Suspension member and method for manufacturing suspension member

Abstract

A suspension member comprising an aluminum alloy having an alloy composition containing 0.3 to 0.5 mass% of Cu, 0.65 to 1.05 mass% of Mg, 0.9 to 1.25 mass% of Si, 0.4 to 0.6 mass% of Mn, 0.15 to 0.30 mass% of Fe, 0.09 to 0.25 mass% of Cr, 0.01 to 0.05 mass% of Ti, and 0.0010 to 0.0050 mass% of B, with the remainder comprising Al and unavoidable impurities, and having a thickness of 1 to 10 [mu] m with respect to a plane perpendicular to a plane formed by a parting line of a bush portion and parallel to a cylindrical axis of the bush portion. The inclination angle of the grain boundary is 45 degrees or less.

Description

Technical Field

[0001] This invention relates to suspension components and a method for manufacturing suspension components.

[0002] This application claims priority based on Japanese Patent Application No. 2023-222058, filed on December 28, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] In recent years, the use of aluminum alloys as structural components in various products has been expanding due to their lightweight properties. For example, high-strength steel has been used in automotive running gear and bumper components until recently, but high-strength aluminum alloys have begun to be used instead. In automotive parts, such as suspension components, iron-based materials were previously used, but for the primary purpose of weight reduction, aluminum or aluminum alloys are increasingly being used instead.

[0004] These automotive parts require excellent corrosion resistance, high strength, and excellent machinability; therefore, Al-Mg-Si alloys, especially A6061, are frequently used as aluminum alloy materials. Moreover, to improve the strength of such automotive parts, aluminum alloy materials are used as blanks for forging, a type of plastic processing.

[0005] In addition, due to the recent need to reduce costs, suspension components that are forged as blanks without extrusion and then subjected to solution treatment and artificial aging treatment (T6 treatment) are beginning to be put into practical use. With the aim of further reducing weight, the development of a high-strength alloy to replace the previous A6061 is being promoted (see Patent Documents 1-3).

[0006] Prior art literature

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 5-059477

[0009] Patent Document 2: Japanese Patent Application Publication No. 5-247574

[0010] Patent Document 3: Japanese Patent Application Publication No. 6-256880 Summary of the Invention

[0011] Driven by the recent focus on reducing CO2 emissions, there is a demand for lightweight automobiles, leading to an increasing demand for aluminum. However, as a substitute for steel, aluminum requires further enhancement in strength. While increasing the addition of Si, Mg, and Cu is a common method for achieving this, it can potentially reduce corrosion resistance. Among corrosion-resistant materials, resistance to stress corrosion cracking becomes crucial for automotive suspension blanks.

[0012] Stress corrosion cracking (SCC) refers to the phenomenon where corrosion occurs in a suspension component under sustained stress, with cracks originating from the corroded area. The most critical part of the suspension system for resisting SCC is the bushings embedded in the suspension. Ensuring the SCC resistance of this area and achieving high strength in the components is essential.

[0013] Factors influencing stress corrosion cracking resistance include, for example, the addition of elements, the state of the compound, and the crystal state of the metal. Controlling the crystal structure is crucial for maintaining high strength and ensuring good stress corrosion cracking resistance. Even with the same amount of added elements, coarse crystal structures will preferentially lead to stress corrosion cracking at grain boundaries, resulting in component failure.

[0014] Forging conditions have a significant impact on the control of crystal structure. For example, when forging is carried out at a low temperature before forging the billet, recrystallization occurs in areas with large strain during processing due to strain accumulation during subsequent heat treatment.

[0015] In automotive suspension components, due to their complex shapes, they are typically formed using flash forging.

[0016] During flash forging, recrystallization easily occurs near the parting line corresponding to the flash due to increased strain. If recrystallization occurs in the bushing portion and covers a large area, it significantly impairs the stress corrosion cracking resistance of components such as ball joints pressed into the bushing, leading to component failure. Furthermore, the parting line is the line exposed after the flash is removed from the forging through grinding. The parting line slightly bulges from the side of the forging. Grinding (dressing) of forgings is usually performed at room temperature.

[0017] However, the more complex the shape of the suspension, the more difficult it is to suppress recrystallization during the forging process.

[0018] The present invention was made in view of the above circumstances, and its object is to provide a suspension component and a method for manufacturing the suspension component that exhibit excellent resistance to stress corrosion cracking even when recrystallization occurs near the parting line.

[0019] To address the aforementioned issues, the present invention provides the following means.

[0020] [1] One aspect of the present invention relates to a suspension component made of an aluminum alloy having the following alloy composition: containing Cu in the range of 0.3% by mass and 0.5% by mass, Mg in the range of 0.65% by mass and 1.05% by mass, Si in the range of 0.9% by mass and 1.25% by mass, Mn in the range of 0.4% by mass and 0.6% by mass, Fe in the range of 0.15% by mass and 0.30% by mass, Cr in the range of 0.09% by mass and 0.25% by mass, Ti in the range of 0.01% by mass and 0.05% by mass, and B in the range of 0.0010% by mass and 0.0050% by mass, with the balance being Al and unavoidable impurities.

[0021] The grain boundary dip angle is 45° or less relative to the surface perpendicular to the parting line of the bushing and parallel to the cylindrical axis of the bushing.

[0022] [2] In the suspension components mentioned above [1], the tensile strength can be above 380 MPa.

[0023] [3] One aspect of the present invention relates to a method for manufacturing a suspension component, comprising:

[0024] A melt-forming process for forming a molten aluminum alloy having the following alloy composition: Cu in the range of 0.3% to 0.5% by mass, Mg in the range of 0.65% to 1.05% by mass, Si in the range of 0.9% to 1.25% by mass, Mn in the range of 0.4% to 0.6% by mass, Fe in the range of 0.15% to 0.30% by mass, Cr in the range of 0.09% to 0.25% by mass, Ti in the range of 0.01% to 0.05% by mass, and B in the range of 0.0010% to 0.0050% by mass, with the balance being Al and unavoidable impurities;

[0025] The casting process involves processing the molten metal to obtain a casting.

[0026] The forging process of obtaining a forged article by heating and forging the cast article;

[0027] A solution treatment process in which the forging is held at a temperature above 500°C;

[0028] An aging process that involves heat treatment of the forged product after the quenching process; and

[0029] A hot finishing process is performed on forgings that have undergone the aging treatment process at a temperature exceeding 100°C but below 250°C.

[0030] [4] In the above-mentioned method for manufacturing suspension components [3], the hot finishing process can be carried out on the forgings that have undergone the aging process at a temperature of 125°C or higher and 250°C or lower.

[0031] [5] In the manufacturing method of the suspension components described in [3] or [4] above, the hot finishing process can be carried out on the forgings that have undergone the aging treatment process at a temperature of 150°C or higher and 250°C or lower.

[0032] [6] The manufacturing method of the suspension components described in [3] to [5] above can be carried out by continuous casting. The cooling rate of the melt in the casting process can be above 10°C / second, and the average crystal grain size of the casting can be below 80μm.

[0033] [7] The manufacturing method of the suspension components described in [3] to [6] above includes a quenching process after the solution treatment process and before the heat finishing process, wherein the forging process is performed at a billet temperature of 450°C or higher and 520°C or lower, the solution treatment process is performed at a temperature of 550°C or lower, the quenching process is performed by water quenching the forging in water at a temperature of 60°C or lower, and the aging process is performed by heating the forging after the quenching process at a temperature of 175°C or higher and 190°C or lower for more than 4 hours.

