Aluminum alloy strip optimized for forming and method for manufacturing

Abstract

The present invention relates to an aluminum alloy strip made of an aluminum alloy, a method for producing said aluminum alloy strip and its preferred uses. The objective of providing an aluminum alloy strip, in particular for the production of automotive body parts, preferably interior body parts, which, in addition to the necessary resistance to intergranular corrosion, provides the necessary strength and at the same time improved forming properties, is to provide an aluminum alloy strip having the following composition in weight percent: Si≦0.10%, Fe≦0.25%, 0.20%≦Mn≦0.30%, 4.72%≦Mg≦4.95%, Cu≦0.10%, Cr≦0.02%, Ni≦0.01%, Zn≦0.10%, Ti≦0.04%, the balance being Al, and an aluminum alloy having an aluminum alloy with an individual content of ≦0.05% and a total content of ≦0.15% unavoidable impurities, the aluminum alloy strip having a thickness of 1000 μm or less. 2 The total number of secondary phases determined in at least 10 measurement areas results in a secondary phase density relative to the total measurement surface of all measurement areas examined, with an average secondary phase density of less than 250 per area.

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy strip made of an aluminum alloy, a method for producing said aluminum alloy strip and preferred uses thereof. [Background technology]

[0002] In particular, aluminum-magnesium (AlMg) alloys of type AA5xxx are used in the form of sheet or strip for the construction of welded or joined components in ship, automobile and aircraft construction. These aluminum-magnesium alloys are characterized by an increased magnesium content due to their high strength and increased formability at magnesium contents above 3%. For this reason, aluminum-magnesium alloys of type AA5xxx can increasingly replace materials made of steel, for example, in automobile construction and can thus contribute to further weight reduction of automobiles.

[0003] AlMg alloys of type AA5xxx, with a Mg content above 3%, and especially above 4%, show an increased tendency to intergranular corrosion when exposed to high temperatures. At temperatures between 70 and 200°C, a non-noble Al5Mg3 phase, called beta grains, precipitates along the grain boundaries, which can be selectively dissolved in corrosive media. As a result, aluminum alloys of type AA5182 (Al 4.5% Mg 0.4% Mn), which have particularly good strength properties and excellent formability, are not used on surfaces exposed to heat when the presence of corrosive media, such as water in the form of humidity, must be expected. This is particularly true for automotive components, which are usually subjected to cathodic dip painting (CDP) and then dried in a baking process, as this baking process can already cause an increase in sensitization to intergranular corrosion in conventional aluminum alloy strip. Furthermore, use in the automotive sector must take into account the forming process during component manufacturing and the subsequent workload of the component.

[0004] An aluminum alloy strip having a magnesium content of more than 4% by weight and suitable for automotive components is known from US Pat. No. 5,623,999. It exhibits very good resistance to intergranular corrosion despite offering high strength. However, it has been shown that the formability of this aluminum alloy strip made from an aluminum alloy of type AA5182, which is particularly resistant to intergranular corrosion, can be improved.

[0005] Consequently, a further development in the formability of this aluminium alloy strip is known from US Pat. No. 5,619,499, in which the formability of this aluminium alloy strip was optimised with an almost identical alloy concept. The subject of both international patent applications is aluminium strip with a Mg content of up to a maximum of 4.50 wt. %, which is within the specification for aluminium alloys of type AA5182. Patent Document 3 discloses aluminum alloys of type AA5xxx in which the secondary phase density of secondary phases having a maximum length of at least 3 μm or more has been determined. US Pat. No. 5,629,999 discloses annealed aluminum alloy strips and a method for their production. From patent document 5, a soft-annealed aluminum alloy strip is known in which the secondary phase density of copper-containing secondary phases having an equivalent circle diameter of 0.3 μm to 4 μm is maximized.

[0006] It has now been determined that there is further potential for improving formability without compromising other performance properties, such as providing the necessary strength and corrosion resistance within the specifications of Type AA5182 aluminum alloy. The usual important values ​​for formability, such as uniform elongation Ag or elongation at break A, 80mm It has been found that the values ​​of are not sufficiently meaningful for the practical use of these aluminum alloy sheets in forming processes.

