Suspension arm member and method for producing suspension arm member

Abstract

To provide a suspension arm member with high strength, having stable characteristics even when exhibiting a recrystallization structure.SOLUTION: A suspension arm member composed of an aluminum alloy that contains Cu in the range of 0.2 mass% to 0.4 mass%, Mg in the range of 0.9 mass% to 1.2 mass%, Si in the range of 0.6 mass% to 0.9 mass%, Mn in the range of 0.05 mass% to 0.15 mass%, Fe in the range of 0.15 mass% to 0.30 mass%, Cr in the range of 0.2 mass% to 0.35 mass%, Ti in the range of 0.01 mass% to 0.05 mass%, and B in the range of 0.0010 mass% to 0.0050 mass%, with the remainder consisting of Al and unavoidable impurities, where the half-width of the diffraction peaks obtained from the Debye ring by X-ray diffraction is 1.58° or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a suspension arm member and a method for manufacturing the suspension arm member.

Background Art

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

[0003] Since these automotive parts are required to have excellent corrosion resistance, high strength, and excellent workability, Al-Mg-Si-based alloys, particularly A6061, are frequently used as aluminum alloy materials. And such automotive parts are manufactured by performing forging, which is one of the plastic working processes, using the aluminum alloy material as a processing material in order to improve the strength.

[0004] Also, recently, since it is necessary to reduce costs, suspension parts obtained by forging a cast member as it is 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 alloys to replace conventional A6061 is underway (see Patent Documents 1 to 3).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] From the perspective of reducing CO2 emissions in recent years, while the demand for aluminum is on the increase in the context of the required weight reduction of automobiles, further strengthening is needed for substitution from steel materials. For strengthening, control of the crystal structure during forging is important. For example, when forging using an A6061 alloy, depending on the forging conditions (forging material heating temperature, equivalent strain amount), recovery behavior of aluminum crystals occurs in the solution treatment process to the aging treatment process after the forging process, and there is a problem that the crystal structure coarsens.

[0007] When the crystal structure coarsens, it may cause variations in mechanical properties and may not satisfy the strength requirements for the members. Fig. 8(a) is an image diagram showing the state of a crystal structure composed of isotropic and sufficient number of particles, and Fig. 8(b) is a diffraction ring (Debye ring) obtained by performing X-ray diffraction on the crystal structure of Fig. 8(a). On the other hand, Fig. 9 is an image diagram when coarsening occurs in the crystal structure. Fig. 9(a) is an image diagram showing a state where coarsening has occurred in some of the particles in a crystal structure composed of a plurality of particles P, and Fig. 9(b) is a diffraction ring (Debye ring) obtained by performing X-ray diffraction on the crystal structure as shown in Fig. 9(a). As shown in Fig. 9(b), in the crystal structure with coarsening as shown in Fig. 9(a), the number of crystals contributing to diffraction is insufficient, and the bias occurs discontinuously.

[0008] Also, when orientation occurs in the crystal structure due to rolling or the like, the grains tend to be biased, so a biased diffraction ring is likely to be observed. Fig. 10(a) is an image diagram showing a state where orientation has occurred in the particles in a crystal structure composed of a plurality of particles P, and Fig. 10(b) is a diffraction ring (Debye ring) obtained by performing X-ray diffraction on the crystal structure as shown in Fig. 10(a).

[0009] When X-ray diffraction is performed on the crystal structure, a normal diffraction ring (Debye ring) is usually obtained. However, depending on the product shape, recrystallization during forging may be inevitable, and when recrystallization occurs, it is considered that the properties are not stable. Specifically, it is considered that when recrystallization occurs, the strength property decreases. Also, it is said that it is difficult to obtain a clean diffraction ring (Debye ring) when a recrystallized structure is exhibited.

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to provide a high-strength suspension arm member having stable properties even when exhibiting a recrystallized structure.

Means for Solving the Problems

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

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

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

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

[0015] [4] The method for manufacturing a suspension arm member according to [3] above In the solution heat treatment step, the forged product is held at a temperature of 530°C or higher and 560°C or lower for 0.3 hours or longer and 3 hours or shorter. In the water quenching step, water quenching is performed using water at 60°C or lower. In the aging treatment step, the forged product that has undergone the water quenching step may be heated at a temperature of 170°C or higher and 220°C or lower for 0.5 hours or longer and 7.0 hours or shorter.

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

Effect of the Invention

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

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show the characteristic parts enlarged for the sake of easy understanding of the characteristics, and the dimensional ratios of each component are not necessarily the same as the actual ones. Also, 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 gist thereof.

[0020] [Suspension Arm Member] First, the suspension arm member according to an embodiment of the present invention will be described. The suspension arm member according to an embodiment of the present invention is an aluminum alloy forging and is a member for a suspension arm. The aluminum alloy forged product of this embodiment is made of an aluminum alloy having an alloy composition in which Cu is in the range of 0.2% by mass or more and 0.4% by mass or less, Mg is in the range of 0.9% by mass or more and 1.2% by mass or less, Si is in the range of 0.6% by mass or more and 0.9% by mass or less, Mn is in the range of 0.05% by mass or more and 0.15% by mass or less, Fe is in the range of 0.15% by mass or more and 0.30% by mass or less, Cr is in the range of 0.2% by mass or more and 0.35% 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, and the balance is Al and inevitable impurities.

