Deformed and optimized aluminum alloy strip and manufacturing method

Abstract

The present invention relates to an aluminum alloy strip made of aluminum alloy, a method for manufacturing the aluminum alloy strip and its preferred applications. The aim is to provide an aluminum alloy strip, especially for manufacturing motor vehicle body parts, preferably interior body parts, which, in addition to providing the necessary resistance to intergranular corrosion, also provides the necessary strength and simultaneously improved deformation characteristics. The above aim is achieved in such a way that the aluminum alloy strip has an aluminum alloy with the following composition by weight: 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 each ≤ 0.05% and in total ≤ 0.15%, wherein the average secondary phase density of the aluminum alloy strip is less than 250 / 1000 μm 2 , where the average secondary phase density is obtained from the total number of secondary phases measured in at least 10 measurement areas relative to the total measurement area of all the investigated measurement areas.

Description

Field of the Invention

[0001] The present invention relates to an aluminum alloy strip made of aluminum alloy, a method for manufacturing the aluminum alloy strip, and its preferred applications. Background Art

[0002] In particular, AA 5xxx series aluminum-magnesium (AlMg) alloys in the form of sheets or strips are used for constructing welded or joined components in shipbuilding, automotive, and aircraft manufacturing. With increasing magnesium content, aluminum-magnesium alloys are characterized by high strength and, in addition, increased deformability when the magnesium content exceeds 3%. Therefore, AA 5xxx series aluminum-magnesium alloys can gradually replace steel materials in vehicle manufacturing, for example, and thus contribute to further weight reduction of vehicles.

[0003] When exposed to higher temperatures, AA 5xxx series AlMg alloys with a Mg content exceeding 3%, especially exceeding 4%, tend to suffer more intergranular corrosion. At temperatures between 70 - 200 °C, the non-noble metal Al5Mg3 phase precipitates along the grain boundaries. These phases are called β particles and can be selectively dissolved in the presence of a corrosive medium. As a result, the AA 5182 aluminum alloy (Al 4.5% Mg 0.4% Mn), which especially has very good strength properties and very good deformability, is not used in areas with thermal loads as long as the presence of a corrosive medium, such as water in the form of moisture, must be taken into account. This especially applies to components of motor vehicles, which are usually subjected to cathodic dip painting (KTL) and then dried during the baking process, since sensitization with respect to intergranular corrosion can already be caused by this baking process in common aluminum alloy strips. In addition, for use in the automotive field, the deformation during component manufacturing and the subsequent operating loads of the components must be considered.

[0004] An aluminum alloy strip is known from international patent application WO 2014 / 0298531 Al, which has a magnesium content higher than four weight percent and is suitable for components of motor vehicles. Although it provides high strength, it has very good intergranular corrosion resistance. However, it has been found that the deformability of this aluminum alloy strip made of AA 5182 aluminum alloy, which is especially resistant to intergranular corrosion, can be improved.

[0005] Therefore, a further improvement solution regarding the deformability of such an aluminum alloy strip is known from international patent application WO 2014 / 029856 Al. Here, within an almost identical alloy concept, the aluminum alloy strip is optimized with respect to deformability. Both international patent applications relate to aluminum strips having a maximum Mg content of 4.50 weight percent within the AA 5182 aluminum alloy specification.

[0006] Japanese Patent Application JP 2001 303164 A discloses an AA5xxx type aluminum alloy, and the secondary phase density thereof is measured for secondary phases with a maximum length of at least 3 μm or greater.

[0007] International Patent Application WO 2016 / 207274 A1 discloses an annealed aluminum alloy strip and a method for manufacturing the same.

[0008] According to US Patent Application US2020 / 0157668 A1, a softened annealed aluminum alloy strip is known, and the secondary phase density thereof is maximized for copper-containing secondary phases with an equivalent circle diameter of 0.3 μm to 4 μm.

[0009] It has now been determined that there is potential for further improvement in terms of deformability within the specifications of AA 5182 type aluminum alloy without reducing other properties such as providing necessary strength and corrosion resistance. It has been confirmed here that for the usual characteristic values of deformability, such as the uniform elongation Ag or the fracture elongation value A 80mm , it is not sufficiently persuasive for the actual use of aluminum alloy sheets during the deformation process.

[0010] Test conditions are given by means of Standard DIN EN ISO 12004-2:2021-07, and these test conditions allow conclusions to be drawn about the allowable main shape changes and secondary shape changes of the aluminum sheet during the deformation process, so that a reliable deformation process can be provided. The main shape changes and secondary shape changes obtained according to this standard are generated by a limit shape change curve, and this limit shape change curve characterizes the specific performance of the sheet to be deformed in the tensile test. By analyzing the shape changes of the damaged tensile component to determine the shape change diagram related to the tensile component and the deformation process, the limit shape change curve is provided.

