EP2924135B1 - Method for producing a sheet made of a high plasticity aluminum alloy having moderate strength for manufacturing semi-finished products or components of motor vehicles - Google Patents

Description

The invention relates to a method for producing a strip of an aluminum alloy, a corresponding aluminum alloy strip or sheet and a structural part of a motor vehicle consisting of an aluminum alloy sheet.

Semi-finished products and components for motor vehicles must meet different requirements depending on their place of use and purpose in the motor vehicle. During the manufacture of the semi-finished products and components for motor vehicles, the forming properties of the aluminum alloy or of the strips and metal sheets produced therefrom are decisive. During later use in motor vehicles, the strength values but also, in particular, the corrosion properties play a significant role.

For example, in structural parts of a motor vehicle, such as, for example, door inner parts, the mechanical properties are primarily determined by the rigidity, which depends above all on the shape of the inner door parts. In contrast, for example, the tensile strength has a rather minor influence. However, the materials used for a door inner part must not be too soft either. On the other hand, good formability is particularly important for the introduction of aluminum alloy materials into the motor vehicle sector, since the components and semi-finished products undergo particularly complex forming processes during their production. This particularly relates to components that are manufactured in a one-piece sheet metal shell construction, such. B. Interior panel door parts with integrated window frame area. Such components have by the saving of integrated window frame area. By eliminating joining operations, such components have considerable cost advantages compared to, for example, a fitted aluminum profile solution for the window frame. The aim is, for example, to be able to produce semi-finished products or components in one piece from an aluminum alloy and to use as few forming operations as possible. This requires maximizing the forming behavior of the aluminum alloy to be used. The AA5005 aluminum alloy (AlMg1), which is sometimes used for similar applications, does not meet these requirements since it does not have sufficient forming capacity due to solidification during forming.

Another important factor is corrosion resistance, as motor vehicle components are often exposed to condensation, splash water and condensation. The aluminum alloy to be used should therefore be as resistant to corrosion as possible, in particular in the painted state against intercrystalline corrosion and against filiform corrosion. Filiform corrosion is understood to mean a type of corrosion which occurs in coated components and exhibits a thread-like course. Filiform corrosion occurs at high humidity in the presence of chloride ions. Although the aluminum alloy AA8006 (AlFe1.5Mn 0.5) has sufficient strength and very high formability, it is susceptible to filiform corrosion. The alloy AA8006 is thus less suitable for coated, in particular painted components such as door inner parts.

$$\mathrm{Si}\le \mathrm{0}\mathrm{,5\%}\mathrm{,}$$

$$\mathrm{0,9}\%\le \mathrm{Mn}\le \mathrm{1}\mathrm{,5\%}\mathrm{,}$$

$$\mathrm{Mg}\le \mathrm{0}\mathrm{,25\%}\mathrm{,}$$

$$\mathrm{Cu}\le \mathrm{0}\mathrm{,20\%}\mathrm{,}$$

$$\mathrm{Cr}\le \mathrm{0}\mathrm{,05\%}\mathrm{,}$$

$$\mathrm{Ti}\le \mathrm{0}\mathrm{,05\%}\mathrm{,}$$

$$\mathrm{V}\le \mathrm{0}\mathrm{,05\%}\mathrm{,}$$

$$\mathrm{Zr}\le \mathrm{0}\mathrm{,05\%}\mathrm{,}$$

From the not yet published international patent application of the applicant PCT / EP2014 / 053323 an aluminum alloy is known as an alternative to the aluminum alloy of the type AA8006, which has the following alloy constituents in% by weight: $$\mathrm{Fe}\le \mathrm{0}\mathrm{,8th\%}\mathrm{.}$$