[0034] According to the present invention, a suspension component and a method for manufacturing the suspension component are provided that exhibit excellent resistance to stress corrosion cracking even when recrystallization occurs near the parting line. Attached Figure Description

[0035] Figure 1 This is a plan view illustrating an example of the configuration of a suspension component according to one aspect of the present invention.

[0036] Figure 2 It is Figure 1 An enlarged schematic diagram of the area near the bushing of the suspension component.

[0037] Figure 3 It is Figure 1 An enlarged plan view of the area near the bushing of the suspension component.

[0038] Figure 4 This is a cross-sectional view showing an example of the configuration near the mold of a horizontal continuous casting apparatus that can be used in the casting process of a suspension arm manufacturing method according to one aspect of the present invention.

[0039] Figure 5 It is Figure 4 An enlarged cross-sectional view of the main part near the cooling water chamber of a horizontal continuous casting device.

[0040] Figure 6 This is an explanatory diagram illustrating the heat flow of the cooling wall section in a horizontal continuous casting apparatus.

[0041] Figure 7 This is a diagram illustrating a method for manufacturing a suspension component according to one aspect of the present invention, and is a plan view showing an example of the structure of a forging before a heat finishing process.

[0042] Figure 8 This is a schematic plan view showing the configuration during the SCC test in Example 1.

[0043] Figure 9 The tissue image is obtained by analyzing an electron microscope image near the apex portion 51 of the bushing portion using electron backscatter diffraction in the suspension component of Example 1. Detailed Implementation

[0044] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0045] Furthermore, in the accompanying drawings used in the following description, the characteristic parts are sometimes shown enlarged for ease of understanding, and the size ratios of the constituent elements are not necessarily the same as the actual dimensions. Also, the materials, dimensions, etc., illustrated in the following description are examples, and the present invention is not necessarily limited to them; it can be implemented with appropriate modifications without changing its essence.

[0046] [Suspension Components]

[0047] First, a suspension component according to one embodiment of the present invention will be described.

[0048] One embodiment of the present invention relates to a suspension component for suspension arms made of forged aluminum alloy.

[0049] The aluminum alloy forging of this embodiment is made of an aluminum alloy having the following alloy composition: Cu in the range of 0.3% to 0.5% by mass, Mg in the range of 0.65% to 1.05% by mass, Si in the range of 0.9% to 1.25% by mass, Mn in the range of 0.4% to 0.6% by mass, Fe in the range of 0.15% to 0.30% by mass, Cr in the range of 0.09% to 0.25% by mass, Ti in the range of 0.01% to 0.05% by mass, and B in the range of 0.0010% to 0.0050% by mass, with the balance consisting of Al and unavoidable impurities.

[0050] The aluminum alloy forging of this embodiment is equivalent to the forging of 6000 series aluminum alloy in that it contains Mg and Si.

[0051] In one embodiment of the present invention, the suspension component has a grain boundary inclination angle of 45° or less relative to a surface perpendicular to the parting line of the bushing portion and parallel to the cylindrical axis of the bushing portion. Details will be described later, but the bushing portion corresponds to reference numeral 50 in the drawings, and the parting line corresponds to reference numeral PL.

[0052] (Cu: ≥0.3% by mass and ≤0.5% by mass)

[0053] Cu has the function of finely dispersing Mg-Si compounds in aluminum alloys and improving the tensile strength of aluminum alloys by precipitating Al-Cu-Mg-Si compounds, primarily the Q phase. The Cu content is in the range of 0.30% by mass or more and 0.50% by mass or less, or in the range of 0.35% by mass or more and 0.45% by mass or less, or 0.42% by mass or less. With the Cu content within the above range, the mechanical properties of aluminum alloy forgings at room temperature can be improved. However, if the Cu content exceeds 0.5%, the amount of Cu coexisting with Mg2Si at the grain boundaries increases, thus increasing the potential difference between the parent phase and the compounds at the grain boundaries, impairing resistance to stress corrosion cracking. Therefore, the above range is preferred.

[0054] (Mg: ≥0.65% by mass and ≤1.05% by mass)

[0055] Mg contributes to the tensile strength of aluminum alloys. It strengthens the alloy through solid solution in the aluminum matrix, or by precipitation as a Mg-Si compound (Mg₂Si) or an Al-Cu-Mg-Si compound dominated by the Q phase. Mg content is typically between 0.65% by mass and 1.05% by mass, or between 0.75% by mass and 1.00% by mass, or between 0.85% by mass and 0.95% by mass. Maintaining Mg content within these ranges improves both the mechanical properties of aluminum alloy forgings at room temperature and their corrosion resistance.

[0056] (Si: ≥0.9% by mass and ≤1.25% by mass)

[0057] Like Mg, Si improves the mechanical properties of aluminum alloy forgings at room temperature while also enhancing their corrosion resistance. However, excessive addition of Si to aluminum alloys can lead to the formation of coarse primary Si grains, potentially reducing the tensile strength of the alloy. The Si content should be within the range of 0.90% by mass to 1.25% by mass, or 0.95% by mass to 1.20% by mass, or 1.00% by mass to 1.18% by mass. Maintaining the Si content within these ranges suppresses the crystallization of primary Si, thus improving both the mechanical properties and corrosion resistance of the aluminum alloy forgings at room temperature.

[0058] (Mn: ≥0.4% by mass and ≤0.6% by mass)

[0059] Mn (metallurgical manganese) increases the tensile strength of aluminum alloys by forming fine granular crystals containing intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Cr-Fe-Si. The Mn content is typically within the range of 0.40% by mass to 0.60% by mass, or within the range of 0.45% by mass to 0.55% by mass, or 0.47% by mass to 0.53% by mass. Maintaining a Mn content within these ranges improves the mechanical properties of aluminum alloy forgings at room temperature.

[0060] (Fe: ≥0.15% by mass and ≤0.3% by mass)

[0061] Fe enhances the tensile strength of aluminum alloys by crystallizing 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. The Fe content is typically within the range of 0.15% by mass to 0.30% by mass, or within the range of 0.20% by mass to 0.27% by mass, or 0.22% by mass. Maintaining a Fe content within these ranges improves the mechanical properties of aluminum alloy forgings at room temperature.

[0062] (Cr: ≥0.09% by mass and ≤0.25% by mass)

[0063] Cr (Cr) increases the tensile strength of aluminum alloys by forming fine granular crystals containing intermetallic compounds such as Al-Mn-Cr-Fe-Si and Al-Fe-Cr. The Cr content is typically within the range of 0.09% by mass to 0.25% by mass, or 0.10% by mass to 0.20% by mass, or 0.12% by mass to 0.18% by mass. Maintaining a Cr content within these ranges improves the mechanical properties of aluminum alloy forgings at room temperature.

[0064] (Ti: ≥0.01% by mass and ≤0.05% by mass)

[0065] Ti (Ti) contributes to grain refinement in aluminum alloys and improves workability. However, when the Ti content is below 0.01% by mass, the grain refinement effect may not be sufficiently achieved. Conversely, if the Ti content exceeds 0.05% by mass, coarse crystals form, potentially reducing workability. Furthermore, the presence of large amounts of coarse Ti-containing crystals in aluminum alloy forgings can sometimes reduce toughness. Therefore, the Ti content is set to be 0.01% by mass or more and 0.05% by mass or less. Preferably, the Ti content is 0.015% by mass or more and 0.030% by mass or less.

