Aluminum alloy, suspension member, method for manufacturing aluminum alloy, method for manufacturing suspension member

Abstract

The present invention provides an aluminum alloy, a suspension member, a method for manufacturing the aluminum alloy, and a method for manufacturing the suspension member, which can suppress the formation of recrystallized grains and the formation of an oxide layer on the surface during heat treatment. [Solution] The alloy has a composition containing Cu 0.3 in the range of 0.5 mass% to 0.5 mass%, Mg in the range of 0.65 mass% to 1.25 mass%, Si in the range of 0.9 mass% to 1.5 mass%, Mn in the range of 0.4 mass% to 1.1 mass%, Fe in the range of 0.15 mass% to 1.0 mass%, Cr in the range of 0.09 mass% to 0.25 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 Be in the range of 0.001 mass% to 0.01 mass%, with the remainder being Al and unavoidable impurities.

Description

Technical Field

[0001] The present invention relates to an aluminum alloy, a suspension member, a method for manufacturing an aluminum alloy, and a method for manufacturing a suspension member.

Background Art

[0002] In recent years, aluminum alloys are being increasingly used as structural members in various products, taking advantage of their light weight. For example, automotive underbody and bumper parts, which were conventionally made of high-tensile steel, are now often made of high-strength aluminum alloy materials. Automotive parts, such as suspension parts, were previously made exclusively of iron-based materials, but are increasingly being replaced with aluminum or aluminum alloy materials for the purpose of weight reduction.

[0003] In an automotive suspension system, the suspension arm is one of the important components and requires excellent corrosion resistance, high strength, and excellent workability. For this reason, as an aluminum alloy material, especially Al-Mg-Si-based alloys, especially A6061, are widely used. And such automotive parts are manufactured by performing forging, which is one of the plastic processing, on an aluminum alloy material as a processing material in order to improve strength.

[0004] Also, recently, due to the need to reduce costs, suspension parts obtained by forging a cast member as a raw material without extrusion and then performing solution treatment and artificial aging treatment (T6 treatment) have begun to be put into practical use, and for the purpose of further weight reduction, the development of high-strength aluminum alloys to replace conventional A6061 is underway (for example, see Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] In recent years, with the need to reduce CO2 emissions in manufacturing processes, there has been a growing demand for further weight reduction in automobiles, while the demand for aluminum alloys is on the rise. However, as a substitute for steel, aluminum alloys need to be as strong as, or even stronger than, steel. Controlling the crystal structure is crucial for achieving this high strength in aluminum alloys.

[0007] The control of the crystalline structure is greatly influenced by the conditions during forging. For example, when forging is performed at a low temperature before heating the material, in areas where the amount of distortion during processing is large, the accumulation of strain may lead to the formation of recrystallized grains in the subsequent heat treatment process. On the other hand, in the case of automotive suspension components, due to their complex shape, it is common to obtain suspension components by forging with deburring and then removing the burrs.

[0008] When this type of deburring forging is performed, the area near the burr experiences a large amount of distortion, making it prone to the formation of recrystallized grains. If these recrystallized grains occur in the bushing, which is a part connected to the vehicle's drive mechanism, and the area affected is large, there is a risk that the stress corrosion cracking resistance in the bushing when it is press-fitted may be significantly impaired.

[0009] To suppress the formation of these recrystallized grains, controlling the temperature-compensated strain rate (Zener-Hollomon factor: Z factor) is crucial. Keeping the Z factor below a certain level during the forging process is essential for suppressing recrystallized grain formation. The parameters of this Z factor are affected by temperature and strain, but temperature has a particularly significant effect; the higher the temperature, the more the formation of recrystallized grains is suppressed.

[0010] However, if the heating temperature of the forging material is increased before the forging process, in alloys containing Mg, the diffusion of Mg to the surface of the forging material is promoted by heating. The Mg diffused on the surface comes into contact with O2 in the atmosphere in a high-temperature heating atmosphere, which can cause an oxide layer (MgO) to form on the surface of the forging material. If an oxide layer is formed on the surface of the forging material, there is a concern that the amount of Mg that contributes to strength improvement through the heat treatment process will decrease, resulting in a decrease in surface hardness.

[0011] Furthermore, the oxide layer formed on the surface of the forged material remains in the product after forging, and during forging, the oxide layer deforms along the metal flow, creating gaps. When a heat treatment process is performed with these gaps present, the surface of the forged product expands, resulting in surface defects (blistering), which poses a problem.

[0012] The present invention has been made in view of the above technical background, and provides an aluminum alloy, a suspension member, a method for manufacturing an aluminum alloy, and a method for manufacturing a suspension member that can suppress the formation of recrystallized grains and the formation of an oxide layer on the surface when heat treatment is performed. [Means for solving the problem]

[0013] To solve the above problems, the aluminum alloy, suspension member, method for manufacturing the aluminum alloy, and method for manufacturing the suspension member according to one embodiment of the present invention are proposed to be the following means. (1) The aluminum alloy according to embodiment 1 of the present invention has an alloy composition containing Cu 0.3 in the range of mass% to 0.5 mass%, Mg in the range of 0.65 mass% to 1.25 mass%, Si in the range of 0.9 mass% to 1.5 mass%, Mn in the range of 0.4 mass% to 1.1 mass%, Fe in the range of 0.15 mass% to 1.0 mass%, Cr in the range of 0.09 mass% to 0.25 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 Be in the range of 0.001 mass% to 0.01 mass%, with the remainder being Al and unavoidable impurities.

[0014] (2) The suspension member of embodiment 2 of the present invention is formed from the aluminum alloy described in embodiment 1.

[0015] (3) The method for producing an aluminum alloy according to aspect 3 of the present invention comprises a molten metal forming step of forming a molten metal having an alloy composition in which Cu is contained in a range of 0.3 mass% to 0.5 mass%, Mg in a range of 0.65 mass% to 1.25 mass%, Si in a range of 0.9 mass% to 1.5 mass%, Mn in a range of 0.4 mass% to 1.1 mass%, Fe in a range of 0.15 mass% to 1.0 mass%, Cr in a range of 0.09 mass% to 0.25 mass%, Ti in a range of 0.01 mass% to 0.05 mass%, B in a range of 0.0010 mass% to 0.0050 mass%, and Be in a range of 0.001 mass% to 0.01 mass%, with the remainder being Al and unavoidable impurities; and a casting step of obtaining an aluminum alloy by casting the molten metal, wherein the casting step is performed at a cooling rate in the range of 10°C / second or more and 100°C / second or less.