$$\mathrm{Si}\le \mathrm{0}\mathrm{,\; 5\%}\mathrm{.}$$

$$0.9\%\le \mathrm{Mn}\le \mathrm{1}\mathrm{,\; 5\%}\mathrm{.}$$

$$\mathrm{mg}\le \mathrm{0}\mathrm{25\%}\mathrm{.}$$

$$\mathrm{Cu}\le \mathrm{0}\mathrm{,\; 20\%}\mathrm{.}$$

$$\mathrm{Cr}\le \mathrm{0}\mathrm{,\; 05\%}\mathrm{.}$$

$$\mathrm{Ti}\le \mathrm{0}\mathrm{,\; 05\%}\mathrm{.}$$

$$\mathrm{V}\le \mathrm{0}\mathrm{,\; 05\%}\mathrm{.}$$

$$\mathrm{Zr}\le \mathrm{0}\mathrm{,\; 05\%}\mathrm{.}$$

Remaining aluminum, unavoidable accompanying elements individually <0.05%, in total <0.15%, the sum of the Mg and Cu contents satisfying the following relation: $$0.15\%\le \mathrm{mg}+\mathrm{Cu}\le \mathrm{0}\mathrm{25\%}\mathrm{,}$$

It has been found that even this aluminum alloy is in need of improvement, especially with regard to its deformation behavior. In addition, the high Mn content can lead to problems in recycling this aluminum alloy when mixed in the scrap cycle with the AA6XXX alloy Al-Mg-Si alloys commonly used in automotive applications.

From the JP 2006-152358 A is an aluminum alloy for the production of beverage cans is known, which has high formability and strength.

Based on this prior art, the present invention therefore has for its object to provide a method for producing an aluminum alloy strip for the production of semi-finished products or components for motor vehicles, which is highly deformable, medium-strength and very resistant to corrosion. In addition, an aluminum strip or sheet, its use and a structural part of a motor vehicle to be proposed.

$$\mathrm{0,6}\%\le \mathrm{Fe}\le \mathrm{1}\mathrm{,0\%}\mathrm{,}$$

$$\mathrm{Cu}\le \mathrm{0}\mathrm{,1\%}\mathrm{,}$$

$$\mathrm{0,6}\%\le \mathrm{Mn}\le \mathrm{0}\mathrm{,9\%}\mathrm{,}$$

$$\mathrm{0,5}\%\le \mathrm{Mg}\le \mathrm{0}\mathrm{,8\%}\mathrm{,}$$

$$\mathrm{Cr}\le \mathrm{0}\mathrm{,05\%}\mathrm{,}$$

The aluminum alloy for the production of semi-finished products or components of motor vehicles has the following alloy constituents in% by weight: $$0.6\%\le \mathrm{Si}\le \mathrm{0}\mathrm{,\; 9\%}\mathrm{.}$$

$$0.6\%\le \mathrm{Fe}\le \mathrm{1}\mathrm{,\; 0\%}\mathrm{.}$$

$$\mathrm{Cu}\le \mathrm{0}\mathrm{,1\%}\mathrm{.}$$

$$0.6\%\le \mathrm{Mn}\le \mathrm{0}\mathrm{,\; 9\%}\mathrm{.}$$

$$0.5\%\le \mathrm{mg}\le \mathrm{0}\mathrm{,8th\%}\mathrm{.}$$

$$\mathrm{Cr}\le \mathrm{0}\mathrm{,\; 05\%}\mathrm{.}$$

Rest Al and impurities, individually not more than 0.05 wt .-%, in total not more than 0.15 wt .-%.

Unlike the previous approaches, the present aluminum alloy is based on the recognition that Al-Mg-Si alloys of the alloy type AA6XXX in the as-annealed state have a very good formability. However, they were too soft for the previous applications. The lower limits of the forcibly provided alloying elements of 0.6 wt% for Si, 0.6 wt% for Fe, 0.6 wt% for Mn and 0.5 wt% for Mg ensure that the Aluminum alloy in soft annealed condition can provide sufficient strength. The upper limits of 0.9% by weight for Si, 1.0% by weight for Fe, 0.9% by weight for Mn and 0.8% by weight for Mg prevent the elongation at break from dropping and thus the forming behavior is deteriorated. For the same reason, the alloying elements Cu are limited to a maximum of 0.1% by weight and Cr to a maximum of 0.05% by weight. The combination of the intended alloy components of Si, Fe, Mg and Mn ensures that, on the one hand, the very good forming behavior of the Al-Mg-Si alloys is combined with increased strength, without having too great losses in ductility. The investigations showed that the specified aluminum alloy in annealed condition meets the requirements for formability and in particular for corrosion resistance and is thus suitable for the production of semi-finished products or components in motor vehicles. With the mentioned ranges of the forcibly provided alloying elements Si, Fe, Mn and Mg, the aluminum alloy according to the invention falls into the class of the Al-Mg-Si alloys of the alloy type AA6XXX. This allows for improved recyclability of this aluminum alloy when used in the scrap cycle with the in Automotive applications commonly used Al-Mg-Si alloys of alloy type AA6XXX be mixed.