[0021] The aluminum alloy forged product of this embodiment corresponds to a forged product of a 6000 - series aluminum alloy in that it contains Mg and Si.

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

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

[0024] (Mg: 0.9% by mass or more, 1.2% by mass or less) Mg has the effect of improving the tensile strength of the aluminum alloy. By dissolving Mg in the aluminum matrix or precipitating as Mg-Si-based compounds (Mg2Si) such as β” phase or Al-Cu-Mg-Si-based compounds such as Q phase, it contributes to the strengthening of the aluminum alloy. The Mg content is in the range of 0.90% by mass or more and 1.20% by mass or less, and may also be in the range of 0.95% by mass or more and 1.10% by mass or less, or 1.00% by mass or more and 1.05% by mass or less. By the Mg content being within the above range, the corrosion resistance can be improved along with the mechanical properties of the aluminum alloy forgings at room temperature.

[0025] (Si: 0.6% by mass or more and 0.9% by mass or less) Si, like Mg, has the effect of improving the mechanical properties and corrosion resistance of aluminum alloy forgings at room temperature. However, if Si is added to the aluminum alloy in excess, there is a risk that the tensile strength of the aluminum alloy will decrease due to the precipitation of coarse primary Si grains. The Si content is in the range of 0.60% by mass or more and 0.90% by mass or less, and may also be in the range of 0.65% by mass or more and 0.85% by mass or less, or 0.70% by mass or more and 0.80% by mass or less. By the Si content being within the above range, it is possible to suppress the precipitation of primary Si and improve the mechanical properties and corrosion resistance of aluminum alloy forgings at room temperature.

[0026] (Mn: 0.05% by mass or more and 0.15% by mass or less) Mn has the effect of improving the tensile strength of the aluminum alloy 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 0.05% by mass or more and 0.15% by mass or less, and may also be in the range of 0.07% by mass or more and 0.14% by mass or less, or 0.10% by mass or more and 0.13% by mass or less. By the Mn content being within the above range, the mechanical properties of the aluminum alloy forgings at room temperature can be improved.

[0027] (Fe: 0.15 mass% or more and 0.3 mass% or less) Fe crystallizes 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 in the aluminum alloy, thereby having the effect of improving the tensile strength of the aluminum alloy. The Fe content is in the range of 0.15 mass% or more and 0.30 mass% or less, and may also be in the range of 0.20 mass% or more and 0.27 mass% or less, or 0.22 mass% or more. By the Fe content being within the above range, the mechanical properties of the aluminum alloy forgings at room temperature can be improved.

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

[0029] (Ti: 0.01 mass% or more and 0.05 mass% or less) Ti has the effect of refining the crystal grains of the aluminum alloy and improving the stretch formability. When the Ti content is less than 0.01 mass%, there is a risk that the effect of refining the crystal grains cannot be sufficiently obtained. On the other hand, when the Ti content exceeds 0.05 mass%, coarse precipitates are formed, and there is a risk that the stretch formability will decrease. Also, when a large amount of coarse precipitates containing Ti are mixed into the aluminum alloy forgings, the toughness may decrease. Therefore, the Ti content is set to 0.010 mass% or more and 0.050 mass% or less. The Ti content is preferably 0.015 mass% or more and 0.030 mass% or less.

[0030] (B: 0.0010 mass% or more and 0.0050 mass% or less) B has the effect of refining the crystal grains of the aluminum alloy and improving the stretch formability. By adding B to the aluminum alloy together with the above-mentioned Ti, the effect of refining the crystal grains is improved. If the content rate of B is less than 0.001% by mass, there is a possibility that the effect of refining the crystal grains cannot be sufficiently obtained. On the other hand, if the content rate of B exceeds 0.0050% by mass, coarse precipitates may be formed and may be mixed into the aluminum alloy forged product as inclusions. Also, when a large amount of coarse precipitates containing B is mixed into the final product of the aluminum alloy, the toughness may decrease. Therefore, the content rate of B is set to 0.0010 to 0.0050% by mass. The content rate of B is preferably 0.0015 to 0.045% by mass.

[0031] (Inevitable impurities) Inevitable impurities are impurities that are inevitably mixed into the aluminum alloy from the raw materials or manufacturing process of the aluminum alloy forged product. Examples of inevitable impurities include Zn, Zr, Ni, Sn, Be, etc. The content rate of these inevitable impurities preferably does not exceed 0.10% by mass.

[0032] FIG. 1 is a plan view showing an example of the configuration of a suspension arm member according to an aspect of the present invention, and FIG. 2 is a cross-sectional view taken along the cutting line A-A' of the suspension arm member of FIG. 1. The suspension arm member 100 shown in FIGS. 1 and 2 is a member for a suspension arm, such as an A-type arm, an A-arm, or a suspension arm having an A-type shape. The suspension arm member may finally have holes drilled in a part of the forged product for attachment to other members such as the vehicle body and wheels, but the suspension arm member may be the member after the drilling process or the forged product before the drilling process.

