the amount of f e at a low level, since primary AlFeSi particles are insoluble in the aluminium matrix, Typically, alloys used for high gloss products have a maximum limit of Fe around 0.12 wt . Gloss is thus also reduced with increasing thickness of the oxide layer formed during anodizing since more particles then will be embedded, Moreover the process parameters used during anodizing also affect the gloss.

Hardening precipitates are formed during the artificial ageing process (e.g. β''-MgSi) from the addition of g and Si, if Cu is added in sufficient amount other phases than $" may form (e.g. Q^! and 1} (Calin D. Marioara, ei al._s improving Thermal Stability in Cu- Containing AI~Mg-Si Alloys by Precipitate Optimization, METALLURGICAL AND MATERIALS TRANSACTIONS A_., March 2014 ), These hardening precipitates are much smaller than 0.3 pm and are therefore not reducing the gloss in the same way as the primary AiFeSi particles. The strength requirement for the alloy determines the necessary amount of Ug_t Si and Cu In the alloy, in order to maximise the gloss it is necessary to process the material in a way where precipitation of larger non-hardening phases (e.g. β^!- fvtgSi and -tVg^SI) of Mg, Si and Cu is avoided. This is easiest to obtain for 6060 and 8063 type of alloys where the fVtg and SI contents are relatively low. Higher alloyed materia! requires higher temperatures in the extrusion or soiuflonislng processes and faster cooling afterwards to avoid precipitation of such particles,

Alloying elements such as tvln, Cr, Zr or So can be added to form dispersoid particles during homogenisation , Frequently, these elements are added in high amounts in order to prevent reerystaiiization in the extruded profile. However, if. can be beneficial to add these elements in smaller amounts to only have some dispersoid particles in the alloy in order to avoid grain growth during homogenisation and after the recrysia!iisation process occurring in the extrusion process or in a separate reerystaiiization and soiutionssing process for the cold deformed material. The size of these particles is typically between 0.01 -0,2 pm . Thus, such particles can be added, at least in a relative low number, without Significantly affecting the gloss. However, the number of dispersoid particles should not be so high that the exposed areas of the profile surface get a mixture of a non- recrysialiized and a recrystallized structure or a fully recrystallized structure with a large and uneven grain size. Addition of elements that form dispersoid particles can also give an unwanted colour of the anodislng layer, or they can give an unwanted surface appearance due to a strong texture of the recrystallized grains.

If an anodl ed surface contains large grains the individual grains can be detected by the naked eye. This surface defect is frequently called mottling. The best surface appearance is obtained when the average grain size is smaller than approximately 70 pm and the grains mainly are randomly orientated.

If the processing of the material is satisfactory there will be no large β'- gSi o fi-Mg&i particles present in the extruded and aged profile samples. In such a case the gloss will be more or less proportional to the amount of Fe In the alloy for a given anodizing process. To maximize the gloss one would like to minimize the Fe content. Reducing the Fe content will increase the price of the aluminium since if will be more costly to produce. If will require alumina with low Fe and low contribution of Fe from the anodes. The processing in the electrolysis and the casihouse also has to be adapted in order to produce aluminium with very low Fe content The main problem by using very low Fe contents is, however, the ability to control the grain size in the billet and in the extruded profile.

From Japanese patent publication No. 10-306336 is known an aluminium alloy extruded material having high surface gloss after anodic oxidation treatment where the surface gloss allegedly is made uniform by specifying the number of the particles of Mg?Si participated in the matrix. This Is obtained with a specific heat treatment procedure prior to and after extrusion. With the present Invention is provided a method for the manufacturing of products with anodized high gloss surfaces from extruded profiles of Al-Mg-Si orAi-Mg-Si-Cu alloys with excellent mechanical properties and at low costs.

The method according the invention is characterized by the features as defined in the accompanying independent claim 1.

Further embodiments are defined in the subordinate claims 2 - 12.

