Suspension arm member and method for manufacturing suspension arm member

Abstract

This suspension arm member is composed of an aluminum alloy having an alloy composition containing 0.2-0.4 mass% of Cu, 0.9-1.2 mass% of Mg, 0.6-0.9 mass% of Si, 0.05-0.15 mass% of Mn, 0.15-0.30 mass% of Fe, 0.2-0.35 mass% of Cr, 0.01-0.05 mass% of Ti, and 0.0010-0.0050 mass% of B, with the remainder consisting of Al and inevitable impurities, and has a full-width at half-maximum of at least 1.58º at a Debye ring diffraction peak, as obtained by X-ray diffraction.

Description

Suspension arm member and method of manufacturing the same

[0001] This application claims priority to Japanese Patent Application No. 2023-220737, filed on December 27, 2023, the contents of which are incorporated herein by reference.

[0002] In recent years, aluminum alloys have been increasingly used as structural components for various products, taking advantage of their light weight. For example, high-tensile steel has traditionally been used for automobile suspension and bumper parts, but in recent years high-strength aluminum alloy materials have been used. While iron-based materials were previously used exclusively for automobile parts, such as suspension parts, they are increasingly being replaced by aluminum or aluminum alloy materials, primarily for the purpose of reducing weight.

[0003] These automobile parts require excellent corrosion resistance, high strength, and excellent workability, and therefore Al-Mg-Si alloys, particularly A6061, are widely used as the aluminum alloy material. To improve the strength of these automobile parts, they are manufactured by forging, a type of plastic processing, using the aluminum alloy material as the processing material.

[0004] Furthermore, due to the need to reduce costs recently, suspension parts have begun to be put into practical use in which cast members are used as raw materials without extrusion, and then subjected to a solution treatment and artificial aging treatment (T6 treatment). With the aim of further weight reduction, development of high-strength alloys to replace the conventional A6061 is underway (see Patent Documents 1 to 3).

[0005] JP-A-5-59477 JP-A-5-247574 JP-A-6-256880

[0006] Recent CO ２With the need to reduce the weight of automobiles in order to reduce carbon emissions, demand for aluminum is on the rise. However, as a replacement for steel, even higher strength is required. To achieve high strength, it is important to control the crystalline structure during forging. For example, when forging A6061 alloy, depending on the forging conditions (forging material heating temperature, equivalent strain amount), aluminum crystals may recover during the solution treatment and aging treatment processes after the forging process, resulting in the problem of coarsening of the crystalline structure.

[0007] Coarsening of the crystalline structure can lead to variations in mechanical properties, making it impossible to satisfy the strength requirements of the component. The upper part (a) of Figure 8 is an image showing the state of a crystalline structure consisting of a sufficient number of isotropic particles, and the lower part (b) of Figure 8 is a diffraction ring (Debye ring) obtained by performing X-ray diffraction on the crystalline structure of Figure 8(a). In contrast, Figure 9 is an image showing the state when coarsening occurs in the crystalline structure. The upper part (a) of Figure 9 is an image showing the state in which coarsening occurs in some particles in a crystalline structure consisting of multiple particles P, and the lower part (b) of Figure 9 is a diffraction ring (Debye ring) obtained by performing X-ray diffraction on the crystalline structure such as Figure 9(a). As shown in Figure 9(b), in a crystalline structure with coarsening such as Figure 9(a), the number of crystals contributing to diffraction is insufficient, resulting in discontinuous bias.

[0008] Furthermore, when orientation occurs in the crystalline structure due to rolling, etc., the grains become biased, making it easier to observe biased diffraction rings. Figure 10(a) is an image diagram showing the state in which orientation occurs in particles in a crystalline structure consisting of multiple particles P, and Figure 10(b) shows diffraction rings (Debye rings) obtained by performing X-ray diffraction on the crystalline structure shown in Figure 10(a).

[0009] Thus, when X-ray diffraction is performed on a crystalline structure, diffraction rings (Debye rings) are usually obtained. However, depending on the product shape, recrystallization may be unavoidable during forging, and it is believed that recrystallization causes unstable properties. Specifically, it is believed that recrystallization reduces strength properties. It is also said that it is difficult to obtain clear diffraction rings (Debye rings) when a recrystallized structure is present.

[0010] The present invention has been made in view of the above circumstances, and has an object to provide a high-strength suspension arm member that has stable characteristics even when it exhibits a recrystallized structure.

[0011] In order to solve the above problems, the present invention provides the following means.

[0012] [1] A suspension arm member according to one aspect of the present invention is made of an aluminum alloy having an alloy composition containing Cu in the range of 0.2 to 0.4 mass %, Mg in the range of 0.9 to 1.2 mass %, Si in the range of 0.6 to 0.9 mass %, Mn in the range of 0.05 to 0.15 mass %, Fe in the range of 0.15 to 0.30 mass %, Cr in the range of 0.2 to 0.35 mass %, Ti in the range of 0.01 to 0.05 mass %, B in the range of 0.0010 to 0.0050 mass %, and the balance being Al and unavoidable impurities, and having a half-width of a diffraction peak of Debye rings obtained by X-ray diffraction of 1.58° or more.

[0013] [2] The suspension arm member of [1] above comprises a wheel side connecting portion, a first vehicle body side connecting portion, a second vehicle body side connecting portion, a first arm portion connecting the wheel side connecting portion and the first vehicle body side connecting portion, and a second arm portion connecting the wheel side connecting portion and the second vehicle body side connecting portion, wherein the first arm portion is longer than the second arm portion, the half width is the half width of a diffraction peak of Debye rings obtained by performing X-ray diffraction on the first arm portion, and the 0.2% proof stress may be 300 MPa or more.

[0014] [3] A method of manufacturing a suspension arm member according to one aspect of the present invention includes: a molten metal forming step of obtaining a molten alloy having an alloy composition containing Cu in the range of 0.2% by mass to 0.4% by mass, Mg in the range of 0.9% by mass to 1.2% by mass, Si in the range of 0.6% by mass to 0.9% by mass, Mn in the range of 0.05% by mass to 0.15% by mass, Fe in the range of 0.15% by mass to 0.30% by mass, Cr in the range of 0.2% by mass to 0.35% by mass, Ti in the range of 0.01% by mass to 0.05% by mass, B in the range of 0.0010% by mass to 0.0050% by mass, with the balance being Al and unavoidable impurities; a casting step of casting the obtained molten metal to obtain a casting; and a forging step of forging the casting at a temperature of 470°C to 500°C to obtain a forged product. The method includes a solution treatment step in which the forged product is maintained at a temperature of 500°C or higher, a water quenching step in which the forged product is water quenched after the solution treatment, and an aging treatment step in which the forged product that has been subjected to the water quenching step is heat treated.

[0015] [4] The method for manufacturing a suspension arm member according to [3] above may include, in the solution treatment step, holding the forged product at a temperature of 530°C or higher and 560°C or lower for 0.3 hours or longer and 3 hours or shorter; in the water quenching step, performing water quenching using water at 60°C or lower; and in the aging treatment step, heating the forged product that has been subjected to the water quenching step at a temperature of 170°C or higher and 220°C or lower for 0.5 hours or longer and 7.0 hours or shorter.

[0016] [5] In the method for manufacturing a suspension arm member according to [3] or [4] above, the casting step may be performed by continuous casting, and in the aging treatment step, the forged product that has been subjected to the water quenching step may be heated at a temperature of 175°C or higher and 190°C or lower for 4 hours or longer.