[0033] The suspension arm member 100 shown in FIGS. 1 and 2 includes, for example, a wheel-side connection portion 4, a first vehicle body-side connection portion 5, a second vehicle body-side connection portion, a first arm portion 1 connecting the wheel-side connection portion 4 and the first vehicle body-side connection portion 5, a second arm portion 2 connecting the wheel-side connection portion 4 and the second vehicle body-side connection portion 6, and an arm connection portion 3 connecting the first vehicle body-side connection portion 5 and the second vehicle body-side connection portion 6. In the suspension arm member 100, the first arm portion 1 is longer than the second arm portion 2. That is, in the suspension arm member formed by forging, it can be said that the first arm portion 1 is a member with a higher processing rate than the second arm portion 2. The processing rate (%) is larger as the change in the cross-sectional area of the material before and after processing is larger, and is calculated by the following formula (1). 100×(A0 - A) / A0 ···(1) (In formula (1), A0: cross-sectional area of the material before processing, A: cross-sectional area of the material after processing) Also, even if the cross-sectional area of the material before processing is unknown, the processing rate can be estimated by inverse analysis such as simulation from the shape of the suspension.

[0034] As described above, FIG. 2 is a cross-sectional view taken along the cutting line A - A' of the suspension arm member of FIG. 1. Also, the cutting line A - A' is a cross-section passing through the midpoint of the wheel-side connection portion 4 and the vehicle body-side connection portion 5. As shown in the cross-section of the first arm portion 1 in FIG. 2, the first arm portion 1, the second arm portion 2, and the arm connection portion 3 each have, for example, an outer peripheral portion 7 constituting the outer shape, an inner peripheral portion 8 close to the region where an opening is formed in a plan view, and a recess 9 located between the outer peripheral portion 7 and the inner peripheral portion 8. The recess 9 is, for example, a region recessed in the z direction with respect to the outer peripheral portion 7 and the inner peripheral portion 8.

[0035] In the suspension arm member 100 according to an embodiment of the present invention, the half-value width at the diffraction peak of the Debye ring obtained by X-ray diffraction for a portion with a high processing rate is 1.58° or more. In the suspension arm member 100 shown in FIG. 1, the region with a high processing rate is a region located in the outer peripheral portion 7 in a cross section along the cutting line A-A' in the first arm portion 1, and is a region corresponding to the symbol R indicated by the two-dot chain line in FIG. 2. In the suspension arm member according to an embodiment of the present invention, the half-value width of the diffraction peak obtained by X-ray diffraction for the region indicated by the symbol R in FIG. 2 is 1.58 or more.

[0036] When performing X-ray diffraction on a polycrystalline metal material, a diffraction line is generated from a crystal plane that satisfies the Bragg reflection condition with respect to the incidence of X-rays. A conical Debye ring with the incident X-ray as the axis is obtained from the diffracted X-rays.

[0037] The shape of the Debye ring is affected by the crystal structure of the metal, and the finer and more uniform the crystal, the stronger the diffraction peak of the Debye ring obtained. On the other hand, if the crystal is coarse, the Debye ring cannot be obtained neatly.

[0038] In a member exhibiting recrystallization, this Debye ring is often not obtained neatly, but the state of the member can be grasped from the locally obtained diffraction peak. In particular, the present inventors have found that the half-value width at the diffraction peak is correlated with the mechanical properties of the member.

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

[0040] In FIGS. 1 and 2, an example of a suspension arm member being an A-shaped arm including a first arm portion 1, a second arm portion 2, and an arm connecting portion 3 is shown. However, the present invention is not limited to the above example and is also applicable to suspension arm members of other shapes. In suspension arm members of other shapes, at a location where the processing rate is considered to be the highest, it is sufficient if the half-value width at the diffraction peak of the devitrification obtained by X-ray diffraction is 1.58° or more.

[0041] [Manufacturing method of suspension arm member] Next, the manufacturing method of the above suspension arm member will be described. The manufacturing method of a suspension arm member according to an embodiment of the present invention includes a molten metal forming step of obtaining a molten metal of an alloy having the same composition as the above aluminum alloy forging, a forging step of forging a casting obtained by casting the molten metal at a temperature of 470°C or higher and 500°C or lower to obtain a forging, a solution treatment step of heating the forging at a temperature of 500°C or higher, a quenching step of quenching the forging after the solution treatment, and an aging treatment step of heat-treating the forging that has undergone the quenching step.

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

[0043] (Molten metal forming step) The molten metal forming step is a step of obtaining an aluminum alloy molten metal by melting raw materials and adjusting the composition. The composition of the aluminum alloy molten metal is adjusted so as to have an alloy composition containing Cu in the range of 0.2 mass% or more and 0.4 mass% or less, Mg in the range of 0.9 mass% or more and 1.2 mass% or less, Si in the range of 0.6 mass% or more and 0.9 mass% or less, Mn in the range of 0.05 mass% or more and 0.15 mass% or less, Fe in the range of 0.15 mass% or more and 0.30 mass% or less, Cr in the range of 0.2 mass% or more and 0.35 mass% or less, Ti in the range of 0.01 mass% or more and 0.05 mass% or less, and B in the range of 0.0010 mass% or more and 0.0050 mass% or less, with the balance being Al and unavoidable impurities.

[0044] By performing the subsequent steps using the molten aluminum alloy of the above composition, it is possible to provide a suspension arm member having stable characteristics even if it exhibits a recrystallized structure. Note that the new aluminum ingot is aluminum with a concentration of 99% or more obtained by performing electrolysis called electrolytic refining on alumina produced from minerals.

[0045] The molten aluminum alloy can be obtained by heating and melting the aluminum alloy. Alternatively, a mixture containing the simple substances of the elements that are the raw materials of the aluminum alloy or a compound containing two or more elements in a ratio that produces the target aluminum alloy may be melted and formed. For example, for the purpose of controlling the crystal grain size of the aluminum alloy produced in the casting process, Ti or B may be mixed as a grain refinement material such as an Al-Ti-B rod.