The invention will be further described in the following by way of examples and with reference to the drawings and figures where; Fig. 1 is a photo of a quarter of a macro etched billet slice (@228 mm in diameter) with abnormal grains,

Fig. 2 is a light optical micrograph showing a typical grain structure through the thickness of a thick solid shape extruded profile which is anodised and viewed In polarized light

Fig. 3 is a principal sketch of an Industrial processing line for performing the cold rolling and the annealing process described in the present invention. shows light optical micrographs of samples from example 1 showing the grain structure in the middle of the cross section for the as extruded profile and for the samples that were cold rolled to give 10, 20, 40 and 80% reduction In the thickness prior to annealing, All samples are anodlsed and viewed in polarized light.

Fig. 5 shows grain structure in an as cast billet (© 5 mm diameter) without grain refiner, which was used in example 2 of the present application. Picture of a macro etched billet slice to the left and anodlsed sample viewed in polarized light in a light optical microscope to the right.

Fig. 6 are light optical micrographs showing the AIFeSs particles in a

homogenised billet cast without grain refiner (upper picture) and In a homogenised billet cast with grain refiner (lower picture). The position of the samples in the billet is approximately half radius.

Fig. 7 is alight optical micrograph of an as extruded sample In example 2 of the application, showing the grain structure close to the surface. Anodlsed and viewed in polarized light.

shows light optical micrographs of samples from example 2, showing the grain structure In the middle of the cross section for the as extruded profile and the samples that were cold rolled to give 20, 30, 40 and 50% reduction in the thickness prior to annealing. All samples are anodisecl and viewed in polarized light,

Fig, 9 shows further light optical micrographs of samples from example 2 of the present application, showing the grain structure in the middle of the cross section for samples that were cold rolled to 40% reduction in the thickness prior to annealing in air (upper) and in a salt bath (lower). Both samples are anodised and viewed In polarized light.

When the Fe content Is below approximately 0,10 wt% the chance of getting abnormal grains (grains that grow and consume other grains that were formed during casting) In the billet during homogenisation becomes very high. Therefore a grain size of several centimeters is very common In billets of alloys with ver low amounts of Fe. An example of abnormal grains In a homogenised billet with low Fe content is shown in Figure 1.

The billet grain size will probably not affect the grain size in the extruded profile much if the extent of deformation is high, for example when extruding thin walled hollow profiles. For solid shapes, and especially for thick walled profiles, the billet grain size will most likely affect the grain size in the extruded profile. An additional challenge is that the billet temperature needs to be rather high in order to dissolve the gsSi particles, and a high billet temperature makes it more difficult to obtain a small grain size after extrusion.

In an extruded profile one usually sees a surface layer of mainly randomly oriented grains and typically one or a few grains in thickness. Underneath this layer one typically finds a region of larger grains. The thickness of this layer varies, and is usually thicker for a thick wailed solid shape profile and thicker towards the back end of the extruded length. An example of a typical grain structure in a cross section of a thick wailed industrially extruded profile can be seen in Figure 2. Below the layer of larger grains the grain structure is iypicaiiy more homogeneous. The grains in the homogeneous center region of the cross section are predominantly aligned in one direction, with a strong cube texture. This is often seen in a micrograph of the grain structure in the cross section by small differences in the colour of the grains. yore and more consumer electronics like mobile phones, tablets and lap tops are made of aluminium from extruded profiles, if the profile surface could have been used without any machining the grain structure in the anodlsed surface would probably be okay in most cases. However, very often there is a need to machine the extruded profile to make the shape and the dimensional tolerances of the final product, in that case the exposed surface can consist of grains from the coarse grain layer beneath the surface layer of the extruded profile. Due to this the entire coarse grain layer has to be removed before starting to machine the shape of the final product. The thickness of the layer that has to be removed due to coarse grains will vary with the size of the profile and the extrusion conditions and Is typically in the range of 0,2 to 1 mm.

The present invention deals with the task to get a homogeneous grain structure with an average grain size below approximately 70 pm irrespective of the Fe content, the grain size in the billet prior to extrusion and the extrusion conditions.