[0017] According to the present invention, it is possible to provide a high-strength suspension arm member that has stable characteristics even when it exhibits a recrystallized structure.

[0018] 1 is a plan view showing an example of the configuration of a suspension arm member according to an embodiment of the present invention.

[0023] FIG. 1 is a cross-sectional view taken along the line A-A' of the suspension arm member of FIG. 1.

[0024] FIG. 2 is a cross-sectional view showing an example of the configuration of the vicinity of a mold of a horizontal continuous casting apparatus that can be used in the casting process of a manufacturing method of a suspension arm member according to an embodiment of the present invention.

[0025] FIG. 3 is an enlarged cross-sectional view of a main portion near the cooling water cavity of the horizontal continuous casting apparatus of FIG. 3.

[0026] FIG. 4 is an explanatory diagram illustrating the heat flux of the cooling wall portion of the horizontal continuous casting apparatus.

[0027] FIG. 5 is an X-ray diffraction result of the first arm portion of the suspension arm member of Example 1.

[0028] FIG. 6 is an analysis result of the diffraction intensity near the diffraction peak of the Debye rings in the X-ray diffraction result of FIG. 6.

[0029] FIG. 7 is an image showing the state of a crystalline structure that is isotropic and consists of a sufficient number of particles, and diffraction rings (Debye rings) obtained by performing X-ray diffraction on such a crystalline structure.

[0029] FIG. 8 is an image showing the state of a crystalline structure consisting of a plurality of particles P, in which coarsening has occurred in some particles, and diffraction rings (Debye rings) obtained by performing X-ray diffraction on such a crystalline structure. 1 shows an image of a crystal structure made up of a plurality of particles P, showing how the particles are oriented, and diffraction rings (Debye rings) obtained by performing X-ray diffraction on such a crystal structure.

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show characteristic portions enlarged for convenience in order to make the features easier to understand, and the dimensional ratios of each component may not necessarily be the same as those in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto, and can be implemented with appropriate changes within the scope of the present invention.

[0020] [Suspension Arm Component] First, a suspension arm component according to one embodiment of the present invention will be described. The suspension arm component according to one embodiment of the present invention is an aluminum alloy forging, and is a component for a suspension arm. The aluminum alloy forging of this embodiment is made of an aluminum alloy having an alloy composition containing Cu in the range of 0.2 mass% to 0.4 mass%, Mg in the range of 0.9 mass% to 1.2 mass%, Si in the range of 0.6 mass% to 0.9 mass%, Mn in the range of 0.05 mass% to 0.15 mass%, Fe in the range of 0.15 mass% to 0.30 mass%, Cr in the range of 0.2 mass% to 0.35 mass%, Ti in the range of 0.01 mass% to 0.05 mass%, B in the range of 0.0010 mass% to 0.0050 mass%, and the balance being Al and unavoidable impurities.

[0021] The aluminum alloy forgings of this embodiment correspond to 6000 series aluminum alloy forgings in that they contain Mg and Si.

[0022] In the suspension arm member according to one embodiment of the present invention, the half-value width of the diffraction peak of the Debye rings obtained by X-ray diffraction is 1.58° or more.

[0023] (Cu: 0.2% by mass or more, 0.4% by mass or less) Cu has the effect of finely dispersing Mg-Si compounds in the aluminum alloy and improving the tensile strength of the aluminum alloy by precipitating as Al-Cu-Mg-Si compounds such as the Q phase. The Cu content is within the range of 0.20% by mass or more and 0.40% by mass or less, and may be within the range of 0.25% by mass or more and 0.35% by mass or less, or 0.30% by mass or more. By having the Cu content within the above range, the mechanical properties of the aluminum alloy forging at room temperature can be improved.

[0024] (Mg: 0.9 mass % or more, 1.2 mass % or less) Mg has the effect of improving the tensile strength of the aluminum alloy. Mg dissolves in the aluminum matrix or forms a Mg-Si compound (Mg ２The magnesium content is in the range of 0.90% by mass to 1.20% by mass, and may be in the range of 0.95% by mass to 1.10% by mass, or 1.00% by mass to 1.05% by mass. By having the magnesium content in the above range, it is possible to improve the corrosion resistance as well as the mechanical properties at room temperature of the aluminum alloy forging.

[0025] (Si: 0.6% by mass or more, 0.9% by mass or less) Like Mg, Si has the effect of improving the corrosion resistance as well as the mechanical properties of aluminum alloy forgings at room temperature. However, if excessive Si is added to an aluminum alloy, coarse primary crystal Si grains may crystallize, potentially reducing the tensile strength of the aluminum alloy. The Si content is within the range of 0.60% by mass or more and 0.90% by mass or less, and may also be within the range of 0.65% by mass or more and 0.85% by mass or less, or 0.70% by mass or more and 0.80% by mass or less. By having the Si content within the above range, it is possible to improve the corrosion resistance as well as the mechanical properties of aluminum alloy forgings at room temperature while suppressing the crystallization of primary crystal Si.

[0026] (Mn: 0.05% by mass or more, 0.15% by mass or less) Mn forms fine granular precipitates containing intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Cr-Fe-Si in the aluminum alloy, thereby improving the tensile strength of the aluminum alloy. The Mn content is within the range of 0.05% by mass or more and 0.15% by mass or less, and may be within the range of 0.07% by mass or more and 0.14% by mass or less, or 0.10% by mass or more and 0.13% by mass or less. By having the Mn content within the above range, the mechanical properties of the aluminum alloy forging at room temperature can be improved.

[0027] (Fe: 0.15% by mass or more, 0.3% by mass or less) Fe crystallizes in the aluminum alloy as fine crystals containing intermetallic compounds such as Al-Mn-Fe-Si, Al-Mn-Cr-Fe-Si, Al-Fe-Si, Al-Cu-Fe, and Al-Mn-Fe, thereby improving the tensile strength of the aluminum alloy. The Fe content is within a range of 0.15% by mass or more and 0.30% by mass or less, and may be within a range of 0.20% by mass or more and 0.27% by mass or less, or 0.22% by mass or more. By having the Fe content within the above range, the mechanical properties of the aluminum alloy forging at room temperature can be improved.

[0028] (Cr: 0.2% by mass or more, 0.35% by mass or less) Cr forms fine granular precipitates containing intermetallic compounds such as Al-Mn-Cr-Fe-Si and Al-Fe-Cr in the aluminum alloy, thereby improving the tensile strength of the aluminum alloy. The Cr content is within the range of 0.20% by mass or more and 0.35% by mass or less, and may be within the range of 0.21% by mass or more and 0.30% by mass or less, or 0.25% by mass or less. By having the Cr content within the above range, the mechanical properties of the aluminum alloy forging at room temperature can be improved.

[0029] (Ti: 0.01% by mass or more, 0.05% by mass or less) Ti has the effect of refining the crystal grains of an aluminum alloy and improving its wrought workability. If the Ti content is less than 0.01% by mass, the effect of refining the crystal grains may not be sufficiently obtained. On the other hand, if the Ti content exceeds 0.05% by mass, coarse crystals may be formed, which may reduce the wrought workability. Furthermore, if a large amount of coarse crystals containing Ti are mixed into an aluminum alloy forging, the toughness may be reduced. Therefore, the Ti content is set to 0.010% by mass or more, and 0.050% by mass or less. The Ti content is preferably 0.015% by mass or more, and 0.030% by mass or less.

