Aluminum alloy sheet

Abstract

To provide a 6000 series aluminum alloy sheet which has excellent formability and shearing properties as those of an automobile panel material, and in which the reduction of material cost is facilitated.SOLUTION: An aluminum alloy sheet containing Si:0.8% by mass to 1.6% by mass, Mn: 0.1% by mass to 0.5% by mass, Mg: 0.3% by mass to 0.7% by mass, Fe: 0.1% by mass to 0.5% by mass, and Ni: 0% by mass to 0.2% by mass, further containing one or more elements selected from the group consisting of Cu: 0.001% by mass to 0.3% by mass, Cr: 0.001% by mass to 0.1% by mass, Zn: 0.1% by mass to 0.5% by mass, and Ti: 0.001% by mass to 0.1% by mass, and a remainder consisting of Al and inevitable impurities.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy sheet, and more particularly to an Al-Mg-Si aluminum alloy sheet. [Background technology]

[0002] In recent years, there has been an increasing social demand for weight reduction of vehicles such as automobiles due to considerations of the global environment, etc. In order to meet this demand, aluminum alloy materials have been used as materials for automobiles instead of steel materials such as steel sheets.

[0003] As aluminum alloy sheets for automobile panel materials such as outer and inner panels of automobiles, Al-Mg-Si based AA to JIS 6000 series (hereinafter simply referred to as 6000 series) aluminum alloy sheets are typically used. These 6000 series aluminum alloy sheets have a composition containing Si and Mg as essential elements and have excellent formability.

[0004] Aluminum alloy automotive panel material is made by forming rolled aluminum alloy sheets, such as by press molding, and then subjecting the formed sheets or formed products (panels) to a shearing process called trimming, which removes the edges (excess material) of the formed sheets or formed products (panels), to produce finished panels. For example, Patent Document 1 describes a shearing method in which, during shearing of a 6000 series aluminum alloy plate, the minimum distance between the lower surface of the upper blade and the upper surface of the lower blade is set to 15 to 70% of the thickness of the aluminum alloy plate.

[0005] In shearing, if the clearance between the upper and lower blades is not appropriate, burrs can occur, potentially resulting in product defects and dimensional defects. Therefore, it is necessary to maintain the clearance at an appropriate level during shearing. However, the clearance can increase due to die wear or missetting, necessitating periodic die replacement and other adjustments, which can reduce productivity. Therefore, there is a demand for aluminum alloy sheets with high shear strength that can suppress burr formation even when the clearance is not appropriate.

[0006] On the other hand, in producing 6000 series aluminum alloy sheets, high purity aluminum ingots are often used as a casting raw material. However, an increase in the amount of ingots used leads to an increase in material costs. Therefore, there is a demand for aluminum alloy sheets with high recyclability that can increase the ratio of scrap aluminum products in the casting raw material. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-320942 Summary of the Invention [Problem to be solved by the invention]

[0008] 6000 series aluminum alloy sheets require a certain level of ductility to ensure press formability, but increasing the Si, Mg, and Fe content to achieve high shear strength and recyclability results in the crystallization of elemental Si, Al(Fe,Mn)Si, Al-Fe-Si compounds, Al-Mn-Fe compounds, and coarse Mg2Si, which reduces elongation and makes it difficult to ensure press formability. In other words, there was still room for further research into aluminum alloy sheets that combine press formability, shear strength, and recyclability.

[0009] The present invention has been made in view of the above background, and aims to provide an aluminum alloy sheet which has high shear strength while maintaining conventional press formability (elongation), and which can be easily produced even with a high scrap content, thereby facilitating reduction in material costs. [Means for solving the problem]

[0010] As a result of extensive research, the present inventors discovered that by using a specific alloy composition, an aluminum alloy sheet can be obtained that has good formability and shearing properties and that facilitates reduction in material costs, and thus created the present invention.