[0011] On a sample with a specific geometry, a deterministic grid or random pattern with precise dimensions is applied or optically projected onto the undeformed surface. Then, for example, according to the Nakajima method, a specific sample component to be cut is deformed until it tears with a precisely determined matrix by means of a defined punch, and then the test is interrupted. All values of the main shape change ε1 mentioned herein are tested according to the Nakajima method in accordance with EN ISO 12004-2:2021-07. Here, the main shape change ε1 is determined on a sample with a width of 100 mm. All values given are the average values of 3 samples.

[0012] All other mechanical characteristic values are measured according to DIN EN ISO 6892. Since the grain size of the material always exists in a distributed form, all provided grain size data are based on the average grain size. The average grain size can be obtained according to ASTM E1382. Summary of the Invention

[0013] The object of the present invention is to provide an aluminum alloy strip, in particular for manufacturing motor vehicle body components, preferably interior body components, which, in addition to providing the necessary resistance to intergranular corrosion, also provides the necessary strength and simultaneously improved deformation properties.

[0014] According to a first teaching of the present invention, the above object is achieved by providing an aluminum alloy strip having an aluminum alloy with the following composition in % by weight:

[0015] Si ≤ 0.10%,

[0016] Fe ≤ 0.25%,

[0017] 0.20% ≤ Mn ≤ 0.30%,

[0018] 4.72% ≤ Mg ≤ 4.95%,

[0019] Cu ≤ 0.10%,

[0020] Cr ≤ 0.02%,

[0021] Ni ≤ 0.01%,

[0022] Zn ≤ 0.10%,

[0023] Ti ≤ 0.04%,

[0024] the balance being Al and unavoidable impurities each ≤ 0.05% and in total ≤ 0.15%, wherein the average secondary phase density of the aluminum alloy strip is less than per 1000 μm 2 250.

[0025] In in-depth research, the inventors have recognized that in an aluminum alloy strip comprising the above aluminum alloy, by limiting the secondary phase density to less than per 1000 μm 2 250, a favorable increase in deformability can be achieved while maintaining the advantages of AA 5182-type aluminum alloy in terms of corrosion resistance and mechanical strength of the aluminum alloy strip. As secondary phases, Al6Mn, alpha-Al(Fe,Mn)Si and Mg2Si usually occur. According to the inventors' recognition, a large amount of secondary phases results in limited deformation behavior and is particularly noticeable in complex deep drawing processes for manufacturing, for example, body components. By selecting a specific alloy composition in combination with a similarly specific manufacturing process, the secondary phase density can be reduced to a value below per 1000 μm 2 250.

[0026] In this document, the secondary phase density, i.e., the (area) density of the disperse phase, is determined in the following manner using an optical microscope. A sample of the aluminum alloy strip to be studied is embedded in a longitudinal grinding section and prepared by the commonly used metallographic method. After the grinding section is ground and polished, the sample is etched for one minute at room temperature in a diluted aqueous solution of sulfuric acid and hydrofluoric acid. For this purpose, a 10% concentrated sulfuric acid solution of 100 cm 3 is mixed with another solution of 100 cm 3 , which consists of 60 cm 3 of water and 40 cm 3 of 5% hydrofluoric acid. After etching, the grinding section is rinsed with distilled water and dried for subsequent optical microscopic studies. The etching performed marks the secondary phase in the microstructure, enabling its areal density to be determined with good precision in an optical microscope. To ensure sufficient statistical relevance, at least 10 statistically distributed image segments serving as measurement areas are analyzed using an oil immersion lens in an optical microscope at a high magnification (1000:1), so that a total of at least 2000 secondary phases are detected. The total number of secondary phases obtained (relating to the total measurement area of all the studied measurement areas) then yields the areal density or secondary phase density of the secondary phase (given as the number per unit area, e.g., the number per 1000 μm 2 ).

[0027] In the alloy composition, for this purpose, the silicon content is reduced to a maximum of 0.10 wt%. In aluminum alloys containing magnesium, silicon forms alpha-Al(Fe,Mn)Si as well as Mg2Si precipitates as secondary phases. As described above, these impair the deformability of the aluminum alloy strip. Therefore, a preferred silicon content is a maximum of 0.08 wt%.

[0028] Iron is mainly bound in the so-called casting phase but also participates in the formation of secondary precipitates. Therefore, reducing the iron content to a maximum of 0.25 wt%, preferably a maximum of 0.20 wt%, contributes to improving the deformability.

[0029] Manganese is a typical disperse phase former, where the disperse phase particles effectively prevent the atoms from performing displacement movements from the metal crystal bonds. Therefore, the disperse phase contributes to the increase in the desired yield limit. In addition, the Mn-containing disperse phase contributes to controlling the grain size of the aluminum alloy strip. However, the disperse phase particles limit the deformation behavior. Therefore, the aluminum alloy strip has a Mn content of 0.20 wt% to 0.30 wt%. When the Mn content is below 0.20 wt%, the strength enhancing effect of the disperse phase is reduced, and the aluminum alloy strip may exhibit an undesired grain growth during the heat treatment process. When the manganese content is greater than 0.30 wt%, the disperse phase hinders the elongation of the material too strongly, such that the deformation behavior is not optimal. A Mn content of 0.20 wt% ≤ Mn ≤ 0.26 wt% can provide an optimized Mn content in terms of the deformation behavior.