[0046] Also, as a raw material for the molten aluminum alloy, 10% or more of scrap materials of aluminum alloys of the 1000 series, 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, and 7000 series are used, and the balance is new aluminum ingots and the above-mentioned additive elements. These may be melted to obtain a molten aluminum alloy with its composition adjusted. In this case, it is possible to obtain an Al-Mg-Si-based suspension arm member that is less likely to generate recrystallization and has excellent mechanical properties at room temperature. Note that the new aluminum ingot is aluminum obtained by performing electrolysis called electrolytic refining on alumina produced from minerals, for example, with a purity of 99% or more.

[0047] (Casting process) In the casting process, the 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 the casting process, for example, a vertical continuous casting method or a horizontal continuous casting method can be used. Hereinafter, taking the case where the casting process is performed by the horizontal continuous casting method as an example, a method for manufacturing a suspension arm member according to an embodiment of the present invention will be described.

[0048] A horizontal continuous casting apparatus that can be used for manufacturing an aluminum alloy casting of the present embodiment is shown in FIGS. 3 and 4. FIG. 3 is a cross-sectional view showing an example near a mold 12 of the horizontal continuous casting apparatus 10. FIG. 4 is an enlarged cross-sectional view of a main part near a cooling water cavity 24 of the horizontal continuous casting apparatus 10.

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

[0050] The molten metal receiving part 11 is composed of a molten metal inflow part 11a that receives the aluminum alloy molten metal M obtained in the above-described molten metal forming step, a molten metal holding part 11b, and an outflow part 11c to the hollow part 21 of the mold 12.

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

[0052] The aluminum alloy molten metal M held in the molten metal holding part 11b in the molten metal receiving part 11 is poured into the hollow part 21 of the mold 12 from a pouring passage 13a provided in the refractory plate-like body 13. Then, the aluminum alloy molten metal M supplied into the hollow part 21 is cooled and solidified by a cooling device 23 described later, and is pulled out from the other end side 12b of the mold 12 as an aluminum alloy bar B that is a solidified ingot.

[0053] A drawing drive device (not shown) for pulling out the cast aluminum alloy bar B at a constant speed may be installed at the other end side 12b of the mold 12. It is also preferable that a synchronous cutting machine (not shown) for cutting the continuously pulled out aluminum alloy bar B into an arbitrary length is installed.

[0054] The refractory plate-like body 13 is a member that blocks heat transfer between the molten metal receiving part 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, graphite, etc. Such a refractory plate-like body 13 can also be composed of a plurality of layers with different constituent materials.

[0055] In this embodiment, the mold 12 is a hollow cylindrical member and is formed of a material selected from one or a combination of two or more of, for example, aluminum, copper, or their alloys. For the material of such a mold 12, an optimal combination may be selected from the viewpoints of thermal conductivity, heat resistance, and mechanical strength.

[0056] The hollow part 21 of the mold 12 is formed to have a circular cross-section in order to make the aluminum alloy bar B to be cast into a cylindrical bar shape, and the mold 12 is held so that the mold central axis (central axis) C passing through the center of the hollow part 21 is substantially along the horizontal direction.

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

[0058] When the elevation angle is less than 0°, when the aluminum alloy bar B is pulled out from the mold 12, casting may become difficult because it receives resistance at the other end side 12b which is the mold outlet. On the other hand, when the elevation angle exceeds 3°, the contact of the inner peripheral surface 21a with the aluminum alloy molten metal M becomes insufficient, and the heat extraction effect from the aluminum alloy molten metal M or the solidified shell formed by its cooling and solidification to the mold 12 decreases, which may cause insufficient solidification. As a result, it is not preferable because it may lead to casting troubles such as remelting marks on the surface of the aluminum alloy bar B or ejection of the non-solidified aluminum alloy molten metal M from the end of the aluminum alloy bar B.

[0059] Note that the cross-sectional shape of the hollow portion 21 of the mold 12 (the planar shape when the hollow portion 21 of the mold 12 is viewed from the other end side 21b) may be selected according to the shape of the aluminum alloy rod to be cast, such as a triangular, rectangular cross-sectional shape, polygon, semi-circle, ellipse, or an irregular cross-sectional shape without an axis of symmetry or plane of symmetry, in addition to the circular shape of the present embodiment.

[0060] A fluid supply pipe 22 for supplying a lubricating fluid into the hollow portion 21 of the mold 12 is disposed at one end side 12a of the mold 12. As the lubricating fluid supplied from the fluid supply pipe 22, any one or two or more kinds of lubricating fluids selected from gas lubricants and liquid lubricants can be used. When supplying both a gas lubricant and a liquid lubricant, it is preferable to provide separate fluid supply pipes respectively. The lubricating fluid pressurized and 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.

[0061] In the present embodiment, the pumped lubricating fluid is supplied from the lubricant supply port 22a to the inner peripheral surface 21a of the mold 12. Note that the liquid lubricant may be configured to be heated and decomposed into a gas and supplied to the inner peripheral surface 21a of the mold 12. Also, a porous material may be disposed at the lubricant supply port 22a, and the lubricating fluid may be exuded to the inner peripheral surface 21a of the mold 12 through this porous material.