[0066] (B: 0.0010% by mass or more and 0.0050% by mass or less)

[0067] Boron (B) has the function of refining the grain size of aluminum alloys and improving their workability. The grain refinement effect is enhanced by adding B together with Ti to the aluminum alloy. When the B content is below 0.0010% by mass, the grain refinement effect may not be sufficiently achieved. On the other hand, if the B content exceeds 0.0050% by mass, coarse crystals are formed and may be incorporated into the aluminum alloy forgings as inclusions. Furthermore, when a large amount of coarse crystals containing B are incorporated into the final aluminum alloy product, the toughness may decrease. Therefore, the B content is set to 0.0010~0.0050% by mass. The preferred B content is 0.0015~0.0045% by mass.

[0068] (Unavoidable impurities)

[0069] Unavoidable impurities are impurities that are unavoidably introduced into the aluminum alloy from the raw materials or manufacturing process of the aluminum alloy forging. Examples of unavoidable impurities include Zn, Zr, Ni, Sn, and Be. The content of these unavoidable impurities is preferably no more than 0.1% by mass.

[0070] Figure 1 This is a plan view illustrating an example of the configuration of a suspension component according to one aspect of the present invention. Figure 2 It is Figure 1 An enlarged schematic diagram of the area near the bushing of the suspension component. Figure 3 It is Figure 1 An enlarged plan view of the area near the bushing of the suspension component.

[0071] Figures 1-3 The suspension component 100 shown includes, for example, a wheel-side connection portion 4, a first vehicle-side connection portion 5, a second vehicle-side connection portion 6, a first arm portion 1, a second arm portion 2, and an arm connection portion 3. The first arm portion 1 connects the wheel-side connection portion 4 and the first vehicle-side connection portion 5. The second arm portion 2 connects the wheel-side connection portion 4 and the second vehicle-side connection portion 6. The arm connection portion 3 connects the first vehicle-side connection portion 5 and the second vehicle-side connection portion 6. The first vehicle-side connection portion 5 and the second vehicle-side connection portion 6 are components also referred to as bushing portions. The suspension component 100 according to this embodiment includes at least one bushing portion 5, 6. The bushing portions 5, 6 can be provided with the same shape.

[0072] Figure 2 and Figure 3 This is a diagram illustrating the features of the bushing portion in the suspension component 100 of this embodiment. Figure 2 and Figure 3 In the diagram, bushing portion 5 is shown enlarged as an example of a bushing portion. Bushing portion 5 is used as an article, for example, in the following state: Figure 2 and Figure 3The region (removed region) indicated by the double-dotted line and the marker H is removed in a manner that penetrates through the x-direction. That is, in Figure 2 and Figure 3 The area marked H with a double-dotted line (the removed area) is where the aluminum alloy has been removed to create an opening. The opening is in... Figure 2 The paper is continuous in the depth direction (x direction), thus effectively becoming a cylindrical shape. Other components, such as ball-and-socket joints, are pressed into this opening in the x direction. In this embodiment, the forged component with cylindrical openings formed in the bushing portions 5 and 6, and the forged component without openings formed in the bushing portions 5 and 6, are collectively referred to as suspension components.

[0073] In the suspension component 100 according to this embodiment, a parting line PL is formed along the outline of the suspension when viewed from the z-direction. The parting line PL is formed by removing the flash 70 of the forging in the forging process of the manufacturing process described in detail later in a hot finishing process. The parting line PL is confirmed when observing the side of the suspension component 100.

[0074] like Figure 2 As shown, in bushing portion 5, the parting line PL is formed, for example, in a manner that forms an xy plane. Furthermore, bushing portions 5 and 6 have vertex portions at their ends in the y-direction. Figure 2 In the diagram, the vertex portion formed in bushing portion 5 is indicated by the symbol 51. The vertex portions of bushing portions 5 and 6 are located at the center of bushing portions 5 and 6 in the z direction of the suspension frame component 100, and are the components at the position with the greatest distance in the y direction from the wheel-side connection portion 4.

[0075] In this embodiment, the suspension member 100, at its apex 51, is positioned relative to the surface formed by the parting line PL of the bushing portions 5 and 6. Figures 1-3 The grain boundary is a plane perpendicular to the xy plane and parallel to the cylindrical axis of bushing portions 5 and 6, with a grain boundary inclination angle of 45° or less. The grain boundary inclination angle is preferably 35° or less, more preferably 25° or less. The grain boundary inclination angle is greater than 0°, for example, 5° or more, or 10° or more.

[0076] The more complex the shape of the suspension component manufactured by forging, the more strain occurs during the forging process, which will be detailed later, leading to recrystallization during the subsequent solution treatment process. Strain is particularly high near the parting line, making it difficult to completely eliminate recrystallization. Furthermore, areas where recrystallization has occurred are more susceptible to stress corrosion cracking under stress, thus becoming a problem. In the bushing portions 5 and 6 of the automotive suspension component 100, a ball-and-socket joint is pressed into the bushing portion 5 and 6, with its apex 51 becoming the area of ​​greatest stress. The direction of stress is the direction in which the ball-and-socket joint is pressed in and its opposite direction. That is, the direction of stress is the axial direction of the opening formed in the bushing portions 5 and 6. Figures 1-3The ±x direction in the equation.

[0077] If the orientation of the long side of the recrystallized crystals is perpendicular to the direction of stress in bushing portions 5 and 6, the resistance to stress corrosion cracking is significantly poor. Conversely, when the orientation of the grains in the region near vertex 51, extending inward in the y-direction from the outermost surface to a predetermined depth (i.e., from mark E0 in the figure to a depth of 300 μm in the -y direction), is such that the long side of the grains is nearly parallel to the stress direction, resistance to stress corrosion cracking is achieved. Regarding this grain orientation, as described above, the outermost point (vertex 51) in the y-direction of the stress concentration parting line PL, relative to the surface formed by the parting line PL of bushing portions 5 and 6 (… Figures 1-3 The xy plane is perpendicular to the cylindrical axis (x-axis) of bushing parts 5 and 6, and the grain boundary inclination angle is less than 45°.

[0078] The suspension component 100 involved in this embodiment has a tensile strength of 380 MPa or more, preferably 385 MPa or more, more preferably 390 MPa or more, and even more preferably 392 MPa or more, as measured according to JIS Z2241:2011.

[0079] exist Figure 1 The example shown is an A-type arm with a first arm portion 1, a second arm portion 2 and an arm connecting portion 3. However, the present invention is not limited to the above example and is also applicable to suspension arms of other shapes that have bushing portions and are formed by forging.

[0080] [Manufacturing method for suspension components]

[0081] Next, a method for manufacturing a suspension component according to an embodiment of the present invention will be described. The method for manufacturing a suspension component according to an embodiment of the present invention includes: a melt-forming step of obtaining an alloy melt with the same composition as the aforementioned aluminum alloy forging; a forging step of heating and forging a casting obtained by casting the alloy melt to obtain a forging; a solution treatment step of heating the forging at a temperature of 500°C or higher; an aging treatment step of heat-treating the forging after the solution treatment; and a heat-finishing step of hot-finishing the forging after the aging treatment at a temperature of 100°C or lower than 250°C.

[0082] One embodiment of the present invention relates to a method for manufacturing suspension components, which includes, for example, a melt formation process, a casting process, a homogenization heat treatment process, a forging process, a solution treatment process, a quenching process, an aging treatment process, and a heat finishing process.

[0083] (Molten liquid formation process)

[0084] The melt formation process is a process of melting raw materials to obtain an aluminum alloy melt with adjusted composition. The composition of the aluminum alloy melt is adjusted to have the following alloy composition: Cu ranging from 0.30% to 0.50% by mass, Mg ranging from 0.65% to 1.05% by mass, Si ranging from 0.90% to 1.25% by mass, Mn ranging from 0.40% to 0.60% by mass, Fe ranging from 0.15% to 0.30% by mass, Cr ranging from 0.09% to 0.25% by mass, Ti ranging from 0.01% to 0.05% by mass, and B ranging from 0.0010% to 0.0050% by mass, with the balance consisting of Al and unavoidable impurities.