[0007] Standard DIN EN ISO 12004-2:2021-07 specifies test conditions that allow for the assessment of the permissible main and minor shape changes of aluminum sheets during forming processes in order to ensure a safe forming process. The main and minor shape changes determined in accordance with this standard result from forming limit change curves that characterize the specific behavior of the sheet being formed in a drawing test. The provision of forming limit change curves is achieved by a shape change analysis of defective drawn parts to determine the shape change diagram, depending on the part being drawn and the forming process.

[0008] In a specimen with a specific geometry, a test grid or estimation pattern with precise dimensions is applied or optically projected onto the undeformed surface. The specified cut specimen part is then deformed, for example with a defined punch, until it breaks according to the Nakajima method in precisely defined rows / columns, after which the test is stopped. All values ​​given herein for the main shape change ε1 refer to tests according to the Nakajima method according to DIN EN ISO 12004-2:2021-07. The main shape change ε1 is determined herein on a specimen with a width of 100 mm. All values ​​given are average values ​​from three specimens.

[0009] All other mechanical parameters are measured in accordance with DIN EN ISO 6892. Since the grain size of a material is always given in the form of a distribution, all information given about grain size refers to the average grain size, which can be determined in accordance with ASTM E1382. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2014 / 0298531(A1) [Patent Document 2] International Publication No. 2014 / 029856(A1) [Patent Document 3] JP 2001-303164(A) [Patent Document 4] International Publication No. 2016 / 207274(A1) [Patent Document 5] U.S. Patent Application Publication No. 2020 / 0157668(A1) Summary of the Invention [Means for solving the problem]

[0011] It is an object of the present invention to provide an aluminum alloy strip which provides the required strength and at the same time improved forming properties, in addition to the resistance to intergranular corrosion required, in particular for the production of automotive body parts, preferably interior body parts.

[0012] According to a first teaching of the present invention, the object is to provide a composition having the following composition in weight percent: Si≦0.10%, Fe≦0.25%, 0.20%≦Mn≦0.30%, 4.72%≦Mg≦4.95%, Cu≦0.10%, Cr≦0.02%, Ni≦0.01%, Zn≦0.10%, Ti≦0.04%, The balance is Al and incidental impurities individually ≤ 0.05% and in total ≤ 0.15%; an aluminum alloy strip having an aluminum alloy having a thickness of 1000 μm; 2 This is achieved by providing an aluminum alloy strip having an average secondary phase density of less than 250 per square inch.

[0013] During intensive investigations, the inventors have found that in aluminum alloy strips having the above-mentioned aluminum alloy, the secondary phase density is 1000 μm 2The inventors have recognized that by limiting the secondary phases to less than 250 per 1000 μm, advantageous increases in formability can be realized while at the same time retaining the advantages of type AA5182 aluminum alloy with respect to corrosion resistance and mechanical strength of the aluminum alloy strip. The secondary phases are typically Al6Mn, α-Al(Fe,Mn)Si and Mg2Si. The inventors have discovered that a large number of secondary phases results in limitations in forming behavior, which are particularly evident in complex deep drawing processes for the manufacture of, for example, car body parts. By selecting a specific alloy composition in combination with an equally specific manufacturing process, it is possible to limit the secondary phase density to less than 1000 μm 2 The value could be reduced to less than 250 per unit.

[0014] The secondary phase density, i.e., the (surface) density of dispersoids, is determined herein by optical microscopy as follows: A sample of the aluminum alloy strip to be examined is mounted using generally accepted metallographic methods and prepared in the form of a longitudinal section. After grinding and polishing this section, the sample is etched for 1 minute at room temperature in a dilute aqueous solution of sulfuric and hydrofluoric acid. For this purpose, a 100 cm 3 A 60cm solution of 10% concentrated sulfuric acid 3 of water and 40cm 3 of 5% hydrofluoric acid and 100 cm 3 After etching, the cross section is rinsed with distilled water and dried for subsequent optical microscopy. The etching performed reveals the secondary phases in the structure so that their surface density can be determined with good accuracy in an optical microscope. To ensure sufficient statistical validity, a minimum of 10 statistically distributed image areas were analyzed at high magnification (1000:1) using an optical microscope with an oil lens as the measurement area, resulting in a total of at least 2000 secondary phases being recorded. The total number of determined secondary phases is compared to the total measured area of ​​all examined measurement areas to determine the surface density of the secondary phases, i.e., the secondary phase density (number per area, e.g., 1000 μm 2 This results in a number of hits (specified by the number of hits).