[0062] Inside the mold 12, a cooling device 23, which is a cooling means for cooling and solidifying the molten aluminum alloy M, is formed. The cooling device 23 of the present embodiment has a cooling water cavity 24 for accommodating cooling water W for cooling the inner peripheral surface 21a of the hollow portion 21 of the mold 12, and a cooling water injection passage 25 for communicating the cooling water cavity 24 and the hollow portion 21 of the mold 12.

[0063] The cooling water cavity 24 is formed in an annular shape so as to surround the hollow portion 21 outside the inner peripheral surface 21a of the hollow portion 21 inside the mold 12, and the cooling water W is supplied through a cooling water supply pipe 26.

[0064] The mold 12 cools the inner peripheral surface 21a with the cooling water W accommodated in the cooling water cavity 24, thereby taking away the heat of the molten aluminum alloy M filled in the hollow portion 21 of the mold 12 from the surface in contact with the inner peripheral surface 21a of the mold 12 and forming a solidified shell on the surface of the molten aluminum alloy M.

[0065] Further, the cooling water injection passage 25 directly applies the cooling water W from the shower opening 25a facing the hollow portion 21 toward the aluminum alloy rod B at the other end side 12b of the mold 12 to cool the aluminum alloy rod B. The longitudinal sectional shape of such a cooling water injection passage 25 may be, for example, a semicircle, a pear shape, or a horseshoe shape in addition to the circular shape of the present embodiment.

[0066] In the present embodiment, the cooling water W supplied through the cooling water supply pipe 26 is first accommodated in the cooling water cavity 24 to cool the inner peripheral surface 21a of the hollow portion 21 of the mold 12, and further the cooling water W in the cooling water cavity 24 is sprayed from the cooling water injection passage 25 toward the aluminum alloy rod B. However, these may be supplied by separate cooling water supply pipes.

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

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

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

[0070] Here, the term "parallel" 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° with respect to the inner bottom surface 24a of the cooling water cavity 24, that is, the case where the inner bottom surface 24a is inclined with respect to the inner peripheral surface 21a by more than 0° and up to 3°.

[0071] As shown in FIG. 4, 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 peripheral 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 of 10×10 5 W / m 2 or more and 50×10 5 W / m 2 or less within the following range.

[0072] 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 peripheral surface 21a of the hollow portion 21 of the mold 12, may be formed such that, for example, it is within the range of 0.5 mm or more and 3.0 mm or less, preferably 0.5 mm or more and 2.5 mm or less. Also, 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 within the range of 100 W / m·K or more and 400 W / m·K or less.

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

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

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

[0076] The height difference between the liquid level of the aluminum alloy melt M stored in the melt receiving part 11 and the upper inner peripheral surface 21a of the mold 12 is preferably 0 mm to 250 mm (more preferably 50 mm to 170 mm). By setting it within such a range, the pressure of the aluminum alloy melt M supplied into the mold 12, the lubricating oil, and the gas vaporized from the lubricating oil are preferably balanced, so that the castability is stabilized.

[0077] As the liquid lubricant, vegetable oil as lubricating oil can be used. For example, rapeseed oil, castor oil, and salad oil can be mentioned. These are preferable because they have little adverse impact on the environment.

[0078] The lubricating oil supply amount 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 amount is too small, the aluminum alloy melt M of the aluminum alloy rod B may leak from the mold 12 without solidifying due to insufficient lubrication. If the supply amount is too large, the excess may mix into the aluminum alloy rod B and cause internal defects.

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

[0080] The amount of cooling water sprayed from the shower opening 25a of the cooling water injection passage 25 is preferably 10 L / min or more and 50 L / min or less (more preferably 25 L / min or more and 40 L / min or less) per mold. 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 rod B may remelt to form a non-uniform structure and remain as an internal defect. On the other hand, if the amount of cooling water is more than this range, the heat extraction of the mold 12 may be too large and solidification may occur halfway.

[0081] The average temperature of the molten aluminum alloy M flowing from the inside of the molten metal receiving part 11 into the mold 12 is preferably, for example, 650 °C or more and 750 °C or less (more preferably 680 °C or more and 720 °C or less). If the temperature of the molten aluminum alloy M is too low, there is a risk of forming coarse crystallized products in the mold 12 and in front of it and being incorporated into 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 is likely to be incorporated into the molten aluminum alloy M and taken into the aluminum alloy rod B as porosity, resulting in internal cavities.

[0082] And in the cooling wall part 27 of the mold 12, the heat flux value per unit area from the molten aluminum alloy M in the hollow part 21 to the cooling water W in the cooling water cavity 24 is 10×10 5 W / m 2 or more and 50×10 5 W / m 2 By setting it within the following range, sticking of the aluminum alloy rod B can be prevented.

