EP2959028B1 - Aluminium alloy for the production of semi-finished products or components for motor vehicles, method for producing an aluminium alloy strip from this aluminium alloy and aluminium alloy strip and uses thereof - Google Patents

Description

The invention relates to an aluminum alloy for the production of semi-finished products or components for motor vehicles. Furthermore, the invention relates to a method for producing an aluminum alloy strip and a correspondingly produced aluminum alloy strip and uses thereof.

Semi-finished products and components for motor vehicles must meet different requirements depending on their place of use and purpose in the motor vehicle, in particular with regard to their mechanical properties and their corrosion properties.

In the case of door inner parts, the mechanical properties are determined, for example, predominantly by the rigidity, which depends in particular on the shape of these parts. In contrast, the strength has a minor influence, but the materials used must not be too soft either. On the other hand, good formability is very important since the components and semi-finished products generally undergo complex forming processes, for example, in the manufacture of interior door parts. This relates in particular to components which are produced in a one-piece sheet metal shell construction, such as, for example, a sheet-metal inner door with integrated window frame area. Such Due to the saving of joining operations, components have cost advantages over a mounted profile solution for the window frame.

It would be advantageous, in particular, if a corresponding semi-finished product or aluminum alloy component could be formed on a tool for steel components, since in this case aluminum or steel components can be manufactured on the same tool, thus reducing investment and operating costs for an additional tool or can be avoided.

For the reasons mentioned above, there is great interest in the automotive industry in high-formable, medium-strength aluminum alloys, which in particular have a better formability than, for example, the standard alloy AA (Aluminum Association) 5005 (AlMg1).

In addition to the mechanical properties, corrosion resistance also plays a major role in motor vehicles, since automotive components such as door interior parts are exposed to spray water, condensation or condensation. It is therefore desirable that the motor vehicle components have good resistance to various corrosion attacks, in particular to intergranular corrosion and to filiform corrosion.

Under Filiform corrosion is a type of corrosion that occurs in coated components and a understood thread-like course shows. Filiform corrosion occurs at high humidity in the presence of chloride ions.

In the past, an attempt was made to produce semi-finished products or components for motor vehicles made from AA 8006 alloy (AlFe1.5Mn0.5). Although this alloy can be used to produce semi-finished products with sufficient strength and high formability, the corresponding components after painting show a high susceptibility to filiform corrosion, so that the AA 8006 alloy is not suitable for coated, in particular painted, components such as door inner parts is.

Curable AA 6xxx alloys have high strength and good resistance to intergranular corrosion and filiform corrosion, but are significantly less malleable than AA 8006 and therefore not very well suited for the manufacture of complex components such as door inner parts. In addition, the production of semi-finished products and components from a AA 6xxx alloy is quite complex and expensive, since it requires a continuous annealing as a special process step.

AA 5xxx alloys with high magnesium content combine high strengths with a very good formability. However, the formability does not match that of steel solutions, which leads to limitations in the design of the components. In addition, these alloys tend to intercrystalline corrosion. Although steel materials are very easy to form, they have a weight disadvantage and are also susceptible to corrosion for the same rigidity. Based on this prior art, the present invention has the object to provide an aluminum alloy for the production of semi-finished products or components for motor vehicles available which is highly deformable, medium-strength and corrosion-resistant. Furthermore, a corresponding method for the production of aluminum alloy strips of this aluminum alloy is to be provided, which is relatively inexpensive to carry out. Finally, the present invention is also based on the object of providing a corresponding aluminum alloy strip as well as advantageous uses for the strip and the alloy.

With regard to the aluminum alloy, the aforementioned object is achieved according to the invention in that the alloy components of the aluminum alloy have the following percentages by weight: Fe ≤ 0.80%, Si ≤ 0.50%, 0.90 ≤ Mn ≤ 1.50%, mg ≤ 0.25%, Cu ≤ 0.125%, Cr ≤ 0.05%, Ti ≤ 0.05%, V ≤ 0.05%, Zr ≤ 0.05%, Balance aluminum, unavoidable accompanying elements individually <0.05%, in total <0.15%,
and the combined proportion of Mg and Cu satisfies the following relation in% by weight: $$0.15\%\le \mathrm{mg}+\mathrm{Cu}\le 0.25\%\mathrm{,}$$

The aluminum alloy according to the invention is based on the alloy type AA 3xxx, in particular AA 3103 (AlMn1). Although such alloys have a very good formability, but are usually too soft for many applications such as components of motor vehicles. The addition of certain alloying elements, in particular Mg and Cu, although the strength of the aluminum alloy can be increased, but this also leads to a significant reduction in ductility and thus in turn to a poorer formability.

In the context of the invention, inter alia, it has been recognized that the combined amount of copper and magnesium in the aluminum alloy according to the invention must be precisely controlled in order to achieve the desired mechanical properties, namely a yield strength Rp _0.2 of at least 45 MPa with an equiaxed Ag of at least 23 % and an elongation at break A _80mm of at least 30%, to achieve good corrosion resistance. It has been found in tests that with a combined proportion of Mg and Cu between 0.15 and 0.25 wt.%, A combination of strength and formability of the aluminum alloy which is advantageous for the aforementioned applications is achieved.

In particular, the combined amount of magnesium and copper must be at least 0.15 wt.%, Preferably at least 0.16 wt.%, In particular at least 0.17 wt the aluminum alloy _achieves sufficient strength, in particular with a yield strength R _p0.2 of at least 45 MPa. On the other hand, the combined amount of Mg and Cu must be limited to at most 0.25% by weight, preferably at most 0.23% by weight, in particular at most 0.20% by weight, since otherwise uniform elongation Ag and breaking elongation A will _increase to _{80 mn} fall very much, namely in particular under 23% for Ag and under 30% for A _80mm . The combined proportion of magnesium and copper is generally understood as the sum of the two individual fractions for Mg and Cu in% by weight.