[0030] Magnesium is contained in the aluminum alloy of the present invention in an amount of 4.72% to 4.95% by weight, preferably 4.80% to 4.92% by weight. It has been found that precisely through this magnesium content, not only is high strength achieved even when the proportion of the strengthening dispersoid formation is reduced, but at the same time the deformation behavior is improved. However, as described above, a higher Mg content leads to high sensitivity of the material to intergranular corrosion.

[0031] To optimize the deformation behavior, the copper content is also limited to a maximum of 0.10% by weight. Copper increases the strength of the aluminum alloy strip even in small amounts, but also causes deterioration of the general corrosion behavior even in small amounts. Therefore, the preferred copper content is a maximum of 0.07% by weight, particularly preferably at least 0.02% and less than 0.04% by weight.

[0032] The alloying element chromium is a very effective dispersoid former and is therefore present in the aluminum alloy in an amount of at most 0.02% by weight, preferably 0.01% by weight, particularly preferably at most 0.008% by weight.

[0033] Since dispersoid particles tend to form even in the smallest amounts, the same applies to the nickel content. Therefore, the Ni content is reduced to a maximum of 0.01% by weight, preferably to 0.005% by weight.

[0034] Zinc has an adverse effect on the corrosion resistance of the aluminum alloy strip and is present in the aluminum alloy in an amount of at most 0.10% by weight, preferably at most 0.01% by weight, particularly preferably at most 0.008% by weight.

[0035] Titanium for grain refinement during melting should be limited to a maximum of 0.04% by weight, preferably a maximum of 0.02% by weight, because titanium also forms dispersoids and strongly tends to segregate at higher concentrations. Since, for example, titanium from the grain refiner contributes to the melting process and thus improves the casting of the rolled ingot, a titanium content of 0.005% to a maximum of 0.02% by weight is preferably provided in the aluminum alloy. A compromise between the melting characteristics and the amount of secondary precipitation can be achieved with this range of titanium.

[0036] According to a first embodiment of the aluminum alloy strip, the aluminum alloy strip has a secondary phase density of less than 220 per 1000 μm 2 and particularly preferably less than 200 per 1000 μm 2 . It can be confirmed that by selecting the combination of aluminum alloying elements and the manufacturing process of the aluminum alloy strip, a further reduction in the secondary phase density in the aluminum alloy strip can be achieved. Here, these aluminum alloy strips show a further improvement in the deformation behavior while providing high mechanical strength and good corrosion resistance.

[0037] This aluminum alloy strip has very good deformation characteristics in the microstructure state O or H111. The microstructure state O is characterized by a recrystallized microstructure, which enables maximum deformation. In the state H111, the aluminum alloy strip in the state O has been slightly solidified, for example, by stretching or straightening the aluminum alloy strip. Therefore, it is preferred to use the state H111 when processing aluminum alloy sheets, because the aluminum alloy sheets have small distortions here and still obtain particularly high deformation values.

[0038] Further studies have shown that, according to another design, the aluminum alloy strip has an average grain size of 15 μm to 30 μm. It has been found that the corrosion resistance of the aluminum alloy with the alloy composition of the present invention at a grain size of 15 μm to 30 μm meets the requirements for body applications. At the same time, the smaller grain size contributes to improved deformability.

[0039] The aluminum alloy strip is preferably cold-rolled to provide the necessary shape accuracy and surface quality for preferred applications in motor vehicle manufacturing.

[0040] According to a design, the final thickness of the cold-rolled aluminum alloy strip is 0.5 mm to a maximum of 4 mm, preferably 0.8 mm to 2.5 mm. Especially within these mentioned thickness ranges, the aluminum alloy strip can provide significantly improved deformation characteristics in combination with traditional deformation methods and tools.

[0041] According to another embodiment of the aluminum alloy strip, the aluminum alloy strip has an Ae value of less than 1.0%, preferably less than 0.9%, transverse to the rolling direction. The Ae value is also known as the yield limit - extensometer - strain. The Ae value transverse to the rolling direction is measured according to DIN EN ISO 6892 and is expressed in %. Here, the Ae value of the aluminum alloy strip characterizes the formation of Lüders bands during the deformation of the aluminum alloy strip, and these Lüders bands are not desired, for example, in body components. The smaller the Ae value, the fewer Lüders bands are generated. With a value of less than 1.0% or less than 0.9% transverse to the rolling direction, the aluminum alloy strip can be called substantially Lüders band-free.