[0015] In this alloy composition, the silicon content has been reduced to a maximum of 0.10 wt.%. Silicon forms α-Al(Fe,Mn)Si and Mg2Si precipitates as secondary phases in magnesium-containing aluminum alloys. As explained above, these impair the formability of the aluminum alloy strip. Therefore, the preferred silicon content is a maximum of 0.08 wt.%.

[0016] Iron is mainly bound in the so-called cast phase, but also participates in the formation of secondary precipitates. A reduction in the iron content to a maximum of 0.25% by weight, preferably 0.20% by weight, therefore contributes to improving formability.

[0017] Manganese is a typical dispersoid former, whereby dispersoid particles effectively prevent displacement of atoms from the metal crystalline bonds. Therefore, dispersoids contribute to the desired increase in yield strength. Furthermore, Mn-containing dispersoids help control the grain size of aluminum alloy strip. However, dispersoid particles limit the forming behavior. Therefore, aluminum alloy strip has a Mn content of 0.20 wt% to 0.30 wt%. At Mn contents below 0.20 wt%, the strength-enhancing effect of these dispersoids decreases, and the aluminum alloy strip may exhibit undesirable grain coarsening during heat treatment. At manganese contents above 0.30 wt%, the dispersions too much hinder the expansion of the material, resulting in suboptimal forming behavior. A Mn content of 0.20 wt%≦Mn≦0.26 wt% may provide an optimized Mn content for various forming behavior aspects.

[0018] Magnesium is present in the aluminum alloy according to the invention in a content of 4.72 to 4.95% by weight, preferably 4.80 to 4.92% by weight. It has been found that at these magnesium contents in particular, not only are high strengths achieved despite a reduced proportion of strength-increasing dispersoid-forming substances, but also that the forming behavior is improved. However, higher Mg contents result in an excessive sensitivity of the material to intergranular corrosion, as described above.

[0019] To optimize the forming behavior, the copper content was also limited to a maximum of 0.10% by weight. Although copper increases the strength of the aluminum alloy strip even at low contents, it also causes a deterioration in the general corrosion behavior at low contents. Therefore, the preferred copper content is a maximum of 0.07% by weight, particularly preferably at least 0.02% by weight and less than 0.04% by weight.

[0020] The alloying element chromium is a very effective dispersoid former and is therefore contained in the present aluminium alloy in a content of 0.02% by weight, preferably a maximum of 0.01% by weight, particularly preferably a maximum of 0.008% by weight.

[0021] The same applies to the nickel content due to its tendency to form dispersoid particles at the lowest contents, so the Ni content is reduced to a maximum of 0.01 wt. %, preferably 0.005 wt. %.

[0022] The corrosion resistance of the aluminum alloy strip is adversely affected by zinc, which is contained in the aluminum alloy in a maximum content of 0.10% by weight, preferably a maximum of 0.01% by weight, and particularly preferably a maximum of 0.008% by weight.

[0023] Titanium used for grain refinement in the melting process should be limited to a maximum of 0.04 wt.%, preferably a maximum of 0.02 wt.%, since titanium also forms dispersoids and tends to segregate strongly at high concentrations. Titanium from, for example, grain refiners, assists the melting process and thus improves the casting of rolled ingots, so a maximum titanium content of 0.005 wt.% to 0.02 wt.% is preferably provided in the present aluminum alloy. This range of titanium allows a compromise between melting characteristics and the number of secondary precipitates to be achieved.

[0024] According to a first embodiment of the aluminum alloy strip, the aluminum alloy strip has a thickness of 1000 μm 2less than 220 μm per 2 The aluminum alloy strips have a secondary phase density of less than 200 per square inch. By selecting the aluminum alloy elements in accordance with the manufacturing process of the aluminum alloy strip, it was possible to show that further reductions in secondary phase density in the aluminum alloy strips can be achieved. These aluminum alloy strips exhibited further increases in forming behavior while simultaneously providing high mechanical strength and good corrosion resistance.

[0025] The present aluminum alloy strip has very good forming properties in microstructural state O or H111. Microstructural state O is characterized by a recrystallized microstructure that allows maximum forming. In state H111, the aluminum alloy strip in state O is slightly solidified, for example by stretching or straightening the aluminum alloy strip. Therefore, state H111 is preferably used in the processing of aluminum alloy sheet, since the aluminum alloy sheet here is less deformed but still achieves particularly high forming values.