[0011] That is, the present invention relates to the following. [1] Si: 0.8% by mass to 1.6% by mass, Mn: 0.1% by mass to 0.5% by mass, Mg: 0.3% by mass to 0.7% by mass, Fe: 0.1% by mass to 0.5% by mass, Ni: 0% by mass to 0.2% by mass and further comprising Cu: 0.001% by mass to 0.3% by mass, Cr:0.001 mass%~0.1 mass%, Zn: 0.1% by mass to 0.5% by mass, and Ti:0.001 mass%~0.1 mass% Contains one or more elements selected from the group consisting of The balance consists of Al and unavoidable impurities. Aluminum alloy plate. [2] The aluminum alloy sheet according to [1], having an elongation of 27% or more. [3] Average particle area of ​​elemental Si, Al(Fe,Mn)Si compounds, Al-Fe-Si compounds, and Al-Mn-Fe compounds with a maximum length of 5 μm or more and less than 50 μm is 9.0 μm 2 or more, and the density is 145 pieces / mm 2 The aluminum alloy sheet according to [1] or [2] above. [4] The number density of Mg2Si particles with a maximum length of 1 μm or more and less than 5 μm is 1400 pieces / mm 2 The aluminum alloy plate according to [1] or [2], wherein the tensile strength is less than 100%. [5] The number density of elemental Si, Al(Fe,Mn)Si compounds, Al-Fe-Si compounds, Al-Mn-Fe compounds, and Mg2Si with a maximum length of 50 μm or more is 0 particles / mm 2 The aluminum alloy sheet according to [1] or [2], [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a 6000 series aluminum alloy sheet suitable for use as an automobile panel material, which has good formability and shearing properties and allows easy reduction in material costs. [Brief explanation of the drawings]

[0013] [Figure 1] Figure 1 shows a cross-sectional image of the fracture surface of test material A4 after the shear test. [Figure 2] FIG. 2 is a schematic diagram for explaining the mold conditions and shearing process in the shear test. [Figure 3] FIG. 3 is a schematic diagram for explaining the mold conditions and shearing process in the shear test. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an aluminum alloy plate according to an embodiment of the present invention will be described in detail. In addition, the aluminum alloy sheet referred to in this specification means an aluminum alloy sheet obtained by subjecting a rolled sheet such as a hot-rolled sheet or a cold-rolled sheet to thermal refining treatment such as solution treatment and quenching treatment, but before paint bake hardening treatment. In the following description, aluminum may be abbreviated as Al. In addition, in this specification, the use of "to" indicating a numerical range means that the numerical values ​​before and after it are included as the lower limit and upper limit.

[0015] [Aluminum alloy plate] The aluminum alloy plate according to this embodiment contains 0.8% by mass to 1.6% by mass of Si, 0.1% by mass to 0.5% by mass of Mn, 0.3% by mass to 0.7% by mass of Mg, 0.1% by mass to 0.5% by mass of Fe, and 0% by mass to 0.2% by mass of Ni, and further contains one or more elements selected from the group consisting of 0.001% by mass to 0.3% by mass of Cu, 0.001% by mass to 0.1% by mass of Cr, 0.1% by mass to 0.5% by mass of Zn, and 0.001% by mass to 0.1% by mass of Ti, with the remainder being Al and unavoidable impurities.

[0016] The aluminum alloy sheet according to this embodiment has the above-described chemical composition, which allows the control of the compound distribution described below, thereby achieving both excellent shear properties and press formability. Furthermore, the increase in strength due to work hardening can be increased without impairing various properties such as strength and bake hardenability. Furthermore, by using the above chemical composition, the proportion of scrap aluminum products in the casting raw material can be increased, or even when all of the casting raw material is scrap aluminum products, the casting material can be easily produced, and material costs can be easily reduced. Hereinafter, each configuration of the aluminum alloy plate according to this embodiment will be described in detail.

[0017] <Chemical composition of aluminum alloy> (Si:0.8 mass%~1.6 mass%) Si is an essential constituent element in the aluminum alloy sheet according to this embodiment, and is contained in the aluminum alloy sheet to promote the precipitation of β″, which is a precipitation-strengthening phase, and to obtain excellent strength and press formability (elongation). Furthermore, crystallization of elemental Si, Al(Fe,Mn)Si-based compounds, and Al-Fe-Si-based compounds reduces the amount of bending deformation until fracture during shearing by shearing between the upper blade and the lower blade (hereinafter also referred to as during shearing), making it less likely to rub against the upper blade, thereby suppressing the generation of burrs and obtaining excellent shearing properties. If the Si content in the aluminum alloy sheet is less than 0.8% by mass, the above effects cannot be achieved. Furthermore, Si in the aluminum alloy sheet is likely to be consumed to form Al-Fe-Si compounds, etc., resulting in an insufficient amount of Si in solid solution, which may result in a decrease in strength and a decrease in strength after paint baking. On the other hand, if the Si content in the aluminum alloy sheet exceeds 1.6% by mass, the yield strength before bake hardening increases, and press formability decreases. Furthermore, a decrease in bending workability and a decrease in elongation due to the crystallization of coarse Mg2Si are likely to occur. Therefore, the Si content is set to 0.8% to 1.6% by mass. The Si content is preferably 0.9% by mass or more, more preferably 1.2% by mass or more, from the viewpoint of improving strength, formability, and shear resistance, and is preferably 1.5% by mass or less, more preferably 1.4% by mass or less, from the viewpoint of suppressing deterioration in bending workability and formability.