[0042] Finally, according to DIN EN ISO 120004-2, in the case of a sheet thickness of 1.2 mm and a sample width b) of 100 mm, an embodiment of the aluminum alloy strip according to the invention has an average principal shape change ε1 greater than 0.200 in the Nakajima test. In the aluminum alloy strip according to the invention, this principal shape change value can be achieved by setting a reduced secondary phase density while considering a manufacturing method coordinated with the material. The principal shape change ε1 according to Nakajima with a sample width b) of 100 mm represents the complex interaction of the microstructure of the aluminum alloy strip during the stretching process with a single parameter, and shows a significant increase compared to the principal shape change ε1 obtained so far for the deformation-optimized AA 5182 type aluminum alloy strip. For all values given here, the data for a sample width of 100 mm relate to the values b) of a sample with an axially parallel recess length a) according to DIN EN ISO120004-2 Figure 2 (6.1.2 Sample geometry).

[0043] At the same time, according to another design, the aluminum alloy strip is provided in the as-cast or H111 condition with a yield limit R of at least 115 MPa, preferably at least 120 MPa, transverse to the rolling direction p0.2 , so that the strength requirements in vehicle manufacturing are also met by the deformation-optimized aluminum alloy strip.

[0044] After being kept at a thermal load of 195 °C for 45 minutes and measured according to ASTM G67, the mass loss of the aluminum alloy strip due to intergranular corrosion is 13 mg / cm 2 to 19 mg / cm 2 . This thermal load corresponds to the maximum thermal load that a component can experience in the KTL painting process and thus shows that no corrosion problems are expected during the subsequent use of the component.

[0045] According to another teaching of the invention, the aluminum alloy strip according to the invention is manufactured using a method comprising the following steps:

[0046] - Casting and rolling an ingot of an aluminum alloy having the following composition:

[0047] Si ≤ 0.10%, preferably ≤ 0.08%,

[0048] Fe ≤ 0.25%, preferably ≤ 0.20%,

[0049] 0.20% ≤ Mn ≤ 0.30%, preferably 0.20% ≤ Mn ≤ 0.26%,

[0050] 4.72% ≤ Mg ≤ 4.95%, preferably 4.80% ≤ Mg ≤ 4.92%,

[0051] Cu ≤ 0.10%, preferably Cu ≤ 0.07, particularly preferably Cu < 0.04%,

[0052] Cr ≤ 0.02%, preferably Cr ≤ 0.01, particularly preferably Cr ≤ 0.008%,

[0053] Ni ≤ 0.01%, preferably Ni ≤ 0.005%,

[0054] Zn ≤ 0.10%, preferably Zn ≤ 0.01%, particularly preferably Zn ≤ 0.008%,

[0055] Ti ≤ 0.04%, preferably Ti ≤ 0.02%,

[0056] The balance is Al and unavoidable impurities, each ≤ 0.05% and the total ≤ 0.15%,

[0057] - Homogenize the rolled ingot at 480 °C to 550 °C for at least 0.5 hours,

[0058] - Hot-roll the rolled ingot to a final thickness of 3 to 6 mm for the hot-rolled strip,

[0059] - Cold-roll the aluminum alloy strip to the final thickness with a rolling reduction of 40% to 60%, preferably 50% to 60%, and

[0060] - Soft-anneal the finished-rolled aluminum alloy strip in a continuous furnace at a temperature above 500 °C, preferably 510 °C to 540 °C.

[0061] In addition to the alloy composition of the aluminum alloy, which is particularly critical and responsible for the secondary phase density, it has been confirmed that, in combination with the alloy composition, the method features and the rolling reduction for cold-rolling to the final thickness are selected to be 40% to 60%, combined with soft-annealing the finished-rolled aluminum alloy strip in a continuous furnace at a temperature greater than 500 °C, preferably at 510 °C to 540 °C, which constitutes the characteristics for ensuring a low secondary phase density per 1000 μm 2 of the secondary phase density.

[0062] According to another variant of the method for manufacturing an aluminum alloy strip according to the present invention, the following method steps are alternatively carried out after hot-rolling:

[0063] - Cold-roll the hot-rolled aluminum alloy strip to an intermediate thickness, which is determined such that the final rolling reduction to the final thickness is 40% to 60%, preferably 50% to 60%,

[0064] - Intermediate-anneal the aluminum alloy strip at 300 °C to 500 °C,

[0065] - Cold roll the aluminum alloy strip to the final thickness with a rolling reduction of 40% to 60%, preferably 50% to 60%.

[0066] - Soft anneal the rolled aluminum alloy strip in a continuous furnace at a temperature above 500 °C, preferably 510 °C to 540 °C.