With regard to the individual components, the aluminum alloy has a Cu content of not more than 0.125% by weight, preferably not more than 0.10% by weight, in particular not more than 0.05% by weight, and a magnesium content of not more than 0, 25 wt .-%, preferably at most 0.2 wt .-%, on. Furthermore, the aluminum alloy preferably has an Mg content of at least 0.06% by weight, more preferably of at least 0.10% by weight, in particular of at least 0.15% by weight. In one embodiment, the aluminum alloy preferably has an Mg content in the range of 0.08% to 0.25% by weight.

The aluminum alloy according to the invention described above has proved to be highly deformable and medium-strong in tests. As a result, the aluminum alloy can be used particularly well for semi-finished products and components of motor vehicles, the production of which involves complex forming processes. Accordingly, the invention also relates to the use of the aforementioned aluminum alloy for producing a semifinished product or component of motor vehicles. With the In some cases, aluminum alloy can in particular even achieve such good formability that semifinished products and components made of the alloy can be converted to forming tools for steel components.

Furthermore, it has been shown in experiments that the aluminum alloy according to the invention has good corrosion resistance. In particular, for alloys of the type AA 3xxx, to which the above-mentioned alloy belongs, no intergranular corrosion occurs. Furthermore, the aluminum alloy according to the invention in laboratory tests showed a significantly better resistance to filiform corrosion than, for example, AA 8006 alloys.

The effect of the individual alloy components will now be explained below:

The Mn content of the alloy of 0.9 to 1.5% by weight, preferably 1.0 to 1.4% by weight, especially 1.0 to 1.2% by weight, results in combination with the Fe and Si components in the specified amounts, in particular to relatively uniformly distributed, compact particles of the quaternary α-Al (Fe, Mn) Si phase, which increase the strength of the aluminum alloy, without other properties such as formability or corrosion behavior to influence negatively.

The elements titanium, chromium, vanadium and in particular zirconium can hinder the recrystallization during the final annealing and thus impair the formability of the aluminum alloy. To achieve better formability, The aluminum alloy therefore has Ti, Cr, V and Zr contents of in each case not more than 0.05% by weight and preferably in particular a Zr content of not more than 0.02% by weight.

The proportions of all other unavoidable accompanying elements are individually less than 0.05 wt .-% and together less than 0.15 wt .-%, so that they do not cause undesirable phase formation and / or negative effects on the material properties.

According to the invention, the Mg content of the aluminum alloy is greater than the Cu content of the aluminum alloy. In this way, the corrosion behavior of the aluminum alloy, in particular with respect to the Filiform corrosion, can be further improved. For example, tests on filiform corrosion on sheet metal samples of various aluminum alloys have shown that aluminum workpieces according to this first embodiment can be used to produce aluminum workpieces, in particular semi-finished products or components for motor vehicles, which show little or only slight filiform corrosion in the tests.

The formability of the aluminum alloy is further improved in one embodiment in that the aluminum alloy has a Cr content ≦ 0.02% by weight, preferably ≦ 0.01% by weight, and / or a V content ≦ 0.02% by weight .-%, preferably ≤ 0.01 wt .-%, and / or has a Zr content ≤ 0.01 wt .-%.

Titanium may be added in the continuous casting of the aluminum alloy as a grain refining agent, for example, in the form of Ti-boride wire or rods. Therefore, the Aluminum alloy in a further embodiment, a Ti content of at least 0.01 wt .-%, preferably of at least 0.015 wt .-%, in particular of at least 0.02 wt .-% to.

The material properties of the aluminum alloy can be improved in a further embodiment in that the aluminum alloy has an Fe content of ≦ 0.7% by weight, preferably ≦ 0.6% by weight, in particular ≦ 0.5% by weight , By further limiting the Fe content, the susceptibility of the aluminum alloy to filiform corrosion is prevented from increasing.

Furthermore, the aluminum alloy preferably has an Si content of ≦ 0.4% by weight, preferably ≦ 0.3% by weight, in particular ≦ 0.25% by weight. By further restricting the Si content, it can be prevented that the formability is reduced too much.

To increase the strength of the aluminum alloy further preferably has an Fe content of at least 0.10 wt .-%, preferably of at least 0.25 wt .-%, in particular of at least 0.40 wt .-%, and / or an Si content of at least 0.06% by weight, preferably at least 0.10% by weight, in particular at least 0.15% by weight.

Good strength and formability are achieved in a preferred embodiment of the aluminum alloy in that the alloying constituents of the aluminum alloy have the following percentages by weight: 0.40% ≤ Fe ≤ 0.70%, 0.10% ≤ Si ≤ 0.25%, 1.00% ≤ Mn ≤ 1.20%, mg ≤ 0.25%, Cu ≤ 0.10%, Cr ≤ 0.02%, Ti ≤ 0.05%, V ≤ 0.05%, Zr ≤ 0.05%, Balance aluminum, unavoidable accompanying elements individually <0.05%, in total <0.15%,
the combined proportion of Mg and Cu satisfying the following relation in% by weight: $$0.15\%\le \mathrm{mg}+\mathrm{Cu}\le 0.25\%\mathrm{,}$$

The formability of this alloy can be improved by the alloy having a V content of ≦ 0.02% by weight and / or a Zr content of ≦ 0.01% by weight. Furthermore, the grain refining can be improved by a Ti content of at least 0.01 wt .-%.