$$\mathrm{0,7}\%\le \mathrm{Fe}\le \mathrm{1}\mathrm{,0\%}\mathrm{,}$$

$$\mathrm{0,7}\%\le \mathrm{Mn}\le \mathrm{0}\mathrm{,9\%}$$

und $$\mathrm{0,6}\%\le \mathrm{Mg}\le \mathrm{0}\mathrm{,8\%}\mathrm{.}$$

According to a first embodiment of the aluminum alloy, the alloying constituents Si, Fe, Mn and Mg have the following proportions in% by weight: $$0.7\%\le \mathrm{Si}\le \mathrm{0}\mathrm{,\; 9\%}\mathrm{.}$$

$$0.7\%\le \mathrm{Fe}\le \mathrm{1}\mathrm{,\; 0\%}\mathrm{.}$$

$$0.7\%\le \mathrm{Mn}\le \mathrm{0}\mathrm{,\; 9\%}$$

and $$0.6\%\le \mathrm{mg}\le \mathrm{0}\mathrm{,8th\%}\mathrm{,}$$

By raising the lower limits for Si, Fe, Mn and Mg, it is achieved that the strength of the aluminum alloy increases even further without deteriorating the deformation behavior or elongation at break of the soft sheets or strips made of aluminum alloy.

$$\mathrm{0,7}\%\le \mathrm{Fe}\le \mathrm{0}\mathrm{,8\%}\mathrm{,}$$

$$\mathrm{0,7}\%\le \mathrm{Mn}\le \mathrm{0}\mathrm{,8\%}$$

und $$\mathrm{0,6}\%\le \mathrm{Mg}\le \mathrm{0}\mathrm{,7\%}\mathrm{.}$$

A further improvement of the aluminum alloy in terms of maximum elongation at break is achieved in that the alloying constituents Si, Fe, Mn and Mg have the following proportions in% by weight: $$0.7\%\le \mathrm{Si}\le \mathrm{0}\mathrm{,8th\%}\mathrm{.}$$

$$0.7\%\le \mathrm{Fe}\le \mathrm{0}\mathrm{,8th\%}\mathrm{.}$$

$$0.7\%\le \mathrm{Mn}\le \mathrm{0}\mathrm{,8th\%}$$

and $$0.6\%\le \mathrm{mg}\le \mathrm{0}\mathrm{7\%}\mathrm{,}$$

It has been found that a very good compromise between achieved strength and elongation at break properties, ie forming properties of the aluminum alloy is achieved by this narrow corridor of constraints with respect to the alloying constituents Si, Fe, Mn and Mg.

Although the aluminum alloy has good corrosion properties, according to a further embodiment of the aluminum alloy, the resistance to intergranular corrosion can be further improved in that the Si content of the alloy exceeds the Mg content by at most 0.2% by weight, preferably at most 0. 1 wt .-% exceeds.

According to a further embodiment of the aluminum alloy, the elongation at break of the aluminum alloy can be further improved by further reducing the Cr content to a maximum value of 0.01% by weight, preferably to a maximum of 0.001% by weight. It has been shown that chromium has a negative effect on the elongation at break even in very low concentrations.

A similar effect also has the reduction of the Cu contents to a maximum of 0.05 wt .-%, preferably at most 0.01 wt .-%, at the same time the tendency to filiform corrosion or intergranular corrosion by reducing the Cu contents generally returns.