[0026] Further investigations have shown that, according to a further embodiment, the present aluminum alloy strip has an average grain size of 15 μm to 30 μm. It has been found that the corrosion resistance of aluminum alloys having the present alloy composition at grain sizes of 15 μm to 30 μm meets the requirements for car body applications. At the same time, smaller grain sizes contribute to improved formability.

[0027] The aluminum alloy strip is preferably cold rolled to provide the necessary dimensional accuracy and surface quality for preferred use in automotive construction.

[0028] The final thickness of the cold rolled aluminum alloy strip is, according to one embodiment, a maximum of 0.5 mm to 4 mm, preferably 0.8 mm to 2.5 mm. In particular, within these specified thickness ranges, the aluminum alloy strip can provide significantly improved forming properties in combination with conventional forming processes and tooling.

[0029] According to the following embodiment of the aluminum alloy strip, it has an Ae value transverse to the rolling direction of less than 1.0%, preferably less than 0.9%. The Ae value is also called yield strength extensometer elongation. The Ae value is measured transverse to the rolling direction in accordance with DIN EN ISO 6892 and is specified in %. The Ae value of the aluminum alloy strip is characteristic for the formation of Lüders bands during the forming of the aluminum alloy strip, which is undesirable for, for example, car body components. The smaller the Ae value, the fewer Lüders bands occur. At values ​​of less than 1.0% or less than 0.9% transverse to the rolling direction, the aluminum alloy strip can be said to be substantially free of Lüders bands.

[0030] Finally, an embodiment of an aluminum alloy strip according to the present invention having a sheet thickness of 1.2 mm and a specimen width b) of 100 mm has an average main shape change ε1 of greater than 0.200 in tests according to the Nakajima method in accordance with DIN EN ISO 120004-2. This main shape change value could be achieved in the aluminum alloy strip according to the present invention by adjusting the reduction in secondary phase density, taking into account a manufacturing process adapted to the material. The main shape change ε1 at a specimen width b) of 100 mm according to Nakajima reflects in a single parameter the complex interaction of the microstructure of the aluminum alloy strip during the drawing process and shows a significant increase compared to the main shape change ε1 of shape-optimized aluminum alloy strip of type AA5182 achieved so far. For all values ​​specified herein, the designation of a specimen width of 100 mm refers to the value b) of a specimen having a relief length a) parallel to the axial direction in accordance with Figure 2 of DIN EN ISO 120004-2 (6.1.2 Specimen Geometry).

[0031] At the same time, according to a further embodiment, the aluminum alloy strip has a yield strength Rp of at least 115 MPa, preferably at least 120 MPa, transverse to the rolling direction in the microstructural state O or H111. 0.2and therefore the strength requirements in automobile construction are also met by the present shape optimized aluminum alloy strip.

[0032] The mass loss of this aluminum alloy strip due to intergranular corrosion is 13 mg / cm2 measured according to ASTM G67 after a heat load of 195°C for 45 minutes. 2 ~19mg / cm 2 This heat load corresponds to the maximum heat load that the component can experience during the cathodic dip coating process, thus indicating that no corrosion problems are to be expected in the subsequent use of the component.

[0033] According to a further teaching of the present invention, the aluminum alloy strip according to the present invention can be produced by the following steps: - the following composition: Si≦0.10%, preferably ≦0.08%, Fe≦0.25%, preferably ≦0.20%, 0.20%≦Mn≦0.30%, preferably 0.20%≦Mn≦0.26%, 4.72%≦Mg≦4.95%, preferably 4.80%≦Mg≦4.92%, Cu≦0.10%, preferably Cu≦0.07%, particularly preferably Cu<0.04%, Cr≦0.02%, preferably Cr≦0.01%, particularly preferably Cr≦0.008%; Ni≦0.01%, preferably Ni≦0.005%, Zn≦0.10%, preferably Zn≦0.01%, particularly preferably Zn≦0.008%, Ti≦0.04%, preferably Ti≦0.02%, The balance is Al and incidental impurities individually ≤ 0.05% and in total ≤ 0.15%; Casting of rolled ingots from an aluminum alloy having - homogenization of the rolled ingot at 480 ° C - 550 ° C for at least 0.5 hours; - Hot rolling of ingots to a final thickness of 3mm-6mm hot strip; - cold rolling of the aluminum alloy strip to a reduction of 40% to 60%, preferably 50% to 60%, at the final thickness; - soft annealing of the finish-rolled aluminium alloy strip in a continuous furnace at temperatures above 500°C, preferably between 510°C and 540°C; The method is produced using the method having the following steps:

[0034] In addition to the particularly important selection of the aforementioned alloying elements of the present aluminum alloy, which influence the secondary phase density, the selection of the degree of cold rolling at a final thickness of 40% to 60% in conjunction with the aforementioned process characteristics and softening annealing of the finish-rolled aluminum alloy strip in a continuous furnace at temperatures above 500°C, preferably 510°C to 540°C, in conjunction with the alloy composition, is also important. 2 It has been found that these represent characteristics that ensure the provision of low secondary phase densities per 1000 .mu.m.

[0035] According to a further variant of the method according to the invention for producing the aluminum alloy strip, after hot rolling the following method steps are carried out: - cold rolling the hot-rolled aluminum alloy strip to an intermediate thickness determined so that the final cold reduction at the final thickness is between 40% and 60%, preferably between 50% and 60%; - intermediate annealing of aluminum alloy strip at 300℃~500℃; - cold rolling of the aluminum alloy strip to a reduction of 40% to 60%, preferably 50% to 60%, at the final thickness; - soft annealing of the finish-rolled aluminium alloy strip in a continuous furnace at temperatures above 500°C, preferably between 510°C and 540°C; is executed instead.

[0036] Whether the aluminum alloy strip is produced with or without an intermediate anneal, it has been surprisingly found that final cold rolling to final thickness combined with a softening anneal under stress in a continuous furnace produces a particular combination of properties for the present aluminum alloy strip. At the same time, softening annealing in a continuous furnace at the above temperatures achieves a grain size of 15 μm to 30 μm, which not only contributes to surprisingly good corrosion resistance but also promotes formability of the correspondingly produced aluminum alloy strip.

[0037] According to a further embodiment of the method according to the invention, the duration of the softening annealing of the finished aluminum alloy strip in the continuous furnace is between 5 and 300 seconds, preferably between 10 and 60 seconds. At the specified time, complete recrystallization of the microstructure can already be achieved in the continuous furnace, whereby the duration is also adapted to the respective thickness of the strip.

[0038] According to a further embodiment of the method, hot rolling of the rolled ingot comprises the steps of pre-rolling to a thickness of 30 mm to 40 mm at a starting temperature of at least 450° C. and finish rolling to a final hot strip thickness at a coiling temperature of 300° C. to 350° C. It has been shown that hot rolling can be advantageously optimized in terms of providing low secondary phase density, and following these parameters contributes to stable process control.

[0039] Finally, the aluminum alloy strip according to the present invention is preferably used for the production of interior body parts of automobiles, in particular door, hood or trunk cover interior parts. Interior body parts are often complexly shaped to provide the specific strength that provides the automobile body structure. This is why interior body parts are also produced from high-strength materials, such as the aluminum alloy in question. At the same time, however, it must also be possible to complexly shape these to provide interior body parts from as few individual components as possible. This eliminates additional work steps in terms of joining technology, such as joining or welding various components. At the same time, interior body parts are also exposed to corrosive conditions and therefore require good corrosion resistance.

[0040] The present aluminum alloy strip meets these conditions to a certain extent and is therefore ideally suited for this use.

[0041] Due to the optimized forming behavior of the aluminum alloy strip according to the invention without any reduction in strength and corrosion resistance, the aluminum alloy strip is optimally suited for the production of complexly shaped interior body parts.

[0042] The invention is described in more detail below using exemplary embodiments in connection with the drawings. [Brief explanation of the drawings]

[0043] [Figure 1] 1 shows a schematic flow diagram of a method for manufacturing an aluminum alloy strip according to the present invention. [Figure 2] In the figure, the secondary phase density / 1000 μm2 is shown as a function of the main shape change ε1 measured according to the Nakajima method on a 100 mm sample width. [Figure 3] A typical use of aluminum alloy strip in the form of an interior door part for an automobile, a so-called "body in white", is shown. [Figure 4]1 shows an etched cross-sectional surface of an aluminum alloy strip according to the present invention for assessing the total number of secondary phases. DETAILED DESCRIPTION OF THE INVENTION