[0085] By using the aluminum alloy molten liquid with the above composition for subsequent processes, it is possible to provide suspension components and a method for manufacturing suspension components that exhibit excellent resistance to stress corrosion cracking even when recrystallization occurs near the parting line. Furthermore, the so-called aluminum ingot is aluminum with a concentration of 99% or higher obtained by electrolysis of alumina produced from minerals through a process called electrolytic refining.

[0086] Molten aluminum alloy can be obtained by heating an aluminum alloy to melt it. Alternatively, it can be formed by melting a mixture of elemental substances containing the raw materials of the aluminum alloy or compounds containing two or more elements in proportions that produce the target aluminum alloy. For example, Ti and B can be mixed in the form of grain-refining materials such as Al-Ti-B rods for the purpose of controlling the grain size of the aluminum alloy produced in the casting process.

[0087] Alternatively, the following raw materials can be used as raw materials for aluminum alloy melt, and they can be melted to obtain an aluminum alloy melt with adjusted composition. These raw materials are scrap containing 10% or more of 1000, 2000, 3000, 4000, 5000, 6000, and / or 7000 series aluminum alloys, with the remainder being new aluminum ingots and the aforementioned additive elements. In this case, Al-Mg-Si suspension arms that are difficult to recrystallize and have excellent mechanical properties at room temperature can be obtained. Furthermore, the so-called new aluminum ingots are aluminum with a purity of, for example, 99% or more, obtained by electrolysis of alumina produced from minerals through a process called electrolytic refining.

[0088] (Casting process)

[0089] In the casting process, molten aluminum alloy (liquid phase) is cooled and solidified into a solid (solid phase) to obtain an aluminum alloy casting. The casting process is preferably performed by continuous casting. For example, vertical continuous casting or horizontal continuous casting can be used. Hereinafter, a method for manufacturing a suspension arm according to an embodiment of the present invention will be described using a horizontal continuous casting method as an example.

[0090] Figure 4 and Figure 5 A horizontal continuous casting apparatus capable of manufacturing aluminum alloy castings for this embodiment is shown. Figure 4 This is a cross-sectional view showing an example of the area near the mold 12 of the horizontal continuous casting apparatus 10. Figure 5 This is an enlarged cross-sectional view of the main part near the cooling water chamber 24 of the horizontal continuous casting device 10.

[0091] Figure 4 and Figure 5 The horizontal continuous casting apparatus 10 shown has a molten material receiving part (tundish) 11, a hollow cylindrical mold 12, and a refractory material plate (insulating member) 13 disposed between one end side 12a of the mold 12 and the molten material receiving part 11.

[0092] The molten metal receiving section 11 consists of a molten metal inflow section 11a that receives the aluminum alloy molten metal M obtained in the above-mentioned molten metal forming process, a molten metal holding section 11b, and an outflow section 11c that flows out into the hollow section 21 of the mold 12.

[0093] The molten aluminum alloy receiving section 11 maintains the liquid level of the upper surface 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, stably distributes the molten aluminum alloy M to each mold 12.

[0094] The molten aluminum alloy M held in the molten metal receiving section 11b is injected into the hollow section 21 of the mold 12 through the injection passage 13a provided in the refractory plate 13. Then, the molten aluminum alloy M supplied to the hollow section 21 is cooled and solidified by the cooling device 23 (described later), and pulled out from the other end 12b of the mold 12 as an aluminum alloy rod B (a solidified ingot).

[0095] At the other end 12b of the mold 12, a pull-out drive device (not shown) is provided to pull out the cast aluminum alloy bar B at a certain speed. Alternatively, a synchronous cutting machine (not shown) is preferably provided to cut the continuously pulled-out aluminum alloy bar B into arbitrary lengths.

[0096] The refractory plate 13 is a component that isolates the heat transfer between the molten receiving part 11 and the mold 12. For example, it can be made of materials such as calcium silicate, alumina, silicon dioxide, a mixture of alumina and silicon dioxide, silicon nitride, silicon carbide, and graphite. Such a refractory plate 13 can also be composed of multiple layers with different constituent materials.

[0097] In this embodiment, the mold 12 is a hollow cylindrical component, formed, for example, from one or more materials selected from aluminum, copper, or alloys thereof. The material of such a mold 12 can be selected based on the optimal combination of thermal conductivity, heat resistance, and mechanical strength.

[0098] The hollow portion 21 of the mold 12 is formed with a circular cross-section in order to make the cast aluminum alloy rod B into a cylindrical rod shape, so that the mold 12 is held in a manner that the central axis (central axis) C of the mold passing through the center of the hollow portion 21 is generally in the horizontal direction.

[0099] The inner circumferential surface 21a of the hollow portion 21 of the mold 12 faces the casting direction of the aluminum alloy rod B (see reference). Figure 4 The inner circumferential surface 21a is formed at an elevation angle of 0° to 3° (more preferably 0° to 1°) relative to the central axis C of the mold. That is, the inner circumferential surface 21a is configured as a cone that opens in a conical shape toward the casting direction. Moreover, the angle at which this cone is formed is an elevation angle.

[0100] When the elevation angle is less than 0°, the aluminum alloy rod B encounters resistance at the other end 12b, which serves as the mold exit, as it is pulled out of the mold 12, potentially making casting difficult. 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, reducing the heat dissipation effect from the molten aluminum alloy M and its cooled solidified shell to the mold 12, thus potentially leading to insufficient solidification. As a result, casting defects such as remelted skin on the surface of the aluminum alloy rod B or unsolidified molten aluminum alloy M ejecting from the end of the aluminum alloy rod B may occur, which is therefore undesirable.

[0101] Furthermore, the cross-sectional shape of the hollow portion 21 of the mold 12 (the planar shape of the hollow portion 21 of the mold 12 when viewed from the other end side 21b) can be, in addition to the circle in this embodiment, a triangular, rectangular, polygonal, semi-circular, elliptical, or irregular cross-sectional shape without an axis of symmetry and / or a plane of symmetry, etc., depending on the shape of the aluminum alloy rod to be cast.

[0102] A fluid supply pipe 22 is disposed on one end side 12a of the mold 12 to supply lubricating fluid into the hollow portion 21 of the mold 12. The lubricating fluid supplied by the fluid supply pipe 22 can be any one or more lubricating fluids selected from gaseous lubricating materials and liquid lubricating materials. When supplying both gaseous and liquid lubricating materials, it is preferable to provide separate fluid supply pipes for each. The lubricating fluid supplied under pressure by the fluid supply pipe 22 is supplied into the hollow portion 21 of the mold 12 through an annular lubricating material supply port 22a.

[0103] In this embodiment, the pressurized lubricating fluid is supplied from the lubricating material supply port 22a to the inner peripheral surface 21a of the mold 12. Alternatively, the liquid lubricating material may be heated to become a decomposition gas and then supplied to the inner peripheral surface 21a of the mold 12. Another option is to place a porous material at the lubricating material supply port 22a, through which the lubricating fluid seeps into the inner peripheral surface 21a of the mold 12.

[0104] A cooling mechanism, namely a cooling device 23, is formed inside the mold 12 to cool and solidify the molten aluminum alloy M. The cooling device 23 of this embodiment has: a cooling water chamber 24 for receiving cooling water W for cooling the inner peripheral surface 21a of the hollow part 21 of the mold 12, and a cooling water spray passage 25 for communicating the cooling water chamber 24 and the hollow part 21 of the mold 12.