• Gießen eines Walzbarrens,
• Homogenisieren bei einer Temp vischen 500°C und 600°C für mindestens 0,5 h
• Warmwalzen des Walzbarrens bei Temperaturen von 280°C bis 500° C, vorzugsweise bei Temperaturen von 300°C bis 400°C auf eine Dicke von 3 mm bis 12 mm,
• Kaltwalzen mit oder ohne Zwischenglühung mit einem Abwalzgrad von mindestens 50%, bevorzugt mindestens 70% auf eine Enddicke von 0,2 mm bis 5 mm und
• Schlussweichglühung bei 300°C bis 400°C, bevorzugt 330°C bis 370°C für mindestens 0,5 h, vorzugsweise mindestens 2 h in einem Kammerofen.

According to a first teaching of the present invention, the object indicated above is achieved by a method for producing a strip from an aluminum alloy mentioned above with the following method steps:

• Casting a rolled bar,
• Homogenize at a temp 500 ° C and 600 ° C for at least 0.5 h
• Hot rolling of the rolling ingot at temperatures of 280 ° C to 500 ° C, preferably at temperatures of 300 ° C to 400 ° C to a thickness of 3 mm to 12 mm,
• Cold rolling with or without intermediate annealing with a degree of rolling of at least 50%, preferably at least 70% to a final thickness of 0.2 mm to 5 mm and
• Final soft annealing at 300 ° C to 400 ° C, preferably 330 ° C to 370 ° C for at least 0.5 h, preferably at least 2 h in a chamber furnace.

After casting, homogenization at a temperature of 500 ° C. to 600 ° C. for at least 0.5 h, preferably at least 2 h, ensures that a homogeneous microstructure is provided for the further processing of the rolling ingot. The hot rolling temperatures allow good recrystallization during hot rolling, so that the structure is as fine as possible after hot rolling. By cold rolling this fine-grained structure is merely stretched and recrystallized again in the final soft annealing. In the case of production without intermediate annealing, the cold rolling produces a particularly high number of dislocations in the microstructure, which produces a very fine-grained, thoroughly recrystallised microstructure in the final soft annealing. For this purpose, the Abwalzgrad to final thickness before the final annealing must have at least 50%, preferably at least 70% to the desired final thickness.

A further positive influence on the fine grain of the structure can be achieved that according to a further embodiment of the method according to the invention, the homogenization is carried out in two stages, the ingot is first heated to 550 ° C to 600 ° C for at least 0.5 h and then the Rolling bar at 450 ° C to 550 ° for at least 0.5 h, preferably at least 2 h is maintained. Subsequently, the rolling ingot is hot rolled.

The corrosion properties can be improved by milling the billet after casting or after homogenization on the top and bottom to exclude impurities from the top and bottom of the rolling billet, which can adversely affect the corrosion resistance.

According to a further embodiment of the method according to the invention at least one intermediate annealing after a first cold rolling in a Temperature of 300 ° C to 400 ° C, preferably at a temperature of 330 ° C to 370 ° C for at least 0.5 h, wherein before and after the intermediate annealing the Abwalzgrad is at least 50%, preferably at least 70%. Due to the selected degrees of finish before the intermediate annealing or after the intermediate annealing, it is achieved that the microstructure is thoroughly recrystallized during the intermediate annealing. The intermediate annealing time is at least 0.5 h, preferably at least 2 h.

If the intermediate annealing at a temperature at 330 ° C to 370 ° C, it is ensured that due to the raised lower temperature of 330 ° C, a sufficient recrystallization takes place and at the same time by reducing the upper limit an efficient intermediate annealing is performed, which is as little heat energy needed.

According to a second teaching of the present invention, the above object is achieved by an aluminum alloy strip or sheet made of an aluminum alloy mentioned above, wherein the strip has a thickness of 0.2 mm to 5 mm and in the soft annealed state, a yield strength R _p0.2 of at least 45 MPa and an _equi- elongation Ag of at least 23% and an elongation at break A _80mm of not less than 35%. In particular, given the specified thickness of the strip in conjunction with the alloy composition and the resulting mechanical properties in the annealed condition, the conditions are given that the aluminum alloy strip or sheet can be used for components in the motor vehicle, which in addition to very good forming properties and a very good Have resistance to intergranular corrosion or filiform corrosion. This is especially true for painted or coated components.