[0030] (B: 0.0010% by mass or more, 0.0050% by mass or less) B has the effect of refining the crystal grains of an aluminum alloy and improving its wrought workability. Adding B to an aluminum alloy together with the above-mentioned Ti improves the effect of refining the crystal grains. If the B content is less than 0.001% by mass, the effect of refining the crystal grains may not be sufficient. On the other hand, if the B content exceeds 0.0050% by mass, coarse crystals may form and be mixed into the aluminum alloy forging as inclusions. Furthermore, if a large amount of coarse crystals containing B are mixed into the final aluminum alloy product, the toughness may be reduced. Therefore, the B content is set to 0.0010 to 0.0050% by mass. The B content is preferably 0.0015 to 0.045% by mass.

[0031] (Inevitable impurities) Inevitable impurities are impurities that are inevitably mixed into the aluminum alloy from the raw materials or manufacturing process of the aluminum alloy forged product. Examples of inevitable impurities include Zn, Zr, Ni, Sn, and Be. It is preferable that the content of these inevitable impurities does not exceed 0.10% by mass, i.e., is 0.10% by mass or less.

[0032] Fig. 1 is a plan view showing an example of the configuration of a suspension arm member according to one embodiment of the present invention, and Fig. 2 is a cross-sectional view of the suspension arm member taken along the line A-A' in Fig. 1. The suspension arm member 100 shown in Figs. 1 and 2 is a member for a suspension arm, also known as an A-arm, A-arm, or A-shaped suspension arm. In some cases, holes are drilled in parts of the forged product of the suspension arm member for final attachment to other members such as the vehicle body or wheels, but the suspension arm member may be a member after drilling has been performed, or a forged product before drilling has been performed.

[0033] The suspension arm member 100 shown in Figures 1 and 2 includes, for example, a wheel side connecting portion 4, a first vehicle body side connecting portion 5, a second vehicle body side connecting portion 6, a first arm portion 1 connecting the wheel side connecting portion 4 and the first vehicle body side connecting portion 5, a second arm portion 2 connecting the wheel side connecting portion 4 and the second vehicle body side connecting portion 6, and an arm connecting portion 3 connecting the first vehicle body side connecting portion 5 and the second vehicle body side connecting portion 6. In the suspension arm member 100, the first arm portion 1 is longer than the second arm portion 2. That is, in a suspension arm member formed by forging, the first arm portion 1 can be said to be a member with a higher processing rate than the second arm portion 2. The processing rate (%) increases as the change in the cross-sectional area of ​​the material before and after processing increases, and is calculated using the following formula (1): 100 x (A ０ -A) / A ０ ...(1) (In formula (1), A ０ (A: cross-sectional area of ​​material before processing, A: cross-sectional area of ​​material after processing) Furthermore, even if the cross-sectional area of ​​the material before processing is unknown, the processing rate can be estimated by reverse analysis such as simulation from the shape of the suspension.

[0034] As described above, Figure 2 is a cross-sectional view of the suspension arm member taken along the section line A-A' in Figure 1. The section line A-A' is a cross-section that passes through the midpoints of the wheel-side coupling portion 4 and the first vehicle-body-side coupling portion 5. As shown in the cross-section of the first arm portion 1 in Figure 2, the first arm portion 1, the second arm portion 2, and the arm coupling portion 3 each have, for example, an outer circumferential portion 7 that forms the outer shape of the suspension arm member 100A, an inner circumferential portion 8 that is close to the area where the opening is formed in plan view, and a recessed portion 9 located between the outer circumferential portion 7 and the inner circumferential portion 8. The recessed portion 9 is, for example, a region that is recessed in the z direction relative to the outer circumferential portion 7 and the inner circumferential portion 8.

[0035] In a suspension arm member 100 according to one embodiment of the present invention, the half-width of the diffraction peak of the Debye rings obtained by X-ray diffraction of a region with a high processing rate is 1.58° or more. In the suspension arm member 100 shown in Figure 1, the region with a high processing rate is a region located in the outer periphery 7 in a cross section along the cutting line A-A' in the first arm portion 1, and is the region corresponding to the symbol R shown by the two-dot chain line in Figure 2. The region corresponding to the symbol R corresponds to the intersection of the width center and thickness center of the outer periphery 7. In a suspension arm member according to one embodiment of the present invention, the half-width of the diffraction peak obtained by X-ray diffraction of the region shown by the symbol R in Figure 2 is 1.58° or more.

[0036] When X-ray diffraction is performed on a polycrystalline metal material, diffracted rays are generated from crystal planes that satisfy the Bragg reflection condition for the incident X-rays. These diffracted X-rays produce conical Debye rings with the incident X-rays as their axis.

[0037] The shape of the Debye rings is affected by the crystal structure of the metal; the finer and more uniform the crystals, the stronger the diffraction peaks of the Debye rings obtained. On the other hand, if the crystals are coarse, the Debye rings will not be clearly visible.

[0038] In materials that have undergone recrystallization, the Debye rings are often not clearly visible, but the condition of the material can be understood from the locally obtained diffraction peaks. In particular, the inventors have found that the half-width of the diffraction peak correlates with the mechanical properties of the material.

[0039] Furthermore, the suspension arm member 100 has a 0.2% yield strength in accordance with JIS Z2241:2011 of, for example, 300 MPa or more, preferably 302 MPa or more, and more preferably 304 MPa or more.

[0040] 1 and 2 show an example in which the suspension arm member is an A-type arm comprising a first arm portion 1, a second arm portion 2, and an arm connecting portion 3, but the present invention is not limited to the above example and can also be applied to suspension arm members of other shapes. In suspension arm members of other shapes, it is sufficient that the half-width of the diffraction peak of the Debye rings obtained by X-ray diffraction at the location where the processing rate is thought to be highest is 1.58° or more.

[0041] [Manufacturing Method of Suspension Arm Member] Next, a manufacturing method of the suspension arm member will be described. A manufacturing method of a suspension arm member according to one embodiment of the present invention comprises a molten metal forming step of obtaining a molten alloy having the same composition as the aluminum alloy forged product, a casting step of casting the molten alloy to obtain a cast product, a forging step of forging the obtained cast product at a temperature of 470°C or higher and 500°C or lower to obtain a forged product, a solution treatment step of heating the forged product at a temperature of 500°C or higher, a water quenching step of water quenching the forged product after the solution treatment, and an aging treatment step of heat treating the forged product that has been through the water quenching step.

[0042] A method for manufacturing a suspension arm member according to an embodiment of the present invention includes, for example, a molten metal forming step, a casting step, a forging step, a solution treatment step, a hardening treatment step, and an aging treatment step.

[0043] (Molten Metal Forming Process) The molten metal forming process is a process of melting raw materials to obtain a molten aluminum alloy having a composition adjusted. The composition of the molten aluminum alloy is adjusted to contain Cu in the range of 0.2 mass% to 0.4 mass%, Mg in the range of 0.9 mass% to 1.2 mass%, Si in the range of 0.6 mass% to 0.9 mass%, Mn in the range of 0.05 mass% to 0.15 mass%, Fe in the range of 0.15 mass% to 0.30 mass%, Cr in the range of 0.2 mass% to 0.35 mass%, Ti in the range of 0.01 mass% to 0.05 mass%, B in the range of 0.0010 mass% to 0.0050 mass%, and the balance consisting of Al and inevitable impurities. The composition of the molten aluminum alloy corresponds to the composition of the aluminum alloy of the suspension arm member according to the above embodiment.