[0018] (Mg:0.3 mass%~0.7 mass%) Mg is an essential constituent element in the aluminum alloy sheet according to this embodiment, and is contained in the aluminum alloy sheet to improve strength and elongation through solid solution strengthening of itself, and to promote precipitation of β″, which is a precipitation-strengthening phase, thereby obtaining excellent strength and press formability (elongation). If the Mg content in the aluminum alloy sheet is less than 0.3% by mass, the above effects cannot be obtained. On the other hand, if the Mg content in the aluminum alloy sheet exceeds 0.7% by mass, the yield strength before bake hardening increases and press formability decreases. Therefore, the Mg content is set to 0.3% to 0.7% by mass. The Mg content is preferably 0.4% by mass or more, more preferably 0.5% by mass or more, from the viewpoint of improving strength and formability, and is preferably 0.6% by mass or less, from the viewpoint of suppressing deterioration in formability.

[0019] (Mn:0.1 mass%~0.5 mass%) Mn is an essential constituent element in the aluminum alloy plate according to this embodiment, and crystallization of Al(Fe,Mn)Si-based compounds and Al-Mn-Fe-based compounds reduces the amount of bending deformation until fracture during shearing, thereby providing excellent shear properties. If the Mn content in the aluminum alloy sheet is less than 0.1%, the size and number of compounds will be small, making it impossible to obtain the above-mentioned effects. On the other hand, if the Mn content in the aluminum alloy sheet exceeds 0.5% by mass, coarse compounds will be generated, which will likely cause a decrease in bending workability. Therefore, the Mn content is set to 0.1% to 0.5% by mass. The Mn content is preferably 0.2% by mass or more from the viewpoint of improving shearing properties, and more preferably 0.4% by mass or less from the viewpoint of suppressing deterioration in bending workability.

[0020] (Fe:0.1 mass%~0.5 mass%) Fe is an essential constituent element in the aluminum alloy plate according to this embodiment, and crystallization of Al(Fe,Mn)Si-based compounds and Al-Fe-Si-based compounds reduces the amount of bending deformation until fracture during shearing, thereby providing excellent shear properties. If the Fe content in the aluminum alloy sheet is less than 0.1%, the above effect cannot be obtained. On the other hand, if the Fe content in the aluminum alloy sheet exceeds 0.5 mass%, the compounds become coarse and the bending workability tends to deteriorate. Therefore, the Fe content is set to 0.1 mass% to 0.5 mass%. The Fe content is preferably 0.2% by mass or more from the viewpoint of improving shearing properties, and is preferably 0.4% by mass or less, more preferably 0.3% by mass or less, from the viewpoint of suppressing deterioration in bending workability.

[0021] (Ni: 0 mass% or more and 0.2 mass% or less) While Ni can improve strength and corrosion resistance through solid solution, if the Ni content exceeds 0.2 mass%, coarse compounds are generated during casting, causing reduced formability. Ni can be mixed in as an unavoidable impurity and is also contained in scrap aluminum products. From a recycling perspective, Ni may be mixed in as an impurity when large amounts of aluminum alloy scrap are used as melting raw materials. However, the impurity levels specified in JIS 6000 series alloys do not impair the objectives and effects of the present invention. Therefore, the Ni content is set to 0.2 mass% or less. The Ni content is preferably 0.001% by mass or more from the viewpoint of obtaining the above-mentioned effects, and more preferably 0.1% by mass or less, and even more preferably 0.05% by mass or less, from the viewpoint of suppressing the formation of coarse compounds.