[0083] The cooling wall portion 27 of the mold 12 receives heat by heat extraction from the molten aluminum alloy M, and heat exchange is performed by cooling this heat with the cooling water W contained in the cooling water cavity 24. Regarding the state of this heat exchange, as shown in the explanatory diagram of FIG. 5, attention was paid to the heat flux per unit area. The heat flux per unit area is represented by the following formula (1) according to Fourier's law. Q = -k×(T1 - T2) / L ···(1) Q: Heat flux k: Thermal conductivity (W / m·K) of the portion through which heat passes (in this embodiment, the cooling wall portion 27 of the mold 12) T1: Low-temperature side temperature of the portion through which heat passes (in this embodiment, the inner bottom surface 24a of the cooling water cavity 24) T2: High-temperature side temperature of the portion through which heat passes (in this embodiment, the inner peripheral surface 21a of the hollow portion 21 of the mold 12) L: Section length (mm) of the portion through which heat passes (in this embodiment, the thickness t of the cooling wall portion 27 of the mold 12)

[0084] Based on the quality, thickness, and temperature measurement data of the cast aluminum alloy obtained with good results even when the amount of lubricating oil is reduced during casting, the heat flux value per unit area is 10×10 5 W / m 2 or more. By configuring the cooling wall portion 27 of the mold 12 in this way, sticking of the cast aluminum alloy bar B can be prevented. Also, it is preferable that the heat flux value per unit area is 50×10 5 W / m 2 or less.

[0085] In order to make the cooling wall portion 27 of the mold 12 within such a range of heat flux values, the mold 12 may be formed such that the thickness t of the cooling wall portion 27 of the mold 12 is, for example, in the range of 0.5 mm or more and 3.0 mm or less. Also, the thermal conductivity of at least the cooling wall portion 27 of the mold 12 may be in the range of 100 W / m·K or more and 400 W / m·K or less.

[0086] When manufacturing the aluminum alloy bar B of the present embodiment, using the horizontal continuous casting apparatus 10 described above, the molten aluminum alloy M stored in the molten metal receiving portion 11 is continuously supplied into the hollow portion 21 from one end side 12a of the mold 12. At the same time, cooling water W is supplied to the cooling water cavity 24, and a lubricating fluid, for example, lubricating oil, is supplied from the fluid supply pipe 22.

[0087] Then, the molten aluminum alloy M supplied into the hollow portion 21 is cooled and solidified under the condition that the heat flux value per unit area in the cooling wall portion 27 is 10×10 5 W / m 2 or more to cast the aluminum alloy bar B. Further, when casting the aluminum alloy bar B, it is preferable that the wall surface temperature of the cooling wall portion 27 of the mold 12 cooled by the cooling water W is 100°C or lower.

[0088] The aluminum alloy bar B thus obtained is cooled and solidified under the condition that the heat flux value per unit area in the cooling wall portion 27 is 10×10 5 W / m 2 or more, whereby the adhesion of reaction products such as carbides due to the contact between the gas of the lubricating oil and the molten aluminum alloy M is suppressed. As a result, it is not necessary to cut and remove carbides and the like on the surface of the aluminum alloy bar B, and the aluminum alloy bar B can be manufactured with a high yield.

[0089] The casting process for obtaining a casting from the molten aluminum alloy M is not limited to the above-described horizontal continuous casting method, and known continuous casting methods such as the vertical continuous casting method can be used. The vertical continuous casting method is classified into the float method and the hot top method according to the supply method of the molten aluminum alloy M to the mold (mold 12). Hereinafter, the case of using the hot top method will be briefly described.

[0090] The casting apparatus used in the hot top method includes a mold, a molten metal receiving container (header), and the like. The molten metal supplied to the molten metal receiving portion passes through the tapping port and the header to adjust the flow rate, and enters a cylindrical mold installed substantially horizontally, where it is forcibly cooled to form a solidified shell on the outer surface of the molten metal.

[0091] Furthermore, cooling water is directly radiated onto the casting drawn from the mold, and the casting is continuously drawn while the solidification of the metal proceeds to the inside of the casting. Generally, a metal member with good thermal conductivity is used for the mold, which has a hollow structure for introducing a refrigerant therein.

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

[0093] The mold used in this embodiment is appropriately selected from metals such as copper and aluminum, or graphite, from the viewpoints of heat transfer performance and durability at the contact portion with the molten metal. The header is generally made of refractory and is installed above the mold. The material and size of the header may be appropriately selected according to the component range of the alloy to be cast and the dimensions of the casting, and there are no particular restrictions.

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

[0095] In the casting method described above, the diameter of the target casting is not particularly limited, and it is preferably used for bars with a diameter of 30 to 100 mm.

[0096] (Homogenization heat treatment process) The homogenization heat treatment process is a process of performing homogenization heat treatment on the aluminum alloy casting obtained in the casting process to homogenize the microsegregation caused by solidification, precipitate supersaturated solid solution elements, and change metastable phases to equilibrium phases.

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

[0098] (Forging process) The forging process is a process of shaping the aluminum alloy casting after casting or after the homogenization heat treatment process into a predetermined size to obtain a forging material, heating the obtained forging material to a predetermined temperature, and then applying pressure with a press to perform die forming.

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

[0100] In this embodiment, for the forging material, forging is performed at a heating temperature of 470°C or higher and 500°C or lower to obtain a forged product (for example, a suspension arm member of an automobile, etc.). For example, in the forging process, after holding (heating) at the above heating temperature (material heating temperature) for 40 minutes or longer, preferably 60 minutes or longer and 3 hours or shorter, forging is performed. By performing forging on the forging material within the above temperature range, the characteristics of the forged product can be stabilized. If the temperature of the forging material at the start of forging is less than 470°C, abnormal recrystallization may be promoted in the solution treatment process after forging, causing a decrease in strength. Also, if it exceeds 500°C, recrystallization may be promoted in the process until entering the solution treatment due to the heat generation during forging, which may also cause a decrease in strength. Further, if the starting temperature of forging of the forging material is too low, the deformation resistance becomes high and sufficient processing cannot be performed, and if it is too high, defects such as forging cracks and eutectic melting are likely to occur. Therefore, it is preferable that the forging material is started to be forged at the above temperature. In addition, it is preferable to heat the mold in order to suppress the temperature of the forging material from decreasing during forging.

