EP2888382B1 - Aluminium alloy strip which is resistant to intercrystalline corrosion and method for producing same - Google Patents

Description

The invention relates to an aluminum alloy strip consisting of an aluminum alloy of the type AA 5xxx, which in addition to Al and unavoidable impurities has a Mg content of at least 4 wt .-%. In addition, the invention relates to a method for producing the aluminum alloy strip according to the invention and a component made from an aluminum alloy strip according to the invention.

Aluminum magnesium (AlMg) alloys of type AA 5xxx are used in the form of sheets or plates or strips for the construction of welded or joined structures in shipbuilding, automotive and aircraft construction. They are characterized in particular by a high strength, which increases with increasing magnesium content.

For example, from the paper Development of twin-belt cast AA5XXX series Zhao et al. an aluminum strip consisting of an AA5182 alloy with a Mg content of 4.65 wt .-%, which is suitable for use in the automotive industry known.

Aluminum alloy ribbons of the type AA5182 with a Mg content of at least 4 wt .-% are also from the article Semi-Solid Processing of Alloys and Composites by Kang et al. and from the paper Comparison of recrystallization textures in cold-rolled DC and CC AA 5182 aluminum alloys by Liu et al., as well as from the US 2003/0150587 A1 known. The article Hot-Tear Susceptibility of Aluminum Wrought Alloys and the Effect of Grain Refining by Lin et al. concerns round bars made of his AA5182 alloy.

The DE 102 31 437 A1 relates to corrosion-resistant aluminum alloy sheets, whereby the addition of Zn in a content of more than 0.4% by weight affords sufficient resistance to intergranular corrosion.

In addition, the document discloses GB 2 027 621 A a method for producing an aluminum strip.

AlMg alloys of the type AA 5xxx with Mg contents of more than 3%, in particular more than 4%, are increasingly prone to intercrystalline corrosion when exposed to elevated temperatures. At temperatures of 70 - 200 ° C, β-Al ₅ Mg ₃ phases separate out along the grain boundaries, which are called β-particles and can be selectively dissolved in the presence of a corrosive medium. This has the consequence that in particular the very good strength properties and a very good formability aluminum alloy of the type AA 5182 (Al 4.5% Mg 0.4% Mn) is not used in heat-stressed areas, provided that with the presence of a corrosive medium, For example, water in the form of moisture, must be expected. This relates in particular to the components of a motor vehicle, which are usually subjected to a cathodic dip coating (KTL) and then dried in a baking process, since sensitization with respect to intercrystalline corrosion can already be caused by this baking process in conventional aluminum alloy tapes. In addition, for use in the automotive sector, the forming during the production of a component and the subsequent operating load of the component must be taken into account.

The susceptibility to intergranular corrosion is usually tested in a standard test according to ASTM G67, in which the samples are exposed to nitric acid and the mass loss due to the release of β-particles is measured. According to ASTM G67, the mass loss for materials which are not resistant to intergranular corrosion is more than 15 mg / cm ² .

Appropriate materials and aluminum strips are therefore not suitable to be used in heat-stressed areas.

Proceeding from this, the object of the present invention is to propose an aluminum alloy strip of an AlMg alloy which, despite high strengths and Mg content of more than 4% by weight, in particular also after deformation and subsequent application of temperature, is resistant to intergranular corrosion , In addition, a manufacturing method is to be specified, with which against intergranular corrosion resistant aluminum strips can be produced. Finally, to be proposed against intergranular corrosion resistant components of a motor vehicle, such as body parts or body parts, such as doors, hoods and tailgates or other structural parts but also component parts of an aluminum alloy type AA 5xxx.

und wobei die Aluminiumlegierung des Aluminiumlegierungsbandes folgende Zusammensetzung in Gew.-% aufweist:

• Si ≤ 0,2 %,
• Fe ≤ 0,35 %,
• 0,04 % ≤ Cu ≤ 0,08 %,
• 0,2 % ≤ Mn ≤ 0,5 %,
• 4,35 % ≤ Mg ≤ 4,8 %,
• Cr ≤ 0,1 %,
• Zn ≤ 0,25 %,
• Ti ≤ 0,1 %,