[0022] (Cu:0.001 mass%~0.3 mass%) Cu has the effect of improving hardening characteristics during baking finish, increasing strength and ductility through solid solution strengthening, and improving formability. If the Cu content is less than 0.001% by mass, particularly less than 0.01%, this effect is not achieved. On the other hand, if the Cu content exceeds 0.3% by mass, it may cause a significant decrease in corrosion resistance, such as the occurrence of thread rust. Therefore, the Cu content is preferably 0.001% to 0.3% by mass. The Cu content is preferably 0.01% by mass or more from the viewpoint of obtaining the above-mentioned effects, and more preferably 0.2% by mass or less, and even more preferably 0.1% by mass or less, from the viewpoint of suppressing a decrease in corrosion resistance.

[0023] (Cr:0.001 mass%~0.1 mass%) Cr forms intermetallic compounds, and the refined intermetallic compounds inhibit recrystallization, resulting in finer grains and improved formability. Addition of less than 0.001% by mass is ineffective. Conversely, addition of more than 0.1% by mass can lead to the formation of coarse compounds during casting, potentially resulting in cracking and other degradation of formability. Cr is sometimes found in scrap aluminum products, and when large amounts of aluminum alloy scrap are used as melting raw materials for recycling, it may be present as an impurity. However, impurity levels specified in JIS 6000-series alloys do not have adverse effects, and even if present in amounts exceeding the impurity level, the objectives and effects of the present invention are not impaired. Therefore, it is preferable to limit the Cr content to 0.001% to 0.1% by mass. The Cr content is preferably 0.005% by mass or more from the viewpoint of obtaining the above-mentioned effects, and more preferably 0.08% by mass or less, and even more preferably 0.05% by mass or less, from the viewpoint of suppressing deterioration of formability.

[0024] (Zn:0.1~0.5% by mass) The inclusion of Zn can provide effects such as improved strength after baking and improved surface treatability. On the other hand, if the Zn content exceeds 0.5% by mass, corrosion resistance decreases. Zn is sometimes contained in scrap aluminum products, and when large amounts of aluminum alloy scrap are used as melting raw materials from a recycling perspective, Zn may be mixed in as an impurity. However, the impurity levels specified for JIS 6000 series alloys do not have any adverse effects and do not impair the objectives and effects of the present invention. Therefore, the Zn content is preferably 0.1% to 0.5% by mass. The Zn content is preferably 0.15 mass % or more, more preferably 0.2 mass % or more, from the viewpoint of obtaining the above-mentioned effects, and is preferably 0.4 mass % or less, from the viewpoint of suppressing a decrease in corrosion resistance.

[0025] (Ti: 0.001 mass% or more and 0.1 mass% or less) Ti refines the ingot structure, suppresses cracking during casting, and improves rollability during hot rolling. On the other hand, if the Ti content exceeds 0.1% by mass, coarse intermetallic compounds may crystallize, causing a significant decrease in press formability. Therefore, the Ti content is preferably 0.001% to 0.1% by mass. From the viewpoint of obtaining the above-mentioned effects, the Ti content is more preferably 0.01 mass % or more, and even more preferably 0.015 mass % or more, and from the viewpoint of suppressing deterioration of formability, it is preferably 0.05 mass % or less.

[0026] (Remainder: Al and unavoidable impurities, etc.) Other elements than those mentioned above, such as B, Zr, and Bi, are generally considered to be unavoidable impurities, but Ti and other elements may be mixed in from scrap.

[0027] When the aluminum alloy sheet according to this embodiment contains Ti, it is more preferable to add 0.05 mass % or less of B (boron) together with Ti, which can further enhance the effect of refining the ingot structure and suppress the formation of abnormal crystal grains such as columnar crystals.

[0028] The aluminum alloy sheet according to this embodiment may further contain less than 0.050 mass% Zr (zirconium) and less than 0.050 mass% Bi (bismuth), without affecting the effects of the present invention.