A very good formability with sufficient strength is achieved in a preferred embodiment of the aluminum alloy in that the alloy components of the aluminum alloy have the following percentages by weight: 0.40% ≤ Fe ≤ 0.70%, 0.10% ≤ Si ≤ 0.25%, 1.00% ≤ Mn ≤ 1.20%, mg ≤ 0.20%, Cu ≤ 0.05%, Cr ≤ 0.02%, Ti ≤ 0.05%, V ≤ 0.05%, Zr ≤ 0.05%, Balance aluminum, unavoidable accompanying elements individually <0.05%, in total <0.15%,
the combined proportion of Mg and Cu satisfying the following relation in% by weight: $$0.15\%\le \mathrm{mg}+\mathrm{Cu}\le 0.20\%\mathrm{,}$$

The formability of this alloy can be improved by the alloy having a V content of ≦ 0.02% by weight and / or a Zr content of ≦ 0.01% by weight. Furthermore, the grain refining can be improved by a Ti content of at least 0.01 wt .-%.

• Gießen eines Walzbarrens aus einer erfindungsgemäßen Aluminiumlegierung,
• Homogenisieren des Walzbarrens bei 480 °C bis 600 °C für mindestens 0,5 h,
• Warmwalzen des Walzbarrens bei 280 °C bis 500 °C zu einem Aluminiumlegierungsband,
• Kaltwalzen des Aluminiumlegierungsbands auf Enddicke und
• rekristallisierendes Schlussglühen des Aluminiumlegierungsbands.

The above-described object is further achieved according to the invention by a method for producing an aluminum alloy strip from an aluminum alloy according to the invention, which method comprises the following method steps:

• Casting a rolling bar from an aluminum alloy according to the invention,
• Homogenizing the rolling ingot at 480 ° C to 600 ° C for at least 0.5 h,
• Hot rolling the rolling ingot at 280 ° C to 500 ° C to an aluminum alloy strip,
• Cold rolling of aluminum alloy strip to final thickness and
• re-crystallizing finish annealing of aluminum alloy strip.

The method steps of the method described above are carried out in particular in the order given.

In experiments, it has been found that this method can produce an aluminum alloy strip which is highly deformable, medium strength and corrosion resistant, especially against intergranular corrosion and filiform corrosion. Furthermore, this process allows for economical production of the aluminum alloy strip, since the process involves standard process steps (i.e., continuous casting, homogenizing, hot rolling, cold rolling, soft annealing) and does not necessarily require special, expensive process steps such as strip continuous annealing.

The casting of the rolling ingot is preferably carried out in DC continuous casting. Alternatively, however, a tape casting method may also be used, for example.

By homogenizing the rolling ingot at 480 ° C to 600 ° C, preferably at 500 ° C to 600 ° C, in particular at 530 ° C to 580 ° C, for at least 0.5 h is achieved that the aluminum alloy strip after the final annealing Having fine-grained structure with good strength and formability. These properties can be further characterized improve homogenization of the rolling billet for at least 2 hours.

The hot rolling of the rolling ingot takes place at a temperature between 280 ° C and 500 ° C, preferably between 300 ° C and 400 ° C, in particular between 320 ° C and 380 ° C. During hot rolling, the ingot is preferably rolled down to a thickness between 3 and 12 mm. In this way it is ensured that in the subsequent cold rolling a sufficiently high degree of rolling, preferably of at least 70%, in particular of at least 80%, is achieved, by which the strength, the formability and the elongation values of the aluminum alloy strip are determined.

The cold rolling of the aluminum alloy strip can be done in one or more passes. The aluminum alloy strip is preferably rolled to a final thickness in the range from 0.2 to 5 mm, preferably from 0.25 to 4 mm, in particular from 0.5 to 3.6 mm. In these thickness ranges, the desired material properties of the aluminum alloy strip can be achieved particularly well.

The final annealing of the aluminum strip allows a fine-grained, thoroughly crystallized microstructure with good strength and formability to be achieved. The final annealing is therefore a recrystallizing soft annealing. The final annealing can be carried out in particular in a chamber furnace at 300 ° C to 400 ° C, preferably at 320 ° C to 360 ° C or in a continuous furnace at 450 ° C to 550 ° C, preferably at 470 ° C to 530 ° C. The chamber furnace is in operation and purchase less expensive than the continuous furnace. The Duration of final annealing in the chamber furnace is typically 1 hour or more.

• Fräsen der Ober- und/oder Unterseite des Walzbarrens.

In a first embodiment of the method, the method additionally comprises the following method step:

• Milling the top and / or bottom of the rolling ingot.

By this process step, the corrosion properties of the produced aluminum alloy strip or an end product made of this aluminum alloy strip can be improved. The milling of the upper and / or lower side of the roll ingot can be carried out, for example, after casting and before homogenizing the rolling ingot.

• erstes Homogenisieren bei 500 °C bis 600 °C, bevorzugt bei 550 °C bis 600 °C, für mindestens 0,5 h, bevorzugt für mindestens 2 h, und
• zweites Homogenisieren bei 450 °C bis 550 °C für mindestens 0,5 h, bevorzugt für mindestens 2 h.

Durch das mindestens zweistufige Homogenisieren kann ein feinkörnigeres Gefüge mit guter Festigkeit und Umformbarkeit nach dem Schlussglühen erzielt werden. Es hat sich gezeigt, dass auf diese Weise nach dem Schlussglühen insbesondere Korngrößen, bestimmt nach ASTM E1382, von kleiner als 45 µm, insbesondere sogar von kleiner als 35 µm, erreicht werden können. Das zweite Homogenisieren wird bevorzugt bei der Warmwalztemperatur durchgeführt, die der Walzbarren zu Beginn des nachfolgenden Warmwalzschrittes aufweist.In a further embodiment of the method, the homogenization is carried out at least in two stages with the following steps:

• first homogenizing at 500 ° C to 600 ° C, preferably at 550 ° C to 600 ° C, for at least 0.5 h, preferably for at least 2 h, and
• second homogenization at 450 ° C to 550 ° C for at least 0.5 h, preferably for at least 2 h.