[0105] The cooling water chamber 24 is formed in a ring around the hollow part 21 inside the mold 12, at a position outside the inner peripheral surface 21a of the hollow part 21, and is supplied with cooling water W via the cooling water supply pipe 26.

[0106] The mold 12 cools its inner circumferential surface 21a by using cooling water W contained in the cooling water chamber 24, thereby taking away heat from the aluminum alloy melt M that fills the hollow part 21 of the mold 12 from the surface in contact with the inner circumferential surface 21a of the mold 12, thereby forming a solidified shell on the surface of the aluminum alloy melt M.

[0107] Additionally, the cooling water spray passage 25 sprays cooling water W directly onto the aluminum alloy rod B from the spray opening 25a facing the hollow portion 21 at the other end 12b of the mold 12 to cool the aluminum alloy rod B. The longitudinal cross-sectional shape of such a cooling water spray passage 25 can be, in addition to the circular shape of this embodiment, for example, a semi-circle, a pear shape, or a horseshoe shape.

[0108] Furthermore, in this embodiment, the cooling water W supplied via the cooling water supply pipe 26 is first collected in the cooling water chamber 24 to cool the inner peripheral surface 21a of the hollow portion 21 of the mold 12, and then the cooling water W in the cooling water chamber 24 is sprayed from the cooling water spray passage 25 toward the aluminum alloy rod B. However, it can also be configured such that these cooling waters are supplied by separate cooling water supply pipes of separate systems.

[0109] The effective mold length L is defined as the length from the point where the extension of the central axis of the spray opening 25a of the cooling water spray passage 25 contacts the surface of the cast aluminum alloy rod B to the contact surface between the mold 12 and the refractory plate 13. This effective mold length L is preferably 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 lack of a good film formation. If it exceeds 40 mm, the forced cooling effect decreases, solidification caused 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, leading to cracks on the casting surface and breakage inside the mold, potentially causing casting instability. Therefore, this is not preferred.

[0110] The supply of cooling water W to the cooling water chamber 24 and the spraying of cooling water W from the spray opening 25a of the cooling water spray passage 25 can preferably be controlled by a control signal from a control device (not shown).

[0111] The cooling water chamber 24 is formed such that the inner bottom surface 24a of the hollow portion 21 near the mold 12 is parallel to the inner peripheral surface 21a of the hollow portion 21 of the mold 12.

[0112] Furthermore, the parallelism mentioned 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 chamber 24, that is, it also includes the case where the inclination angle of the inner bottom surface 24a relative to the inner peripheral surface 21a is greater than 0° and less than 3°.

[0113] like Figure 5 As shown, the cooling wall portion 27 of the mold 12, which is the part of the inner bottom surface 24a of the cooling water chamber 24 that faces the inner peripheral surface 21a of the hollow portion 21 of the mold 12, is designed such that the heat flux per unit area from the molten aluminum alloy M in the hollow portion 21 to the cooling water W in the cooling water chamber 24 is 10 × 10⁻⁶. 5 W / m 2 Above and 50×10 5 W / m 2 The following methods are used to form the form.

[0114] The mold 12 can be formed such that the thickness t of the cooling wall portion 27, i.e., the distance between the inner bottom surface 24a of the cooling water chamber 24 and the inner peripheral surface 21a of the hollow portion 21 of the mold 12, is in the range of, for example, 0.5 mm or more and 3.0 mm or less, preferably 0.5 mm or more and 2.5 mm or less. Furthermore, the forming material of the mold 12 can be selected such that the thermal conductivity of at least the cooling wall portion 27 of the mold 12 is in the range of 100 W / m·K or more and 400 W / m·K or less.

[0115] exist Figure 5 In the process, the molten aluminum alloy M in the molten receiving part 11 is supplied from one end 12a of the mold 12 through the refractory plate 13, and is forcibly cooled at the other end 12b of the mold 12 to become an aluminum alloy rod B. The mold 12 is held in such a way that the central axis C of the mold is approximately horizontal.

[0116] The aluminum alloy bar B is pulled out at a certain speed by a pull-out drive device (not shown) located near the other end 12b of the mold 12, thus continuously casting to form a long aluminum alloy bar B. The pulled-out aluminum alloy bar B is cut to the desired length, for example, by a synchronous cutting machine (not shown).

[0117] Furthermore, the composition ratio of the cast aluminum alloy rod B can be confirmed using, for example, a photoelectric emission spectrometer (e.g., a PDA-5500 manufactured by Shimadzu Corporation of Japan) as described in "JIS H1305".

[0118] The difference between the height of the molten aluminum alloy M stored in the molten aluminum alloy receiving section 11 and the height of the inner circumferential surface 21a on the upper side of the mold 12 is preferably set to 0 mm to 250 mm (more preferably 50 mm to 170 mm). By setting it within such a range, the pressure of the molten aluminum alloy M supplied to the mold 12 and the lubricating oil and the gas generated by the vaporization of the lubricating oil are properly balanced, thus ensuring stable casting performance.

[0119] Liquid lubricants can be vegetable oils used as lubricants. Examples include rapeseed oil, castor oil, and salad oil. They have minimal adverse environmental impact and are therefore preferred.

[0120] The lubricating oil supply rate is preferably 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 too low, the molten aluminum alloy M of 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 mix into the aluminum alloy rod B and become an internal defect.

[0121] The casting speed, i.e., the speed at which the aluminum alloy rod B is pulled out of 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, at casting speeds within this range, the network structure of the crystals formed by casting becomes more uniform and fine, increasing the resistance to deformation of the aluminum billet at high temperatures and improving its high-temperature mechanical strength.

[0122] The amount of cooling water sprayed from the spray opening 25a of the cooling water spray passage 25 is preferably 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, the molten aluminum alloy M may leak from the mold 12 without solidifying. In addition, the surface of the cast aluminum alloy bar B may remelt, forming an uneven structure and remaining as an internal defect. On the other hand, if the amount of cooling water is more than this range, the heat dissipation of the mold 12 may be too great, causing it to solidify midway.

[0123] The average temperature of the molten aluminum alloy M flowing into the mold 12 from the molten metal receiving section 11 is preferably 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 crystals may form in and around the mold 12, thus entering the interior of the aluminum alloy rod B as internal defects. On the other hand, if the temperature of the molten aluminum alloy M is too high, a large amount of hydrogen gas can easily enter the molten aluminum alloy M, potentially entering the aluminum alloy rod B as pores and becoming internal voids.

[0124] Furthermore, by setting the heat flux per unit area from the molten aluminum alloy M in the hollow portion 21 to the cooling water W in the cooling water chamber 24 within the cooling wall portion 27 of the mold 12 to 10 × 10⁻⁶, 5 W / m 2 Above and 50×10 5 W / m 2 The following range can prevent thermal adhesion of aluminum alloy rod B.

[0125] The cooling wall 27 of the mold 12 is heated by the heat dissipated from the molten aluminum alloy M. This heat is exchanged by cooling the cooling water W contained in the cooling water chamber 24. However, regarding the state of this heat exchange, such as... Figure 6 As shown in the explanatory diagram, we focus on the heat flux per unit area. The heat flux per unit area is expressed by the following equation (1) according to Fourier's law.

[0126] Q= -k×(T1-T2) / L···(1)

[0127] Q: Heat flux

[0128] k: Thermal conductivity (W / m·K) of the portion through which heat passes (in this embodiment, the cooling wall 27 of the mold 12).

[0129] T1: Low-temperature side temperature of the heat-passing part (in this embodiment, the inner bottom surface 24a of the cooling water chamber 24)

[0130] T2: The high-temperature side temperature of the part through which heat passes (in this embodiment, it is the inner circumferential surface 21a of the hollow part 21 of the mold 12).