[0029] <Compound distribution> (Elemental Si, Al(Fe,Mn)Si compounds, Al-Fe-Si compounds, and Al-Mn-Fe compounds with a maximum length of 5 μm or more and less than 50 μm) The aluminum alloy sheet according to the embodiment of the present invention is made of a material having a maximum length of 5 μm or more and less than 50 μm, such as elemental Si, Al(Fe,Mn)Si-based compounds, Al-Fe-Si-based compounds, and Al-Mn-Fe-based compounds, and has an average grain area of ​​9.0 μm 2 or more, and the density is 145 pieces / mm 2In this case, the compound acts as a starting point and propagation path for cracks during bending, improving fracture resistance during bending, thereby achieving the above-mentioned excellent shear resistance.

[0030] The average particle area is 12 μm 2 More preferably, it is 13.5 μm or more. 2 The above is even more preferable. The density of the particles is 170 particles / mm 2 More preferably, it is 240 / mm or more. 2 The above is even more preferable.

[0031] (Mg2Si with a maximum length of 1 μm or more and less than 5 μm) In the aluminum alloy plate according to the embodiment of the present invention, the number density of Mg2Si particles having a maximum length of 1 μm or more and less than 5 μm is 1400 particles / mm 2 It is preferable that it is less than 10 ... Compounds with a maximum length of 1 μm or more and less than 5 μm have little effect on fracture resistance during bending, but the above number density of 1400 pieces / mm 2 By making it less than this, it is possible to suppress a decrease in strength and a decrease in press formability due to an insufficient amount of Si and Mg dissolved in the Al matrix caused by the crystallization of Mg2Si. The density of the above is 850 pieces / mm 2 The following is more preferable: There is no particular lower limit to the number density.

[0032] (Elemental Si with a maximum length of 50 μm or more, Al(Fe,Mn)Si compounds, Al-Fe-Si compounds, Al-Mn-Fe compounds, and Mg2Si) In the aluminum alloy plate according to the embodiment of the present invention, the number density of elemental Si, Al(Fe,Mn)Si-based compounds, Al-Fe-Si-based compounds, Al-Mn-Fe-based compounds, and Mg2Si having a maximum length of 50 μm or more is 0 particles / mm 2 It is preferable that the number density is 0 pieces / mm 2In other words, by not containing excessively coarse elemental Si or the above-mentioned intermetallic compounds, it is possible to prevent the occurrence of cracks originating from the compounds during press forming, and to suppress a decrease in press formability.

[0033] The maximum length, average particle area, and number density of the above compounds can be calculated by polishing the surface of the aluminum alloy plate, observing it with an SEM device (e.g., JSM-7001F manufactured by JEOL Ltd.) and an optical microscope (e.g., PMG3 manufactured by OLYMPUS Corporation), and measuring the size, number, and area of ​​the above compounds.

[0034] <Mechanical properties> (stretch) The elongation (%) of the aluminum alloy sheet according to the embodiment of the present invention is preferably 27% or more. By making it 27% or more, the occurrence of cracks during forming can be suppressed, and restrictions on dimensions, shapes, and processing conditions can be reduced, thereby suppressing a decrease in productivity. The elongation of the aluminum alloy sheet can be adjusted by using the above-mentioned chemical composition and the manufacturing method described below.

[0035] (0.2% yield strength) The 0.2% yield strength of the aluminum alloy sheet according to the embodiment of the present invention is preferably 100 MPa or more. By making it 100 MPa or more, the yield strength after baking finish can be made 200 MPa or more. The 0.2% yield strength is more preferably 110 MPa or more. The yield strength of the aluminum alloy plate can be adjusted by using the above-mentioned chemical composition and the manufacturing method described below.

[0036] The elongation and 0.2% proof stress of an aluminum alloy sheet can be measured by a metallic material tensile test in accordance with JIS Z 2241 (revised edition, 2011). Specifically, a 13B tensile test piece (12.5 mm × 50 mm GL × sheet thickness) specified in the JIS is taken from the sample, and a tensile test is performed at room temperature (25°C). The test piece is tensile in the rolling direction, and the tensile speed is 5 mm / min. The number of samples in the mechanical property measurement is 4, and the average value is calculated for each. In this way, the elongation and 0.2% proof stress can be calculated.

[0037] [Method of manufacturing aluminum alloy sheets] The 6000 series aluminum alloy sheet according to the embodiment of the present invention is produced by a conventional method in which an ingot is subjected to homogenizing heat treatment, followed by hot rolling and further cold rolling to produce a cold-rolled sheet, which is then further subjected to tempering such as solution treatment. That is, the sheet is produced through the conventional production steps of casting, homogenizing heat treatment, and hot rolling to produce an aluminum alloy hot-rolled sheet having a thickness of about 2 to 10 mm. The sheet is then cold-rolled to produce a cold-rolled sheet having a thickness of 4 mm or less. Each step will be described in more detail below.