By at least two-stage homogenization a finer grain structure with good strength and formability can be achieved after the final annealing. It has been found that, in particular, after the final annealing, in particular grain sizes determined according to ASTM E1382 of less than 45 μm, in particular even less than 35 μm, can be achieved. The second homogenization is preferably performed at the hot rolling temperature exhibited by the rolling billet at the beginning of the subsequent hot rolling step.

• erstes Homogenisieren bei 500 °C bis 600 °C, bevorzugt bei 550 °C bis 600 °C, für mindestens 0,5 h, bevorzugt für mindestens 2 h,
• Abkühlen des Walzbarrens nach dem ersten Homogenisieren auf die Temperatur für das zweite Homogenisieren und
• zweites Homogenisieren bei 450 °C bis 550 °C für mindestens 0,5 h, bevorzugt für mindestens 2 h.

The at least two-stage homogenization in a further embodiment preferably comprises the following steps:

• first homogenization at 500 ° C to 600 ° C, preferably at 550 ° C to 600 ° C, for at least 0.5 h, preferably for at least 2 h,
• Cooling of the rolling ingot after the first homogenization to the temperature for the second homogenization and
• second homogenization at 450 ° C to 550 ° C for at least 0.5 h, preferably for at least 2 h.

• erstes Homogenisieren bei 500 °C bis 600 °C, bevorzugt bei 550 °C bis 600 °C, für mindestens 0,5 h, bevorzugt für mindestens 2 h,
• Abkühlen des Walzbarrens nach dem ersten Homogenisieren auf Raumtemperatur,
• Anwärmen des Walzbarrens auf die Temperatur für das zweite Homogenisieren und
• zweites Homogenisieren bei 450 °C bis 550 °C für mindestens 0,5 h, bevorzugt für mindestens 2 h.

In an alternative embodiment, the at least two-stage homogenization preferably comprises the following steps:

• first homogenization at 500 ° C to 600 ° C, preferably at 550 ° C to 600 ° C, for at least 0.5 h, preferably for at least 2 h,
• Cooling of the rolling ingot after the first homogenization to room temperature,
• Heating the rolling ingot to the temperature for the second homogenizing and
• second homogenization at 450 ° C to 550 ° C for at least 0.5 h, preferably for at least 2 h.

In another embodiment, milling of the top and / or bottom of the rolling billet may be performed between the first homogenizing and the second homogenizing, more preferably after cooling the rolling bar to room temperature.

In a further embodiment of the method, the degree of rolling during cold rolling is at least 70%, preferably at least 80%. Through this Mindestabwalzgrad In the aluminum alloy strip after the final annealing, a fine-grained microstructure with good strength and formability can be achieved.

In a further embodiment of the method, the degree of rolling during cold rolling is at most 90%, preferably at most 85%. This maximum degree of rolling can prevent an excessive decrease in the elongation values of the aluminum alloy strip.

In a further embodiment, the method can be carried out particularly economically by carrying out the cold rolling without intermediate annealing. It has been found that the desired properties of the aluminum alloy strip can also be achieved without intermediate annealing. In the production of the aluminum alloy strip, no expensive and expensive continuous strip annealing is preferably carried out.

In an alternative embodiment of the method, the aluminum alloy strip is annealed between two cold rolling passes, in particular at a temperature of 300 ° C to 400 ° C, preferably at a temperature of 330 ° C to 370 ° C. The intermediate annealing can be done for example in a chamber furnace. The intermediate annealing is in particular an intermediate annealing of the strip.

Although the manufacturing process by the intermediate annealing is more complex, however, this can be positively influenced in a relatively thick hot strip, the microstructure, so that the produced aluminum alloy strip in the result has better material properties. The intermediate annealing will preferably carried out when the degree of rolling during cold rolling is more than 85%, in particular more than 90%. The cold rolling and the intermediate annealing is then preferably carried out so that the degree of rolling after the intermediate annealing is less than 90%, in particular less than 85%. The degree of rolling after the intermediate annealing is particularly preferably between 70% and 90%, in particular between 80% and 85%.

The above-described object is achieved according to the invention in an aluminum alloy strip, which is preferably produced by one of the methods described _above , in that the aluminum alloy _strip consists of an alloy _{according to the} invention and has a yield strength R _p0.2 of at least 45 MPa, a uniform elongation A _g of at least 23% and an elongation at break A _80mm of at least 30%.

Experiments have shown that with the alloy according to the invention and in particular also by the method according to the invention an aluminum alloy strip can be produced, which has the abovementioned material properties and also good corrosion resistance to intercrystalline corrosion and filiform corrosion. Thus, the aluminum alloy strip according to the invention is particularly well suited for components and semi-finished products for motor vehicles, especially for coated components such as interior door components.

The yield strength R _p0.2 is determined according to DIN EN ISO 6892-1: 2009. The uniform elongation Ag and the elongation at break A _80mm are also according to DIN EN ISO 6892-1: 2009 with a Flat tensile specimen according to DIN EN ISO 6892-1: 2009, Annex B, form 2.

In one embodiment, the aluminum alloy strip has a thickness in the range of 0.2 to 5 mm, preferably 0.25 to 4 mm, in particular 0.5 to 3.6 mm. In these thickness ranges, the desired material properties of the aluminum alloy strip can be achieved particularly well.

The object described above is furthermore achieved by the use of the aluminum alloy according to the invention for semifinished products or components for motor vehicles, in particular for coated components for motor vehicles. It has been found that with the aluminum alloy material properties can be achieved, which are particularly advantageous for these uses. The aluminum alloy can be used according to an embodiment particularly advantageous for interior door components of a motor vehicle.

The above-described object is further achieved by the use of a metal sheet, produced from an aluminum alloy strip according to the invention, as a component in the motor vehicle. As described above, the material properties of the aluminum alloy strip and thus also the material properties of a sheet produced from this are particularly suitable for use in motor vehicles, especially as a door inner panel.