According to a first teaching of the present invention, the above-described object is achieved by an aluminum alloy strip having a recrystallized structure, wherein the particle size (KG) of the microstructure in μm fulfills the following dependence on the Mg content (c_Mg) in% by weight: $$\mathrm{KG}\ge 22+2*\mathrm{c\_Mg}\mathrm{,}$$

and wherein the aluminum alloy of the aluminum alloy strip has the following composition in% by weight:

• Si ≤ 0.2%,
• Fe ≤ 0.35%,
• 0.04% ≤ Cu ≤ 0.08%,
• 0.2% ≤ Mn ≤ 0.5%,
• 4.35% ≤ Mg ≤ 4.8%,
• Cr ≤ 0.1%,
• Zn≤0.25%,
• Ti ≤ 0.1%,

Residual Al and unavoidable impurities individually a maximum of 0.05 wt .-%, in total not more than 0.15 wt .-%.

With a Cu content of 0.04 wt .-% to 0.08 wt .-% is achieved that copper participates in an increase in strength, but still does not reduce the corrosion resistance too strong. In addition, by limiting the Mg range to 4.35 wt.% To 4.8 wt.%, Very good strength can be obtained with moderate grain size. Consequently, a resistance to intergranular corrosion can be achieved particularly reliably, since the necessary grain sizes of the microstructure can be reliably achieved in the process.

An aluminum alloy ribbon having a recrystallized structure may be provided by hot strips or soft annealed cold strips. Extensive research has found that there is a correlation between grain size, magnesium content, and intergranular corrosion resistance. Since the grain size of a material is always in the form of a distribution, all information given the grain size on the average grain size. The mean grain size can be determined according to ASTM E1382. If the grain size is sufficiently large, that is, if the grain size is greater than or equal to the lower limit of the grain size of the present invention, resistance to intergranular corrosion can be achieved, so that mass loss is less than 15 mg in the ASTM G67 test / cm ² drops. Corresponding aluminum strips can therefore be termed resistant to intergranular corrosion. This was demonstrated for the above-mentioned aluminum strips in the undeformed state after a simulated KTL cycle and after a simulated KTL cycle including a subsequent operating load of up to 500 hours at 80 ° C. Also, for the above-mentioned tapes, the resistance to intergranular corrosion if the material is stretched at 15% before the KTL cycle and the operating load in order to simulate the transformation to a component. As a result, the aluminum alloy ribbon of the present invention, because of its relatively high Mg content, provides high strengths and yield strengths while being resistant to intergranular corrosion. It is therefore very suitable for use in heat-stressed areas in the automotive industry.

• mit KG in µm und c_Mg in Gew.-%,
• kann sichergestellt werden, dass die Streckgrenze R_p0,2 des Aluminiumlegierungsbandes größer als 110 MPa ist. Die Zugfestigkeit des Bandes liegt dabei üblicherweise oberhalb von 255 MPa.

According to a next embodiment of the aluminum alloy strip according to the invention, the grain size additionally satisfies the following condition: $$\mathrm{KG}<{\left(253/\left(265-50*\mathrm{<figure-callout\; id="2"\; label="c\_Mg"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c\_Mg</figure-callout>}\right)\right)}^2$$

• with KG in μm and c_Mg in% by weight,
• can be ensured that the yield strength R _{p0,2 of} the aluminum alloy _{strip is} greater than 110 MPa. The tensile strength of the band is usually above 255 MPa.