Solid shape profiles which are blanks for consumer electronics will be more or less fiat, but could possibly have some features in the cross section in order to save material and machining. Such profiles are therefore very well suited for cold rolling after extrusion. By cold rolling a profile by a minimum of 10% followed b flash annealing a new recrystalllzafion process will take place. With sufficient deformation and a proper annealing process the resulting grain structure will be homogeneous over the cross section with a much more random orientation of the grains than In the as extruded profile. The grain size will in addition to the alloy content, depend on the degree of cold deformation, the annealing temperature, the heat up conditions and the time at the annealing temperature, in an alloy with very low Fa and no dlspersoid particles the recrysiaiiisation will take place at a low temperature, most likely during heating to the annealing temperature. One issue will then be to avoid grain growth at the annealing temperature when there are almost no particles in the material to pin the grains.

The annealing temperature should preferably be above the soivus temperature for UgzSi particles in order to avoid particles that can reduce the strength and the gloss of the anodised material, in additio , the time at this annealing temperature should be as short as possible in order to avoid grain growth. Therefore, the material should be processed through extrusion in a way that MgsSI particles are avoided. This means sufficiently high billet temperature in combination with a high enough exit temperature from extrusion and fast cooling of the profile after extrusion. With no Mg?.S\ particles in the material prior to cold rolling and annealing there is no need for a holding time for the material at the a nealing temperatu e .

The consequence of annealing at temperatures below the soivus temperature will be that ivlg-Si containing precipitates larger than approximately 0.3 pm may form. These particles will contribute to a reduction In the gloss and in the strength of the material. The amount of this reduction will depend on the actual time- temperature history during the flash annealing and cooling operation and the composition of the alloy.

An industrial process to perform the cold rolling and the annealing process could be done as shown schematically in Figure 3. The cold rolling station should be followed by a station for performing fast heating to the annealing temperature. Using Induction heating is probably the best way to do this. With enough power and induction coils that fit the shape of the profile and good process control, if should be possible to heat the material to a temperature around 50CTC (depending on the composition and thereby the soivus temperature of the alloy) within a very short time and with sufficient accuracy in temperature. in order to avoid precipitation of Mg-Si containing particles larger than approximately 0,3 prn the profile needs to be cooled rather rapidly down to room temperature. The reason for this is described in a previous section, Thus, prefeerrably according to the present invention, the profile is fiash annealed with a heating time of maximum two minutes to a temperature of between 450 - 530 ^*C for not more than 5 minutes and subsequently -quenched.

After the annealing operation one option could be a second cold roiling operation to remove residual stresses from the quenching operation. An alternative to cold roiling to remove residual stresses would be to stretch the material in way similar to what is done after extrusion, or performing a cold forging operation on blanks from the flash annealed and cooied material.

Further, to obtain a more homogeneous distribution of deformation and more accumulated energy in the material the profile could optionally be subjected to ageing after extrusion and prior to cold deforming. Preferably the profile could be averaged to a 17 condition, for example at 200 - 230 ^'C for 1 ···· 5 hours.

Alter the annealing process the final ageing of the material can for example be done with the patented dual rate ageing cycle {U. Tundai and O. R&iso, EP 1 155 161 81) to get maximum strength with minimum amount of alloying elements.

The invention will he further described In the following by way of examples. Ex¾ te.1

Billets with diameter 95 mm were cast In a lab casting facility using the Hycast hot-fop gas-slip technology (as described in EP 0 778 097 B1 ) and a T182 based grain refiner. The composition of the alloy Is shown in Table 1 . Table 1. Chemical composition of the alloy used in example 1 Si Fe n Cr Cu Zn Zr Ti B A!

0.354 0.539 0.1 10 0.001 0.001 0.001 0.002 0.001 0.012 0.002 98.95

The billets were homogenised at 575 for 2 hours and 15 minutes followed by cooling at a rate of approximately 400°C per hour. Extrusion of the billets was performed at an 8 H laboratory extrusion press with a 0 mm diameter container to a profile with 5x40 mm² cross section . The billet preheating temperature was approximately 5Q0^*C and the extrusion speed 20 m/min. After extrusion the profile was quenched in water.