Because of the good resistance to filiform corrosion, the aluminum alloy according to the invention or an aluminum alloy produced from the aluminum alloy according to the invention Sheet metal particularly preferably used for coated, in particular painted components of a motor vehicle.

Further features and advantages of the invention can be taken from the following description of several embodiments, reference being also made to the accompanying drawings.

Fig. 1

ein Ablaufdiagramm für mehrere Ausführungsbeispiele des erfindungsgemäßen Verfahrens,

Fig. 2

ein Ablaufdiagramm für weitere Ausführungsbeispiele des erfindungsgemäßen Verfahrens,

Fig. 3

ein Diagramm mit Messergebnissen von Ausführungsbeispielen der erfindungsgemäßen Legierung bzw. des erfindungsgemäßen Aluminiumlegierungsbands,

Fig. 4a-c

fotografische Abbildungen dreier Blechproben von drei verschiedenen Aluminiumlegierungsbändern zu einem Test auf Filiform-Korrosion und

Fig. 5

ein Bauteil für ein Kraftfahrzeug gemäß einem weiteren Ausführungsbeispiel.

In the drawing show

Fig. 1

a flow chart for several embodiments of the method according to the invention,

Fig. 2

a flowchart for further embodiments of the method according to the invention,

Fig. 3

a diagram with measurement results of embodiments of the invention Alloy or aluminum alloy strip according to the invention,

Fig. 4a-c

photographic images of three sheet metal samples from three different aluminum alloy tapes for a test on filiform corrosion and

Fig. 5

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

Fig. 1 shows a flowchart for a first embodiment of the inventive method for producing an aluminum alloy strip.

In a first step 2, a rolling ingot is first cast from an aluminum alloy according to the invention. The casting can be done for example in DC continuous casting or strip casting. After casting, the ingot is homogenized in step 4 at a temperature in the range of 480 ° C to 600 ° C for at least 0.5 hours. In step 6, the ingot is then hot rolled at a temperature in the range of 280 ° C to 500 ° C to a final thickness of between 3 and 12 mm. The hot strip hot rolled from the billet is then cold rolled in step 8 to a final thickness of preferably 0.2 mm to 5 mm. Finally, after the cold rolling, a final annealing of the aluminum alloy strip takes place in step 10, for example in a chamber furnace at a temperature between 300 ° C. and 400 ° C. or in a continuous furnace between 450 ° C. and 550 ° C.

Between the casting of the rolling ingot in step 2 and the homogenization in step 4, optionally in a step 12 the top and / or bottom of the rolling ingot are milled.

Further, during the cold rolling in step 8, the aluminum alloy strip may optionally be annealed in a step 14, preferably in a chamber furnace at a temperature between 300 ° C and 400 ° C. The intermediate annealing is particularly suitable for improving the material properties of the aluminum alloy strip when the hot strip is relatively thick and therefore the degree of rolling during cold rolling is more than 85%, in particular more than 90%.

For example, with a hot strip thickness of 12 mm and a final thickness of 0.4 mm, the degree of rolling in cold rolling is approximately 96.7%. In this case, for example, the hot strip can first be rolled to 2 mm in a first cold-rolled pass, then intermediate-annealed, and finally rolled to 0.4 mm in a second cold-rolled pass. The Abwalzgrad after the intermediate annealing is then only 80% and is thus in a preferred range.

FIG. 2 shows a part of a flowchart for further embodiments of the method according to the invention. The process flow of these embodiments is substantially the same as the process flow of FIG FIG. 1 match described method. The homogenization of the rolling ingot takes place in the embodiments according to FIG. 2 not in step 4, but in a step 16, which is divided into several steps. FIG. 2 shows possible sequences of the individual steps of step 16.

Accordingly, after casting of the rolling ingot in step 2 or after milling of the rolling ingot in step 12 in the first partial step 18 of step 16, a first homogenization at a temperature between 550 and 600 ° C for at least 0.5 h, preferably for at least 2 h. In a subsequent step 20, the ingot is cooled to the temperature of the second homogenization in the range of 450 ° C and 550 ° C, before then in the subsequent step 22 at this temperature, the second homogenization for at least 0.5 h, preferably for at least 2 h, takes place.

Alternatively, after the first homogenization in step 18, the ingot may be first cooled to room temperature in a step 24 and heated in a subsequent step 26 to the temperature for the second homogenization. Between step 24 and step 26, optionally the top and / or bottom of the rolling billet can be milled.

Within the scope of the invention, aluminum alloys of the AA 3xxx type, in particular based on AA 3103, were produced with different Mg and Cu contents. The alloy compositions of these aluminum alloys are summarized in the following Table 1, wherein the individual alloy portions are each given in wt .-%. Table 1 No. Si Fe Cu Mn mg Cr Zn Ti V Zr Cu + Mg 1 V 0.063 0.54 0.0029 1.07 0.0102 0.0005 0.0051 0.0053 0.0038 0.0005 0,013 2 V 0.23 0.55 0,055 0.93 0.059 0.0096 0.0131 0.0151 0.0099 0.0008 0.114 3 V 0.208 0.546 0.064 1,026 0,071 0,004 0.005 0,018 0.0081 0.0006 0.135 4 V 0.154 0.51 0,152 1.02 0.0019 0.0005 0.0034 0.0602 0.0073 0.0005 0.154 5 V 0.176 0.511 0.092 1.01 0.063 0,003 0,006 0.0169 0.0107 0.0008 0,155 6 e 0,128 0.57 0.031 1.0 0.15 0,006 0,007 0.0166 0.0114 0.0008 0,181 7 V 0.23 0.5 0.18 1.06 0.0109 0.0101 0.0055 0.0093 0.0112 0.0008 0.191 8th e 0,142 0.62 0.0019 1.1 0.19 0.0004 0.0011 0.0066 0.0091 0.0005 0.192 9 V 0.17 0, 54 0.19 1.03 0.053 0.0005 0.0032 0.0217 0.0064 0.0005 0.243 10 V 0.42 0.45 0.086 1.01 0.19 0.0331 0.0058 0.028 0.0066 0.0006 0.276 11 V 0,052 0.21 0.28 0.87 0.22 0.0006 0.0028 0,018 0.0061 0.0005 0.5 12 V 0.162 0.59 0.0016 1.1 0.52 0.0002 0.001 0.0055 0.0072 0.0005 0.522 13 V 0,179 0.38 0.116 1.05 0.51 0,003 0,006 0,014 0.0068 0.0006 0.626

In the last column of Table 1, the combined amount of copper and magnesium is given, which has been found to be particularly important for the desired material properties. Alloys Nos. 6 and 8 are examples of the invention alloy (E), while alloys Nos. 1-5, 7 and 9-13 are comparative examples (V).