[0038] (Melting, casting) First, in the melting and casting process, the molten aluminum alloy melt adjusted to have the above-mentioned composition range is cast by an appropriately selected ordinary melting and casting method such as continuous casting or semi-continuous casting (DC casting). As the casting raw material, for example, aluminum ingot or scrap of aluminum products can be used. Examples of scrap that can be used as the casting raw material include offcuts removed as unnecessary parts in the manufacturing process of aluminum products, and scrap automobile parts such as body sheets, body panels, heat exchanger fins and tubes, and header tanks. From the viewpoint of further reducing the material cost of the aluminum alloy sheet, the proportion of aluminum product scrap in the casting raw material is preferably 50 mass% or more, more preferably 75 mass% or more, and particularly preferably 100 mass%, i.e., it is particularly preferable to use only aluminum product scrap as the casting raw material.

[0039] (Homogenized heat treatment) The cast aluminum alloy ingot is then subjected to a homogenization heat treatment prior to hot rolling. This homogenization heat treatment (soaking) is important not only for homogenizing the structure, i.e., for eliminating segregation within the crystal grains in the ingot structure, but also for sufficiently dissolving Mg and Si. Here, the soaking temperature is preferably 560°C or higher and the melting temperature or lower. By setting the soaking temperature to 560°C or higher and the melting temperature or lower, Mg2Si, which has a maximum length of 1 μm or higher and less than 5 μm and does not contribute to shear properties, is solid-dissolved, ensuring sufficient elongation. In addition, the soaking temperature is maintained for 4 to 12 hours.

[0040] After the homogenization heat treatment, the material is maintained at or near the hot rolling start temperature before starting hot rolling. Alternatively, the material may be cooled once after the homogenization heat treatment. In this case, the cooling rate after the homogenization heat treatment is set to 20°C / hr or more and less than 100°C / hr, and the material is reheated to a predetermined temperature in the range of 350 to 450°C before starting hot rolling.

[0041] (hot rolling) The ingot that has undergone homogenization heat treatment is hot-rolled to produce a hot-rolled sheet with a thickness of approximately 2 to 10 mm. Hot rolling consists of a rough rolling process and a finish rolling process for the ingot (slab), depending on the thickness to be rolled. In these rough rolling and finish rolling processes, a rolling mill such as a reverse type or tandem type is appropriately used.

[0042] If the hot rolling start temperature (i.e., rough rolling start temperature) exceeds the solidus temperature, burning (i.e., partial melting of the ingot) occurs, which may make the hot rolling itself difficult. Also, if the hot rolling start temperature is less than 350°C, the load during hot rolling becomes too high, which may make the hot rolling itself difficult. Therefore, the hot rolling (rough rolling) start temperature is preferably 350°C to the solidus temperature, and more preferably 400°C to the solidus temperature.

[0043] (cold rolling) In cold rolling, the hot-rolled sheet is rolled to produce a cold-rolled sheet (including coil) of the desired final thickness. However, in order to further refine the crystal grains, the cold-rolling reduction ratio is preferably 30% or more. During cold rolling, annealing and intermediate annealing may be performed as necessary.

[0044] (solution and quenching treatment) After cold rolling, the material is subjected to solution treatment followed by quenching to room temperature. In this solution treatment and quenching, it is desirable to heat the material to a solution treatment temperature of 500°C or higher but below the melting point in order to obtain sufficient amounts of solid solution of elements such as Mg and Si. Furthermore, from the viewpoint of suppressing the formation of coarse grain boundary compounds that reduce elongation and suppressing a decrease in bake hardening properties due to a decrease in the amount of Mg, Si, and other elements dissolved in solid solution, it is desirable to set the average cooling rate from the solution treatment temperature to the quenching stop temperature (room temperature) to 20°C / s or more. To ensure this cooling rate, the quenching treatment can be performed using air cooling such as with a fan, or water cooling means and conditions such as mist, spray, and immersion. The holding time at the solution treatment temperature is appropriately selected from the range of 0 to 60 seconds.