• Si ≤ 0,2 %,
• Fe ≤ 0,35 %,
• 0,04 % ≤ Cu ≤ 0,08 %,
• 0,2 % ≤ Mn ≤ 0,5 %,
• 4,45 % ≤ Mg ≤ 4,8 %,
• Cr ≤ 0,1 %,
• Zn ≤ 0,25 %,
• Ti ≤ 0,1 %,

A further advantageous embodiment of the aluminum alloy strip is achieved in that the aluminum alloy of the aluminum alloy strip has the following composition in% by weight:

• Si ≤ 0.2%,
• Fe ≤ 0.35%,
• 0.04% ≤ Cu ≤ 0.08%,
• 0.2% ≤ Mn ≤ 0.5%,
• 4.45% ≤ Mg ≤ 4.8%,
• Cr ≤ 0.1%,
• Zn≤0.25%,
• Ti ≤ 0.1%,

Residual Al and unavoidable impurities individually a maximum of 0.05 wt .-%, in total not more than 0.15 wt .-%. By limiting the Mg range to 4.45 wt .-% to 4.8 wt .-% is also a very good strength with a moderate grain size can be achieved.

According to a next embodiment of the aluminum alloy strip according to the invention, the grain size is a maximum of 50 microns, since in the production of aluminum strips with grain sizes of more than 50 microns from an aluminum alloy of type AA 5xxx with a Mg content of at least 4 wt .-%, the process reliability drops , On the other hand, a grain size of maximum 50 μm can be achieved with process stability. The process stability for the production of microstructures with controlled grain size increases with decreasing grain size. Thus, the production of an aluminum alloy strip having a grain size of not more than 45 μm, preferably not more than 40 μm, is associated with increasing process stability.

According to a next embodiment of the aluminum alloy strip according to the invention, this has a thickness of 0.5 mm - 5 mm and is thus outstandingly suitable for most applications, for example in the automotive industry.

In addition, the aluminum alloy strip according to the invention can advantageously be configured by being cold rolled and finally soft annealed. A recrystallizing soft annealing usually takes place at temperatures of 300 ° C - 500 ° C and makes it possible to eliminate the introduced in the rolling process solidifications and to ensure a good formability of the aluminum alloy strip. In addition, cold end, soft annealed and therefore recrystallized tapes can provide lower final thicknesses than recrystallized hot tapes.

Finally, according to another embodiment, the aluminum alloy _{strip has} a yield strength R _p0.2 of more than 120 MPa and a tensile strength R _m of more than 260 MPa. Thus, the aluminum alloy strip according to the invention which is resistant to intercrystalline corrosion also exceeds the strength properties of an aluminum alloy of the AA5182 type required in accordance with DIN485-2. At the same time, the elongation values with an even expansion Ag of at least 19% and an elongation at break A ₈₀ mm of at least 22% far exceed the values required in DIN485-2.

• Gießen eines Walzbarrens bestehend aus einer erfindungsgemäßen Aluminiumlegierungszusammensetzung,
• Homogenisieren des Walzbarrens bei 480 °C bis 550 °C für mindestens 0,5 h,
• Warmwalzen des Walzbarrens bei einer Temperatur von 280 °C bis 500 °C,
• Kaltwalzen des Aluminiumlegierungsbandes an Enddicke mit einem Abwalzgrad von weniger als 40%, bevorzugt maximal 30 %, besonders bevorzugt maximal 25%,
• Weichglühen des fertig gewalzten Aluminiumlegierungsbandes bei 300 °C bis 500 °C.

According to a second teaching of the present invention, the above object is achieved by a method for producing an aluminum alloy strip comprising the following method steps:

• Casting a rolling billet consisting of an aluminum alloy composition according to the invention,
• Homogenizing the rolling ingot at 480 ° C to 550 ° C for at least 0.5 h,
• Hot rolling of the rolling ingot at a temperature of 280 ° C to 500 ° C,
• Cold rolling of the aluminum alloy strip to final thickness with a rolling degree of less than 40%, preferably not more than 30%, particularly preferably not more than 25%,
• Annealing the finished rolled aluminum alloy strip at 300 ° C to 500 ° C.