[0044] 1 shows a schematic representation of the process steps and sequence of an exemplary embodiment of a process for producing aluminum alloy strip. In step 1, the following alloying elements are added, for example in DC continuous casting: Si≦0.10%, preferably ≦0.08%, Fe≦0.25%, preferably ≦0.20%, 0.20%≦Mn≦0.30%, preferably 0.20%≦Mn≦0.26%, 4.72%≦Mg≦4.95%, preferably 4.80%≦Mg≦4.92%, Cu≦0.10%, preferably Cu≦0.07%, particularly preferably Cu<0.04%, Cr≦0.02%, preferably Cr≦0.01%, particularly preferably Cr≦0.008%; Ni≦0.01%, preferably Ni≦0.005%, Zn≦0.10%, preferably Zn≦0.01%, particularly preferably Zn≦0.008%, Ti≦0.04%, preferably Ti≦0.02%, The balance is Al and incidental impurities of ≤ 0.05% individually and ≤ 0.15% in total; A rolling ingot is cast from an aluminum alloy having the following composition:

[0045] The rolled ingot is then subjected to homogenization in method step 2, which can be carried out in one or more stages. During homogenization, the temperature of the rolled ingot reaches 480°C to 550°C for at least 0.5 hours. Next, in method step 3, the rolled ingot is hot rolled. The final thickness of the hot strip is, for example, 3 mm to 6 mm. The final thickness of the hot strip can be selected so that only the cold rolling step 4 is carried out after hot rolling, in which the hot strip is reduced to the final thickness by 40% to 60%, preferably 50% to 60%. The cold-rolled aluminum alloy strip at the final thickness is then subjected to softening annealing. Softening annealing is carried out in a continuous furnace at temperatures above 500°C, preferably 510°C to 540°C.

[0046] As also shown in FIG. 1 , an alternative manufacturing method can be used in which the hot-rolled aluminum alloy strip is first cold-rolled to an intermediate thickness in step 4a. The intermediate thickness is determined so that the final reduction of the cold-rolled aluminum alloy strip to the final thickness is 40% to 60%, preferably 50% to 60%. The intermediate annealing of the aluminum alloy strip is carried out, for example, in a chamber furnace for at least 1.5 hours or in a continuous furnace for up to 300 seconds, preferably at 300°C to 500°C. The intermediate annealing in step 4b can be preferably carried out in a continuous furnace at 400°C to 500°C or in a chamber furnace at 330°C to 450°C. The cold rolling of the aluminum alloy strip to the final thickness is carried out in step 4c to a reduction of 40% to 60%, preferably 50% to 60%. The finish-rolled aluminum alloy strip is then soft-annealed in a continuous furnace in step 5 at a temperature above 500°C, preferably 510°C to 540°C.

[0047] To ensure comparability in forming behavior testing, various aluminum alloy strips were produced using this alternative manufacturing method by performing an intermediate anneal with a final thickness of 1.2 mm for the exemplary and comparative examples.

[0048] Table 1 shows various alloy compositions, all containing the balance aluminum and unavoidable impurities having a maximum of 0.05 wt. % individually and a maximum of 0.15 wt. % in total.

[0049] Comparative Examples 1, 2 and 7, like Exemplary Embodiments 3-6, have aluminum alloy compositions according to the present invention.

[0050] The manufacturing parameters for Exemplary Embodiments 1-7 are specified in Table 2. Homogenization of the rolled ingots was the same for all aluminum alloy strips produced, at 480°C-550°C for at least 0.5 hours. Pre-rolling of the rolled ingots, using a starting temperature of at least 450°C, was completed at a sheet thickness of 32 mm in Comparative Examples 1 and 7. Exemplary Embodiments 3-6 of the present invention were pre-rolled to a sheet thickness of 36 mm. In Comparative Examples 1, 2, and 7 and Exemplary Embodiments 3-6, hot rolling was completed at a coiling temperature of 300°C-350°C to a final hot strip thickness of 3 mm-6 mm.

[0051] Comparative Example 7 was cold rolled to a final reduction of 20% based on an intermediate annealing thickness of 1.5 mm, and Comparative Example 1 was cold rolled to a final reduction of 14.3%. Comparative Example 2 was produced to a final reduction of 50% and was soft annealed in a continuous furnace at 400°C for 300 seconds. Comparative Example 1 underwent the same annealing process for a duration of 60 seconds.

[0052] Exemplary embodiments 3-6 were annealed in a continuous furnace above 500° C., here 530° C., for 60 seconds, and then quenched in air, as were all other examples.