[0131] L: Length of the section through which heat passes (mm) (in this embodiment, it is the thickness t of the cooling wall 27 of the mold 12)

[0132] Based on mold material, thickness, and temperature measurement data that yield good results even with reduced lubricant during casting, the heat flux per unit area is defined as 10 × 10⁻⁶. 5 W / m 2 The above-described cooling wall 27 of the mold 12 prevents the cast aluminum alloy rod B from sticking due to heat. Furthermore, a heat flux of 50 × 10⁻⁶ per unit area is preferred. 5 W / m 2 the following.

[0133] To ensure that the cooling wall portion 27 of the mold 12 is within such a range of heat flux values, the mold 12 can be formed such that the thickness t of the cooling wall portion 27 is, for example, in the range of 0.5 mm or more and 3.0 mm or less. Furthermore, the thermal conductivity of at least the cooling wall portion 27 of the mold 12 can be set to the range of 100 W / m·K or more and 400 W / m·K or less.

[0134] When manufacturing the aluminum alloy bar B of this embodiment, the horizontal continuous casting apparatus 10 described above is used to continuously supply molten aluminum alloy M stored in the melt receiving section 11 from one end side 12a of the mold 12 into the hollow section 21. In addition, cooling water W is supplied to the cooling water chamber 24, and lubricating fluid, such as lubricating oil, is supplied from the fluid supply pipe 22.

[0135] Then, the heat flux per unit area in the cooling wall section 27 is 10 × 10 5 W / m 2 Under the above conditions, the molten aluminum alloy M supplied to the hollow section 21 is cooled and solidified to cast the aluminum alloy rod B. In addition, when casting the aluminum alloy rod B, it is preferable to keep the wall surface temperature of the cooling wall section 27 of the mold 12, which is cooled by cooling water W, below 100°C.

[0136] The aluminum alloy rod B obtained in this way has a heat flux per unit area of ​​10 × 10⁻⁶ in the cooling wall section 27. 5W / m 2 Cooling and solidification under the above conditions can suppress the adhesion of reaction products, such as carbides, caused by the contact between the lubricating oil gas and the molten aluminum alloy M. Therefore, it is not necessary to cut away carbides or other substances from the surface of the aluminum alloy rod B, allowing for the production of aluminum alloy rod B with a high yield.

[0137] The casting process for obtaining castings 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 be used. Vertical continuous casting is classified into float casting and hot-top casting based on the method of supplying molten aluminum alloy M to the mold (mold 12). The following is a brief explanation of the case using the hot-top casting method.

[0138] The casting apparatus used for the hot-top method includes a mold, a melt receiver (manifold), etc. The melt supplied to the melt receiver passes through the outlet and through the manifold, thereby adjusting the flow rate, and enters the roughly horizontally positioned cylindrical mold, where it is forcibly cooled to form a solidified shell on the outer surface of the melt.

[0139] Then, cooling water is directly sprayed onto the castings pulled from the mold, and the castings are continuously pulled out as the metal solidifies into the interior of the casting. Typically, the mold uses a metal component with good thermal conductivity and has a hollow structure for introducing the cooling medium into its interior.

[0140] The cooling medium used can be selected from those available in industrial applications, but water is recommended from the perspective of ease of use.

[0141] In this embodiment, the mold is appropriately selected from metals such as copper and aluminum, or graphite, considering the heat transfer performance and durability of the contact portion in contact with the molten metal. The manifold is generally made of refractory material and is located on the upper side of the mold. The material and size of the manifold can be appropriately selected based on the composition range of the alloy to be cast and the size of the casting, without any particular restrictions.

[0142] The average cooling rate during casting can be appropriately selected, for example, from a range of 10°C / second or higher to 300°C / second or lower. The casting speed can be appropriately selected, for example, from a range of 200 to 600 mm / min.

[0143] (Homogeneous heat treatment process)

[0144] Next, a homogenization heat treatment process can be performed as appropriate. The homogenization heat treatment process involves heat treating the aluminum alloy castings obtained through the casting process to homogenize the microsegregation caused by solidification, precipitate supersaturated solid solution elements, and change the metastable phase towards the equilibrium phase.

[0145] In the homogenization heat treatment process, the aluminum alloy casting obtained in the casting process is held at a temperature above 370°C and below 560°C for 4 to 10 hours. By performing homogenization heat treatment within this temperature range, the homogenization of the aluminum alloy casting and the incorporation of solute atoms are fully achieved. Therefore, the strength is further improved through subsequent aging treatment. The homogenization heat treatment process can also be omitted.

[0146] (Forging process)

[0147] The forging process involves shaping aluminum alloy castings into specified dimensions to obtain forging blanks, heating the obtained forging blanks to a specified temperature, and then applying pressure using a press to form the blanks using a mold.

[0148] In this embodiment, a forged product (a suspension arm component for automobiles) is obtained by forging the forging raw material at a heating temperature of 450°C or higher and 560°C or lower. In this case, the forging start temperature of the forging raw material is preferably set to 450°C or higher and 560°C or lower. When the start temperature is below 450°C, the deformation resistance increases, and it may be impossible to perform sufficient processing. On the other hand, when the temperature exceeds 560°C, defects such as forging cracks and eutectic melting may easily occur. Furthermore, it is more preferable to keep the billet temperature of the forging blank within the range of 480°C or higher and 520°C or lower.

[0149] The average in-plane grain size of the forging billet is preferably 100 μm or less, more preferably 80 μm or less. The average in-plane grain size of the forging billet is, for example, 30 μm or more.

[0150] (Solution treatment process)

[0151] Solution treatment is a process in which the forged product obtained in the forging process is heated at a temperature above 500°C to dissolve the solute elements, thereby mitigating the strain introduced into the casting.

[0152] In this embodiment, solution treatment is performed by holding the forged article at a processing temperature of 530°C or higher and 560°C or lower for 0.3 hours or more and 5 hours or less, preferably by holding it at a processing temperature of 530°C or higher and 550°C or lower for 1 hour or more and 4 hours or less. The solution treatment time can also be set to 3 hours or less. The heating rate from room temperature to the above-mentioned processing temperature is preferably 5.0°C / min or higher. If the processing temperature is insufficient, the solid solution of the solute elements may become insufficient. On the other hand, when the processing temperature is too high, although the solid solution of the solute elements is further promoted, eutectic melting and recrystallization may easily occur. In addition, if the heating rate is lower than 5.0°C / min, coarse Mg2Si may precipitate. On the other hand, if the processing temperature is lower than 530°C, solid solution is not performed, and it may be difficult to achieve the high strength resulting from aging precipitation. Therefore, as described above, it is preferable to perform the treatment at a temperature of 530°C or higher.

[0153] (Quenching process)

[0154] The quenching process is a process in which a forged product in a solution-treated state obtained by the solution treatment process is rapidly cooled to form a supersaturated solid solution.

[0155] In this embodiment, the forging is subjected to water quenching by submerging it in a water tank containing water (quenching water). The water temperature in the tank is preferably above 20°C and below 60°C. The forging is preferably added to the water tank at a time between 5 and 60 seconds after solution treatment, ensuring that the entire surface of the forging is in contact with the water. The submersion time varies depending on the size of the casting, and may be, for example, between 5 and 40 minutes.

[0156] (Aging process)

[0157] The aging process involves heating and holding the forged product at a relatively low temperature to allow supersaturated dissolved elements to precipitate out, thereby imparting appropriate hardness.