In this respect, the use of the aluminum alloy strip according to the invention for the production of semi-finished products or components of a motor vehicle, in particular structural parts of a motor vehicle, solves the above-mentioned Task. In particular, structural parts can be produced with very large degrees of deformation and assume very complex shapes without requiring particularly complicated forming operations. In particular, these are also particularly resistant to corrosion in lacquered form, in particular against intergranular corrosion and filiform corrosion.

According to a further teaching of the present invention, the object indicated is achieved by a structural part of a motor vehicle, in particular a door inner part of a motor vehicle comprising at least one formed sheet of an aluminum alloy strip according to the invention. As already stated above, the investigations have shown that the abovementioned aluminum alloy not only provides the required forming properties in the as-annealed state, but at the same time also ensures the necessary corrosion resistance and strength of the structural parts.

In order to achieve the optimum degree of deformation, the structural part according to the invention is produced from a strip which has been produced by the method according to the invention. It has been shown that with the method according to the invention, the forming properties as well as the strength properties of the structural part can be achieved in a process-reliable manner, so that an economic production of the structural parts which meet the conditions mentioned, is possible.

Fig. 1

ein Ablaufdiagramm eines ersten Ausführungsbeispiels des erfindungsgemäßen Verfahrens zur Herstellung eines Aluminiumlegierungsbandes,

Fig. 2

ein Ablaufdiagramm für ein weiteres Ausführungsbeispiel des erfindungsgemäßen Verfahrens und

Fig. 3

ein schematisch dargestelltes Ausführungsbeispiel eines Strukturteils eines Kraftfahrzeugs.

In addition, the invention will be explained in more detail with reference to embodiments in conjunction with the drawings. The drawing shows in

Fig. 1

a flow chart of a first embodiment of the inventive method for producing an aluminum alloy strip,

Fig. 2

a flowchart for a further embodiment of the inventive method and

Fig. 3

a schematically illustrated embodiment of a structural part of a motor vehicle.

A first embodiment in a schematic flow diagram now shows Fig. 1 , In a first step 2, the rolling ingot is cast, for example in the DC continuous casting process or in the strip casting process. In process step 4, the bar is then heated to a temperature of 500 ° C to 600 ° C and held for at least 0.5 h, preferably at least 2 h at this temperature for homogenization. The so homogenized ingot is then hot rolled at a temperature of 280 ° C to 500 ° C, preferably 300 ° C to 400 ° C to a final thickness of 3 to 12 mm. Subsequently, in step 8, a cold rolling to final thickness, followed by a recrystallizing final soft annealing according to step 10 followed. During cold rolling to final thickness in one or more passes, the degree of rolling must be at least 50%, preferably at least 70%, in order to produce a sufficiently fine-grained microstructure in the final soft annealing. The final soft annealing, at which the strip recrystallizes again, takes place in the chamber furnace at 300 ° C. to 400 ° C., preferably at 330 ° C. to 370 ° C. in step 10. Despite the alloy components according to the invention of Mg, Si, Fe and Mn, the use is a continuous furnace for the production of the aluminum alloy strip according to the invention is not possible because other structures would be provided due to the different heating and cooling rates.

Alternatively to the production of the aluminum alloy strip without intermediate annealing, an intermediate annealing in a chamber furnace at 300 ° C to 400 ° C, preferably at 330 ° C to 370 ° C, according to step 14, wherein both before the intermediate annealing and after the intermediate annealing a rolling degree of at least 50%, preferably at least 70%, should be ensured in order to favor the fine graininess of the microstructure after the recrystallizing final soft annealing influence. Optionally, after casting the rolling ingot in step 2, milling may also be performed according to step 12 of the top and bottom of the rolling billet to minimize the impact of contaminants at the edges of the billets in the ingot fabrication on the finished product. In particular, this has a positive influence on the corrosion resistance of the components.