[0044] By carrying out the subsequent steps using a molten aluminum alloy of the above composition, it is possible to provide a suspension arm component having stable properties even if it exhibits a recrystallized structure. Note that virgin aluminum is aluminum with a concentration of 99% or more, obtained by subjecting alumina produced from minerals to electrolysis, a process known as electrorefining.

[0045] A molten aluminum alloy can be obtained by heating and melting an aluminum alloy. Alternatively, the aluminum alloy may be formed by melting a mixture containing the elements or compounds containing two or more elements that are raw materials for the aluminum alloy, in proportions that produce the desired aluminum alloy. For example, to control the grain size of the aluminum alloy produced in the casting process, Ti or B may be mixed as a grain refiner, such as an Al-Ti-B rod.

[0046] Alternatively, the molten aluminum alloy may be prepared by melting 10% or more of scrap aluminum alloys of 1000, 2000, 3000, 4000, 5000, 6000, or 7000 series, with the remainder being new aluminum ingots and the above-mentioned additive elements, to obtain a molten aluminum alloy having a composition adjusted. In this case, an Al-Mg-Si suspension arm component that is less susceptible to recrystallization and has excellent mechanical properties at room temperature can be obtained. Note that new aluminum ingots are aluminum with a purity of, for example, 99% or higher, obtained by subjecting alumina produced from minerals to electrolysis, a process known as electrolytic refining.

[0047] (Casting Process) In the casting process, a molten aluminum alloy (liquid phase) is cooled and solidified into a solid (solid phase) to obtain an aluminum alloy cast product. The casting process is preferably carried out by continuous casting. For example, a vertical continuous casting method or a horizontal continuous casting method can be used for the casting process. Below, a method for manufacturing a suspension arm member according to one embodiment of the present invention will be described, taking as an example a case where the casting process is carried out by horizontal continuous casting.

[0048] Horizontal continuous casting apparatuses that can be used to produce the aluminum alloy cast product of this embodiment are shown in Figures 3 and 4. Figure 3 is a cross-sectional view showing an example of the vicinity of the mold 12 of the horizontal continuous casting apparatus 10. Figure 4 is an enlarged cross-sectional view of a main portion of the horizontal continuous casting apparatus 10 near the cooling water cavity 24.

[0049] The horizontal continuous casting apparatus 10 shown in Figures 3 and 4 has a molten metal receiving portion (tundish) 11, a hollow cylindrical mold 12, and a refractory plate-like body (heat insulating member) 13 arranged between one end side 12a of the mold 12 and the molten metal receiving portion 11.

[0050] The molten metal receiving portion 11 is composed of a molten metal inlet portion 11 a that receives the molten aluminum alloy M obtained in the molten metal forming process described above, a molten metal holding portion 11 b, and an outlet portion 11 c that flows into the hollow portion 21 of the mold 12.

[0051] The molten metal receiving portion 11 maintains the upper liquid level of the molten aluminum alloy M at a position higher than the upper surface of the hollow portion 21 of the mold 12, and in the case of multiple casting, stably distributes the molten aluminum alloy M to each mold 12.

[0052] The molten aluminum alloy M held in the molten metal holding portion 11b in the molten metal receiving portion 11 is poured into the hollow portion 21 of the mold 12 through a pouring passage 13a provided in the refractory plate 13. The molten aluminum alloy M supplied into the hollow portion 21 is then cooled and solidified by a cooling device 23 (described later) and drawn out from the other end 12b of the mold 12 as an aluminum alloy rod B, which is a solidified ingot.

[0053] A drawing drive device (not shown) that draws out the cast aluminum alloy rod B at a constant speed may be installed at the other end 12b of the mold 12. It is also preferable that a synchronized cutting machine (not shown) that cuts the continuously drawn aluminum alloy rod B to a desired length be installed.

[0054] The refractory plate 13 is a member that blocks heat transfer between the molten metal receiver 11 and the mold 12, and may be made of materials such as calcium silicate, alumina, silica, a mixture of alumina and silica, silicon nitride, silicon carbide, graphite, etc. Such a refractory plate 13 may also be made up of multiple layers made of different materials.

[0055] In this embodiment, the mold 12 is a hollow cylindrical member made of, for example, one or a combination of two or more materials selected from aluminum, copper, or alloys thereof. The materials for the mold 12 may be selected from an optimum combination in terms of thermal conductivity, heat resistance, and mechanical strength.

[0056] The hollow portion 21 of the mold 12 is formed to have a circular cross section in order to cast the aluminum alloy rod B into a cylindrical rod shape, and the mold 12 is held so that the mold central axis (central axis) C passing through the center of this hollow portion 21 is aligned approximately horizontally.

[0057] The inner peripheral surface 21a of the hollow portion 21 of the mold 12 is formed at an elevation angle of 0° to 3° (more preferably 0° to 1°) with respect to the mold central axis C toward the casting direction of the aluminum alloy bar B (see FIG. 3). That is, the inner peripheral surface 21a is configured in a tapered shape that opens like a cone toward the casting direction. The angle of this taper is the elevation angle.

[0058] If the elevation angle is less than 0°, the aluminum alloy rod B encounters resistance at the other end 12b, which is the mold outlet, when it is drawn out of the mold 12, which may make casting difficult. On the other hand, if the elevation angle exceeds 3°, the inner peripheral surface 21a will not be in sufficient contact with the molten aluminum alloy M, which may reduce the heat transfer effect from the molten aluminum alloy M and the solidified shell formed by cooling and solidifying it to the mold 12, which may result in insufficient solidification. As a result, this is not preferable because it may lead to casting problems such as the formation of a remelted skin on the surface of the aluminum alloy rod B or the ejection of unsolidified molten aluminum alloy M from the end of the aluminum alloy rod B.

[0059] The cross-sectional shape of the hollow portion 21 of the mold 12 (the planar shape when the hollow portion 21 of the mold 12 is viewed from the other end side 21b) may be selected to match the shape of the aluminum alloy rod to be cast, such as a triangular or rectangular cross-sectional shape, a polygonal, semicircular, elliptical, or an irregular cross-sectional shape having no axis or plane of symmetry, in addition to the circular shape of this embodiment.

[0060] A fluid supply pipe 22 is disposed at one end 12a of the mold 12 to supply a lubricating fluid into the hollow portion 21 of the mold 12. The lubricating fluid supplied from the fluid supply pipe 22 can be one or more lubricating fluids selected from a gas lubricant and a liquid lubricant. When supplying both a gas lubricant and a liquid lubricant, it is preferable to provide separate fluid supply pipes for each. The lubricating fluid supplied under pressure from the fluid supply pipe 22 is supplied into the hollow portion 21 of the mold 12 through an annular lubricant supply port 22a.

[0061] In this embodiment, the lubricating fluid is supplied under pressure from the lubricant supply port 22a to the inner circumferential surface 21a of the mold 12. Note that the liquid lubricant may be heated to decompose into a gas and then supplied to the inner circumferential surface 21a of the mold 12. Alternatively, a porous material may be disposed in the lubricant supply port 22a, and the lubricating fluid may be allowed to seep out onto the inner circumferential surface 21a of the mold 12 through the porous material.