[0045] (reheat treatment) After such solution treatment, the cold-rolled sheet is preferably quenched and cooled to room temperature, and then heat-treated within one hour in a temperature range of 30°C to 100°C for 5 hours to 500 hours. Alternatively, it is preferable to heat-treat the cold-rolled sheet within one hour in a temperature range of 100°C to 300°C for 5 seconds to 300 seconds, and then heat-treat the cold-rolled sheet within a temperature range of 30°C to 100°C for 5 hours to 500 hours. This ensures sufficient elongation and work hardenability. [Example]

[0046] The present invention will be specifically described below with reference to examples of the present invention, but the technical scope of the present invention is not limited thereto.

[0047] <Production of aluminum alloy plate> First, an aluminum alloy ingot having the chemical composition shown in Table 1 was produced by DC casting. The symbol "Bal." in Table 1 indicates that the component is the balance component.

[0048] [Table 1]

[0049] Next, the obtained ingots were subjected to a soaking treatment (homogenization heat treatment). As shown in Table 2, the holding temperature (i.e., soaking temperature) was changed for each ingot during the soaking treatment. After the soaking treatment, each ingot was subjected to rough hot rolling to obtain a hot-rolled sheet. This hot-rolled sheet was then subjected to cold rolling at a processing rate of 67% to obtain a cold-rolled sheet with a thickness of 1.0 mm.

[0050] Each of the obtained cold-rolled sheets was subjected to solution treatment and quenching treatment using a saltpeter furnace under the conditions shown in Table 2, and then cooled to room temperature. Within one hour after this cooling, a reheating treatment was performed by holding at 70°C for 5 hours. After the reheating treatment, the sheet was air-cooled to room temperature.

[0051] [Table 2]

[0052] <Mechanical properties> A tensile test was conducted on each aluminum alloy sheet in accordance with JIS Z 2241 (revised edition, 2011). Tensile test specimens (12.5 mm × 50 mm GL × sheet thickness) of JIS 13B were taken from each aluminum alloy sheet, and the tensile test was conducted at room temperature. The test specimens were tensile in the rolling direction. The tensile speed was 5 mm / min. The number of samples in the mechanical property measurement was 4, and each was calculated as an average value. Then, the 0.2% proof stress and elongation were calculated for each example. The obtained results are shown in Table 3. All of the materials A1 to A4 satisfy the requirements for yield strength (evaluation: ◯), but material A3, which has a low soaking temperature, has low elongation and does not satisfy the requirements of the present invention (evaluation: ×).

[0053] [Table 3]

[0054] <Compound distribution> A cross section of each aluminum alloy plate parallel to the rolling direction was embedded in resin and polished to prepare a specimen for cross-sectional observation. Using a scanning electron microscope (JEOL Ltd.) "JSM-7001F," an accelerating voltage of 15 kV and a magnification of 500x, COMPO images (composition images) were taken in the region sandwiched between the upper and lower positions 1 / 4t from the center of the thickness of the aluminum plate material, with 20 fields of view (approximately 0.8 mm) each. 2 ) were photographed. Using the obtained COMPO image, the maximum length and area of ​​each particle of elemental Si, Al(Fe,Mn)Si-based compounds, Al-Fe-Si-based compounds, Al-Mn-Fe-based compounds, and Mg2Si were measured. The maximum length was calculated by measuring the distance between the two most distant points in the particle. The average particle area was calculated based on the number of the above compounds in the measured area and their individual areas. The number of the above compounds per unit area was also calculated to obtain the number density.

[0055] In Table 4, the crystallized substance group a represents Mg2Si having a maximum length of 1 μm or more and less than 5 μm; the crystallized substance group b represents elemental Si, Al(Fe,Mn)Si-based compounds, Al-Fe-Si-based compounds, and Al-Mn-Fe-based compounds having a maximum length of 5 μm or more and less than 50 μm; and the crystallized substance group c represents elemental Si, Al(Fe,Mn)Si-based compounds, Al-Fe-Si-based compounds, Al-Mn-Fe-based compounds, and Mg2Si having a maximum length of 50 μm or more.