The enumerated process steps lead in sum to the fact that due to the small Abwalzgrads in the cold rolling of the aluminum alloy strip to final thickness, a grain size can be provided after annealing, which meets the above-mentioned dependence on the Mg content. About the Abwalzgrad to final thickness, the solidification of the strip is set before annealing, which determines the resulting grain size. With decreasing Abwalzgrad of less than 40%, over a maximum of 30% and a maximum of 25%, so different grain size can be set, which can be tailored to the alloy composition. In this respect, an aluminum alloy strip which is resistant to intergranular corrosion can be produced.

• Kaltwalzen des warmgewalzten Aluminiumlegierungsbandes mit einem Abwalzgrad von mindestens 30 %, vorzugsweise mindestens 50 %,
• Zwischenglühen des Aluminiumlegierungsbandes bei 300 °C bis 500 °C,
• anschließendes Kaltwalzen an Enddicke mit einem Abwalzgrad von weniger als 40%, bevorzugt maximal 30 %, besonders bevorzugt maximal 25%,
• Weichglühen des fertig gewalzten Aluminiumlegierungsbandes bei 300 °C bis 500 °C.

According to a further embodiment of the method according to the invention, the following method steps are alternatively carried out after hot rolling:

• Cold rolling of the hot-rolled aluminum alloy strip with a rolling degree of at least 30%, preferably at least 50%,
• Intermediate annealing of the aluminum alloy strip at 300 ° C to 500 ° C,
• subsequent cold rolling to final thickness with a degree of reduction of less than 40%, preferably not more than 30%, particularly preferably not more than 25%,
• Annealing the finished rolled aluminum alloy strip at 300 ° C to 500 ° C.

Common to both methods mentioned above is that the degree of rolling before soft annealing, ie the degree of rolling at the final thickness during cold rolling, is limited to less than 40%, preferably not more than 30%, particularly preferably not more than 25%. In the second embodiment of the method according to the invention, an additional cold rolling step after an intermediate annealing at 300 ° C - 500 ° C instead. In the intermediate annealing, the aluminum alloy ribbon strongly solidified by the cold rolling is recrystallized and again converted into a workable state. The subsequent cold-rolling step with a degree of reduction of less than 40%, preferably not more than 30%, particularly preferably not more than 25%, results in that, in conjunction with the Mg contents of the aluminum alloy used, the particle size can be adjusted in accordance with the claimed ratio. As a result, a strip is then produced in the annealed state, which is both resistant to intergranular corrosion and has the necessary forming or strength properties.

According to a next embodiment of the method according to the invention, the soft annealing and / or the intermediate annealing take place in a batch furnace, in particular a chamber furnace or a continuous furnace. Both furnaces lead to the provision of a sufficiently coarse grain structure, which ensures the resistance to intergranular corrosion. Batch ovens are usually not as expensive to operate and purchase as continuous ovens.

According to a third teaching of the present invention, the above-described object is achieved by a component for a motor vehicle, which at least partially consists of an aluminum alloy strip according to the invention. The component is usually subjected to a coating, preferably a cathodic dip coating. Nevertheless, there are also possible uses of unpainted components made from the aluminum alloy strip according to the invention.

As already stated above, the aluminum alloy strip has excellent properties in terms of strength, forming properties and resistance to intergranular corrosion, so that in particular the heat load in a painting, a baking process typically 20 minutes at about 185 ° C takes little effect on the resistance of the component against intergranular corrosion. Also, the transformation to a component, which was simulated by means of a stretching by 15% transverse to the original rolling direction, has only a small influence on the resistance to intergranular corrosion. Even after 15% stretching, the mass loss values according to ASTM G67 are less than 15 mg / cm ² . Furthermore, the operation in temperature-stressed areas, which was simulated by a heat load of 200 or 500 hours at 80 ° C, only a small effect on the resistance to intergranular corrosion. The mass loss values according to ASTM G67 are less than 15 mg / cm ² even after a corresponding temperature load.