From these aluminum alloys Nos. 1-13, aluminum alloy ribbons were then produced by the method described above. Specifically, each of these alloys 1 to 13 was cast in DC continuous casting in each case a rolling bar with a thickness of 600 mm, which was then homogenized in two stages, first for several hours at about 580 ° C and then for several hours at about 500 ° C. After homogenization, the ingots were hot rolled at about 500 ° C into aluminum alloy hot tapes having a thickness of 4 to 8 mm. These aluminum alloy hot tapes were then each cold-rolled to a final thickness of 1.2 mm and finally subjected to a recrystallizing final annealing at 350 ° C for 1 h.

Subsequently, the aluminum alloy strips were examined for their mechanical properties, in particular their strength and formability.

The results of these investigations are summarized in Table 2 below. Furthermore, Table 2 in the last line shows the corresponding material properties of an alloy of the type AA 8006, as known from the prior art. Table 2 No. R _p0.2 [MPa] R _m [MPa] Ag [%] A _80mm [%] n-value r-value SZ 32 [mm] 1 V 42 101 25.1 41.3 0.214 0.472 16.7 2 V 42 103 24.6 35.7 0,216 0.579 16.3 3 V 43 111 24.5 36.1 0.218 0.484 16.4 4 V 48 111 25.3 35.9 0.214 0,417 16.6 5 V 45 114 24.8 36.4 0.217 0.484 16.5 6 e 46 116 24.5 35.1 0.217 0.662 16.7 7 V 49 115 25.1 34.2 0.218 0,420 16.2 8th e 50 113 24.2 35.0 0.210 0,598 16.4 9 V 53 118 23.8 32.5 0,216 0.344 15.9 10 V 51 119 21.8 29.5 0.207 0,635 15.9 11 V 58 134 21.2 26.9 0,220 0.556 15.4 12 V 57 135 20.8 28.0 0.221 0.652 15.5 13 V 66 152 19.7 21.0 0.225 0.582 14.9 AA 8006 V 49 104 27.5 42.0 0.223 0,431 17.3

• die Dehngrenze R_p0,2 in MPa sowie die Zugfestigkeit R_m in MPa, gemessen im Zugversuch senkrecht zur Walzrichtung des Blechs nach DIN EN ISO 6892-1:2009,
• die Gleichmaßdehnung Ag in Prozent sowie die Bruchdehnung A_80mm in in Prozent, gemessen im Zugversuch senkrecht zur Walzrichtung des Blechs mit einer Flachzug-Probe nach DIN EN ISO 6892-1:2009, Anhang B, Form 2,
• den Verfestigungsexponenten n (n-Wert), gemessen im Zugversuch senkrecht zur Walzrichtung des Blechs nach DIN ISO 10275:2009,
• die senkrechten Anisotropie r (r-Wert), gemessen im Zugversuch senkrecht zur Walzrichtung des Blechs nach DIN ISO 10113:2009, und
• die beim Streckziehen erreichte Tiefung SZ 32 in Millimeter als weiteres Maß für die Umformbarkeit der Legierung. Die Tiefung SZ 32 wurde im Erichsen-Tiefungsversuch nach DIN EN ISO 20482 ermittelt, aber mit einem auf die Blechdicke abgestimmten Stempelkopfdurchmesser von 32 mm und Matrizendurchmesser von 35,4 mm und unter Zuhilfenahme einer Teflon-Ziehfolie zur Reduzierung der Reibung.

Table 2 shows the following measured values:

• the yield strength R _p0.2 in MPa and the tensile strength R _m in MPa, measured in the tensile test perpendicular to the rolling direction of the sheet according to DIN EN ISO 6892-1: 2009,
• the uniform elongation Ag in percent and the elongation at break A _{80 mm} in percent, measured in the tensile test 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 solidification exponent n (n-value), measured in the tensile test perpendicular to the rolling direction of the sheet according to DIN ISO 10275: 2009,
• the vertical anisotropy r (r value), measured in the tensile test perpendicular to the rolling direction of the sheet according to DIN ISO 10113: 2009, and
• the depression SZ 32 in millimeters achieved during ironing as a further measure of the formability of the alloy. The depression SZ 32 was determined in the Erichsen cupping test according to DIN EN ISO 20482, but with a stamp head diameter of 32 mm and die diameter of 35.4 mm matched to the sheet thickness and with the aid of a Teflon drawing film to reduce friction.

In FIG. 3 _{For example} , the yield strength R _p0.2 ( _open squares), the elongations at break A _80mm (filled diamonds), and the sag values SZ 32 (filled triangles) of the aluminum alloy ribbons Nos. 1 to 13 are plotted against the combined Cu and Mg contents of the respective aluminum alloy , The R _p0,2 values are plotted in MPa according to the scale on the left ordinate axis. The A _80mm values are _plotted in percent and the SZ 32 values are plotted in mm according to the scale on the right axis of the ordinate. The combined Cu and Mg content is indicated on the abscissa in wt.%.