[0101] As shown in the examples and comparative examples, the half-value width and the 0.2% proof stress at the diffraction peak of the Debye ring obtained by X-ray diffraction show a correlation. When the half-value width is large, it means that the variation between the aluminum crystal lattices is large. The variation between the crystal lattices increases as the dislocation density between the crystal lattices is higher. The dislocation density has a correlation with strength. In this embodiment, by deliberately setting the half-value width within the above range, even when recrystallization occurs, the 0.2% proof stress can be stably increased.

[0102] (Solution treatment process) The solution treatment process is a process of heating and solutionizing the forged product obtained in the forging process to relieve the strain introduced into the cast product and perform solid solution of solute elements.

[0103] In this embodiment, the solution treatment is performed by holding the forged product at a treatment temperature of 530°C or higher and 560°C or lower for 0.3 hours or longer and 4 hours or shorter, and it is preferable to perform the solution treatment by holding at a treatment temperature of 550°C or lower for 1.5 hours or longer and 3 hours or shorter. The heating rate from room temperature to the above-described treatment temperature is preferably 5.0°C / min or higher. If the treatment temperature is less than 530°C, there is a risk that the solid solution of solute elements will be insufficient. On the other hand, if it exceeds 560°C, although the solid solution of solute elements is more promoted, eutectic melting and recrystallization are likely to occur. Also, when the heating rate is less than 5.0°C / min, Mg2Si may precipitate coarsely, so the heating rate is preferably 5.0°C / min or higher as described above. On the other hand, when the treatment temperature is less than 530°C, solution treatment may not proceed and it may be difficult to achieve high strength by age precipitation.

[0104] (Quenching treatment process) The quenching treatment process is a process of rapidly cooling the forged product in a solid solution state obtained by the solution treatment process to form a supersaturated solid solution.

[0105] In this embodiment, the quenching treatment is performed by immersing the forged product in a water tank (quenching water) in which water is stored. The water temperature in the water tank is preferably 20°C or higher and 60°C or lower. The forged product is preferably put into the water tank so that all surfaces of the forged product come into contact with water within 5 seconds or longer and 60 seconds or shorter after the solution treatment. The immersion time of the forged product varies depending on the size of the casting, but is, for example, more than 5 minutes and within 40 minutes.

[0106] (Aging treatment process) The aging treatment process is a process of heating and holding the forged product at a relatively low temperature to precipitate elements that are supersaturated in solid solution and impart appropriate hardness.

[0107] In this embodiment, the forged product after the quenching treatment step is heated to a temperature of 170°C or higher and 220°C or lower, and aging treatment is performed by holding at that temperature for 0.5 hours or longer and 7.0 hours or shorter. Preferably, aging treatment is performed by heating to a temperature of 175°C or higher and 190°C or lower and holding at that temperature for 4 hours or longer. If the heating temperature is less than 170°C or the holding time is less than 0.5 hours, Mg2Si-based precipitates that improve the tensile strength may not grow sufficiently. On the other hand, if the treatment temperature exceeds 220°C, the Mg2Si-based precipitates may become too coarse, that is, the Mg2Si-based precipitates may be coarsely formed, and there is a possibility that the tensile strength cannot be sufficiently improved.

[0108] According to the manufacturing method of the suspension arm member according to this embodiment, the suspension arm member according to the above embodiment can be manufactured. According to the above embodiment, it is possible to provide a high-strength suspension arm member having stable characteristics even when presenting a recrystallized structure.

Example

[0109] Hereinafter, the effects of the present invention will be made clearer by examples. Note that the present invention is not limited to the following examples, and can be appropriately modified and implemented without changing the gist thereof.

[0110] [Example 1] First, a molten aluminum alloy having the following alloy composition was prepared. Cu: 0.33 mass%, Mg: 1.02 mass%, Si: 0.73 mass%, Mn: 0.11 mass%, Fe: 0.24 mass%, Cr: 0.22 mass%, Ti: 0.023 mass%, B: 0.0026 mass%, Al: the balance

[0111] Using the prepared molten aluminum alloy as a raw material and using the horizontal continuous casting apparatus as described above, a 200L continuous casting rod having a circular cross-section with a diameter of 78 mm was produced.

[0112] The continuous casting bar was sized to fit the mold in the forging process to obtain a forging material. The obtained forging material was heated at a heating temperature (material heating temperature) of 470 °C for 1 hour, and then forging was performed to obtain a forged product. The temperature of the mold used at this time was 200 °C. The average crystal grain size (average line length per crystal) of the forging material was measured by JIS G0551:2020 Appendix A A.2 (cutting method) and was 65 μm.

[0113] Next, solution heat treatment was performed on the obtained forged product under the following conditions. Heating rate: 10 °C / min, temperature: 530 °C, holding time: 3 hours

[0114] Next, a water quenching process was performed under the following conditions. Quenching water temperature: 40 °C Time from solution heat treatment to quenching: 10 seconds Immersion time of the forged product: 10 minutes

[0115] Next, an aging treatment process was performed under the following conditions. Temperature: 180 °C, holding time: 6 hours By the above method, the A-type suspension arm member of Example 1 was manufactured.