[0062] A cooling device 23, which is a cooling means for cooling and solidifying the molten aluminum alloy M, is formed inside the mold 12. The cooling device 23 of this embodiment has a cooling water cavity 24 that accommodates cooling water W for cooling the inner circumferential surface 21 a of the hollow portion 21 of the mold 12, and a cooling water injection passage 25 that connects the cooling water cavity 24 with the hollow portion 21 of the mold 12.

[0063] The cooling water cavity 24 is formed in a ring shape surrounding the hollow portion 21 outside the inner circumferential surface 21 a of the hollow portion 21 inside the mold 12 , and cooling water W is supplied to the cavity 24 via a cooling water supply pipe 26 .

[0064] The inner surface 21a of the mold 12 is cooled by the cooling water W contained in the cooling water cavity 24, which removes heat from the molten aluminum alloy M filling the hollow portion 21 of the mold 12 from the surface in contact with the inner surface 21a of the mold 12, forming a solidified shell on the surface of the molten aluminum alloy M.

[0065] The cooling water jetting passages 25 spray cooling water W directly from shower openings 25a facing the hollow portion 21 toward the aluminum alloy rods B at the other end 12b of the mold 12 to cool the aluminum alloy rods B. The vertical cross-sectional shape of the cooling water jetting passages 25 may be, for example, semicircular, pear-shaped, or horseshoe-shaped, in addition to the circular shape of this embodiment.

[0066] In this embodiment, the cooling water W supplied through the cooling water supply pipe 26 is first stored in the cooling water cavity 24 to cool the inner peripheral surface 21 a of the hollow portion 21 of the mold 12, and then the cooling water W in the cooling water cavity 24 is sprayed toward the aluminum alloy rod B through the cooling water spray passage 25. However, it is also possible to configure these to be supplied by separate cooling water supply pipes.

[0067] The length from the position where the extension of the central axis of the shower opening 25a of the cooling water injection passage 25 hits the surface of the cast aluminum alloy rod B to the contact surface between the mold 12 and the refractory plate 13 is called the effective mold length L, and this effective mold length L is preferably, for example, 10 mm or more and 40 mm or less. If this effective mold length L is less than 10 mm, a good coating cannot be formed, making casting impossible. If it exceeds 40 mm, the effect of forced cooling is reduced, solidification by the mold wall becomes dominant, and the contact resistance between the mold 12 and the molten aluminum alloy M or the aluminum alloy rod B increases, which may cause cracks on the casting surface or tearing inside the mold, making casting unstable.

[0068] It is preferable that the supply of the cooling water W to the cooling water cavity 24 and the spray of the cooling water W from the shower opening 25a of the cooling water spray passage 25 can be controlled by control signals from a control device (not shown).

[0069] The cooling water cavity 24 is formed so that an inner bottom surface 24 a near the hollow portion 21 of the mold 12 is parallel to the inner peripheral surface 21 a of the hollow portion 21 of the mold 12 .

[0070] Note that "parallel" here also includes the case where the inner peripheral surface 21a of the hollow portion 21 of the mold 12 is formed at an elevation angle of 0° to 3° relative to the inner bottom surface 24a of the cooling water cavity 24, i.e., the case where the inner bottom surface 24a is inclined from 0° to 3° relative to the inner peripheral surface 21a.

[0071] As shown in FIG. 4 , the cooling wall portion 27 of the mold 12, which is the portion where the inner bottom surface 24 a of the cooling water cavity 24 faces the inner peripheral surface 21 a of the hollow portion 21 of the mold 12, has a heat flux value per unit area of ​​10×10 20 from the molten aluminum alloy M in the hollow portion 21 to the cooling water W in the cooling water cavity 24. ５ W / m ２ That's it, 50 x 10 ５ W / m ２ It is formed so as to fall within the following range.

[0072] The mold 12 may be formed so that the thickness t of the cooling wall portion 27 of the mold 12, i.e., the distance between the inner bottom surface 24a of the cooling water cavity 24 and the inner peripheral surface 21a of the hollow portion 21 of the mold 12, is within a range of, for example, 0.5 mm to 3.0 mm, preferably 0.5 mm to 2.5 mm. The material for forming the mold 12 may be selected so that the thermal conductivity of at least the cooling wall portion 27 of the mold 12 is within a range of 100 W / m·K to 400 W / m·K.

[0073] In FIG. 4 , molten aluminum alloy M in a molten metal receiving portion 11 is supplied through a refractory plate 13 to one end 12 a of a mold 12, which is held so that the central axis C of the mold is substantially horizontal, and is forcibly cooled at the other end 12 b of the mold 12 to form an aluminum alloy rod B.

[0074] The aluminum alloy rod B is drawn out at a constant speed by a drawing drive device (not shown) installed near the other end 12b of the mold 12, and is continuously cast to form a long aluminum alloy rod B. The drawn aluminum alloy rod B is then cut to a desired length by, for example, a synchronous cutting machine (not shown).

[0075] The composition ratio of the cast aluminum alloy rod B can be confirmed, for example, by a method using a photoelectric emission spectrophotometer (e.g., PDA-5500 manufactured by Shimadzu Corporation, Japan) as described in "JIS H 1305".

[0076] The difference in height between the liquid level of the molten aluminum alloy M stored in the molten metal receiver 11 and the upper inner circumferential surface 21a of the mold 12 is preferably 0 mm to 250 mm (more preferably 50 mm to 170 mm). By setting the difference in height within this range, the pressure of the molten aluminum alloy M supplied into the mold 12 and the lubricating oil and the gas produced by vaporizing the lubricating oil are suitably balanced, resulting in stable castability.

[0077] The liquid lubricant may be a vegetable oil, such as rapeseed oil, castor oil, or salad oil, which are preferred because they have little adverse effect on the environment.

[0078] The lubricating oil supply rate is preferably 0.05 mL / min to 5 mL / min (more preferably 0.1 mL / min to 1 mL / min). If the supply rate is too low, the molten aluminum alloy M in the aluminum alloy rod B may not solidify due to insufficient lubrication and may leak from the mold 12. If the supply rate is too high, the excess may get mixed into the aluminum alloy rod B and cause internal defects.

[0079] The casting speed, which is the speed at which the aluminum alloy rod B is withdrawn from the mold 12, is preferably 200 mm / min or more and 1500 mm / min or less (more preferably 400 mm / min or more and 1000 mm / min or less). This is because, if the casting speed is within this range, the network structure of the crystallized matter formed by casting becomes uniform and fine, which increases the resistance of the aluminum matrix to deformation at high temperatures and improves the high-temperature mechanical strength.

[0080] The amount of cooling water sprayed from the shower openings 25a of the cooling water spray passages 25 is preferably 10 L / min to 50 L / min (more preferably 25 L / min to 40 L / min) per mold. If the amount of cooling water is less than this range, the molten aluminum alloy M may not solidify and leak from the mold 12. Furthermore, the surface of the cast aluminum alloy rod B may remelt, forming an inhomogeneous structure that may remain as internal defects. On the other hand, if the amount of cooling water is greater than this range, the mold 12 may lose too much heat, causing it to solidify prematurely.