Furthermore, in FIG. 3 For a better overview in each case even _{regression lines} to the measured values of R _p0,2 , A _80mm and SZ 32 drawn. Two vertical dashed lines also indicate the inventive lower and upper limits for the combined Cu and Mg content.

As the measured values for the aluminum alloy strips from the aluminum alloys Nos. 4-9 show, the adjustment of the combined Cu and Mg content in one Range of 0.15 wt .-% to 0.25 wt .-%, that the desired combination of strength (R _p0.2 ≥ 45MPa) and formability (A _g ≥ 23% and ≥ 30% A _80mm) is achieved.

At combined Mg and Cu contents of less than 0.15% by weight (Nos. 1-3), the strength proves to be too low (R _p0.2 <45 MPa) and combined Mg and Cu contents of more than 0.25% by weight (Nos. 10 to 13), the elongation values and thus the formability decrease too much (A _g <23% and / or A _{80 mm} <30%).

The good formability is also reflected in particular by the measured depth value, which in the case of the alloy according to the invention preferably has a value SZ 32 ≥ 15.8 mm, in particular ≥ 15.9 mm.

As a result, the aluminum alloys Nos. 4-9 have only a slightly poorer formability at the same strength than the comparison alloy AA 8006. The aluminum alloys Nos. 4-9, however, have the advantage over the alloy AA 8006 that they have a significantly better Have corrosion resistance. Thus intercrystalline corrosion does not occur in alloys of type AA 3xxx.

Furthermore, supplementary laboratory tests for corrosion resistance were carried out on the aluminum alloy strips made of the aluminum alloys Nos. 4-9. These laboratory tests have shown that the aluminum alloys Nos. 4-9 show a much better resistance to filiform corrosion than the alloy type AA 8006. Thus, aluminum alloys are like the aluminum alloys Nos. 4-9 or aluminum alloy strips made of these aluminum alloys particularly suitable for coated components.

1. 1. 30 s Beizen der gewalzten und weichgeglühten Blechproben in einem sauren Beizmedium mit einem Abtrag von 0,5 g/m². (Dieser Materialabtrag entspricht in etwa einem typischen Materialabtrag bei der Vorbehandlung von Halbzeugen und Bauteilen für Kraftfahrzeuge, z.B. bei einem OEM-Vorbehandlungsprozess, so dass die Filiformergebnisse des hier beschriebenen Tests gut mit den Ergbnissen im Realbauteil korrelieren.)
2. 2. Beschichten der gebeizten Blechprobe mit einem transparenten Acrylharzlack.
3. 3. Einbrennen des aufgetragenen Lacks für 5 min. bei 160 °C.
4. 4. Einbringen einer Ritzlinie in die Blechprobe mit Hilfe eines Ritzstichels, und zwar quer zur Walzrichtung.
5. 5. Tröpfchen-Impfung in der Ritzlinie mit einer wässrigen, 18-prozentigen Salzsäurelösung.
6. 6. Auslagerung der Blechprobe im Klimaschrank, und zwar
   1. a) zunächst für 24 h bei 40 °C und 80 % relativer Luftfeuchtigkeit und
   2. b) anschließend für 72 h bei 23 °C und 65 % relativer Luftfeuchtigkeit.
7. 7. Optische Auswertung der Blechprobe, und zwar Auswertung der Unterwanderungstiefe (Ausbreitung der Korrosion unter dem Lack) ausgehend von der Ritzlinie).

In particular, the following test for filiform corrosion was carried out on sheet metal samples of the various aluminum alloy strips. The test includes the following steps in the order listed:

1. 1. 30 s pickling of the rolled and annealed sheet samples in an acid pickling medium with a removal of 0.5 g / m ² . (This material removal corresponds approximately to a typical material removal in the pretreatment of semi-finished products and components for motor vehicles, eg in an OEM pretreatment process, so that the filiform results of the test described here correlate well with the results in the real component.)
2. 2. Coat the pickled sheet sample with a transparent acrylic resin paint.
3. 3. baking the applied paint for 5 min. at 160 ° C.
4. 4. Introduction of a scribe line in the sheet metal sample with the aid of a scribe prick, transversely to the rolling direction.
5. 5. Droplet vaccination in the scribe line with an aqueous, 18% hydrochloric acid solution.
6. 6. Outsourcing of the sheet sample in the climatic chamber, namely
   1. a) first for 24 h at 40 ° C and 80% relative humidity and
   2. b) then for 72 h at 23 ° C and 65% relative humidity.
7. 7. Optical evaluation of the sheet sample, namely evaluation of the subterranean depth (propagation of corrosion under the paint) starting from the scribe line).

The aforementioned test was carried out in particular on sheet metal samples for the comparative example no. 5 and example no. 6 listed in tables 1 and 2 and for a correspondingly produced sheet metal sample of the comparative alloy AA8006. In the FIGS. 4a-c Photographs of the sample surfaces are shown at the end of the test. FIG. 4a shows the sheet sample of the comparative alloy AA8006, FIG. 4b shows the sheet sample of Comparative Example No. 5 and Figure 4c shows the sample sheet according to Embodiment No. 6.

In the FIGS. 4a-c In each case, the scribe line introduced into the sheet sample is to be seen (dark line running from top to bottom). The filiform corrosion spreads starting from the scribe line substantially transversely to the extension direction of the scribe line and is shown in the figures as a light thread-like structures. For a simpler size comparison, the figures each show a ruler with centimeter scale placed on the sample.

The sheet sample of the comparative alloy AA8006 shows a strong Filiform corrosion. The scribe line is in Fig. 4a almost completely surrounded by the white filiform structures of filiform corrosion. The subterranean depth, ie the extent of the threadlike structures starting from the scribe line, is up to 6 mm.