Fig. 2 now shows another flowchart which shows the step 16 of the homogenization as an alternative to step 4. The homogenization has an influence on the fine grain of the desired end structure of the strip or finished component. In order to further improve the fine grain of the structure, the homogenization is carried out in several stages. So instead of step 4 in Fig. 1 in Fig. 2 a Homogenisierungsschritt 16 performed. The homogenization step 16 initially has a first homogenization phase, step 18, in which the milled or unmilled roll ingot is heated to a temperature of 550 ° C. to 600 ° C. for at least 0.5 h, preferably at least 2 h. In a next step 20, the so heated ingot is cooled to a temperature of 450 ° C to 550 ° C and held at this temperature for at least 0.5 h, preferably at least 2 h, which in Fig. 2 is shown in step 22.

Alternatively, after the first homogenization step 18, the ingot may also be cooled to room temperature in a step 24 and heated in a subsequent step 26 to the temperature for the second homogenization. This is necessary, for example, if the rolling ingot has to be stored between the homogenization step. Optionally, this phase can be used at room temperature to mill the ingot at the top and bottom, step 28. After the second homogenization step 22, the hot rolling is carried out as in Fig. 1 represented with the parameters specified there. It has been shown that the multi-stage homogenization, in particular the two-stage homogenization leads to a finer structure in the final product.

The effect according to the invention of providing a medium-strength and very highly deformable aluminum alloy or an aluminum alloy strip was demonstrated on the basis of 10 exemplary embodiments.

Initially, 10 different billets consisting of different alloys were cast in DC continuous casting. The tops and bottoms of the ingots were milled after casting according to step 12. This was followed by a two-stage homogenization, in which first the rolling ingots were kept at 600 ° C. for 3.5 hours and then at 500 ° C. for 2 hours. Immediately after homogenization, the ingots were directly hot rolled at about 500 ° C to an aluminum alloy hot strip having a thickness of 8 mm. The 8 mm thick hot strip was finally cold rolled without intermediate annealing to a final thickness of 1.5 mm, ie with a degree of rolling of more than 70%. The recrystallizing final annealing of the cold-rolled aluminum alloy strips having a thickness of 1.5 mm was carried out for 1 h at 350 ° C in a box furnace. The various aluminum alloys tested are shown in Table 1. Table 1 (V): comparison (E); invention Aluminum alloy components in% by weight, variant Si Fe Cu M _n mg Cr 1 V 0.66 0.66 0.26 0.7 0.62 0.14 2 V 0.53 0.46 0.19 0.52 0.44 0.13 3 V 0.67 0.66 0.27 0.69 0.61 0.0005 4 V 0.73 0.68 0.0016 1.0 0.67 0.0002 5 e 0.72 0.69 0.0016 0.74 0.66 0.0006 6 e 0.67 0.65 0.07 0.69 0.61 0.0005 7 e 0.72 1.0 0.0017 0.72 0.66 0.0004 8th e 0.8 0.68 0.0015 0.72 0.63 0.0003 9 V 0.4 0.41 0,004 0.47 0.41 0.001 10 V 0.5 12:27 0.0013 0.66 0.42 0.0008

Variants 1 to 4 and 9 and 10 are comparative examples which do not correspond to the aluminum alloy according to the invention. By contrast, embodiments 5 to 8 correspond to the aluminum alloy compositions claimed according to the invention.