[0158] In this embodiment, aging treatment is performed by heating the forged product after the quenching process to a temperature of 170°C or higher and 220°C or lower, and holding it at this temperature for 0.5 hours or higher and 7.0 hours or lower, preferably 4 hours or higher. If the heating temperature is lower than 180°C or the holding time is lower than 0.5 hours, the Mg2Si precipitates that increase tensile strength may not grow sufficiently. On the other hand, if the treatment temperature exceeds 220°C, the Mg2Si precipitates may become too coarse, thus failing to sufficiently increase tensile strength.

[0159] (Hot finishing process)

[0160] In the hot finishing process, forgings that have undergone aging treatment are hot finished at a temperature exceeding 100°C but below 250°C.

[0161] Figure 7 This is a diagram illustrating a method for manufacturing a suspension component according to one aspect of the present invention, and is a plan view showing an example of the structure of the forged part before the hot finishing process. (As shown) Figure 7 As shown, the forged part 100X before the hot finishing process has a flash (excess material) 70 formed on its outer periphery. The flash 70 is made of forging blank that did not enter the groove or hole of the mold used to form the suspension component 100 during the forging process. The flash 70 is formed on the outer periphery of the first arm 1, the second arm 2, the arm connection 3, the wheel side connection 4, the first body side connection 5, and the second body side connection 6 of the suspension component 100. That is, when the forged part 100X is viewed from the z direction, the flash 70 is formed in a manner that surrounds these components in the x and y directions.

[0162] In the hot finishing process, the flash 70 is trimmed while the forging 100X is heated. The suspension component 100 is formed by removing the flash from the forging 100X during the hot finishing process. In the suspension component 100, when the flash 70 is removed, the parting line PL corresponding to the root of the flash 70 is exposed.

[0163] If the billet temperature in the hot finishing process is too low, the forging flash may be removed by shearing, preventing the crystals at the parting line from tilting. On the other hand, if the billet temperature in the hot finishing process is too high, the billet may soften and fail to be finished smoothly, preventing the removal of the flash. Therefore, the billet temperature in the hot finishing process is in the range of 100°C to 250°C, preferably 125°C or higher, more preferably 150°C or higher, and even more preferably 175°C or higher.

[0164] According to the manufacturing method of the suspension component according to this embodiment, the suspension component according to the above embodiment can be manufactured. According to the above embodiment, a suspension component and a suspension component with excellent resistance to stress corrosion cracking can be provided even when recrystallization occurs near the parting line. Furthermore, the suspension component according to this embodiment can possess both excellent resistance to stress corrosion cracking and strength.

[0165] The upper and / or lower limits of the numerical ranges described in this specification can be arbitrarily combined to define preferred ranges. For example, the upper and lower limits of the numerical ranges can be arbitrarily combined to define preferred ranges, the upper limits of the numerical ranges can be arbitrarily combined with each other to define preferred ranges, and the lower limits of the numerical ranges can be arbitrarily combined with each other to define preferred ranges.

[0166] Furthermore, the composition of the molten liquid in the embodiment of the suspension component manufacturing method becomes the alloy composition of the manufactured suspension component.

[0167] It should be understood that, throughout this disclosure, unless otherwise specified, the singular form includes the concept of its plural form. Therefore, it should be understood that, unless otherwise specified, articles in the singular form (e.g., "a," "an," "the," etc. in the English context) also include the concept of their plural forms.

[0168] Example

[0169] The effects of the present invention will be further illustrated below through examples. Furthermore, the present invention is not limited to the following examples and can be implemented with appropriate modifications without altering its spirit.

[0170] [Example 1]

[0171] First, a molten aluminum alloy with the alloy composition shown as symbol 1 in Table 1 was prepared.

[0172] Using the prepared molten aluminum alloy as raw material, a continuous casting bar with a cross-section of 82 mm in diameter was produced using the horizontal continuous casting apparatus described above.

[0173] A continuously cast bar is formed to the required dimensions to match the die used in the forging process and used as forging material. The forging material is heated to 500°C and forged to obtain a forged product. Furthermore, the average grain size (average segment length of each crystal) of the forging billet is determined according to Appendix AA.2 (cutting method) of JIS G0551:2020, and the result is 65 μm.

[0174] Next, the obtained forging was subjected to solution treatment under the following conditions.

[0175] Heating rate: 10℃ / min; Temperature: 530℃; Holding time: 3 hours.

[0176] Next, an aging process was carried out under the following conditions.

[0177] Temperature: 180℃; Holding time: 4 hours.

[0178] Next, the forging is heated to 200°C for hot finishing. This hot finishing process removes burrs from the outer periphery of the forging.

[0179] This is how the presentation was created. Figures 1-3 The suspension component of Example 1 is an A-shaped structure as shown.

[0180] (Stress corrosion cracking test)

[0181] From the bushing portion 5 of the manufactured suspension component along... Figure 2 The C-shaped ring is cut out by a single-dotted line, shown together with the mark CR. A conditional yield strength σ is assigned to this C-shaped ring. 0.2 The SCC test was conducted at 90% load using the method based on JIS H8711:2000.

[0182] The following shows the implementation environment for the SCC test.

[0183] Test solution: Boiling test with dichromic acid solution

[0184] Test duration: 80 hours

[0185] Test piece: C-ring test piece

[0186] Stress applied: 80% of the tensile strength of 380 MPa.

[0187] Under the above conditions, the C-ring was visually inspected to observe whether stress corrosion cracks had formed after the test period (80 hours). Furthermore, regarding the test solution, this means immersing the C-ring in a boiled dichromic acid solution for the test.

[0188] The stress on the C-ring is applied by bolt tightening.

[0189] When applying stress, attach a strain gauge to the apex of the C-ring and tighten the bolts until the specified stress is achieved. After applying stress, shield the area around the bolts to prevent contact with the solution. Figure 8 This is a schematic plan view showing the configuration during the SCC test in Example 1. (Example) Figure 8 As shown, bolt 71 and nut 72 are fastened to C-ring C. 50 Strain gauge 73 is attached to the apex.

[0190] (Tensile strength test)

[0191] Test pieces conforming to the international standard ASTM-R5 were prepared from the bushing section.

[0192] The tensile strength of this test piece was determined using a method based on JIS H8711:2000.

[0193] (Determination of grain boundary dip angle)

[0194] After cutting out the area near the apex of the bushing and grinding it, electron backscatter diffraction (EBSD) was performed.

[0195] Observation equipment: JEOL JSM-7900 EBSD (backscattering) FE-SEM (Japanese Electron Device)

[0196] Accelerating voltage: 20kV

[0197] Sample tilt: tilted 70° relative to a plane perpendicular to the electron beam incident direction.

[0198] Figure 9 For the suspension component of Embodiment 1, electron backscattering diffraction was used to examine the cross-section of the bushing portion near the vertex 51, at the midpoint of the bushing portion in the x-direction (along... Figure 3 The tissue image is obtained by analyzing an electron microscope image of a cross-section of the center line (shown by a single-dotted line). Figure 9 Multiple grain boundaries, represented by solid black lines, were identified in the data. Figure 9 It is an image of a plane perpendicular to the parting line of the bushing. In Figure 9 In the bushing section, the outermost surface S0 in the -y direction is represented by a single-dotted line, and the surface S300 located at a depth of 300 μm from surface S0 in the +y direction is represented by a double-dotted line.

[0199] exist Figure 9 In the text, E0 is marked as the point on the grain boundary closest to the -y direction at the vertex. Additionally, in... Figure 9 In the diagram, E300 is a point on the grain boundary of surface S0, located at a depth of 300 μm from surface S0 and passing through point E0. The line passing through the grain boundaries of points E0 and E300 has an angle θ of 30° relative to surface S0. Angle θ is the inclination angle relative to a surface perpendicular to the surface formed by the parting line of the bushing and parallel to the cylindrical axis of the bushing.