A 50 cm long piece from the front part of the extruded profile was cold rolled to give 10, 20, 40 and 60% reduction in the thickness. The samples that were col rolled to different thicknesses were then annealed in a salt bath which had been preheated to 500T, A hole was drilled into each of the samples to fit a thermocouple, The heating time to temperature was in the range 5 - 10 seconds, depending on the thickness of the sample. When a sample was put into the salt hath a holding time of 10 seconds started when the temperature reached 490 . After annealing the samples were quenched h water,

Prior to extrusion the billets had an even and small grain size. The as extruded sample in Figure 4 shows a homogeneous grain size throughout the cross section, in this case there is no coarse grain layer below the surface. This is maybe because the sample Is smaller than the sample shown in Figure 2 and maybe also because it Is taken from the front part of the extruded length. It is evident thai the grains under the randomly oriented i^'ayer of grains In the profile surface area are predominantly aligned in one direction since the colour contrast between the grains is low.

As can be seen from the large colour contrast, the cold rolled and annealed samples show a much more random orientation of the grains than the as extruded sample. This confirms that these samples are fully recrysialiized after annealing. The samples that were cold rolled to 10 and 20% reduction in thicknesses clearly have an uneven grain structure with the largest grains in the middle of the cross section. The samples that were cold rolled to 40 and 80% reduction in thicknesses have an even grain structure throughout the cross section, The grain sizes of the samples shown in figure 4 (measured 250 pro below the surface of the cross sections) are shown in Table 2, Table 2. Average grain sizes as measured 250 pm below the surface of the cross section. The as extruded grain size is very uncertain due to the very low contrast between the individual grains.

10% cold roiled 20% cold rolled 40% cold rolled 60% cold rolled

As extruded

annealed + annealed ·*· annealed * annealed

-87 pm 79 μηι 60 urn 44 pm 33 pm

Example 2

Billets with diameter 95 mm were cast in a lab casting facility using the Hycast hot-top gas-slip technology without using a grain refiner, A picture of a macro etched billet slice is shown In Figure 5 together with a micrograph showing an anodized sample viewed in polarized light in the light optical microscope. Towards the surface there are some relatively large e uiaxe grains, but a large part of the cross section of the billet slice consists of feather crystals. The composition of the alloy is shown in Table 3,

Table 3. Chemical composition of the alloy used In example 2

g Si Fe n Cr Cu Zn Zr II B Ai

0.380 0.473 0.092 0.002 0.001 0.001 0.006 0.000 0.004 0.000 89.00 The cast billets were homogenised at 575^* C for 2 hours and 15 minutes followed by cooling at a rate of approximately 400°C per hour, Micrographs of the particle structure in the billets from the two different alloys In examples 1 and 2 are shown in Figure 8. The material cast without grain refiner (upper picture} shows Fe containing particles (mainly -AIFeSI) that are smaller and much more evenly distributed than the Fe containing particles (mainly β-AIFeSi) in material cast with grain refiner (lower picture), In the latter case the A!FeSi particles mainiy are located at the grain boundaries, in both cases the Fe/Si ratio is very low, which makes B~AlFeSi particles very stable in the homogenising process. A particle structure as shown in the material cast without a grain refiner would be beneficial In avoiding alignment of particles and possible visible dark lines in the extruded and anodized high gloss surface.

The billets where extruded at an 8 iVIN laboratory extrusion press with a 100 mm diameter container to a profile with a cross section of 5x40 mm². The billet preheating temperature was approximately S0Q^*C and the extrusion speed 20 m/mln. After extrusion the profile was quenched in water.

A 100 cm long piece from the back part of the extruded profile was cold rolled to give 20, 30, 40 and 50% reduction in the thickness. The samples that were cold roiled to different thicknesses were then annealed in a salt bath which had been preheated to 500°C. A hole was drilled Into each of the samples to fit a thermocouple. When a sample was put into the salt bath the holding time of 10 seconds started when the temperature reached 490^*0. After annealing the samples were quenched in wafer. In addition one sample of the material cold rolled to 40 % reduction in thickness was held 5 minutes at 500ⁿC. Yet another sample of the material cold roiled to 40% reduction in thickness was heated in an air circulating oven at a considerably lower heating rate to the annealing temperature than that obtained in a salt bath.

A micrograph of the as extruded sample is shown in Figure 7. It seems like some of the grains below the surface are considerably larger than 100 pm, which could give some unwanted effects in the surface appearance, inside the surface region the grains are strongly aligned in one direction, which gives very little contrast between each individual grain In the micrograph.