[0081] The average temperature of the molten aluminum alloy M flowing from the molten metal receiver 11 into the mold 12 is preferably, for example, 650°C or higher and 750°C or lower (more preferably 680°C or higher and 720°C or lower). If the temperature of the molten aluminum alloy M is too low, coarse crystallized products may be formed in the mold 12 or before that, and may be incorporated as internal defects inside the aluminum alloy rod B. On the other hand, if the temperature of the molten aluminum alloy M is too high, a large amount of hydrogen gas may be easily incorporated into the molten aluminum alloy M, which may be incorporated as porosity in the aluminum alloy rod B and cause internal cavities.

[0082] In the cooling wall portion 27 of the mold 12, the heat flux value per unit area from the molten aluminum alloy M in the hollow portion 21 to the cooling water W in the cooling water cavity 24 is 10×10 ５ W / m ２ Above 50 x 10 ５ W / m ２ By keeping the temperature within the following range, it is possible to prevent the aluminum alloy rod B from seizing.

[0083] The cooling wall 27 of the mold 12 receives heat from the molten aluminum alloy M and performs heat exchange by cooling this heat with the cooling water W contained in the cooling water cavity 24. Regarding the state of this heat exchange, attention was focused on the heat flux per unit area, as shown in the explanatory diagram in Figure 5. The heat flux per unit area is expressed by the following equation (1) using Fourier's law. Q = -k × (T1 - T2) / L (1) Q: heat flux k: thermal conductivity (W / m·K) of the location through which heat passes (in this embodiment, the cooling wall 27 of the mold 12) T1: low-temperature side temperature of the location through which heat passes (in this embodiment, the inner bottom surface 24 a of the cooling water cavity 24) T2: high-temperature side temperature of the location through which heat passes (in this embodiment, the inner circumferential surface 21 a of the hollow portion 21 of the mold 12) L: section length (mm) of the location through which heat passes (in this embodiment, the thickness t of the cooling wall 27 of the mold 12)

[0084] Good results were obtained even when the amount of lubricating oil was reduced during casting. Based on the mold material, thickness, and temperature measurement data, the heat flux value per unit area was 10 × 10 ５ W / m ２ By configuring the cooling wall portion 27 of the mold 12 so that the heat flux value per unit area is 50×10 or more, it is possible to prevent the cast aluminum alloy rod B from seizing. ５ W / m ２ It is preferable to do the following:

[0085] To set the heat flux value of the cooling wall portion 27 of the mold 12 within this range, the mold 12 may be formed so that the thickness t of the cooling wall portion 27 of the mold 12 is, for example, in the range of 0.5 mm to 3.0 mm. Also, the thermal conductivity of at least the cooling wall portion 27 of the mold 12 may be set in the range of 100 W / m·K to 400 W / m·K.

[0086] When producing the aluminum alloy rod B of this embodiment, the horizontal continuous casting apparatus 10 described above is used to continuously supply the molten aluminum alloy M stored in the molten metal receptacle 11 from one end 12a of the mold 12 into the hollow portion 21. In addition, cooling water W is supplied to the cooling water cavity 24, and a lubricating fluid, for example, lubricating oil, is supplied from the fluid supply pipe 22.

[0087] The molten aluminum alloy M supplied into the hollow portion 21 is cooled to a temperature at which the heat flux value per unit area of ​​the cooling wall portion 27 is 10×10 ５ W / m ２ The aluminum alloy rod B is cooled and solidified under the above conditions to be cast. During casting of the aluminum alloy rod B, it is preferable to set the wall surface temperature of the cooling wall portion 27 of the mold 12, which is cooled by the cooling water W, to 100° C. or less.

[0088] The aluminum alloy rod B thus obtained has a heat flux value per unit area in the cooling wall portion 27 of 10×10 ５ W / m ２ Cooling and solidification under the above conditions suppresses adhesion of reaction products, such as carbides, that occur due to contact between the lubricating oil gas and the molten aluminum alloy M. This eliminates the need to remove carbides and the like from the surface of the aluminum alloy rod B by cutting, and allows the aluminum alloy rod B to be produced with a high yield.

[0089] The casting process for obtaining a cast product from the molten aluminum alloy M is not limited to the above-mentioned horizontal continuous casting method, and known continuous casting methods such as vertical continuous casting can be used. Vertical continuous casting methods are classified into the float method and the hot top method depending on the method of supplying the molten aluminum alloy M to the mold (casting die 12), and the following will briefly explain the case where the hot top method is used.

[0090] The casting equipment used in the hot top method is equipped with a mold, a molten metal receiving vessel (header), etc. The molten metal supplied to the molten metal receiving vessel passes through a tapping port and then through the header, where the flow rate is adjusted, and enters a cylindrical mold placed almost horizontally, where it is forcibly cooled and a solidified shell is formed on the outer surface of the molten metal.

[0091] Furthermore, cooling water is sprayed directly onto the casting as it is pulled out of the mold, allowing the solidification of the metal to progress throughout the casting as it is continuously pulled out. Molds are generally made of metal materials with good thermal conductivity and have a hollow structure to allow the introduction of a coolant inside.

[0092] The refrigerant to be used may be selected from among those that are industrially available, but water is recommended from the viewpoint of ease of use.

[0093] The mold used in this embodiment is appropriately selected from metals such as copper and aluminum, or graphite, from the viewpoint of heat transfer performance and durability at the contact point with the molten metal. The header is generally made of a refractory material and is installed above the mold. The material and size of the header may be appropriately selected depending on the composition range of the alloy to be cast and the dimensions of the cast product, and are not particularly limited.

[0094] The average cooling rate during casting may be appropriately selected from a generally recommended range, such as 10 to 300°C / sec. The casting speed may be appropriately selected from a range generally used in horizontal continuous casting, such as 200 to 600 mm / min.

[0095] In the casting method described above, there is no particular limitation on the diameter of the cast product to be produced, and the method is suitably used for rods having a diameter of 30 to 100 mm.

[0096] (Homogenization Heat Treatment Step) The homogenization heat treatment step is a step in which the aluminum alloy casting obtained in the casting step is subjected to homogenization heat treatment to homogenize microsegregations caused by solidification, precipitate supersaturated solid solution elements, and transform metastable phases into equilibrium phases.

[0097] In this embodiment, the aluminum alloy casting obtained in the casting process may be subjected to a homogenization heat treatment in which the aluminum alloy casting is held at a temperature of 370°C or higher and 560°C or lower for 4 to 10 hours, or the homogenization heat treatment may be omitted. By performing the homogenization heat treatment within this temperature range, the aluminum alloy casting is homogenized and solute atoms are sufficiently introduced. Therefore, the required strength can be increased by the subsequent aging treatment. When the homogenization heat treatment is performed, the aluminum alloy casting is heated and then cooled. For example, the aluminum alloy forged product is cooled to room temperature.

[0098] (Forging process) The forging process is a process in which an aluminum alloy casting after casting or after the homogenization heat treatment process is formed into a predetermined size to obtain a forging material, the obtained forging material is heated to a predetermined temperature, and then pressure is applied in a press to form it into a mold.

[0099] The forging material preferably has an in-plane average grain size of 100 μm or less, more preferably 80 μm or less, and for example, 30 μm or more.