[0067] Regardless of whether the aluminum alloy strip is manufactured through intermediate annealing, it has been found that the final cold rolling to the final thickness combined with the required soft annealing in a continuous furnace surprisingly produces a special combination of properties of the aluminum alloy strip. At the same time, a grain size of 15 μm to 30 μm is achieved through soft annealing in the continuous furnace at the said temperature, which not only contributes to the unexpectedly good corrosion resistance of the correspondingly manufactured aluminum alloy strip, but also promotes the deformation properties.

[0068] In another embodiment of the method according to the invention, the duration of the soft annealing of the finished aluminum alloy strip in a continuous furnace is between 5 seconds and 300 seconds, preferably aiming for an interval of 10 seconds to 60 seconds. During this time, complete recrystallization of the microstructure can already be achieved in the continuous furnace, and the duration is also matched to the corresponding thickness of the strip.

[0069] According to another design of the method, the hot rolling of the ingot includes the following steps: pre-roll to a thickness of 30 mm to 40 mm at an initial temperature of at least 450 °C; and complete rolling to the final thickness of the hot-rolled strip at a coiling temperature of 300 °C to 350 °C. It has been shown that with these parameters maintained, the hot rolling can be advantageously optimized in terms of providing a small secondary phase density and contributing to stable process control.

[0070] Finally, the aluminum alloy strip according to the invention is preferably used for manufacturing interior body parts of a motor vehicle, in particular door interior parts, hood interior parts or trunk lid interior parts. Interior body parts are usually complexly deformed to provide specific strength, thereby providing the motor vehicle body structure. Therefore, interior body parts are also made of high-strength materials such as the said aluminum alloy. But at the same time, they must also be able to be complexly formed so that the interior body parts can be provided by as few individual components as possible. This saves additional work steps in connection technology, such as the joining or welding of different components. At the same time, interior body parts are also exposed to corrosive conditions, thus also requiring good corrosion resistance. The aluminum alloy strip meets these conditions to a special extent, so it is particularly suitable for this application.

[0071] Due to the optimized deformation performance of the aluminum alloy strip according to the invention without loss of strength and corrosion resistance, the aluminum alloy strip is optimally suitable for manufacturing complexly formed interior body parts. Description of the Drawings

[0072] The present invention will be described below in connection with embodiments with reference to the accompanying drawings. The drawings show:

[0073] Figure 1 A schematic flow chart showing the manufacturing method of the aluminum alloy strip of the present invention,

[0074] Figure 2 The relationship between the secondary phase density / lOOOμm in the case of a 100 mm sample width according to the Nakajima method and the measured main shape change εl is shown in the chart, 2 And the relationship with the measured main shape change εl,

[0075] Figure 3 Typical applications of the aluminum alloy strip in the form of door interior components of motor vehicles, the so-called "white body", and

[0076] Figure 4 An etched grinding surface of the aluminum alloy strip according to the present invention is shown for analyzing the total number of secondary phases. Detailed embodiments

[0077] Figure 1 The method steps and processes of an embodiment of the method for manufacturing an aluminum alloy strip are schematically shown. In step 1, for example, a rolling ingot is cast from an aluminum alloy having the following alloy components by DC continuous casting:

[0078] Si ≤ 0.10%, preferably ≤ 0.08%,

[0079] Fe ≤ 0.25%, preferably ≤ 0.20%,

[0080] 0.20% ≤ Mn ≤ 0.30%, preferably 0.20% ≤ Mn ≤ 0.26%,

[0081] 4.72% ≤ Mg ≤ 4.95%, preferably 4.80% ≤ Mg ≤ 4.92%,

[0082] Cu ≤ 0.10%, preferably Cu ≤ 0.07, particularly preferably Cu < 0.04%,

[0083] Cr ≤ 0.02%, preferably Cr ≤ 0.01, particularly preferably Cr ≤ 0.008%,

[0084] Ni ≤ 0.01%, preferably Ni ≤ 0.005%,

[0085] Zn ≤ 0.10%, preferably Zn ≤ 0.01%, particularly preferably Zn ≤ 0.008%,

[0086] Ti ≤ 0.04%, preferably Ti ≤ 0.02%,

[0087] The balance is Al and unavoidable impurities with a maximum of 0.05% each and a total maximum of 0.15%.

[0088] Subsequently, in method step 2, the rolled ingot is subjected to homogenization, which can be carried out in one or more stages. During homogenization, the temperature of the rolled ingot reaches 480 to 550 °C for at least 0.5 hours. Then in method step 3, the rolled ingot is hot-rolled. The final thickness of the hot-rolled strip is, for example, 3 to 6 mm. The final thickness of the hot-rolled strip can be selected such that only one cold rolling step 4 is carried out after hot rolling, in which the thickness of the hot-rolled strip is reduced to the final thickness with a rolling reduction of 40% to 60%, preferably 50% to 60%. Then, the aluminum alloy strip that has been cold-rolled to the final thickness is subjected to softening annealing. The softening annealing is carried out in a continuous furnace at a temperature above 500 °C, preferably at 510 °C to 540 °C.