[0116] [Example 2] An A-type suspension arm member was manufactured in the same manner as in Example 1, except that the heating temperature of the forging material in the forging process was changed to 480 °C.

[0117] [Example 3] An A-type suspension arm member was manufactured in the same manner as in Example 1, except that the heating temperature of the forging material in the forging process was changed to 500 °C.

[0118] [Comparative Example 1] An A-type suspension arm member was manufactured in the same manner as in Example 1, except that the heating temperature of the forging material in the forging process was changed to 520 °C.

[0119] [Comparative Example 2] An A-shaped suspension arm member was fabricated in the same manner as in Example 1, except that the heating temperature of the forging material in the forging process was changed to 510°C.

[0120] [Comparative Example 3] An A-shaped suspension arm member was fabricated in the same manner as in Example 1, except that the heating temperature of the forging material in the forging process was changed to 450°C.

[0121] (X-ray Diffraction) Among the A-shaped suspension arm members made of polycrystalline metal materials of Examples 1 to 3 and Comparative Examples 1 to 3, X-ray diffraction was performed on the position corresponding to the region R in FIG. 2. That is, X-ray diffraction was performed on a part of the outer peripheral portion of a cross-section passing through the midpoint in the axial direction of the longer arm portion among the arm portions connecting the wheel-side connecting portion and the vehicle-body-side connecting portion, which is the region with the highest processing ratio. This part had a processing ratio exceeding 80%, specifically 85%.

[0122] The conditions for X-ray diffraction are shown below. · X-ray diffractometer: μ-x360s manufactured by Pulstec · X-ray incident angle: 28.8 degrees · X-ray tube current: 1 mA · X-ray tube voltage: 30 kV · Measurement device - sample distance: 50 mm · Diffraction planes of aluminum: 311, 222 planes · Tube target: Co tube target · X-ray tube wavelength Kα: 1.79021 Å · X-ray tube wavelength Kβ: 1.62075 Å

[0123] Figure 6 shows the X-ray diffraction results for the first arm portion of the suspension arm member of Example 1. As shown in Figure 6, the deburring of the polycrystalline metal material constituting the suspension arm member of Example 1 was not obtained neatly. From this, it is considered that in Example 1, recrystallization occurred and a part of the crystal was coarse. Figure 7 shows the analysis results of the diffraction intensity in the vicinity of the diffraction peak of the deburring of the X-ray diffraction results in Figure 6. From the analysis results shown in Figure 7, the half-value width was 1.587 (degree).

[0124] X-ray diffraction was performed on the suspension arm members of Example 2, Example 3, and Comparative Examples 1 to 3 in the same manner as in Example 1. Deburring could not be obtained neatly in any of the samples, but diffraction peaks were confirmed. For these samples as well, the half-value width was measured from the analysis results of the diffraction intensity.

[0125] (0.2% proof stress) Tensile test pieces were taken from the suspension arm members of Example 1 to Example 3 and Comparative Examples 1 to 3, and tensile tests were conducted by a method in accordance with JIS Z2241:2011. The tensile test piece was taken from the middle point in the axial direction of the longer arm portion among the concave portions of the arm portion connecting the wheel side connecting portion and the vehicle body side connecting portion of the suspension arm member, and was a test piece having a longitudinal direction in the axial direction of the arm portion.

[0126] The forging process conditions (material heating temperature and material heating time) when manufacturing the aluminum alloy forging members of Example 1 to Example 3 and Comparative Examples 1 to 3, the half-value width of the diffraction peak of the obtained samples, and the results of the 0.2% proof stress are summarized in Table 1.

[0127]

Table 1

[0128] As shown in Table 1, the half-width of the diffraction peak in X-ray diffraction varies depending on the temperature in the forging process, and it has been confirmed that the half-width shows a correlation with the 0.2% proof stress. In Examples 1 to 3, the half-width was in the range of 1.580° to 1.610°. This correlation was first discovered by the inventors of the present invention. As described above, Examples 1 to 3 and Comparative Examples 1 to 3 are all unable to obtain clean decarburization and exhibit a recrystallized structure. However, it has been confirmed that according to the present invention, it is possible to provide a suspension arm member having stable characteristics showing a high 0.2% proof stress.

Explanation of Signs

[0129] 1 First arm part 2 Second arm part 3 Arm connection part 4 Wheel-side connection part 5 First vehicle-body-side connection part 6 Second vehicle-body-side connection part 7 Outer peripheral part 8 Inner peripheral part 9 Concave part 10 Horizontal continuous casting device 11 Molten metal receiving part (tundish) 11a Molten metal inflow part 11b Molten metal holding part 11c Outflow part 12 Mold 12a One end side 12b The other end side 13 Refractory plate-like body (heat insulation member) 13a Pouring passage 21 Hollow part 21a Inner peripheral surface 21b The other end side 22 Fluid supply pipe 22a Lubricant supply port 23 Cooling device 24 Cooling water cavity 24a Inner bottom surface 25 Cooling water injection passage 25a Shower opening 26 Cooling water supply pipe 27 Cooling wall part 100 Suspension arm member B Aluminum alloy rod C Mold central axis (central axis) M Aluminum alloy molten metal P Particles PDA - 5500 manufactured by Shimadzu Corporation, Japan R Symbol R Region Si Primary crystal W Cooling water X Incidence μ - x360s manufactured by Pulstec

Claims

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

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

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

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

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

Images