Particularly advantageous is a component, if this is designed as a body or a body attachment of a motor vehicle. Typical body parts are the fender or parts of the floor assembly, the roof, etc. As body parts usually doors and tailgates etc. are referred to, which are not firmly connected to the motor vehicle. Preferably, non-visible body parts or body parts are made from the aluminum alloy strip according to the invention. These are, for example, door inner parts or inner parts of tailgates but also floor panels, etc. A typical heat load for such components of a motor vehicle, for example, of door inner parts is given, for example, by the solar radiation during the operation of a motor vehicle. In addition, bodywork or bodywork components of a motor vehicle are generally also exposed to moisture, for example in the form of sprayed water or condensation, so that resistance to intergranular corrosion must be required. The body or body parts according to the invention, made of an aluminum alloy strip according to the present invention, meet these conditions and also ensure a weight advantage over the steel structures used to date.

Fig. 1

ein schematisches Ablaufschema für ein Ausführungsbeispiele eines Herstellverfahrens,

Fig. 2

in einem Diagramm die Korngröße in Abhängigkeit vom Magnesiumgehalt der Ausführungsbeispiele und

Fig. 3

ein Bauteil für ein Kraftfahrzeug gemäß einem weiteren Ausführungsbeispiel.

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

Fig. 1

a schematic flowchart for an embodiment of a manufacturing process,

Fig. 2

in a graph, the grain size as a function of the magnesium content of the embodiments and

Fig. 3

a component for a motor vehicle according to a further embodiment.

Based on extensive tests, it was investigated whether there is an association between the grain size of an aluminum alloy ribbon of AA 5xxx type aluminum alloy and the Mg content in terms of resistance to intergranular corrosion. Various aluminum alloys were used and different process parameters were used. Table 1 shows the various alloy compositions used to investigate the relationship between grain size, resistance to intergranular corrosion and yield strength. In addition to the contents of the alloying elements Si, Fe, Cu, Mn, Mg, Cr, Zn and Ti in% by weight, the aluminum alloys listed in Table 1 contain aluminum and impurities individually as a maximum of 0.05% by weight and in total as a maximum 0.15% by weight.

Since the final soft annealing and the degree of final rolling in particular have an influence on the grain size, these have been varied or measured in the respective experiments. The grain size varied for example from 16 microns to 61 microns, the final rolling degree of 17% to 57%. The final soft annealing was carried out either in the chamber furnace (KO) or in the belt continuous furnace (BDLO).

Fig. 1 shows the sequence of embodiments for the production of aluminum strips. The flowchart of Fig.1 shows schematically the various process steps of the manufacturing process of the aluminum alloy strip according to the invention.

In step 1, an ingot of aluminum AA 5xxx alloy having a Mg content of at least 4% by weight is cast, for example, in DC continuous casting. Subsequently, the rolling ingot in process step 2 is subjected to homogenization, which can be carried out in one or more stages. In a homogenization temperatures of the rolling ingot are reached from 480 to 550 ° C for at least 0.5 h. In process step 3, the rolling ingot is then hot rolled, with typical temperatures of 280 ° C to 500 ° C can be achieved. The final thicknesses of the hot strip are for example 2 to 12 mm. The hot strip thickness can be selected so that after hot rolling only a single cold rolling step 4 takes place, in which the hot strip is reduced with a rolling degree of less than 40%, preferably not more than 30%, more preferably not more than 25% in thickness.

Subsequently, the aluminum alloy strip cold rolled to final thickness is subjected to soft annealing. The soft annealing was carried out in a continuous furnace or in a chamber furnace to test the dependence of the corrosion properties of the chamber or continuous furnace. In the embodiments shown in Table 1, the second route was used with an intermediate annealing. For this purpose, the hot strip after hot rolling according to process step 3 is fed to a cold rolling 4a, which has a rolling degree of more than 30% or more than 50%, so that the aluminum alloy strip is preferably recrystallized throughout in a subsequent intermediate annealing. The intermediate annealing was carried out in the embodiments either in a continuous furnace at 400 ° C to 450 ° C or in the chamber furnace at 330 ° C to 380 ° C.