[0016] (4) A method for manufacturing a suspension member according to aspect 4 of the present invention is a method for manufacturing a suspension member using the aluminum alloy of aspect 3, comprising: a forging step of heating the aluminum alloy in the range of 500°C to 570°C and forging to obtain a forged product; a solution treatment step of performing a solution treatment on the forged product in the range of 500°C to 570°C; a quenching step of performing a hardening treatment on the forged product that has undergone the solution treatment step at a temperature of 480°C or higher; and an aging treatment step of heating the forged product that has undergone the hardening step at a range of 175°C to 190°C for 4 hours or more.

[0017] (5) The method for manufacturing a suspension member according to aspect 5 of the present invention further comprises, in the method for manufacturing a suspension member according to aspect 4, a cold trimming step in which the excess material of the forged product is trimmed at 60°C or below as a post-forging step. [Effects of the Invention]

[0018] According to the present invention, it is possible to provide an aluminum alloy, a suspension member, a method for manufacturing an aluminum alloy, and a method for manufacturing a suspension member that suppress the generation of recrystallized grains during heat treatment and suppress the generation of an oxide layer on the surface.

Brief Description of the Drawings

[0019] [Figure 1] It is a schematic diagram enlarging the vicinity of the bush portion of the suspension member of one embodiment of the present invention. [Figure 2] It is a plan view enlarging the vicinity of the bush portion of the suspension member shown in FIG. 1. [Figure 3] It is a flowchart showing step by step the method for manufacturing an aluminum alloy and the method for manufacturing a suspension member as a series of processes. [Figure 4] It is a cross-sectional view showing a horizontal continuous casting apparatus that can be used in the casting process of the method for manufacturing an aluminum alloy of the present embodiment. [Figure 5] It is a partial enlarged cross-sectional view enlarging the vicinity of the cooling water cavity of the horizontal continuous casting apparatus. [Figure 6] It is a surface enlargement image in the bulge evaluation of the present invention example and the comparative example. [Figure 7] It is a surface enlargement image in the recrystallized grain evaluation of the comparative example.

Embodiments for Carrying Out the Invention

[0020] 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 enlarged portions of characteristic parts for convenience of understanding the characteristics, and the dimensional ratios of each component are not necessarily the same as the actual ones. Further, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto, and it can be appropriately changed and implemented without changing the effects.

[0021] [Aluminum Alloy] This document describes an aluminum alloy relating to one embodiment of the present invention.

[0022] The aluminum alloy of this embodiment has an alloy composition in which Cu 0.3 is contained in a range of 0.5 mass% to 0.5 mass%, Mg in a range of 0.65 mass% to 1.25 mass%, Si in a range of 0.9 mass% to 1.5 mass%, Mn in a range of 0.4 mass% to 1.1 mass%, Fe in a range of 0.15 mass% to 1.0 mass%, Cr in a range of 0.09 mass% to 0.25 mass%, Ti in a range of 0.01 mass% to 0.05 mass%, B in a range of 0.0010 mass% to 0.0050 mass%, and Be in a range of 0.001 mass% to 0.01 mass%, with the remainder being Al and unavoidable impurities.

[0023] The aluminum alloy in this embodiment corresponds to the 6000 series aluminum alloy in that it contains Mg and Si.

[0024] (Cu: 0.3 mass% or more, 0.5 mass% or less) Cu has the effect of finely dispersing Mg-Si compounds in aluminum alloys and improving the tensile strength of aluminum alloys by precipitating as Al-Cu-Mg-Si compounds, including the Q phase. The Cu content is in the range of 0.30% by mass or more and 0.50% by mass or less, and may also be in the range of 0.35% by mass or more and 0.45% by mass or less and 0.42% by mass or less.

[0025] By keeping the Cu content within the above range, the mechanical properties of the aluminum alloy at room temperature can be improved. Furthermore, if the Cu content exceeds 0.5 mass%, the amount of Cu coexisting with Mg2Si at the grain boundaries increases, which increases the potential difference between the matrix phase and the compound at the grain boundaries, impairing stress corrosion cracking resistance. Therefore, it is preferable to keep the Cu content within the above range.

[0026] (Mg: 0.65 mass% or more, 1.25 mass% or less) Magnesium (Mg) has the effect of improving the tensile strength of aluminum alloys. Mg contributes to strengthening the aluminum alloy by solid dissolution into the aluminum matrix, or by precipitation as Mg-Si compounds such as the β'' phase (Mg2Si), or as Al-Cu-Mg-Si compounds such as the Q phase. The Mg content is within the range of 0.65% by mass to 1.25% by mass, and may also be within the range of 0.75% by mass to 1.00% by mass, or exceeding 0.85% by mass and not exceeding 0.95% by mass. By having a Mg content within the above range, the corrosion resistance of the aluminum alloy can be improved along with its mechanical properties at room temperature.

[0027] (Si: 0.9 mass% or more, 1.5 mass% or less) Like magnesium, silicon (Si) improves the mechanical properties and corrosion resistance of aluminum alloys at room temperature. However, adding excessive amounts of Si to an aluminum alloy may lead to the crystallization of coarse primary Si grains, potentially reducing the tensile strength of the alloy.

[0028] The Si content is within the range of 0.90% by mass or more and 1.5% by mass or less, and may also be within the range of 0.95% by mass or more and 1.20% by mass or 1.00% by mass or more and 1.18% by mass. By having the Si content within the above range, it is possible to suppress the crystallization of primary Si while improving the corrosion resistance as well as the mechanical properties at room temperature of the aluminum alloy.

[0029] (Mn: 0.4% by mass or more, 1.1% by mass or less) Mn improves the tensile strength of aluminum alloys by forming fine granular precipitates containing intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Cr-Fe-Si in the aluminum alloy. The Mn content is in the range of 0.40% by mass or more and 1.1% by mass or less, and may also be in the range of 0.45% by mass or more and 1.0% by mass or less, or 0.5% by mass or more and 0.8% by mass or less. By having a Mn content within the above range, the mechanical properties of the aluminum alloy at room temperature can be improved.