On the cold-rolled aluminum alloy strips thus produced, both the yield strength R _p0 , ₂ , the tensile strength R _m , the uniform elongation Ag, the elongation at break A were _{measured 80 mm} and the draft SZ 32 obtained in the ironing was measured in millimeters. The values for the yield strength R _p0.2 and the tensile strength R _m were measured in the tensile test perpendicular to the rolling direction of the sheet according to DIN EN ISO 6892-1: 2009. According to the same standard, the uniform elongation Ag and the elongation at break A were _{measured 80 mm} in each case perpendicular to the rolling direction of the sheet with a flat tensile specimen according to DIN EN ISO 6892-1: 2009, Annex B, Form 2. The forming behavior can also be used in a Stretch drawing test SZ 32 can be measured by a cupping test according to Erikson (DIN EN ISO 20482), in which a test piece is pressed against the sheet, so that a cold deformation occurs. During cold working, the force as well as the punch travel of the test specimen are measured until there is a load drop, which causes the formation of a crack. In the present exemplary embodiments, the cupping test was carried out with a punch head diameter of 32 mm and die diameter of 35.4 mm coordinated with the sheet metal blanket with the aid of a Teflon drawing film to reduce friction. The overview of the results is shown in Table 2. Table 2 variant (V): Comparison (E) invention R _p0.2 N / mm ² R _m N / mm ² A _g % A _80mm % SZ 32 mm 1 V 65 145 19.6 26.5 15.8 2 V 52 131 21.9 30.3 16.2 3 V 60 135 22.7 30.3 16.4 4 V 51 122 22.3 33.5 15.6 5 e 48 112 23.1 35.3 16.0 6 e 47 118 23.5 35.0 16.5 7 e 50 120 23.4 36.2 16.1 8th e 47 112 23.8 36.6 15.0 9 V 41 98 23.6 37.9 16.5 10 V 41 102 24.2 38.0 16.3

By comparing, for example, variant 2 with variants 5 to 8 according to the invention, the exemplary embodiments show that excessive reduction of the contents Si, Fe, Mn, Mg with an increase in the contents of Cu and Cr results in the yield limit values above 45 MPa remains, but the elongation at break drops significantly to about 30%. This effect can also be demonstrated if the Mn content alone is 1.0%, for example, which already pushes the breaking elongation A _{80 mm} below 35%, variant 4. The variants 9 and 10 show the effect of reduced contents of Si, Fe, Mn and Mg. Comparative _Examples 9 and 10 show a very good elongation at break A _80mm with more than 35%, however, the yield strength with 41 MPa is below that of the inventive embodiments 5 to 8.

The embodiments according to the invention showed a very good forming behavior, especially in the case of strong deformations, which can be deduced from the very good stretch drawing results SZ 32 and the high elongation _values both in the uniform expansion Ag and in the elongation at break A _{80 mm} . From this it can be seen that overall the interaction of the alloy contents Si, Fe, Mn, Mg is important, whereby the components Cr and Cu have to be kept particularly low, preferably the Cu content is ≤0.05 wt.%, Preferably ≤ 0.01 wt% and the chromium content ≤ 0.01 wt%, preferably ≤ 0.001 wt%. Coupled with the very good corrosion resistance of the embodiments can be provided for vehicles semi-finished products and components, in particular structural components such as door inner parts, which not only ensures the specifications of the field of application in terms of mechanical and chemical properties, but can be economically produced by a few forming operations.

The aluminum alloy strips according to the invention are therefore ideally suited, for example, structural parts of a motor vehicle, such as in Fig. 3 to provide shown door inner parts 30 and to be used for their preparation. The door inner part is made of a sheet metal of an aluminum alloy according to the invention with a thickness of 1.5 mm, which provides only by forming operations, but without joining operations a window frame.

Claims (13)

1. Method for the manufacture of a strip made of an aluminium alloy, which comprises the following alloy components in % by weight: $$0.6\%\le \mathrm{Si}\le 0.9\%\mathrm{,}$$

   

   $$0.6\%\le \mathrm{Fe}\le 1.0\%,$$

   

   $$\mathrm{Cu}\le 0.1\%\mathrm{,}$$

   

   $$0.6\%\le \mathrm{Mn}\le 0.9\%\mathrm{,}$$

   

   $$0.5\%\le \mathrm{Mg}\le 0.8\%\mathrm{,}$$

   

   $$\mathrm{Cr}\le 0.05\%\mathrm{,}$$

   

   the remainder Al and impurities, individually up to a maximum of 0.05% by weight, in total up to a maximum of 0.15% by weight
   with following method steps:

   - casting (2) of a rolling ingot,

   - homogenisation (4, 16) at a temperature of between 500°C and 600°C for at least 0.5 h,

   - hot rolling (6) of the rolling ingot at temperatures of 280°C to 500°C to a thickness of 3 mm to 12 mm,