The intermediate annealing is in Fig. 1 represented by the method step 4b. In method step 4c according to Fig. 1 Finally, the temporarily annealed aluminum alloy strip is fed to cold rolling to its final thickness, the degree of reduction in step 4c being less than 40%, preferably not more than 30%, particularly preferably not more than 25%. Subsequently, the Aluminum alloy ribbon again in the soft state by a soft annealing, wherein the soft annealing is carried out either in a continuous furnace at 400 ° C to 450 ° C or in the chamber furnace at 330 ° C to 380 ° C. In the various tests, different degrees of rolling were set after intermediate annealing in addition to different aluminum alloys. The values for the degree of rolling after the intermediate annealing are also shown in Table 1. In addition, the grain size of the soft-annealed aluminum alloy strip was measured in each case.

Mechanical properties, in particular the yield strength R _p0.2 , tensile strength R _m , the uniform elongation Ag and the elongation A _{80 mm were} determined on the correspondingly produced aluminum alloy _strips . In addition, the corrosion resistance against intergranular corrosion was measured according to ASTM G67, without additional heat treatment in the initial state (output 0h). In addition to the mechanical properties of the aluminum alloy strips measured according to EN 10002-1 or ISO 6892, the calculated grain sizes according to the intergranular corrosion resistance formulas (1) set out below and the formula (2) to obtain the necessary mechanical properties, in particular sufficiently large yield strength, shown in Table 2 as column KG (IK) and as column KG (Rp). The grain sizes were determined according to ASTM E1382 and are given in μm.

In order to simulate use in motor vehicles, the aluminum alloy strips were subjected to different heat treatments before the corrosion test. A first heat treatment consisted of storing the aluminum strips for 20 minutes at 185 ° C to image the KTL cycle. In a further series of measurements, the aluminum alloy strips were additionally stored for 200 hours or 500 hours at 80 ° C. and then subjected to the corrosion test. In addition, since transformations of aluminum alloy tapes or sheets may affect the corrosion resistance, the aluminum alloy tapes were further stretched by about 15%, subjected to heat treatment at elevated temperature, and then subjected to intergranular corrosion test according to ASTM G67, in which the mass loss was measured.

It was found that there is a close correlation between the grain size, the Mg content and the resistance to intergranular corrosion. The embodiments 11 to 19 are all classified as resistant to intergranular corrosion. This also applies to their use in motor vehicles with heat load and the presence of moisture or a corrosive medium. In addition, the exemplary embodiments 12, 14, 16 and 17 showed the mechanical characteristics of an aluminum alloy strip of type AA 5182 required by DIN EN 485-2.

mit c_Mg als Mg-Gehalt in Gew.-%.In Fig. 2 the measured grain sizes are shown in the diagram as a function of the Mg content in% by weight. In addition to the measuring points, the diagram also contains two curves A and B. The straight line A indicates the grain sizes above which, at a specific Mg content, the aluminum alloy strip can be termed resistant to intergranular corrosion. The corresponding particle size (KG) results from the following equation: $$\mathrm{KG}=22+2*\mathrm{c\_Mg}.$$

with c_Mg as Mg content in% by weight.

The curve B, however, shows the limit from which the aluminum alloy strips have too low a yield strength of less than 110 MPa, so that they are not to be regarded as alloy AA 5182 according to DIN EN485-2. The curve B is determined by the following equation: $$\mathit{KG}={\left(\frac{253}{265-50*\mathit{<figure-callout\; id="2"\; label="c\_Mg"\; filenames="imgf0001.png"\; state="\{\{state\}\}">c\_Mg</figure-callout>}}\right)}^2$$

All embodiments to the right of the curve B thus meet the requirement of a yield strength of more than 110 MPa.

Finally shows Fig. 3 a typical component of a motor vehicle, shown schematically in the form of an inner door part. Inner door parts 6 are usually made of a steel. However, the aluminum alloy ribbons produced show that even the provision of high strengths with resistance to intergranular corrosion can be achieved, provided that the grain size ratio with respect to the Mg content is adjusted according to the invention. The inventive component according to Fig. 3 has a significantly lower weight than a comparable steel component and is nevertheless resistant to intercrystalline corrosion.