[0030] (Fe: 0.15% by mass or more, 1.0% by mass or less) Fe crystallizes in aluminum alloys as fine precipitates 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 in the range of 0.15% by mass or more and 0.30% by mass or less, and may also be in the range of 0.20% by mass or more and 0.27% by mass or more and 0.22% by mass or more. By having an Fe content within the above range, the mechanical properties of the aluminum alloy at room temperature can be improved.

[0031] (Cr: 0.09 mass% or more, 0.25 mass% or less) Cr improves the tensile strength of aluminum alloys by forming fine granular precipitates containing intermetallic compounds such as Al-Mn-Cr-Fe-Si and Al-Fe-Cr in the aluminum alloy. The Cr content is in the range of 0.09 mass% to 0.25 mass%, and may also be in the range of 0.10 mass% to 0.20 mass% or 0.12 mass% to 0.18 mass%. By having a Cr content within the above range, the mechanical properties of the aluminum alloy at room temperature can be improved.

[0032] (Ti: 0.01 mass% or more, 0.05 mass% or less) Ti has the effect of refining the crystal grains of aluminum alloys and improving their wroughtability. If the Ti content is less than 0.01 mass%, the effect of refining the crystal grains may not be sufficiently obtained. On the other hand, if the Ti content exceeds 0.05 mass%, coarse precipitates may form, which may reduce the wroughtability. In addition, if a large amount of coarse precipitates containing Ti are mixed into the aluminum alloy, the toughness may decrease. Therefore, the Ti content should be between 0.01 mass% and 0.05 mass%. Preferably, the Ti content is between 0.015 mass% and 0.030 mass%.

[0033] (B: 0.0010 mass% or more, 0.0050 mass% or less) B has the effect of refining the crystal grains of aluminum alloys and improving their wroughtability. By adding B to aluminum alloys together with the aforementioned Ti, the effect of refining the crystal grains is enhanced.

[0034] If the B content is less than 0.001 mass%, the grain refinement effect may not be sufficiently obtained. On the other hand, if the B content exceeds 0.0050 mass%, coarse precipitates may form and be mixed into the aluminum alloy forging as inclusions. Furthermore, if a large amount of coarse precipitates containing B are mixed into the final aluminum alloy product, the toughness may decrease. Therefore, the B content should be 0.001 to 0.0050 mass%. Preferably, the B content is 0.0015 to 0.045 mass%.

[0035] (Be: 0.0010 mass% or more, 0.01 mass% or less) Be is a metal that oxidizes more easily than Mg, and by adding Be, a very thin Be oxide film (BeO) forms on the surface that comes into contact with O2 in the atmosphere. The formation of this oxide film has the effect of suppressing the oxidation of Mg contained in aluminum alloys.

[0036] If the Be content is less than 0.0010 mass%, a sufficient oxide film will not be formed, and the effect of suppressing Mg oxidation will be limited. Also, since Be is more expensive than Al and other metals, adding more than 0.01 mass% will lead to increased manufacturing costs. Therefore, the Be content is 0.0010 mass% or more and 0.01 mass% or less, preferably 0.0015 mass% or more and 0.0050 mass% or less.

[0037] (Inevitable impurities) Unavoidable impurities are impurities that inevitably become mixed into the aluminum alloy from the raw materials or manufacturing process. Examples of unavoidable impurities include Zn, Zr, Ni, Sn, and Be. It is preferable that the content of these unavoidable impurities does not exceed 0.1% by mass.

[0038] [Suspension components] Figure 1 is a schematic diagram showing an enlarged view of the vicinity of the bushing portion of the suspension member, and Figure 2 is a plan view showing an enlarged view of the vicinity of the bushing portion of the suspension member in Figure 1.

[0039] The suspension member of this embodiment is a suspension arm used in a vehicle suspension mechanism, and for example, the whole is roughly triangular in shape, and a wheel-side connecting portion, a first vehicle body-side connecting portion, a second vehicle body-side connecting portion, and an arm portion connecting them are integrally molded. Of these, the first vehicle body-side connecting portion and the second vehicle body-side connecting portion are also referred to as bushing portions.

[0040] As shown in Figures 1 and 2, the bush portion 5 of the suspension member (suspension arm) of this embodiment is removed, for example, when used as a product, so that the area indicated by the dashed line with the symbol H penetrates in the x direction. That is, the aluminum alloy is removed from the cylindrical area indicated by the dashed line with the symbol H in Figures 1 and 2, and an opening is formed.

[0041] Other components, such as ball joints, are press-fitted into these openings in the x-direction. In this embodiment, forged members with cylindrical openings formed in the bushing portions 5 and 6, and forged members without openings formed in the bushing portions 5 and 6, are collectively referred to as suspension members.

[0042] In the suspension member according to this embodiment, a parting line PL is formed along the outer shape of the suspension in a plan view from the z direction. The parting line PL is formed in the forging process of the manufacturing process, which will be described in detail later, when excess material (burrs) of the forged product is removed in the trimming process. The parting line PL can be confirmed by observing the side surface of the suspension member.

[0043] As shown in Figure 1, the parting line PL in the bush portion 5 is molded to form, for example, an xy plane. Furthermore, the bush portions 5 and 6 have vertices at their ends in the y-direction. In Figure 1, the vertex formed on the bush portion 5 is indicated by reference numeral 51. The vertices of the bush portions 5 and 6 are located on the x-direction center of the bush portions 5 and 6 of the suspension member.

[0044] In this embodiment, the suspension member has a grain boundary at its apex 51 that is perpendicular to the plane formed by the parting line PL of the bush portion 5 (the xy plane in Figures 1 and 2), and has an inclination of 45° or less with respect to a plane parallel to the cylindrical axis of the bush portion 5. The inclination of the grain boundary is preferably 35° or less, and more preferably 25° or less.

[0045] The more complex the shape of the suspension component manufactured by forging, the greater the amount of distortion during the forging process, which will be described in detail later. This makes it easier for recrystallized grains to form during the subsequent solution treatment process. In particular, the amount of distortion is very large near the parting line, making it difficult to completely eliminate these recrystallized grains. On the other hand, areas where recrystallized grains have formed are areas that are preferentially susceptible to stress corrosion cracking when stress is applied.

[0046] In the bush portion 5 of the suspension member, for example, a ball joint is press-fitted, and its apex 51 is the point where the greatest stress is applied. The direction in which the stress is applied is the direction in which the ball joint is press-fitted and the opposite direction. That is, the direction in which the stress is applied is the axial direction of the opening formed in the bush portion 5, which is the ±x direction in Figures 1 and 2.