[0089] Similarly, as Figure 1 shown, an alternative manufacturing path can also be used, in which, first, the hot-rolled aluminum alloy strip is cold-rolled to an intermediate thickness in step 4a. The intermediate thickness is determined such that the final rolling reduction to the final thickness is 40% to 60%, preferably 50% to 60%. The intermediate annealing of the aluminum alloy strip is preferably carried out at 300 °C to 500 °C, for example, for at least 1.5 hours in a box furnace or for at most 300 seconds in a continuous furnace. The intermediate annealing in step 4b can preferably be carried out in a continuous furnace at 400 °C to 500 °C, or in a box furnace at 330 °C to 450 °C. In step 4c, the aluminum alloy strip is cold-rolled to the final thickness with a rolling reduction of 40% to 60%, preferably 50% to 60%. Then in step 5, the finished-rolled aluminum alloy strip is subjected to softening annealing in a continuous furnace at a temperature above 500 °C, preferably at 510 °C to 540 °C.

[0090] Different aluminum alloy strips are manufactured by an alternative manufacturing path with intermediate annealing, where the final thickness of the examples and comparative examples is 1.2 mm to ensure comparability of the formability tests.

[0091] The different alloy compositions are shown in Table 1, where in all compositions, aluminum and unavoidable impurities with a maximum of 0.05% by weight each and a total maximum of 0.15% by weight are additionally included as "the balance".

[0092] Similar to Examples 3 to 6, Comparative Examples 1, 2, and 7 include the aluminum alloy composition according to the present invention.

[0093] The manufacturing parameters of Examples 1 to 7 are given in Table 2. The homogenization of the rolled ingots is consistent for all the produced aluminum alloy strips and is at least 0.5 hours at 480°C to 550°C. In Comparative Examples 1 and 7, the pre-rolling of the rolled ingots was ended at a starting temperature of at least 450°C when the slab thickness was 32 mm. Examples 3 to 6 of the present invention were pre-rolled to a slab thickness of 36 mm. In Comparative Examples 1, 2 and 7 and Examples 3 to 6, the hot rolling was ended at a final hot-rolled strip thickness of 3 to 6 mm at a coiling temperature of 300 to 350°C.

[0094] Comparative Example 7 was cold-rolled from an intermediate annealing thickness of 1.5 mm to the final thickness with the last 20% rolling reduction, and Comparative Example 1 was cold-rolled to the final thickness with a rolling reduction of 14.3%. Comparative Example 2 was manufactured with a rolling reduction to the final thickness of 50% and was softened and annealed at 400°C for 300 seconds in a continuous furnace. The same annealing process for Comparative Example 1 lasted for 60 seconds.

[0095] Examples 3 to 6 were annealed at a temperature higher than 500°C, here at 530°C for 60 seconds in a continuous furnace, and then air quenched as in all other examples.

[0096] The test results are shown in Table 3. For Comparative Example 7, no Ae value was obtained. There is no clear difference in the comparison of the conventional mechanical property values of the deformation (here the uniform elongation Ag and the fracture elongation A 80mm ) between the comparative examples and the examples according to the present invention. However, the deformation performances of the comparative examples and the examples are in principle different during the manufacturing process of complex-shaped components, which is attributed to the difference in the microstructure. This is clearly shown by the study of the main shape change ε1 measured in the Nakajima manner according to DIN EN ISO 120004-2 with a sample width of 100 mm.

[0097] Here, Examples 3 to 6 of the present invention reach values between 9% higher and nearly 20% higher compared to the comparative examples. The test results of the main shape change ε1 with a sample width of 100 mm are reflected in the material where the secondary phase density is significantly reduced to less than 250 per 1000 μm 2 . Here, the secondary phase density is obtained according to the method given above. Figure 2 The obtained values are shown here for comparison in the graph.

[0098] Figure 4 An etched longitudinal ground surface according to an example of the present invention is shown. After the sample was ground and polished on a grinding disc, it was etched by etching for 1 minute at room temperature in a diluted aqueous solution of sulfuric acid and hydrofluoric acid. The solution consisted of 100 cm 3 of 10% concentrated sulfuric acid and 100 cm 3 of additional 60 cm3 of water and 40 cm 3 consisting of a solution composed of 5% hydrofluoric acid. After etching, the longitudinal ground section was rinsed with distilled water and dried for subsequent optical microscopic studies. The etching marked the secondary phase.

[0099] The secondary phase was analyzed with an optical microscope with an oil immersion lens at a magnification of 1000:1. With this method, objects with a diameter of at least 0.39 μm could be detected and counted. When using etching, the actual secondary phase was extracted, and etching pits with dimensions significantly larger than the size of the extracted secondary phase remained. Thus, with this method, the secondary phase could be clearly detected at an optical resolution of 0.39 μm. A comparison of the optical method used with scanning electron microscopic studies showed that phases starting from approximately 50 nm could be determined statistically reliably. The total area of all the examined measurement areas was 20331 μm 2 . In Figure 4 one of the measurement areas is shown exemplarily.