[0053] The test results are shown in Table 3. The Ae value was not determined for Comparative Example 7. Typical mechanical property values ​​for molding, herein uniform elongation Ag and elongation at break A 80mmThe comparison of the results does not show any obvious differences between the comparative example and the exemplary embodiment according to the invention. Nevertheless, the forming behavior of the comparative example and the exemplary embodiment in the manufacturing process of the complex-shaped component is fundamentally different, which difference is due to the differences in the microstructure. This is clearly shown by the study of the main shape change ε1 in a 100 mm sample width by the Nakajima method, measured in accordance with DIN EN ISO 120004-2.

[0054] The exemplary embodiments 3 to 6 according to the present invention achieve values ​​9% to almost 20% higher than the comparative examples. The results of the test of the main shape change ε1 in the 100 mm sample width are shown in Table 1. 2 This was reflected in the material by a significant decrease of less than 250 per 1000 kJ / mol. The secondary phase density was then determined by the method described above. Figure 2 shows the determined values ​​for comparison in a diagram.

[0055] 4 shows an etched longitudinal cross-sectional surface of an exemplary embodiment according to the present invention. After grinding and polishing the cross-section, the sample was etched in a dilute aqueous solution of sulfuric acid and hydrofluoric acid at room temperature for 1 minute. The solution contained 100 cm 3 It consists of 10% concentrated sulfuric acid and 100 cm 3 The solution was mixed with another solution of 60 cm 3 of water and 40cm 3 of 5% hydrofluoric acid and 100 cm 3 After etching, the longitudinal sections were rinsed with distilled water and dried for subsequent optical microscopy. Etching reveals a secondary phase.

[0056] The secondary phases were analyzed using an optical microscope with an oil lens at a magnification of 1000:1. This method allows the detection and counting of objects with a diameter of at least 0.39 μm. In the etching used, the actual secondary phase is dissolved, leaving behind pits whose size is significantly larger than the size of the dissolved secondary phase. This method can therefore be used to detect secondary phases significantly smaller than the optical resolution of 0.39 μm. A comparison of the optical-optical method used with scanning electron microscopy showed that phases from about 50 nm can be determined statistically reliably. The total area of ​​all measured regions examined was 20331 μm. 2 Figure 4 shows an example of one of the measurement areas.

[0057] The yield strength value of the exemplary embodiment of 120 MPa transverse to the rolling direction also indicated good suitability for the preferred use of aluminum alloy strip for automotive interior body parts. This also applies to the Ae measurements transverse to the rolling direction, which allow forming at 0.7% and 0.6%, respectively, without Lueders bands.

[0058] Table 3 does not show the results of particle size measurements, which gave an average particle size for an exemplary embodiment according to the present invention of 20 μm to 29 μm according to ASTM E1382. Table 3 does show the average particle size of 13.8 mg / cm3 measured after heat treatment at 195°C for 45 minutes according to ASTM G67. 2 ~18.8mg / cm 2 Nor do they show the results of corrosion tests that show mass loss.

[0059] Finally, Figure 3 shows a preferred use of the aluminum alloy strip, in which a sheet is separated from the aluminum alloy strip and an interior part for an automobile body in the form of a door interior part 6 is produced by forming, for example, drawing. These are usually produced from steel. The aluminum alloy strip according to the present invention is therefore preferably used for the production of interior body parts due to its improved forming behavior with the same strength and corrosion resistance.

[0060] Table 1

[0061] Table 2

[0062] Table 3

Claims

1. The following composition in mass %: Si≦0.10%, Fe≦0.25%, 0.20%≦Mn≦0.30%, 4.72%≦Mg≦4.95%, Cu≦0.10%, Cr≦0.02%, Ni≦0.01%, Zn≦0.10%, Ti≦0.04%, the balance being Al and unavoidable impurities individually ≦0.05% and in total ≦0.15%; An aluminum alloy strip comprising an aluminum alloy having The aluminum alloy strip has a thickness of 250 / 1000 μm. ２ and the average secondary phase density is the result of a total number of secondary phases determined over a total measurement surface of all examined measurement areas in at least 10 measurement areas. Aluminum alloy strip.