[0056] [Table 4]

[0057] <Shear test> Each aluminum alloy plate was sheared using a shearing device, and the length of the burrs formed on each cut aluminum alloy plate was measured as a shear test. The die conditions and shearing process in the shear test are shown in Figures 2 and 3. As shown in Figure 2, an aluminum alloy sheet 11, which serves as a shear test specimen, is sandwiched and supported between a fixed lower blade 21 and a pad 31, which serves as a sheet support member. While sandwiched between the lower blade 21 and the pad 31, the aluminum alloy sheet 11 is sheared by an upper blade 22, which descends vertically from above the lower blade 21 and the aluminum alloy sheet 11. The portion of the aluminum alloy sheet 11 that protrudes from the lower blade 21 is cut off, yielding a sheared sheet piece 11'. The shearing tool conditions were: the cutting edge R (reference symbol R1) of the lower blade 21 was 0 mm; the cutting edge R (reference symbol R2) of the upper blade 22 was 0.05 mm; the relief angle (shear angle) of the upper blade was 0°; and the clearance 41 between the lower blade and the upper blade 22 was 10% of the sheet thickness (0.08 mm). The pad was supported by a spring with a load of 37.1 kgf. The shear test specimens were aluminum alloy plates 0.8 mm thick and 50 mm wide, and the above tool conditions were used for two types of plates: one with the shear surface parallel to the rolling direction and the other perpendicular to the rolling direction. Burr evaluation was performed by cutting two observation points from each cut plate, embedding them in resin, polishing them, and then observing the cross section with an optical microscope and measuring the burrs. The burr length obtained was the average of these two measurements. Figure 1 shows a cross-sectional image of the area near the fracture surface of test material A4 after a shear test. This is a cross-section of A4 material after a shear test. The length of the part (a in Figure 1) that protruded from the surface of the test material during the shear test was measured as the burr length. Measurement of the burr length generated during the shear test for test materials A1, A2, and A4. The results are shown in Table 5. If the burr length is long, product scratches due to broken pieces are more likely to occur. A burr length of 120 μm or less was marked as ◯, and a burr with a length of more than 120 μm was marked as ×.

[0058] [Table 5]

[0059] From the above results, test materials A1 and A2, which satisfy the chemical composition requirements of the present invention, have chemical compositions that are easy to manufacture even with a high scrap content, and are excellent in both elongation (formability) and shear strength. On the other hand, test material A4, which does not satisfy the chemical composition requirements of the present invention, showed poor shear strength. Although test material A3 satisfies the chemical composition requirements, the soaking temperature in the manufacturing process was low, resulting in fine dispersion of Mg2Si and low elongation, and therefore does not satisfy the compound distribution requirement of the present invention. [Explanation of symbols]

[0060] 11 Aluminum alloy plate 11' board piece 21 Lower blade 22 Upper blade 31 Pad 41 Clearance R1, R2 cutting edge radius

Claims

1. Si: 0.8% by mass to 1.6% by mass, Mn: 0.1% by mass to 0.5% by mass, Mg: 0.3% by mass to 0.7% by mass, Fe: 0.1% by mass to 0.5% by mass, Ni: 0% by mass to 0.2% by mass and further comprising Cu: 0.001% by mass to 0.3% by mass, Cr: 0.001% by mass to 0.1% by mass, Zn: 0.1% by mass to 0.5% by mass, and Ti: 0.001% by mass to 0.1% by mass Contains one or more elements selected from the group consisting of The balance consists of Al and unavoidable impurities. Aluminum alloy plate.

2. The aluminum alloy sheet according to claim 1, having an elongation of 27% or more.

3. The average particle area of ​​the elemental Si, Al(Fe, Mn)Si-based compounds, Al-Fe-Si-based compounds, and Al-Mn-Fe-based compounds having a maximum length of 5 μm or more and less than 50 μm is 9.0 μm ２ or more, and the number density is 145 pieces / mm ２ The aluminum alloy sheet according to claim 1 or 2.

4. Mg with a maximum length of 1 μm or more and less than 5 μm ２ The number density of Si is 1400 pieces / mm ２ The aluminum alloy sheet according to claim 1 or 2, wherein the tensile strength is less than 1000 kJ / cm.

5. Elemental Si with a maximum length of 50 μm or more, Al(Fe, Mn)Si compounds, Al—Fe—Si compounds, Al—Mn—Fe compounds, and Mg ２ The number density of Si is 0 pieces / mm ２ The aluminum alloy sheet according to claim 1 or 2,

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