Figure 8 shows micrographs of the grain structure in the as extruded sample as well as samples that have been cold rolled 20, 30. 40 and 50% and thereafter annealed, As also seen in example 1 , one can see from the large colour contrast that the cold roiled and annealed samples show a much more random orientation of the grains than the as extruded sample. The samples that were cold rolled to 20% reduction in thickness clearly have an uneven grain structure with the largest grains in the middle o? the cross section. The sample cold rolled to 30% reduction in thickness has smaller grains and a more even grain structure, but the grains In the middle still are somewhat larger than those towards the surfaces. The samples that were cold rolled to 40 and 50% reduction in thicknesses have a smaller grain size and an even grain structure throughout the cross section. As also shown in Table 4 the grain size seems to be similar for the samples cold roiled to 40 and 60% reduction in thicknesses.

Table 4. Average grain sizes as measured 250 pro below the surface of the cross section. The as extruded grain size is very uncertain due to the very low contrast between the individual grains.

20% cold rolled 30% cold rolled 40% cold rolled 50% cold rolled

As extruded

•f- annealed ·* annealed ·*· annealed ^•s- annealed

-88 pm 101 pm 95 pm 52 pm 5? pm

The sample that was cold rolled to 40% reduction in thickness and held at S00°C for 5 minutes did not show any grain growth. The reason for this is probably that the number of AlFeSI -particles is high enough to prevent grain growth. With even lower Fe contents than 0,09 wt% a holding time of 5 minutes at this temperature could cause grain growth in the sample.

Figure 3 shows that the sample heated in an air-circulating furnace (6-7 minutes heating time) has a more uneven grain structure and a slightly larger grain size than the sample that was rapidly heated (5-1 seconds) in a salt bath up to the soiutlonising temperature. The reason for this Is probably linked to precipitation of Mg-Sl particles at the grain boundaries, which are pinning the nuclei for new grains during the heat up process. In a sample which is slowly heated in air there is enough time for precipitation of g-Si particles to prevent the nuclei for new grains from growing until the particles start to dissolve again, s.e, when the sample is approaching the soivus temperature of the alloy. In this process some grains will probably start to grow earlier than others and therefore get larger, resulting in an uneven grain structure when the recrysta!!i ation process is complete.

Example 2 shows that it is beneficial to heat the cold roiled sample fast to the solutionising temperature to obtain en even grain size and that a holding time of only 10 seconds is sufficient to obtain a fully recrystailized grain structure.

Example 2 also shows that the final grain structure in the blanks could be perfect for providing attractive high gloss anodized surfaces even though the billet grain structure is regarded as being far from optimum when it Is cast without grain refiner. The main benefit of the present invention is a grain structure with an even grain size and a close to random texture throughout the cross section of the profile irrespective of the grain size prior to cold rolling (and thus also of the grain structure of the billet). An extruded thick walled flat profile will in most cases have a coarse grain layer that has to be removed in order to obtain a smooth anodized surface with a minimum of de ects in the final product. The amount of material that, would have to be removed in the as extruded cross section is typically In the range 7-15%.

Moreover, the cold roiling will ensure a very accurate thickness and flatness of the profile, and for that reason considerably reduce the need for machining. An extruded profile will have much more variation in the thickness, typically ± 0,1 mm.

Since the grain size In the billet and the extruded profile is of little importance for the resulting grain size in the cold rolled and annealed blanks there is a possibility of casting the billets with a minimum or even completely without the use of a grain refiner. In order to avoid centre cracks in the billets In the startup of the cast it could be beneficial to add some grain refiner in the first metal to cast. The grain refiner Itself could be a source for inclusions that can cause failures in the anocilzed surface. Another benefit of not using a grain refiner is thai the melt cleaning with the use of ceramic foam filters will be more effective on other type of Inclusions ⁽Nicholas Towsey, Woifgang Schneider and Hans- Peter Krug, A comprehensive study of ceramic foam filtration, 7th Australasian Asian Pacific Course & Conference, Aluminium Cast House Technology: Theory & Practice, P Whiteiey and J. Grandfieid (IMS: 2001)

The possibility of reducing the Fe content and still obtain an adequate grain structure will significantly improve with the use of the present invention. The lower Fe content can either be used to Improve the gloss, or to keep the current gloss but add a thicker and more wear resistant oxide layer to the anodized product. The latter will make the product more durable. Even though there is extra cost associated with the cold rolling and annealing process to obtain the uniform and random grain structure, this will probably be more than compensated for by the savings due to reduced machining and reduced material consumption.