[0200] [Example 2, Example 3]

[0201] Except for changing the temperature of the forging (bill temperature) in the hot finishing process, the suspension components were manufactured using the same method as in Example 1. Furthermore, the analysis was performed using the same method as in Example 1.

[0202] In Example 2, the temperature of the heat finishing process is set to 150°C.

[0203] In Example 3, the temperature of the heat finishing process is set to 250°C.

[0204] [Comparative Examples 1 to 3]

[0205] Except for changing the temperature of the forging (bill temperature) in the hot finishing process, the suspension components were manufactured using the same method as in Example 1. Furthermore, the analysis was performed using the same method as in Example 1.

[0206] In Comparative Example 1, the temperature of the heat finishing process was set to 100°C.

[0207] In Comparative Example 2, the temperature of the heat finishing process was set to 50°C.

[0208] In Comparative Example 3, the temperature of the heat finishing process was set to 30°C.

[0209] [Comparative Examples 4-6]

[0210] First, a molten aluminum alloy with the alloy composition shown as symbol 2 in Table 1 was prepared. Under the same conditions as in Example 1, a suspension component of Comparative Example 4 was fabricated and analyzed in the same manner as in Example 1.

[0211] Except for changing the temperature of the forging (bill temperature) in the hot finishing process, the suspension components of Comparative Examples 5 and 6 were manufactured using the same method as Comparative Example 4. Furthermore, the analysis was performed using the same method as in Example 1.

[0212] In Comparative Example 5, the temperature of the heat finishing process was set to 150°C.

[0213] In Comparative Example 6, the temperature of the heat finishing process was set to 250°C.

[0214] [Comparative Example 7, Comparative Example 8]

[0215] First, a molten aluminum alloy with the alloy composition shown as symbol 3 in Table 1 was prepared. Except for setting the temperature of the forging in the hot finishing process to 100°C, the other conditions were the same as in Example 1. The suspension component of Comparative Example 7 was manufactured and analyzed in the same way as in Example 1.

[0216] Except for changing the temperature of the forging (bill temperature) in the hot finishing process, the suspension component of Comparative Example 8 was manufactured using the same method as Comparative Example 7. Furthermore, the analysis was performed using the same method as in Example 1.

[0217] In Comparative Example 8, the temperature of the heat finishing process was set to 200°C.

[0218] Table 2 summarizes the composition of the alloy melt in Examples 1-3 and Comparative Examples 1-8, the forging temperature during the heat finishing process, the angle of inclination of the grain boundary at the apex relative to the plane perpendicular to the parting line of the bushing and parallel to the cylindrical axis of the bushing, the presence or absence of stress corrosion cracking in the SCC test, the results of the tensile strength test, and the judgment after considering the SCC test and the tensile strength test. In the judgment column of Table 2, forgings with good properties are marked "A", and forgings with poor properties are marked "B".

[0219]

[0220]

[0221] As shown in Table 2, Examples 1 to 3, in which the hot finishing process was performed at a temperature of 150°C or higher and 250°C or lower, did not develop stress corrosion cracking. However, Comparative Examples 1 to 3, in which conditions other than the temperature during the hot finishing process were the same, developed stress corrosion cracking. This result confirms that by hot finishing a forging that satisfies the above alloy composition within the above temperature range, it is possible to suppress the removal of flash from the forging by shearing, suppress the generation of stress corrosion cracking, and achieve high tensile strength.

[0222] In Comparative Examples 4 and 5, which have alloy compositions 2 with low Cu content, the C-rings themselves have low strength. Consequently, even if the grain boundary angle is less than 45°, they cannot withstand stress concentration, resulting in stress corrosion cracking. Comparative Examples 4 to 6, which have the same alloy composition, including Comparative Example 6, cannot simultaneously achieve both tensile strength and stress corrosion cracking suppression.

[0223] In Comparative Examples 7 and 8, which have high Cu and Fe contents, the amount of Cu coexisting with Mg2Si at the grain boundaries increases. This leads to a larger potential difference between the parent phase and the compound at the grain boundaries, impairing resistance to stress corrosion cracking. Furthermore, fine crystals containing intermetallic compounds crystallize out, causing stress corrosion cracking, and the tensile strength is not excellent. In contrast, it was confirmed that the forgings of Examples 1 to 3 suppress the formation of stress corrosion cracks and exhibit excellent tensile strength.

[0224] [Explanation of reference numerals in the attached figures]

[0225] 1: First arm; 2: Second arm; 3: Arm connection; 4: Wheel side connection; 5: First body side connection (bushlet); 6: Second body side connection (bushlet); 70: Flash; 100: Suspension component; 100X: Forged part; PL: Parting line; θ: Grain boundary angle relative to surface S0.

Claims

1. A suspension frame component, The alloy is composed of aluminum alloy having the following alloy composition: Cu in the range of 0.3% to 0.5% by mass, Mg in the range of 0.65% to 1.05% by mass, Si in the range of 0.9% to 1.25% by mass, Mn in the range of 0.4% to 0.6% by mass, Fe in the range of 0.15% to 0.30% by mass, Cr in the range of 0.09% to 0.25% by mass, Ti in the range of 0.01% to 0.05% by mass, and B in the range of 0.0010% to 0.0050% by mass, with the balance being Al and unavoidable impurities. The grain boundary dip angle is 45° or less relative to the surface perpendicular to the parting line of the bushing and parallel to the cylindrical axis of the bushing.

2. The suspension component according to claim 1, The tensile strength is above 380 MPa.

3. A method for manufacturing a suspension component, comprising: A melt-forming process for forming a molten aluminum alloy having the following alloy composition: Cu in the range of 0.3% to 0.5% by mass, Mg in the range of 0.65% to 1.05% by mass, Si in the range of 0.9% to 1.25% by mass, Mn in the range of 0.4% to 0.6% by mass, Fe in the range of 0.15% to 0.30% by mass, Cr in the range of 0.09% to 0.25% by mass, Ti in the range of 0.01% to 0.05% by mass, and B in the range of 0.0010% to 0.0050% by mass, with the balance being Al and unavoidable impurities; The casting process involves processing the molten metal to obtain a casting. The forging process of obtaining a forged article by heating and forging the cast article; A solution treatment process in which the forging is held at a temperature above 500°C; An aging process involving heat treatment of the forged product that has undergone the solution treatment process; and A hot finishing process is performed on forgings that have undergone the aging treatment process at a temperature exceeding 100°C but below 250°C.

4. The method for manufacturing the suspension component according to claim 3, In the hot finishing process, the forgings that have undergone the aging process are hot finished at a temperature of 125°C or higher and 250°C or lower than the billet temperature.

5. The method for manufacturing the suspension component according to claim 3, In the hot finishing process, the forgings that have undergone the aging process are hot finished at a temperature of 150°C or higher and 250°C or lower than the billet temperature.

6. The method for manufacturing the suspension component according to claim 3, The casting process is performed using continuous casting. The cooling rate of the molten metal in the casting process is above 10°C / second. The average crystal grain size of the casting is below 80 μm.

7. The method for manufacturing a suspension component according to any one of claims 3 to 6, After the solution treatment process and before the heat finishing process, there is a quenching process to quench the forging. In the forging process, the billet is heated and forged at a temperature above 450°C and below 520°C. In the solution treatment process, the forging is held at a temperature below 550°C. In the quenching process, the forging is water-quenched in water at a temperature below 60°C. In the aging process, the forgings that have undergone the quenching process are heated at a temperature of 175°C or higher and 190°C or lower for more than 4 hours.

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