[0100] The yield limit value of 120 MPa transverse to the rolling direction in the example also showed good suitability of the aluminum alloy strip for the preferred application in motor vehicle body interior parts. This also applies to the Ae value measured transverse to the rolling direction, which achieved deformation without Lüder's bands at 0.7% or 0.6%.

[0101] The grain size measurement results are not shown in Table 3, which show an average grain size of 20 μm to 29 μm according to ASTM E 1382 for the examples according to the invention. The corrosion test results are also not shown in Table 3, which show a mass loss of 13.8 mg / cm measured according to ASTM G67 after a heat treatment at 195 °C for 45 minutes 2 to 18.8 mg / cm 2 .

[0102] Finally, Figure 3 the preferred application of the aluminum alloy strip is shown schematically, where a sheet is separated from the aluminum alloy strip and interior parts of a motor vehicle body in the form of door interior parts 6 are manufactured by deformation, such as deep drawing. Usually, these interior parts are made of steel. Therefore, due to the improved deformation behavior while maintaining strength and corrosion resistance, the aluminum alloy strip according to the invention is preferably used for manufacturing body interior parts.

[0103] Table 1

[0104] number Si Fe Cu Mn Mg Cr Ni Zn Ti Comparative Example 1 0.08％ 0.18％ 0.0270％ 0.23％ 4.84％ 0.0016％ 0.0049％ 0.0040％ 0.0120％ Comparative Example 2 0.08％ 0.22％ 0.0801％ 0.28％ 4.75％ 0.0078％ 0.0045％ 0.0081％ 0.0170％ The present invention 3 0.06％ 0.16％ 0.0302％ 0.26％ 4.86％ 0.0029％ 0.0045％ 0.0099％ 0.0129％ The present invention 4 0.08％ 0.17％ 0.0227％ 0.24％ 4.90％ 0.0036％ 0.0045％ 0.0062％ 0.0130％ The present invention 5 0.07％ 0.17％ 0.0233％ 0.23％ 4.80％ 0.0043％ 0.0049％ 0.0051％ 0.0145％ The present invention 6 0.07％ 0.17％ 0.0245％ 0.25％ 4.82％ 0.0022％ 0.0043％ 0.0047％ 0.0145％ Comparative Example 7 0.07％ 0.22％ 0.0754％ 0.29％ 4.73％ 0.0052％ 0.0000％ 0.0071％ 0.0135％

[0105] Table 2

[0106]

[0107] Table 3

[0108]

Claims

1. An aluminum alloy strip, the aluminum alloy strip having an aluminum alloy with the following composition by weight percentage: 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 each ≤ 0.05% and in total ≤ 0.15%, wherein the average secondary phase density of the aluminum alloy strip is less than 250 / 1000μm 2 , wherein The aluminum alloy strip samples were embedded in longitudinal grinding slices and prepared by metallographic method. After grinding and polishing, the grinding slices were placed at 100 cm 3 10% concentrated sulfuric acid solution with 100cm 3 From 60cm 3 of water and 40cm 3 The sample is etched at room temperature for one minute in a diluted aqueous solution obtained by mixing with another solution consisting of 5% hydrofluoric acid. After etching, the polished piece is rinsed with distilled water and dried. Then, at least 10 statistically distributed image segments as the measurement area are analyzed using an optical microscope using an oil objective at a high magnification of 1000:1, thereby detecting a total of at least 2000 secondary phases. The average secondary phase density is calculated from the total number of secondary phases determined in at least 10 measurement areas relative to the total measurement area of ​​all the measurement areas studied.

2. The aluminum alloy strip according to claim 1, wherein, one or more alloy components of the aluminum alloy of the aluminum alloy strip have the following contents by weight percentage: Si ≤ 0.08%, Fe ≤ 0.20%, 0.20% ≤ Mn ≤ 0.26%, 4.80% ≤ Mg ≤ 4.92%, Cu ≤ 0.07, Cr≤0.01， Ni ≤ 0.005%, Zn ≤ 0.01%, 0.005% ≤ Ti ≤ 0.02%.

3. The aluminum alloy strip according to claim 2, wherein, Cu < 0.04%.

4. The aluminum alloy strip according to claim 2, wherein, Cr≤0.008％。 5. The aluminum alloy strip according to claim 2, wherein, Zn ≤ 0.008%.

6. The aluminum alloy strip according to claim 1 or 2, wherein, The aluminum alloy strip has an average secondary phase density of less than 220 / 1000 μm 2 .

7. The aluminum alloy strip according to claim 6, wherein, The aluminum alloy strip has an average secondary phase density of less than 200 / 1000 μm 2 .