[0047] When the orientation of the long side of the crystals in the area where recrystallized grains have formed is perpendicular to the direction in which stress is applied to the bush portion 5, the stress corrosion cracking resistance is significantly poor. In contrast, in the vicinity of the apex portion 51, if the orientation of the crystal grains in the region from the outermost surface inward in the y-direction to a predetermined depth, from the symbol E0 in the figure to a depth of approximately 300 μm in the -y direction, is oriented so that the long side of the crystal grains is nearly parallel to the stress direction, resistance to stress corrosion cracking can be obtained. As described above, this crystal grain orientation is such that, at the outermost point (apex portion 51) in the y-direction of the parting line PL where stress is concentrated, the plane is perpendicular to the plane formed by the parting line PL of the bush portion 5 (the xy plane in Figures 1 and 2), and the inclination of the crystal grain boundary is 45° or less with respect to the plane parallel to the cylindrical axis (x-axis) of the bush portion 5.

[0048] In this embodiment, the suspension member has a tensile strength of, for example, 380 MPa or more, preferably 385 MPa or more, more preferably 390 MPa or more, and even more preferably 392 MPa or more.

[0049] Furthermore, the shapes of the suspension members in this embodiment are not limited to the examples described above, and can also be applied to suspension members of any shape that are formed by forging and include a bushing portion.

[0050] [Manufacturing method for aluminum alloy, manufacturing method for suspension components] Next, a method for manufacturing an aluminum alloy according to one embodiment of the present invention, and a method for manufacturing a suspension member using the aluminum alloy obtained thereby will be described. Figure 3 is a flowchart illustrating the manufacturing process of aluminum alloy and suspension components in a step-by-step manner.

[0051] A method for producing an aluminum alloy according to one embodiment of the present invention comprises: a molten metal forming step S1 in which a molten metal having an alloy composition containing Cu 0.3 in a range of 0.5 mass% or more by mass, Mg in a range of 0.65 mass% or more by mass, Si in a range of 0.9 mass% or more by mass, Mn in a range of 1.5 mass% or more by mass, Fe in a range of 0.15 mass% or more by mass, Cr in a range of 0.09 mass% or more by mass, Ti in a range of 0.05 mass% or more by mass, B in a range of 0.0010 mass% or more by mass, and Be in a range of 0.001 mass% or more by mass, with the remainder being Al and unavoidable impurities; and a casting step S2 in which the obtained molten metal is cast to obtain an aluminum alloy (cast product).

[0052] Furthermore, a method for manufacturing a suspension member according to one embodiment of the present invention comprises at least a forging step S3 in which an aluminum alloy (cast product) obtained by the above-described method for manufacturing an aluminum alloy is heated in a range of 500°C to 570°C and forged to obtain a forged product; a solution treatment step S4 in which the forged product is subjected to a solution treatment in a range of 500°C to 570°C; a quenching step S5 in which the forged product that has undergone the solution treatment step S4 is subjected to a quenching treatment at a temperature of 480°C or higher; and an aging treatment step S6 in which the forged product that has undergone the quenching step S5 is subjected to a heat treatment in a range of 175°C to 190°C for 4 hours or more.

[0053] [Manufacturing method for aluminum alloy] (Molten metal formation process) The molten metal forming step S1 is a step in which aluminum alloy raw materials are melted to obtain molten aluminum alloy with a prepared composition. The composition of the molten aluminum alloy is adjusted to contain Cu 0.3 in the range of 0.5 mass% to 0.5 mass%, Mg in the range of 0.65 mass% to 1.25 mass%, Si in the range of 0.9 mass% to 1.5 mass%, Mn in the range of 0.4 mass% to 1.1 mass%, Fe in the range of 0.15 mass% to 1.0 mass%, Cr in the range of 0.09 mass% to 0.25 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 Be in the range of 0.001 mass% to 0.01 mass%, with the remainder being Al and unavoidable impurities.

[0054] By using the molten aluminum alloy of the above composition for the subsequent steps, the formation of recrystallized grains during heat treatment is suppressed, particularly by the action of Be, and the formation of an oxide layer (MgO) on the surface is also suppressed.

[0055] Molten aluminum alloy can be obtained by heating and melting aluminum alloy raw materials. Alternatively, it may be formed by melting a mixture containing the elements that make up the aluminum alloy raw materials, or a compound containing two or more elements, in a proportion that produces the desired aluminum alloy. For example, to control the grain size of the aluminum alloy produced in the casting process, it is permissible to mix in Ti or B as grain refiners such as Al-Ti-B rods.

[0056] Alternatively, a molten aluminum alloy may be obtained by using 10% or more of scrap material from 1000 series, 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, and 7000 series aluminum alloys as raw materials, with the remainder being new aluminum ingots and the aforementioned additive elements, and then melting these to adjust the composition.

[0057] In this case, an Al-Mg-Si suspension member with excellent mechanical properties at room temperature and less susceptible to recrystallization can be obtained. Note that "new aluminum ingot" refers to aluminum with a purity of 99% or higher, obtained by electrolysis, a process called electrolytic refining, on alumina produced from minerals.

[0058] (Casting process) In casting process S2, the molten aluminum alloy (liquid phase) is cooled and solidified into a solid (solid phase) to obtain the aluminum alloy (casting). The casting process is preferably carried out by continuous casting. For example, the casting process can be carried out by vertical continuous casting or horizontal continuous casting. Below, as an example of a casting method, the case in which the casting process is carried out by horizontal continuous casting will be described.

[0059] Figures 4 and 5 show a horizontal continuous casting apparatus that can be used in the casting process of the aluminum alloy manufacturing method of this embodiment. Figure 4 is a cross-sectional view showing an example of the area around the mold 12 of the horizontal continuous casting apparatus 10. Figure 5 is an enlarged cross-sectional view of the main part of the horizontal continuous casting apparatus 10, showing the area around the cooling water cavity 24.

[0060] The horizontal continuous casting apparatus 10 shown in Figures 4 and 5 includes a molten metal receiving section (tundish) 11, a hollow cylindrical mold 12, and a refractory plate-like body (insulating member) 13 positioned between one end 12a of the mold 12 and the molten metal receiving section 11.

[0061] The molten metal receiving section 11 consists of a molten metal inlet section 11a for receiving the molten aluminum alloy M obtained in the molten metal forming process described above, a molten metal holding section 11b, and an outlet section 11c for outflow to the hollow section 21 of the mold 12.