[0100] In this embodiment, a forging material is forged at a heating temperature of 470°C or higher and 500°C or lower to obtain a forged product (e.g., an automobile suspension arm component, etc.). For example, the forging process involves holding (heating) the material at the above heating temperature (material heating temperature) for 40 minutes or longer, preferably 60 minutes or longer and 3 hours or shorter, followed by forging. Forging the forging material within the above temperature range can stabilize the properties of the forged product. If the temperature of the forging material at the start of forging is lower than 470°C, abnormal recrystallization may be promoted in the solution treatment process after forging, resulting in a decrease in strength. Furthermore, if the temperature exceeds 500°C, the influence of processing heat during forging may promote recrystallization in the process up to the solution treatment, which may also result in a decrease in strength. Furthermore, if the starting temperature of forging of the forging material is too low, the deformation resistance will increase, preventing sufficient processing, while if it is too high, defects such as forging cracks and eutectic melting may occur. Therefore, it is preferable to start forging the forging material at the above temperature. It is preferable to heat the die in order to prevent the temperature of the forging material from decreasing during the forging process. The heating temperature of the cast product in the forging process may be 480°C or higher or 490°C or lower.

[0101] As shown in the examples and comparative examples, there is a correlation between the half-width of the diffraction peak of the Debye rings obtained by X-ray diffraction and the 0.2% proof stress. A large half-width indicates a large variation between the aluminum crystal lattices. The variation between the crystal lattices increases as the dislocation density between the crystal lattices increases. The dislocation density correlates with strength. In this embodiment, by deliberately setting the half-width within the above range, it is possible to stably increase the 0.2% proof stress even when recrystallization occurs.

[0102] (Solution Treatment Step) The solution treatment step is a step in which the forged product obtained in the forging step is heated to bring about a solution, thereby alleviating the strain introduced into the cast product and causing the solute elements to dissolve.

[0103] In this embodiment, it is preferable to perform solution treatment by holding the forged product at a treatment temperature of 530°C or higher and 560°C or lower for 0.3 hours to 4 hours, and then holding the product at a treatment temperature of 550°C or lower for 1.5 hours to 3 hours. The heating rate from room temperature to the above-mentioned treatment temperature is preferably 5.0°C / min or higher. If the treatment temperature is lower than 530°C, the solute elements may not be dissolved sufficiently. On the other hand, if the treatment temperature exceeds 560°C, the solute elements may be dissolved more easily, but eutectic melting or recrystallization may occur. Furthermore, if the heating rate is lower than 5.0°C / min, the Mg ２ Since coarse Si precipitates may occur, the heating rate is preferably set to 5.0°C / min or more as described above. On the other hand, if the treatment temperature is less than 530°C, the solution treatment may not progress, making it difficult to achieve high strength by aging precipitation.

[0104] (Quenching Treatment Step) The quenching treatment step is a step in which the forged product in the solid solution state obtained by the solution treatment step is rapidly cooled to form a supersaturated solid solution.

[0105] In this embodiment, the forged product is quenched by being placed in a water tank containing water (quenching water). The water temperature in the water tank is preferably 20°C or higher and 60°C or lower. The forged product is preferably placed in the water tank after the solution treatment for 5 seconds or higher and 60 seconds or lower so that the entire surface of the forged product is in contact with the water. The submersion time of the forged product varies depending on the size of the casting, but is, for example, between 5 minutes and 40 minutes.

[0106] (Aging Treatment Step) The aging treatment step is a step in which the forged product is heated and held at a relatively low temperature to precipitate supersaturated solid-solution elements, thereby imparting an appropriate hardness.

[0107] In this embodiment, the forged product after the quenching process is heated to a temperature of 170°C or higher and 220°C or lower, and is held at that temperature for 0.5 hours or longer and 7.0 hours or shorter, thereby carrying out aging treatment. Preferably, the forged product is heated to a temperature of 175°C or higher and 190°C or lower, and is held at that temperature for 4 hours or longer, thereby carrying out aging treatment. If the heating temperature is lower than 170°C or the holding time is shorter than 0.5 hours, the Mg content, which improves the tensile strength, will be lower. ２ On the other hand, if the treatment temperature exceeds 220°C, the Si-based precipitates may not grow sufficiently. ２ The Si-based precipitates become too coarse, i.e., Mg ２ If the Si-based precipitates are formed coarsely, there is a risk that the tensile strength will not be improved sufficiently.

[0108] The method for manufacturing a suspension arm component according to this embodiment makes it possible to manufacture the suspension arm component according to the above embodiment, and to provide a suspension arm component with high strength and stable characteristics even when it exhibits a recrystallized structure.

[0109] The upper and / or lower limits of the numerical ranges described herein can be arbitrarily combined to define a preferred range. For example, the upper and lower limits of the numerical ranges can be arbitrarily combined to define a preferred range, the upper limits of the numerical ranges can be arbitrarily combined to define a preferred range, and the lower limits of the numerical ranges can be arbitrarily combined to define a preferred range.

[0110] Throughout this disclosure, singular terms should be understood to include the plural concept unless otherwise specified. Thus, singular articles (e.g., "a," "an," "the," etc. in English) should be understood to include the plural concept unless otherwise specified.

[0111] The effects of the present invention will be made clearer by the following examples. Note that the present invention is not limited to the following examples and can be practiced with appropriate modifications within the scope of the present invention.

[0112] Example 1 First, a molten aluminum alloy having the following alloy composition was prepared: Cu: 0.33 mass%, Mg: 1.02 mass%, Si: 0.73 mass%, Mn: 0.11 mass%, Fe: 0.24 mass%, Cr: 0.22 mass%, Ti: 0.023 mass%, B: 0.0026 mass%, Al: balance.

[0113] The prepared molten aluminum alloy was used as a raw material, and a continuously cast rod of 200 L with a diameter of 78 mm and a circular cross section was produced using the horizontal continuous casting apparatus described above.

[0114] The continuously cast rod was sized to fit the die used in the forging process to produce a forging blank. The resulting forging blank was heated at a heating temperature (blank heating temperature) of 470°C for 1 hour and then forged to produce a forged product. The die temperature used was 200°C. The average grain size (average line length per crystal) of the forging blank was measured using JIS G0551:2020, Annex A, A.2 (intercept method) and was found to be 65 μm.

[0115] Next, the obtained forged product was subjected to a solution treatment under the following conditions: heating rate: 10°C / min, temperature: 530°C, holding time: 3 hours

[0116] Next, a water quenching process was carried out under the following conditions: Quenching water temperature: 40°C Time from solution treatment to quenching: 10 seconds Time for submerging the forged product in water: 10 minutes

[0117] Next, an aging treatment step was carried out under the following conditions: temperature: 180° C., holding time: 6 hours. By the above method, an A-shaped suspension arm member of Example 1 was produced.

[0118] Example 2 An A-shaped suspension arm member was produced in the same manner as in Example 1, except that the heating temperature of the forging material in the forging process was changed to 480°C.

[0119] Example 3 An A-shaped suspension arm member was produced in the same manner as in Example 1, except that the heating temperature of the forging material in the forging process was changed to 500°C.

[0120] Comparative Example 1 An A-shaped suspension arm member was produced in the same manner as in Example 1, except that the heating temperature of the forging material in the forging step was changed to 520°C.

[0121] Comparative Example 2 An A-shaped suspension arm member was produced in the same manner as in Example 1, except that the heating temperature of the forging material in the forging step was changed to 510°C.

[0122] Comparative Example 3 An A-shaped suspension arm member was produced in the same manner as in Example 1, except that the heating temperature of the forging material in the forging step was changed to 450°C.