Claims (12)

1. Aluminium alloy strip composed of an AA 5 xxx -type aluminium alloy, which apart from A1 and inevitable impurities has an Mg content of at least 4 wt.%, characterised in that the aluminium alloy strip has a recrystallized microstructure, wherein the grain size (GS) of the microstructure satisfies the following dependency on the Mg content (c_Mg) in wt.%: $$\mathrm{GS}>22+2*\mathrm{c\_Mg}\mathrm{.}$$

   

   and in that the aluminium alloy of the aluminium alloy strip has the following composition in wt.%:

   Si ≤ 0.2%,

   Fe ≤ 0.35%,

   0.04% ≤ Cu ≤ 0.08%,

   0.2% ≤ Mn ≤ 0.5%.

   4.35% ≤ Mg ≤ 4.8%,

   Cr ≤ 0.1%,

   Zn ≤ 0.25%,

   Ti ≤ 0.1%,

   the remainder being Al and inevitable impurities, amounting to a maximum of 0.05 wt.% individually and a maximum of 0.15 wt.% in total.
2. Aluminium alloy strip according to Claim 1, characterised in that the grain size (GS) of the microstructure of the aluminium alloy strip also satisfies the following dependency on the Mg content (c_Mg) in wt.%: $$\mathit{GS}<{\left(\frac{253}{265-50*\mathit{c\_Mg}}\right)}^2$$

   
3. Aluminium alloy strip according to any one of Claims 1 or 2, characterised in that the aluminium alloy of the aluminium alloy strip has 4.45% ≤ Mg ≤ 4.8%.
4. Aluminium alloy strip according to any one of Claims 1 to 3, characterised in that the grain size is a maximum of 50 µm, preferably a maximum of 40 µm.
5. Aluminium alloy strip according to any one of Claims 1 to 4, characterised in that the aluminium alloy strip has a thickness of 0.5 mm to 5 mm.
6. Aluminium alloy strip according to any one of Claims 1 to 5, characterised in that the aluminium alloy strip is cold rolled and soft annealed.
7. Aluminium alloy strip according to one of Claims 1 to 6, characterised in that the aluminium alloy strip has a yield point R_p0.2 of greater than 120 MPa and a tensile strength R_m of greater than 260 MPa.
8. Method for producing an aluminium alloy strip according to any one of Claims 1 to 7 comprising the following process steps:

   - casting a rolling ingot;

   - homogenisation of the rolling ingot at 480°C to 550°C for at least 0.5 hours;

   - hot rolling of the rolling ingot at a temperature of 280°C to 500°C

   - cold rolling of the aluminium alloy strip to the final thickness with a degree of rolling of less than 40%, preferably a maximum of 30%, particularly preferably a maximum of 25%;

   - soft-annealing of the finished-rolled aluminium alloy strip at 300°C to 500°C..
9. Method according to Claim 8, wherein after the hot rolling alternatively the following process steps are carried out:

   - cold rolling of the hot-rolled aluminium alloy strip with a degree of rolling of at least 30%, preferably at least 50%;

   - intermediate annealing of the aluminium alloy strip at between 300°C and 500°C;

   - subsequent cold rolling to the final thickness with a degree of rolling of less than 40%, preferably a maximum of 30%, particularly preferably a maximum of 25%;

   - soft annealing of the finish-rolled aluminium alloy strip at between 300°C and 500°C.
10. Method according to Claim 8 or 9, characterised in that the intermediate annealing and/or the soft annealing is/are carried out in a batch furnace or a continuous furnace.
11. Component for a motor vehicle at least partially composed of an aluminium alloy strip according to any one of Claims 1 to 7.
12. Component according to Claim 11, characterised in that the component is a body part or a body accessory of a motor vehicle.

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