[0062] The molten metal receiving section 11 maintains the upper liquid level of the molten aluminum alloy M at a position higher than the upper surface of the hollow section 21 of the mold 12, and in the case of multi-casting, it stably distributes the molten aluminum alloy M to each mold 12.

[0063] The molten aluminum alloy M held in the molten metal holding section 11b within the molten metal receiving section 11 is poured into the hollow section 21 of the mold 12 through the pouring passage 13a provided in the refractory plate-shaped body 13. The molten aluminum alloy M supplied into the hollow section 21 is then cooled and solidified by a cooling device 23 (described later), and is pulled out from the other end 12b of the mold 12 as a solidified ingot, an aluminum alloy rod B.

[0064] The other end 12b of the mold 12 may be equipped with a draw-out drive device (not shown) for drawing out the cast aluminum alloy rod B at a constant speed. It is also preferable to have a synchronized cutting machine (not shown) for cutting the continuously drawn aluminum alloy rod B to any desired length.

[0065] The refractory plate-like body 13 is a member that blocks heat transfer between the molten metal receiving section 11 and the mold 12, and may be composed of materials such as calcium silicate, alumina, silica, a mixture of alumina and silica, silicon nitride, silicon carbide, or graphite. Such a refractory plate-like body 13 can also be composed of multiple layers made of different materials.

[0066] In this embodiment, the mold 12 is a hollow cylindrical member and is formed from one or more materials selected from, for example, aluminum, copper, or alloys thereof. The materials for such a mold 12 should be selected in an optimal combination in terms of thermal conductivity, heat resistance, and mechanical strength.

[0067] The hollow portion 21 of the mold 12 is formed with a circular cross-section in order to cast the aluminum alloy rod B into a cylindrical shape, and the mold 12 is held such that the mold central axis (central axis) C, which passes through the center of this hollow portion 21, is aligned in a nearly horizontal direction.

[0068] The inner circumferential 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's central axis C, in the casting direction of the aluminum alloy rod B (see Figure 4). In other words, the inner circumferential surface 21a is configured as a tapered shape that opens in a cone shape toward the casting direction. The angle formed by this taper is the elevation angle.

[0069] If the elevation angle is less than 0°, casting may become difficult because the aluminum alloy rod B encounters resistance at the other end 12b, which is the mold exit, when it is pulled out of the mold 12. On the other hand, if the elevation angle exceeds 3°, the contact between the inner circumferential surface 21a and the molten aluminum alloy M becomes insufficient, and the heat dissipation effect from the molten aluminum alloy M and the solidified shell formed therefrom to the mold 12 decreases, which may result in insufficient solidification. As a result, a remelted surface may form on the surface of the aluminum alloy rod B, or unsolidified molten aluminum alloy M may spurt out from the end of the aluminum alloy rod B, which is undesirable as it may lead to casting problems.

[0070] Furthermore, 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 21b) can be selected according to the shape of the aluminum alloy rod to be cast, in addition to the circular shape of this embodiment. For example, it can be a triangular, rectangular, polygonal, semicircular, elliptical, or an irregularly shaped cross-section without an axis of symmetry or plane of symmetry.

[0071] A fluid supply pipe 22 is located at one end 12a of the mold 12 to supply 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 types of lubricating fluid selected from gaseous lubricants and liquid lubricants. When supplying both gaseous and liquid lubricants, it is preferable to provide separate fluid supply pipes for each. The pressurized lubricating fluid supplied from the fluid supply pipe 22 is supplied into the hollow portion 21 of the mold 12 through an annular lubricant supply port 22a.

[0072] In this embodiment, the pressurized lubricating fluid is supplied to the inner circumferential surface 21a of the mold 12 from the lubricant supply port 22a. Alternatively, the liquid lubricant may be heated and decomposed into a gas before being supplied to the inner circumferential surface 21a of the mold 12. Alternatively, a porous material may be placed at the lubricant supply port 22a, allowing the lubricating fluid to seep out onto the inner circumferential surface 21a of the mold 12 through this porous material.

[0073] 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 in this embodiment has a cooling water cavity 24 that contains cooling water W for cooling the inner circumferential surface 21a of the hollow portion 21 of the mold 12, and a cooling water injection passage 25 that connects the cooling water cavity 24 and the hollow portion 21 of the mold 12.

[0074] The cooling water cavity 24 is formed in an annular shape inside the mold 12, outside the inner circumferential surface 21a of the hollow portion 21, and cooling water W is supplied via the cooling water supply pipe 26.

[0075] 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, causing a solidified shell to form on the surface of the molten aluminum alloy M.

[0076] Furthermore, the cooling water injection passage 25 cools the aluminum alloy rod B by directly applying cooling water W to the aluminum alloy rod B at the other end 12b of the mold 12 from the shower opening 25a facing the hollow portion 21. The longitudinal cross-sectional shape of the cooling water injection passage 25 may be other than the circular shape of this embodiment, for example, a semicircle, a pear shape, or a horseshoe shape.

[0077] In this embodiment, the cooling water W supplied via the cooling water supply pipe 26 is first contained in the cooling water cavity 24 to cool the inner circumferential surface 21a of the hollow portion 21 of the mold 12, and then the cooling water W from the cooling water cavity 24 is injected from the cooling water injection passage 25 toward the aluminum alloy rod B. However, it is also possible to configure the system so that these are supplied by separate cooling water supply pipes.

[0078] The effective mold length L is defined as the distance from the point where the extension of the central axis of the shower opening 25a of the cooling water injection passage 25 strikes the surface of the cast aluminum alloy rod B to the contact surface between the mold 12 and the refractory plate-like body 13. This effective mold length L is preferably, for example, 10 mm or more and 40 mm or less. If the effective mold length L is less than 10 mm, casting becomes impossible due to the inability to form a good coating, and if it exceeds 40 mm, the effect of forced cooling decreases, solidification by the mold wall becomes dominant, and the contact resistance between the mold 12 and the molten aluminum alloy M or aluminum alloy rod B increases, which may cause cracks in the casting surface or breakage inside the mold, making casting unstable and therefore undesirable.

[0079] Preferably, the supply of cooling water W to these cooling water cavities 24 and the injection of cooling water W from the shower openings 25a of the cooling water injection passages 25 can be controlled by control signals from a control device (not shown).