[0123] (X-ray diffraction) X-ray diffraction was performed on the A-type suspension arm members made of the polycrystalline metal material of Examples 1 to 3 and Comparative Examples 1 to 3 at a position corresponding to region R in Figure 2. That is, X-ray diffraction was performed on a part of the outer periphery of a cross section passing through the axial midpoint of the longest arm section of the arm section connecting the wheel-side connecting section and the vehicle body-side connecting section, which is the region with the highest processing rate. This portion was a section with a processing rate of over 80%, specifically 85%.

[0124] The conditions for X-ray diffraction are as follows: X-ray diffraction apparatus: Pulstec μ-x360s X-ray incident angle: 28.8 degrees X-ray tube current: 1 mA X-ray tube voltage: 30 kV Distance between measuring apparatus and sample: 50 mm Aluminum diffraction planes: 311, 222 planes Tube: Co tube X-ray tube wavelength Kα: 1.79021 Å X-ray tube wavelength Kβ: 1.62075 Å

[0125] Figure 6 shows the results of X-ray diffraction analysis of the first arm portion of the suspension arm member of Example 1. As shown in Figure 6, the Debye rings of the polycrystalline metal material that constitutes the suspension arm member of Example 1 were not clearly obtained. This suggests that in Example 1, recrystallization occurs and some of the crystals are coarse. Figure 7 shows the results of analysis of the diffraction intensity near the diffraction peaks of the Debye rings in the X-ray diffraction results of Figure 6. The analysis results shown in Figure 7 indicated that the half-value width was 1.587 (degrees).

[0126] X-ray diffraction was performed on the suspension arm members of Examples 2 and 3 and Comparative Examples 1 to 3 in the same manner as in Example 1. Although clear Debye rings could not be obtained in any of the samples, diffraction peaks were confirmed. For these samples as well, the half-width was measured from the analysis results of the diffraction intensity.

[0127] (0.2% proof stress) Tensile test specimens were taken from the suspension arm members of Examples 1 to 3 and Comparative Examples 1 to 3, and tensile tests were carried out using a method in accordance with JIS Z2241: 2011. The tensile test specimens were taken from the recesses of the arm portion connecting the wheel side connecting portion and the vehicle body side connecting portion of the suspension arm member, with the longitudinal direction extending from the midpoint in the axial direction of the longer arm portion.

[0128] Table 1 summarizes the forging process conditions (material heating temperature and material heating time) when producing the aluminum alloy forged members of Examples 1 to 3 and Comparative Examples 1 to 3, as well as the half widths of the diffraction peaks of the obtained samples and the 0.2% proof stress.

[0129]

[0130] As shown in Table 1, the half-width of the diffraction peak in X-ray diffraction varies depending on the temperature in the forging process, and it was confirmed that this half-width correlates with the 0.2% proof stress. In Examples 1 to 3, the half-width was within the range of 1.580° to 1.610°. This correlation was first discovered by the present inventors. As described above, in all of Examples 1 to 3 and Comparative Examples 1 to 3, it was not possible to obtain clean Debye rings and the samples exhibited recrystallized structures. However, it was confirmed that the present invention can provide a suspension arm member with stable properties that exhibit a high 0.2% proof stress.

[0131] REFERENCE SIGNS LIST 1 First arm portion 2 Second arm portion 3 Arm connecting portion 4 Wheel side connecting portion 5 First vehicle body side connecting portion 6 Second vehicle body side connecting portion 7 Outer periphery 8 Inner periphery 9 Recessed portion 10 Horizontal continuous casting device 11 Molten metal receiving portion (tundish) 11a Molten metal inlet portion 11b Molten metal holding portion 11c Outlet portion 12 Mold 12a One end side 12b Other end side 13 Refractory plate body (heat insulating member) 13a Molten metal pouring passage 21 Hollow portion 21a Inner periphery surface 21b Other end side 22 Fluid supply pipe 22a Lubricant supply port 23 Cooling device 24 Cooling water cavity 24a Inner bottom surface 25 Cooling water injection passage 25a Shower opening 26 Cooling water supply pipe 27 Cooling wall portion 100 Suspension arm member B Aluminum alloy rod C Mold central axis (central axis) M Molten aluminum alloy P Particles PDA-5500 Manufactured by Shimadzu Corporation, Japan R Region Si Primary crystal W Cooling water X Incident μ-x360s Manufactured by Pulstec

Claims

1. An aluminum alloy having an alloy composition containing Cu in the range of 0.2% by mass or more and 0.4% by mass or less, Mg in the range of 0.9% by mass or more and 1.2% by mass or less, Si in the range of 0.6% by mass or more and 0.9% by mass or less, Mn in the range of 0.05% by mass or more and 0.15% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Cr in the range of 0.2% by mass or more and 0.35% by mass or less, Ti in the range of 0.01% by mass or more and 0.05% by mass or less, and B in the range of 0.0010% by mass or more and 0.0050% by mass or less, with the balance being Al and inevitable impurities, and having a half-value width at the diffraction peak of Debye obtained by X-ray diffraction of 1.58° or more, a suspension arm member.

2. A suspension arm member according to claim 1, comprising a wheel-side connecting portion, a first vehicle-body-side connecting portion, a second vehicle-body-side connecting portion, a first arm portion connecting the wheel-side connecting portion and the first vehicle-body-side connecting portion, and a second arm portion connecting the wheel-side connecting portion and the second vehicle-body-side connecting portion, wherein the first arm portion is longer than the second arm portion, the half-value width is the half-value width at the diffraction peak of Debye obtained by X-ray diffraction with respect to the first arm portion, and the 0.2% proof stress is 300 MPa or more.

3. A molten metal forming step of obtaining a molten alloy having an alloy composition containing Cu in the range of 0.2% by mass or more and 0.4% by mass or less, Mg in the range of 0.9% by mass or more and 1.2% by mass or less, Si in the range of 0.6% by mass or more and 0.9% by mass or less, Mn in the range of 0.05% by mass or more and 0.15% by mass or less, Fe in the range of 0.15% by mass or more and 0.30% by mass or less, Cr in the range of 0.2% by mass or more and 0.35% by mass or less, Ti in the range of 0.01% by mass or more and 0.05% by mass or less, B in the range of 0.0010% by mass or more and 0.0050% by mass or less, and the balance being Al and unavoidable impurities; a casting step of obtaining a cast product by casting the molten alloy; a forging step of forging the cast product at a temperature of 470°C or more and 500°C or less to obtain a forged product; a solution treatment step of holding the forged product at a temperature of 500°C or more; a quenching step of quenching the forged product after the solution treatment; and an aging treatment step of heat-treating the forged product that has undergone the quenching step. A method for manufacturing a suspension arm member.

4. In the solution treatment step, the forged product is held at a temperature of 530°C or more and 560°C or less for 0.3 hours or more and 3 hours or less. In the quenching step, quenching is performed using water at 60°C or less. In the aging treatment step, the forged product that has undergone the quenching step is heated at a temperature of 170°C or more and 220°C or less for 0.5 hours or more and 7.0 hours or less. The method for manufacturing a suspension arm member according to claim 3.

5. The casting step is performed by continuous casting. In the aging treatment step, the forged product that has undergone the quenching step is heated at a temperature of 175°C or more and 190°C or less for 4 hours or more. The method for manufacturing a suspension arm member according to claim 4.

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