Claims

1. Method for the manufacturing of products with anodized high gloss surfaces from extruded profiles of Ai- g-Si or Ai-Mg-Si-Cu alloys, where the alloys Initially are cast to extrusion billef(s), containing in wt.%

Si: 0,25 - 1 ,00

Mg 0,25 ~ 1 ,00

Fe; 0.00^■·^■· 0,15

Cu: 0,00 - 0,30

n; 0,00 - 0,20

Or. 0,00 - 0,10

Zr: 0,00 - 0,10

Sc: 0,00 -Ό,Ι Ο

Zn: 0,00 - 0, 10

Tr. 0,00 - 0,05, and

including incidental impurities and balance Ai,

a) where the billet is homogenised at a holding temperature between 480°C and 620*C and soaked at this temperature for 0-12 hours, where after the billet is subjected to cooling from the no ogenisatlon temperature at a rate of 150^*C/h or faster,

b) the billet is preheated to a temperature between 400 and 540*0 and extruded preferably to a solid shape profile and cooled rapidly down to room temperature,

c) optionally artificially ageing the profile,

d) deforming the profile more than 1 % by a cold rolling operation, where after

e) the profile is flash annealed with a heating time of maximum two minutes to a temperature of between 450 - 530 for not more than 5 minutes and subsequently quenched, and f) optionally the profile after flash annealing Is further subjected to a cold deforming operation to remove residual stresses from cooling and adjusting dimensional tolerances, and

g) the profile is finally aged.

Method according to claim 1

characterised in thai

the composition of the alloys measured in wl.% lies preferably within

Si: 0,35 - 0,8

Mg: 0,35- 0,6

and with the following maximum levels (wt.%) of the following elements

Fe.0,09.

Cu: 0,15

: 0,06

Cr: 0,04

Zrr 0,03

Ti: 0,02, and

including incidental impurities and balance Al.

Method according to claim 1 ,

charact rised in t at

the composition of the alloys measured in wt.% lies preferably within

Si: 0,35 - 0,6

g: 0,35 -0,6

and with the following maximum levels (wt%) of the following elements

Fe: 0,06..

Cu: 0.12

n 0,06

Cr: 0,04

Zrr.0,03 Ti: 0,02_; and

including incidental impurities and balance Al.

Method according to claims 1 ·· 3,

c aracterised i th

the profile in accordance with step c) optionally is overaged to a T? condition at 200 - 230 ^*C tor 1 ~ 5 hours,

Method according to claims 1^■- 4,

c ar ct ised i that,

the profile according to step d) is deformed more than 20%,

Method according to claims 1 - 4

characte rised in that

the profile according to step d) preferably is deformed between 30 and 60%,

Method according to claims 1-8,

c h a r a cf e r I s e d i n tha i

the profile is flash annealed according to step e) with a heating time of maximum 20 seconds to a temperature of between 460 - 530 *C for not more than 1 mi ute .

Method according to claims 1 - ?

ch acterised i that

the flash anneal heating according to step e) is obtained by induction heating of the profile.

Method according to Claims 1-7,

ch racte rised in th t the Hash anneal heating according to step e} is obtained by subjecting the profile to a salt bath or other convection or radiation heating means providing high heating rates.

Method according to claims 1-9,

c h a r a c t e r i s e d in t h a I

the alloys are cast without the use of grain refiner, except in the start-up of the casting operation.

Method according to claims 1-10,

ch rac e sed i that

the ageing, step g) is a one step or dual rate ageing operation to a final hold temperature between 160°C and 220°C and where the total ageing cycle is performed in a time span of between 3 and 24 hours.

12. Method according to claims 1- 11

cha racf e rised in th a t

the optional cold deforming after flash annealing, step f) is a rolling operation, a stretching operation or a forging operation