[0080] The cooling water cavity 24 is formed such that the inner bottom surface 24a of the mold 12 near the hollow portion 21 is parallel to the inner circumferential surface 21a of the hollow portion 21 of the mold 12.

[0081] In this context, "parallel" includes cases where the inner circumferential surface 21a of the hollow portion 21 of the mold 12 is formed at an elevation angle of 0° to 3° with respect to the inner bottom surface 24a of the cooling water cavity 24, that is, cases where the inner bottom surface 24a is inclined to the inner circumferential surface 21a at an angle greater than 0° and up to 3°.

[0082] As shown in Figure 5, the cooling wall portion 27 of the mold 12, which is the portion where the inner bottom surface 24a of the cooling water cavity 24 and the inner circumferential surface 21a of the hollow portion 21 of the mold 12 face each other, has a 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, for example, 10 × 10 5 W / m 2 The above 50 x 10 5 W / m 2 It is sufficient if it is formed within the following range.

[0083] The thickness t of the cooling wall portion 27 of the mold 12, that is, the distance between the inner bottom surface 24a of the cooling water cavity 24 and the inner circumferential surface 21a of the hollow portion 21 of the mold 12, should be, for example, within the range of 0.5 mm to 3.0 mm, preferably 0.5 mm to 2.5 mm, if the mold 12 is formed in this manner. Furthermore, the forming material of the mold 12 may be selected such that the thermal conductivity of at least the cooling wall portion 27 of the mold 12 is, for example, within the range of 100 W / m·K to 400 W / m·K.

[0084] In Figure 5, the molten aluminum alloy M in the molten metal receiving section 11 is supplied from one end 12a of the mold 12, which is held so that the mold central axis C is approximately horizontal, via a refractory plate-like body 13, and is forcibly cooled at the other end 12b of the mold 12 to form an aluminum alloy rod B.

[0085] 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, so that it is continuously cast and a long aluminum alloy rod B is formed. The drawn-out aluminum alloy rod B is then cut to a desired length by, for example, a synchronized cutting machine (not shown).

[0086] The composition ratio of the cast aluminum alloy rod B can be confirmed by spectroscopic analysis using a photoelectric emission spectrometer (example: PDA-5500 manufactured by Shimadzu Corporation of Japan), as described in "JIS H 1305".

[0087] The difference in height between the liquid level of the molten aluminum alloy M stored in the molten metal receiving section 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 keeping it 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 the vaporization of the lubricating oil are suitably balanced, resulting in stable castability.

[0088] Liquid lubricants can be vegetable oils, which are also known as lubricating oils. Examples include rapeseed oil, castor oil, and salad oil. These are preferable because they have a small negative impact on the environment.

[0089] The lubricating oil supply rate is preferably, for example, 0.05 mL / min to 5 mL / min (more preferably 0.1 mL / min or more and 1 mL / min or less). If the supply rate is less than this range, there is a concern that the molten aluminum alloy M of the aluminum alloy rod B will not solidify due to insufficient lubrication and may leak from the mold 12. Conversely, if the supply rate is excessive, there is a risk that the excess will mix into the aluminum alloy rod B and cause internal defects.

[0090] The casting speed, which is the speed at which the aluminum alloy rod B is drawn out of the mold 12, is preferably, for example, 200 mm / min or more and 1500 mm / min or less (more preferably 400 mm / min or more and 1000 mm / min or less). Within this range of casting speed, the network structure of the precipitates formed by casting becomes uniform and fine, increasing the resistance of the aluminum material to deformation at high temperatures and improving the mechanical strength in high-temperature environments.

[0091] The amount of cooling water sprayed from the shower opening 25a of the cooling water injection passage 25 is preferably, for example, 10 L / min or more and 50 L / min or less per mold (more preferably 25 L / min or more and 40 L / min or less). If the amount of cooling water is less than this, there is a concern that the molten aluminum alloy M will leak out of the mold 12 without solidifying. In addition, the surface of the cast aluminum alloy rod B may remelt, forming an uneven structure that may remain as an internal defect. On the other hand, if the amount of cooling water is more than this range, there is a risk that the heat dissipation from the mold 12 will be too great, causing solidification during casting.

[0092] The average temperature of the molten aluminum alloy M flowing from the molten metal receiving section 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 compared to the above range, there is a risk that coarse crystals will form in and in front of the mold 12 and be incorporated into the aluminum alloy rod B as internal defects.

[0093] On the other hand, if the temperature of the molten aluminum alloy M is too high compared to the range mentioned above, a large amount of hydrogen gas is likely to be incorporated into the molten aluminum alloy M, which may then be incorporated into the aluminum alloy rod B as porosity, potentially creating internal cavities.

[0094] Then, the aluminum alloy casting is performed such that the cooling rate of the molten aluminum alloy M in the cooling wall portion 27 of the mold 12 is in the range of 10°C / second or more and 100°C / second or less. If the cooling rate is less than 10°C / second, there is a concern that the molten aluminum alloy M will not solidify and will leak out of the mold 12. Also, the surface of the cast aluminum alloy rod B may remelt, forming an uneven structure that may remain as internal defects. On the other hand, if the cooling rate exceeds 100°C / second, there is a risk that the heat dissipation from the mold 12 will be too great, causing solidification during the casting process.

[0095] In manufacturing the aluminum alloy rod B of this embodiment, the molten aluminum alloy M stored in the molten metal receiving section 11 is continuously supplied to the hollow section 21 from one end 12a of the mold 12 using the horizontal continuous casting apparatus 10 described above. Cooling water W is supplied to the cooling water cavity 24, and a lubricating fluid, such as lubricating oil, is supplied from the fluid supply pipe 22.

[0096] In the aluminum alloy rod B obtained in this way, for example, if the cooling rate of the molten aluminum alloy M is kept within the range of 10°C / second or more and 100°C / second or less, the adhesion of reaction products, such as carbides, due to contact between the lubricating oil gas and the molten aluminum alloy M is suppressed. As a result, there is no need to cut off carbides and other materials from the surface of the aluminum alloy rod B, and the aluminum alloy rod B can be manufactured in high yield.

[0097] Furthermore, the casting process for obtaining a casting from molten aluminum alloy M is not limited to the horizontal continuous casting method described above; known continuous casting methods such as vertical continuous casting can also be used. Vertical continuous casting is 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 mold 12), but the case using the hot-top method will be briefly explained below.