   - cold rolling (8) with or without intermediate annealing with a degree of reduction of at least 50%, preferably at least 70% to a final thickness of 0.2 mm to 5 mm and

   - final soft annealing (10) at 300°C to 400°C for at least 0.5h in a chamber furnace.
2. Method according to claim 1, characterised in that the homogenisation (16) takes place in at least two stages, wherein the rolling ingot is first heated to 550°C to 600°C for at least 0.5 h and then the rolling ingot is cooled to 450°C to 550°C, held at this temperature for at least 0.5 h and then hot-rolled.
3. Method according to claim 1 or 2, characterised in that the rolling ingot is milled (12) on the upper side and underside after casting (2) or after homogenisation (4, 16).
4. Method according to one of the claims 1 to 3, characterised in that an intermediate annealing (14) takes place, after a first cold rolling (8), at a temperature of 300°C to 400°C for at least 0.5 h, wherein the degree of reduction amounts to at least 50%, preferably at least 70%, before and after the intermediate annealing.
5. Method according to claim 4, characterised in that the intermediate annealing (14) is carried out at a temperature of 330°C to 370°C.
6. Aluminium alloy strip or sheet manufactured of an aluminium alloy, which comprises the following alloy components in % by weight: $$0.6\%\le \mathrm{Si}\le 0.9\%\mathrm{,}$$

   

   $$0.6\%\le \mathrm{Fe}\le 1.0\%\mathrm{,}$$

   

   $$\mathrm{Cu}\le 0.1\%\mathrm{,}$$

   

   $$0.6\%\le \mathrm{Mn}\le 0.9\%\mathrm{,}$$

   

   $$0.5\%\le \mathrm{Mg}\le 0.8\%\mathrm{,}$$

   

   $$\mathrm{Cr}\le 0.05\%\mathrm{,}$$

   

   the remainder Al and impurities, individually up to a maximum of 0.05% by weight, in total up to a maximum of 0.15% by weight,
   characterised in that
   the strip has a thickness of 0.2 mm to 5 mm and in the soft-annealed state has a yield strength R_p0.2 of at least 45 MPa and an elongation at break A_80mm of at least 35%.
7. Aluminium alloy strip according to claim 6, characterised in that the alloy components Si, Fe, Mn and Mg have the following contents in % by weight: $$0.7\%\le \mathrm{Si}\le 0.9\%\mathrm{,}$$

   

   $$0.7\%\le \mathrm{Fe}\le 1.0\%\mathrm{,}$$

   

   $$0.7\%\le \mathrm{Mn}\le 0.9\%$$

   

   and $$0.6\%\le \mathrm{Mg}\le 0.8\%\mathrm{.}$$

   
8. Aluminium alloy strip according to claim 7, characterised in that the alloy components Si, Fe, Mn and Mg have the following contents in % by weight: $$0.7\%\le \mathrm{Si}\le 0.8\%\mathrm{,}$$

   

   $$0.7\%\le \mathrm{Fe}\le 0.8\%\mathrm{,}$$

   

   $$0.7\%\le \mathrm{Mn}\le 0.8\%$$

   

   and $$0.6\%\le \mathrm{Mg}\le 0.7\%\mathrm{.}$$

   
9. Aluminium alloy strip according to one of the claims 6 to 8, characterised in that the aluminium alloy has the following Cr content in % by weight: $$\mathrm{Cr}\le 0.01\%\mathrm{.}$$

   
10. Aluminium alloy strip according to one of the claims 6 to 9, characterised in that the aluminium alloy has the following Cu content in % by weight: $$\mathrm{Cu}\le 0.05\%\mathrm{.}$$

    
11. Use of an aluminium alloy strip according to claim 6 for the manufacture of semi-finished products or components for motor vehicles, in particular of a structural component of a motor vehicle.
12. Structural component, in particular interior door part (30) of a motor vehicle comprising at least one formed sheet manufactured from an aluminium alloy strip according to one of the claims 6 to 10.
13. Structural component according to claim 12, characterised in that the sheet is cut from a strip produced using a method according to one of the claims 1 to 5.

Images