2. The aluminum alloy strip has one or more alloying elements, in mass %, of: Si≦0.08%, Fe≦0.20%, 0.20%≦Mn≦0.26%, 4.80%≦Mg≦4.92%, Cu≦0.07%, or <0.04%, Cr≦0.01%, or ≦0.008%, Ni≦0.005%, Zn≦0.01%, or ≦0.008%, 0.005%≦Ti≦0.02%, 2. The aluminum alloy strip of claim 1, wherein

3. The aluminum alloy strip is 220 / 1000 μm ２ Less than or 200 / 1000 μm ２ 3. An aluminium alloy strip according to claim 1 or 2, characterized in that it has an average secondary phase density of less than

4. 2. The aluminum alloy strip of claim 1, wherein the aluminum alloy strip has a microstructural state of O or H111.

5. 2. The aluminum alloy strip according to claim 1, wherein the aluminum alloy strip has an average grain size of 15 μm to 30 μm as measured in accordance with ASTM E1382.

6. The aluminum alloy strip of claim 1, wherein the aluminum alloy strip is cold rolled and optionally has a thickness of 0.5 mm to 4 mm.

7. 2. The aluminum alloy strip according to claim 1, wherein the aluminum alloy strip has an Ae value according to DIN EN ISO 6892 transverse to the rolling direction of less than 1.0%, or less than 0.9%.

8. 2. The aluminum alloy strip according to claim 1, wherein the aluminum alloy strip having a sheet thickness of 1.2 mm has, in a test according to the Nakajima method, a mean main shape change ε1 of greater than 0.200 in accordance with DIN EN ISO 120004-2 with a sample width of 100 mm.

9. 2. Aluminium alloy strip according to claim 1, characterized in that the aluminium alloy strip has a yield strength Rp0.2 transverse to the rolling direction according to DIN EN ISO 6892 of at least 115 MPa, or at least 120 MPa.

10. 10. A method for producing the aluminum alloy strip of claim 1, comprising: The method comprises the steps of: - the following composition: Si≦0.10%, or ≦0.08%, Fe≦0.25%, or ≦0.20%, 0.20%≦Mn≦0.30%, or 0.20%≦Mn≦0.26%, 4.72%≦Mg≦4.95%, or 4.80%≦Mg≦4.92%, Cu≦0.10%, or Cu≦0.07%, or Cu<0.04%, Cr≦0.02%, or Cr≦0.01%, or Cr≦0.008%, Ni≦0.01%, or Ni≦0.005%, Zn≦0.10%, or Zn≦0.01%, or Zn≦0.008%, Ti≦0.04%, or Ti≦0.02%, the balance being Al and unavoidable impurities individually ≦0.05% and in total ≦0.15%; Casting of rolled ingots from an aluminum alloy having - homogenization of said rolled ingot at 480°C to 550°C for at least 0.5 hours; - hot rolling of said rolled ingot to a final hot strip thickness of 3 mm to 6 mm; - cold rolling of said aluminium alloy strip to a reduction of 40% to 60%, or 50% to 60% at final thickness; and - soft annealing of finish-rolled aluminium alloy strip in a continuous furnace at temperatures above 500°C or between 510°C and 540°C; A method having the following.

11. After hot rolling, the following method steps: - cold rolling the hot rolled aluminium alloy strip to an intermediate thickness determined so as to provide a final cold reduction at final thickness of between 40% and 60%, or between 50% and 60%; - an intermediate annealing of said aluminium alloy strip at 300°C to 500°C; - cold rolling of said aluminium alloy strip to a reduction of 40% to 60%, or 50% to 60% at final thickness; - soft annealing of finish-rolled aluminium alloy strip in a continuous furnace at temperatures above 500°C or between 510°C and 540°C; The method of claim 10, wherein:

12. 12. A method according to claim 10 or 11, characterized in that the duration of the soft annealing of the finished aluminium alloy strip in the continuous furnace is between 5 seconds and 300 seconds.

13. 11. The method according to claim 10, characterized in that the hot rolling of the rolled ingot comprises a step of pre-rolling to a thickness of 30 mm to 40 mm at a starting temperature of at least 450°C, and a step of finish hot rolling to a final hot strip thickness at a recoiling temperature of 300°C to 350°C.

14. 10. Use of the aluminum alloy strip according to claim 1 for manufacturing interior bodywork parts of an automobile.

15. The use of the aluminum alloy strip according to claim 14, wherein the automobile body interior part is a door interior part, a bonnet interior part or a trunk cover interior part.

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