[0098] The casting apparatus used in the hot top method includes a mold, a molten metal receiving container (header), etc. The molten metal supplied to the receiving section passes through a spout and then through the header, where its flow rate is adjusted. It then enters a cylindrical mold that is installed almost horizontally, where it is forcibly cooled and a solidified shell is formed on the outer surface of the molten metal.

[0099] Furthermore, cooling water is directly sprayed onto the casting as it is removed from the mold, allowing the metal to solidify inside the casting as it is continuously removed. Generally, molds are made of metal materials with good thermal conductivity and have a hollow structure to introduce a coolant into the interior.

[0100] The refrigerant used can be selected from industrially available options, but water is recommended for ease of use.

[0101] The mold used in this embodiment is appropriately selected from metals such as copper or aluminum, or graphite, from the viewpoint of heat transfer performance and durability at the contact area with the molten metal. The header is generally made of refractory material and is installed on the upper side of the mold. The material and size of the header can be appropriately selected depending on the composition range of the alloy to be cast and the dimensions of the casting, and are not particularly restricted.

[0102] The cooling rate during casting can be selected from a range of, for example, 10°C / second or more and 100°C / second or less. Similarly, the casting speed can be selected from a range of, for example, 200 mm / min or more and 600 mm / min or less.

[0103] (Homogenization heat treatment process) Furthermore, a homogenization heat treatment step S11 may be performed as a post-processing step after the casting step S2. The homogenization heat treatment step S11 is a process in which the aluminum alloy (casting) obtained in the casting step is heat-treated to homogenize the microsegregation caused by solidification, precipitate supersaturated solid solution elements, and change the metastable phase to an equilibrium phase.

[0104] The homogenization heat treatment step S11 can be carried out by holding the aluminum alloy (casting) obtained in the casting process at a temperature of, for example, 370°C or higher and 560°C or lower for about 4 to 10 hours. By performing homogenization heat treatment within this temperature range, the aluminum alloy (casting) is sufficiently homogenized and solute atoms are dissolved into it. Note that this homogenization heat treatment step S11 is not mandatory and can be omitted.

[0105] [Manufacturing method for suspension components] (Forging process) Forging process S3 is a process in which the aluminum alloy (cast product) obtained by the above-described method for manufacturing aluminum alloy is shaped to a predetermined size to obtain a material for forging, the obtained material for forging is heated to a predetermined temperature, and pressure is applied using a press machine with a die to form the die.

[0106] In this embodiment, a forging process is performed on the forging material at a heating temperature range of 500°C to 570°C, preferably 550°C to 570°C, to obtain a forged suspension member (suspension arm). If the forging start temperature of the forging material is below 500°C, the deformation resistance will increase, and sufficient processing may not be possible. On the other hand, if it exceeds 570°C, defects such as forging cracks and eutectic melting may easily occur.

[0107] Furthermore, the forging material preferably has an average particle size in the plane of 100 μm or less, and more preferably 80 μm or less. The average particle size in the plane of the forging material is, for example, 30 μm or more.

[0108] (Solution treatment process) The solution treatment process S4 is a process in which the forged product obtained in the forging process S3 is heated to a temperature in the range of 500°C to 570°C to induce solution treatment, thereby relieving the strain introduced into the casting and performing solid solution of solute elements, such as Mg2Si.

[0109] In this embodiment, the forged product is subjected to solution treatment by holding it at a processing temperature in the range of 500°C to 570°C for, for example, 0.3 hours to 5 hours. Preferably, the solution treatment is performed by holding it at a processing temperature in the range of 530°C to 550°C for 1 hour to 4 hours. The solution treatment time may be 3 hours or less.

[0110] The heating rate from room temperature to the above-mentioned processing temperature range is preferably, for example, 5.0°C / min or higher. If the processing temperature is below 500°C, the solid solution of the solute element (e.g., Mg2Si) will be insufficient, and solution formation will not progress, making it difficult to achieve high strength through age precipitation. On the other hand, if the processing temperature exceeds 570°C, the solid solution of the solute element is further promoted, but eutectic melting and recrystallization may occur more easily. Also, if the heating rate is less than 5.0°C / min, there is a risk of coarse precipitation of Mg2Si.

[0111] (Heat treatment process) The quenching process S5 is a process in which a supersaturated solid solution is formed by rapidly cooling the forged product in the solid solution state obtained in the solution treatment process S4.

[0112] In the quenching process S5 of this embodiment, the forged product is placed in a water tank containing water (quenching water) and submerged to perform water quenching. The water temperature in the tank is preferably 20°C or higher and 60°C or lower. The temperature of the forged product when it is placed in the water tank should be 480°C or higher, preferably 500°C or higher. In addition, in the quenching process S5, it is preferable that all surfaces of the forged product come into contact with water within 5 seconds to 60 seconds after the solution treatment. The submersion time of the forged product varies depending on the size of the casting, but for example, it is between 5 minutes and 40 minutes.

[0113] (Statute of Limitations Process) The aging treatment process S6 is a process in which the forged product is heated and held at a relatively low temperature to precipitate supersaturated dissolved elements, thereby imparting appropriate hardness.

[0114] In this embodiment, the forged product that has undergone the quenching process S5 is subjected to aging treatment by heat treatment at a temperature of 175°C to 190°C for 4 hours or more. If the heating temperature is less than 175°C or the holding time is less than 4 hours, there is a risk that the Mg2Si fine precipitates that improve tensile strength will not grow sufficiently. On the other hand, if the treatment temperature exceeds 190°C, there is a risk that the Mg2Si fine precipitates will become too coarse, and it will not be possible to sufficiently improve the tensile strength.

[0115] (Hot trimming process) After this, a hot trimming process (hot trimming process) S12 may be performed if necessary. In the hot trimming process (hot trimming process) S12, the forged product that has undergone the aging treatment process S6 is hot trimmed at a temperature in the range of over 100°C and up to 250°C.

[0116] In the hot trimming process S12, the forged product that has undergone the aging treatment process S6 is heated, and the excess material, which is called burr, is trimmed. In this hot trimming process S12, the burr is removed from the forged product, and a suspension member is obtained. After the burr is removed, the parting line corresponding to the base of the burr is exposed on the suspension member.