On the other hand, the Sample No. 5 metal sample shows a considerably lower amount of filiform corrosion. The density of thread-like structures of filiform corrosion is at the scribe line in Fig. 4b considerably less than the scribe line in Fig. 4a so that the sheet sample in Fig. 4b has a much greater resistance to filiform corrosion than the sheet sample in Fig. 4a , Nevertheless, some filiform structures of filiform corrosion, some of which have a large infiltration depth of up to approximately 6 mm, also occur in this sample of sheet metal.

The best results in the Filiform corrosion were achieved for the embodiments of the invention, in which the Mg content of the alloy composition is greater than the Cu content. Thus, the sample of sheet metal for Embodiment No. 6 with an Mg content of 0.15% by weight and a Cu content of 0.031% by weight shows only minimal filiform corrosion. The scribe line in Fig. 4c is only occasionally surrounded by short filiform structures of filiform corrosion up to 3 mm in length. The sheet sample for Embodiment No. 6 thus has a very good resistance to filiform corrosion.

Finally, the measured values in Table 2 show that the exemplary embodiments of the aluminum alloy according to the invention also achieve good values for the tensile strength R _m and for the n and r values, which are in particular within the scope of conventional AA 3xxx alloys or even better.

FIG. 5 shows a schematic representation of a typical component of a motor vehicle in the form of a door inner part.

Such door inner parts 40 are usually made of steel. However, steel components are heavy and susceptible to corrosion with equal rigidity.

It has been found that with the aluminum alloys described above, such as aluminum alloys Nos. 6 and 8, aluminum alloy ribbons can be produced that are highly deformable, medium strength, and highly corrosion resistant, particularly to intergranular corrosion as well as to filiform corrosion.

The material properties of these aluminum alloy strips or of the sheets produced therefrom are therefore particularly favorable for the production of motor vehicle components, such as the door inner part 40. The good resistance to filiform corrosion is especially when using the aluminum alloys for coated, in particular painted components, such as the door inner part 40, advantageous.

In particular, the components produced from these aluminum alloys have a better corrosion resistance than corresponding components made of steel or of an alloy of the type AA 8006. At the same time they have a significantly lower weight than components made of steel.

Claims (14)

1. Aluminium alloy for producing semi-finished products or components for motor vehicles,
   characterized in that
   the alloying components of the aluminium alloy have the following contents in percent by weight: Fe ≤ 0.80%, Si ≤ 0.50%, 0.90% ≤ Mn ≤ 1.50%, Mg ≤ 0.25%, Cu ≤ 0.125%, Cr ≤ 0.05%, Ti ≤ 0.05%, V ≤ 0.05%, Zr ≤ 0.05%, the remainder being aluminium, unavoidable impurity elements individually <0.05%, in total <0.15%,
   and the combined content of Mg and Cu satisfies the following relation in percent by weight $$0.15\%\le \mathrm{Mg}+\mathrm{Cu}\le 0.25\%,$$

   

   wherein the Mg content of the aluminium alloy is greater than the Cu content of the aluminium alloy.
2. Aluminium alloy according to claim 1,
   characterized in that
   the aluminium alloy has a Cu content of at most 0.10% by weight and/or a Mg content in the range of 0.06% by weight to 0.20% by weight.
3. Aluminium alloy according to claim 1 or 2,
   characterized in that
   the aluminium alloy has a Cr content ≤ 0.02% by weight, and/or a V content ≤ 0.02% by weight, and/or a Zr content ≤ 0.02% by weight, particularly ≤ 0.01% by weight.
4. Aluminium alloy according to any one of claims 1 to 3,
   characterized in that
   the aluminium alloy has an Fe content from 0.4 to 0.7% by weight, and/or a Si content from 0.1 to 0.25% by weight, and/or a Mn content from 1.0 to 1.2% by weight.
5. Aluminium alloy according to any one of claims 1 to 4,
   characterized in that
   the aluminium alloy has a Ti content of at least 0.01% by weight.
6. Method for producing an aluminium alloy strip from an aluminium alloy according to any one of claims 1 to 5, comprising the following method steps:

   - Casting a rolling ingot from an aluminium alloy according to any one of claims 1 to 5;

   - Homogenizing the rolling ingot at 480 °C to 600 °C for at least 0.5 h;

   - Hot rolling the rolling ingot at 280 °C to 500 °C to form an aluminium alloy strip;

   - Cold rolling the aluminium alloy strip to final thickness; and

   - Subjecting the aluminium alloy strip to recrystallizing final annealing.
7. Method according to claim 6,
   characterized in that
   the method further comprises the following method step:

   - Milling the upper and/or lower side of the rolling ingot.
8. Method according to either of claims 6 or 7,
   characterized in that
   homogenization is carried out in at least two stages and comprises the following steps:

   - first homogenization at 500 °C to 600 °C for at least 0.5 h; and

   - second homogenization at 450 °C to 550 °C for at least 0.5 h.
9. Method according to any one of claims 6 to 8,
   characterized in that
   the degree of rolling reduction during cold rolling is between 70% and 90%, preferably between 80% and 85%.
10. Method according to any one of claims 6 to 9,
    characterized in that
    the cold rolling is carried out with or without intermediate annealing.
11. Aluminium alloy strip, particularly produced by a method according to any one of claims 6 to 10,
    characterized in that
    the aluminium alloy strip consists of an alloy according to any one of claims 1 to 5 and has an offset yield strength R_p0.2 of at least 45 MPa, a uniform elongation A_g of at least 23%, and an elongation at break A_80mm of at least 30%.
12. Aluminium alloy strip according to claim 11,
    characterized in that
    the aluminium alloy strip has a thickness in the range from 0.2 mm to 5 mm.
13. Use of an aluminium alloy according to any one of claims 1 to 5 for semi-finished products or components for motor vehicles, particularly for interior door panels.
14. Use of a metal sheet made from an aluminium alloy strip according to claim 11 or 12 as a component in the motor vehicle, particularly as an interior door panel.

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