8. The aluminum alloy strip according to claim 1, wherein, the aluminum alloy strip has a texture state of O or H111.

9. The aluminum alloy strip according to claim 1, wherein, the aluminum alloy strip has an average grain size of 15 μm to 30 μm measured according to ASTM E1382.

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

11. The aluminum alloy strip according to claim 1, wherein, the Ae value according to DIN EN ISO 6892 of the aluminum alloy strip transverse to the rolling direction is less than 1.0%.

12. The aluminum alloy strip according to claim 11, wherein, the Ae value according to DIN EN ISO 6892 of the aluminum alloy strip transverse to the rolling direction is less than 0.9%.

13. The aluminum alloy strip according to claim 1, wherein, when the sheet thickness is 1.2 mm, the aluminum alloy strip has an average major shape change ε1 greater than 0.200 in the Nakajima test with a sample width of 100 mm according to DIN EN ISO 120004-2.

14. The aluminum alloy strip according to claim 1, wherein, the aluminum alloy strip has a yield limit Rp0.2 of at least 115 MPa transverse to the rolling direction according to DIN EN ISO 6892.

15. The aluminum alloy strip according to claim 1, wherein, The aluminum alloy strip has a yield limit Rp0.2 of at least 120 MPa transversely to the rolling direction in accordance with DIN EN ISO 6892.

16. A method for manufacturing an aluminum alloy strip according to any one of claims 1 to 15, wherein the method has the following steps: - Casting a rolling ingot from an aluminum alloy having the following composition: 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 each ≤ 0.05% and in total ≤ 0.15%, - Homogenizing the rolling ingot at 480 °C to 550 °C for at least 0.5 hours, - Hot rolling the rolling ingot to a final thickness of the hot-rolled strip of 3 to 6 mm, - Cold rolling the aluminum alloy strip to the final thickness with a rolling reduction of 40% to 60%, and - Soft annealing the finished-rolled aluminum alloy strip in a continuous furnace at a temperature above 500 °C.

17. The method according to claim 16, characterized in that Si ≤ 0.08%.

18. The method according to claim 16, characterized in that Fe ≤ 0.20%.

19. The method according to claim 16, characterized in that 0.20% ≤ Mn ≤ 0.26%.

20. The method according to claim 16, characterized in that 4.80% ≤ Mg ≤ 4.92%.

21. The method according to claim 16, characterized in that Cu ≤ 0.

07.

22. The method according to claim 21, characterized in that Cu < 0.04%.

23. The method according to claim 16, characterized in that Cr≤0.01。 24. The method according to claim 23, characterized in that Cr≤0.008％。 25. The method according to claim 16, characterized in that Ni ≤ 0.005%.

26. The method according to claim 16, characterized in that Zn ≤ 0.01%.

27. The method according to claim 26, characterized in that Zn ≤ 0.008%.

28. The method according to claim 16, characterized in that Ti ≤ 0.02%.

29. The method according to claim 16, characterized in that Cold rolling the aluminum alloy strip to the final thickness with a rolling reduction of 50% to 60%.

30. The method according to claim 16, characterized in that Soft annealing the finished-rolled aluminum alloy strip in a continuous furnace at 510 °C to 540 °C.

31. The method according to claim 16, wherein After hot rolling, alternatively, the following method steps are carried out: - Cold rolling the hot-rolled aluminum alloy strip to an intermediate thickness which is determined such that the final rolling reduction to the final thickness is 40% to 60%, - Intermediate annealing the aluminum alloy strip at 300 °C to 500 °C, - Cold rolling the aluminum alloy strip to the final thickness with a rolling reduction of 40% to 60%, - Soft annealing the finished-rolled aluminum alloy strip in a continuous furnace at a temperature above 500 °C.

32. The method according to claim 31, wherein, the intermediate thickness is determined such that the final cold rolling degree to the final thickness is 50% to 60%.

33. The method according to claim 31, wherein, the aluminum alloy strip is cold rolled to the final thickness with a rolling degree of 50% to 60%.

34. The method according to claim 31, wherein, the rolled aluminum alloy strip is subjected to soft annealing in a continuous furnace at 510°C to 540°C.

35. The method according to claim 16, wherein, the duration of soft annealing of the completed aluminum alloy strip in the continuous furnace is between 5 seconds and 300 seconds.

36. The method according to claim 16, wherein, the hot rolling of the cast block consists of the following steps: pre-rolling to a thickness of 30 mm to 40 mm at an initial temperature of at least 450°C, and completing the hot rolling to the final thickness of the hot rolled strip at a coiling temperature of 300°C to 350°C.

37. Use of the aluminum alloy strip according to any one of claims 1 to 15 for manufacturing interior parts of a motor vehicle body, interior parts of an engine hood or interior parts of a luggage compartment lid.

38. The use according to claim 37, wherein the interior part of the motor vehicle body is an interior part of a door.

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