[0117] If the temperature in the hot trimming process S12 is too low, the forging burrs may be removed by shearing, making it impossible to create a tilt in the crystals of the parting line. On the other hand, if the temperature in the hot trimming process S12 is too high, the forging may soften, making it difficult to trim the burrs properly, and there is a risk that burrs will remain. Therefore, the temperature of the forging in the hot trimming process is preferably in the range of over 100°C and 250°C or less, more preferably 125°C or higher, even more preferably 150°C or higher, and most preferably 175°C or higher.

[0118] (Cold trimming process) In addition to removing burrs from the forged product by the hot trimming process S12, it is also possible to trim the burrs from the forged product, which has been cooled to below 60°C by water quenching, by the cold trimming process S13 as a post-quenching process after the quenching process S5. If the cold trimming process S13 is performed, the subsequent processes will be carried out on the suspension member from which the burrs have been removed, and the hot trimming process S12 will not be performed.

[0119] Although one embodiment of the present invention has been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be carried out in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention, as well as in the claims and their equivalents. [Examples]

[0120] The effects of the embodiments of the present invention were verified. In accordance with the embodiments described above, aluminum alloy rods with a diameter of 80 mm were cast by horizontal continuous casting. The aluminum alloy rods of the present invention examples 1-5 and comparative examples 1-3 that were cast had the same composition as shown in Table 1, except for Be.

[0121] [Table 1]

[0122] The amount of Be added was then varied for each sample as shown in Table 2. After heating to the temperatures shown in Table 2, each sample was forged, and then each forged product (sample) was subjected to solution treatment (540°C, 3 hours), water quenching (water temperature 25°C, 10 minutes immersion), and aging treatment (180°C, 4 hours) sequentially under the same conditions.

[0123] [Table 2]

[0124] The surface of each obtained sample was observed using a digital microscope, and samples with blistering were evaluated as "present" and those without as "absent". In addition, each sample was cut at a point with a high amount of strain, and samples with recrystallized grains were evaluated as "present" and those without as "absent". As an overall evaluation, samples with both blistering and recrystallized grains absent were marked as "○", and samples with either or both absent were marked as "×". The results of these evaluations are shown in Table 2.

[0125] Furthermore, Figure 6(a) shows a magnified surface image of the blister evaluation (no blister) of Example 1 of the present invention, and Figure 6(b) shows a magnified surface image of the blister evaluation (with blister) of Comparative Example 1. Furthermore, Figure 7 shows a magnified surface image of the recrystallized grain evaluation (with recrystallized grains) for Comparative Example 3.

[0126] According to the results shown in Table 2, no blistering occurred in any of the samples containing 0.001% by mass or more of Be (Examples 1-5, Comparative Example 3). On the other hand, blistering was observed on the surface in Comparative Example 1, which contained only 0.0005% by mass of Be (less than 0.001% by mass), and in Comparative Example 2, which contained no Be at all.

[0127] Furthermore, in each sample (Examples 1-5, Comparative Examples 1 and 2) where the heating temperature of the alloy material during forging was 500°C or higher, no recrystallized grains were observed. On the other hand, in Comparative Example 3, where the heating temperature of the alloy material during forging was 470°C (below 500°C), the formation of recrystallized grains was observed.

[0128] Therefore, it was confirmed that by using an aluminum alloy containing 0.001% by mass or more of Be and setting the heating temperature during forging to 500°C or higher, both surface blistering and the generation of recrystallized grains in the forged product can be suppressed. [Industrial applicability]

[0129] According to the present invention, the aluminum alloy, suspension member, method for manufacturing the aluminum alloy, and method for manufacturing the suspension member suppresses stress corrosion cracking by suppressing the generation of recrystallized grains, and also suppresses the decrease in surface hardness due to blistering on the surface and improves the appearance. Therefore, it becomes possible to realize a suspension member for vehicles that suppresses stress corrosion and improves surface hardness, contributing to the improvement of vehicle driving performance and safety. Accordingly, it has industrial applicability. [Explanation of Symbols]

[0130] 10…Horizontal continuous casting apparatus 11…Molten metal receiving section (tundish) 12…Mold 13…Refractory plate-like material (insulating material) M...Molten aluminum alloy

Claims

1. Cu0.3 in the range of 0.5% by mass or more, Mg in the range of 0.65% by mass or more and 1.25% by mass or less, Si in the range of 0.9% by mass or more and 1.5% by mass or less, Mn in the range of 0.4% by mass or more and 1.1% by mass or less, Fe is within the range of 0.15% by mass or more and 1.0% by mass or less. Cr in the range of 0.09% by mass or more and 0.25% by mass or less, Ti is in the range of 0.01% by mass or more and 0.05% by mass or less. B is in the range of 0.0010% by mass or more and 0.0050% by mass or less. Each contains Be in an amount of 0.001% by mass or more and 0.01% by mass or less. An aluminum alloy having an alloy composition in which the remainder consists of Al and unavoidable impurities.

2. A suspension member formed from the aluminum alloy described in claim 1.

3. A molten metal forming step involves forming a molten metal having an alloy composition in which Cu is contained in the range of Cu 0.3% to 0.5% by mass, Mg in the range of Mg 0.65% to 1.25% by mass, Si in the range of Si 0.9% to 1.5% by mass, Mn in the range of Mn 0.4% to 1.1% by mass, Fe in the range of Fe 0.15% to 1.0% by mass, Cr in the range of Cr 0.09% to 0.25% by mass, Ti in the range of Ti 0.01% to 0.05% by mass, B in the range of B 0.0010% to 0.0050% by mass, and Be in the range of B 0.001% to 0.01% by mass, with the remainder being Al and unavoidable impurities. The process includes a casting step of casting the molten metal to obtain an aluminum alloy, A method for manufacturing an aluminum alloy, wherein the casting process is carried out at a cooling rate in the range of 10°C / second or more and 100°C / second or less.

4. A method for manufacturing a suspension member using the aluminum alloy of claim 1, A forging process to obtain a forged product by heating the aforementioned aluminum alloy in a range of 500°C to 570°C and forging it, The solution treatment step involves performing a solution treatment on the forged product in a range of 500°C to 570°C. A quenching process in which the forged product that has undergone the solution treatment process is subjected to a quenching process at a temperature of 480°C or higher, A method for manufacturing a suspension member, comprising: an aging treatment step of heating the forged product that has undergone the aforementioned quenching step at a temperature of 175°C to 190°C for 4 hours or more.

5. The method for manufacturing a suspension member according to claim 4, further comprising a cold trimming step as a post-forging step, in which the excess material of the forged product is trimmed at a temperature of 60°C or lower.

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