Aluminum alloy forging material, aluminum alloy forged product, and method for manufacturing same

Abstract

This aluminum alloy forging material has an alloy composition which contains Cu within a range of 0.25-0.55 mass%, Mg within a range of 0.85-1.25 mass%, Si within a range of 1.02-1.4 mass%, Mn within a range of 0.55-1.0 mass%, Fe within a range of 0.32-0.65 mass%, Zn within a range of 0.25 mass% or less, Cr within a range of 0.050-0.30 mass%, Ti within a range of 0.01-0.1 mass%, B within a range of 0.0010-0.030 mass%, and Zr within a range of 0.0010-0.050 mass%, and in which the ratio Fe / Mn of the Fe content with respect to the Mn content is 0.3-1.1, and the remaining portion is Al and unavoidable impurities. In a thermal analysis curve obtained by performing a differential thermal analysis (DSC) on the aluminum alloy forging material, exothermic peaks emerge within 200-300°C and within 400-500°C.

Description

Aluminum alloy forging material, aluminum alloy forging product and manufacturing method thereof

[0001] This application claims priority to Japanese Patent Application No. 2024-022300, filed February 16, 2024, the contents of which are incorporated herein by reference.

[0002] In recent years, aluminum alloys have been increasingly used as structural components for various products, taking advantage of their light weight. For example, while high-tensile steel has traditionally been used for automobile suspension and bumper parts, high-strength aluminum alloys have recently come into use.

[0003] Furthermore, while iron-based materials have been used exclusively for automobile parts, particularly suspension parts, in recent years, aluminum or aluminum alloy materials have increasingly been used instead, primarily for the purpose of reducing weight.

[0004] These automobile parts require excellent corrosion resistance, high strength, and excellent workability, and therefore Al-Mg-Si alloys, particularly A6061, are widely used as the aluminum alloy material. In order to improve the strength of these automobile parts, they are manufactured by forging, which is a type of plastic processing, using the aluminum alloy material as the processing material.

[0005] Recently, due to the need to reduce costs, suspension parts have begun to be put into practical use, in which cast members are used as raw materials without extrusion, and then subjected to a solution treatment and artificial aging treatment (T6 treatment).With the aim of further weight reduction, development of high-strength alloys to replace the conventional A6061 is underway (see, for example, Patent Documents 1 to 3).

[0006] JP-A-5-59477 JP-A-5-247574 JP-A-6-256880

[0007] However, the above-mentioned high-strength Al-Mg-Si alloys have a problem in that the processed structure recrystallizes during the forging and heat treatment processes, resulting in the generation of coarse crystal grains, making it impossible to obtain sufficient strength. Therefore, some alloys have been modified to prevent the generation of coarse recrystallized grains by adding Zr (zirconium) (see, for example, Patent Documents 1 and 2).

[0008] However, although adding Zr is effective in preventing recrystallization, it has the following problems: (1) The addition of Zr weakens the grain refinement effect of the Al-Ti-B alloy, coarsening the grains of the ingot itself, resulting in a decrease in the strength of the processed product (forged product) after plastic working. (2) Because the grain refinement effect of the ingot itself is weakened, the ingot is more likely to crack, increasing internal defects and reducing yield. (3) Zr forms compounds with the Al-Ti-B alloy, which accumulate at the bottom of the furnace storing the molten alloy and contaminate the furnace. In addition, these compounds also crystallize coarsely in the produced ingot, reducing its strength.

[0009] Thus, although the addition of Zr is effective in preventing recrystallization, it is difficult to maintain stability in strength.

[0010] The present invention has been made in view of the above technical background, and aims to provide an aluminum alloy forging material having excellent mechanical properties at room temperature, an aluminum alloy forging product, and a method for manufacturing the same.

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

[0012] Aspect 1 of the present invention is a steel sheet containing Cu in the range of 0.25 mass% or more and 0.55 mass% or less, Mg in the range of 0.85 mass% or more and 1.25 mass% or less, Si in the range of 1.02 mass% or more and 1.4 mass% or less, Mn in the range of 0.55 mass% or more and 1.0 mass% or less, Fe in the range of 0.32 mass% or more and 0.65 mass% or less, Zn in the range of 0.25 mass% or less, Cr in the range of 0.050 mass% or more and 0.30 mass% or less, Ti in the range of 0.01 mass% or more and 0.1 mass% or less, and B in the range of 0. The aluminum alloy forging material has an alloy composition containing 0.0010% by mass or more and 0.030% by mass or less of Zr, 0.0010% by mass or more and 0.050% by mass or less of Zr, a ratio of the Fe content to the Mn content (Fe / Mn) of 0.3 to 1.1 by mass, and the balance being Al and unavoidable impurities, and in a thermal analysis curve obtained by carrying out differential thermal analysis (DSC), exothermic peaks occur between 200 and 300°C and between 400 and 500°C.

[0013] Aspect 2 of the present invention is an aluminum alloy forging containing Cu in the range of 0.25% by mass to 0.55% by mass, Mg in the range of 0.85% by mass to 1.25% by mass, Si in the range of 1.02% by mass to 1.4% by mass, Mn in the range of 0.55% by mass to 1.0% by mass, Fe in the range of 0.32% by mass to 0.65% by mass, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass to 0.30% by mass, Ti in the range of 0.01% by mass to 0.1% by mass, B in the range of 0.0010% by mass to 0.030% by mass, and Zr in the range of 0.0010% by mass to 0.050% by mass, wherein the ratio of the Fe content to the Mn content (Fe / Mn) is 0.3 to 1.1 in mass ratio, and the balance is Al and inevitable impurities, After conducting the corrosion resistance test according to H8502, 1999, the corrosion rate was 0.045% or less, and the corrosion area rate was 3% / 1.05E+09μm 2 ] or less, and the corrosion depth is 300 μm or less.

[0014] 2 In a third aspect of the present invention, the aluminum alloy forged product of the second aspect is used for a suspension arm.

[0015] Aspect 4 of the present invention is a method for producing an aluminum alloy forged product according to either aspect 2 or aspect 3, comprising the steps of: a molten metal forming step of obtaining a molten aluminum alloy; a casting step of obtaining a cast product by casting the obtained molten metal; a forging step of heating the cast product at a temperature of 500°C to the melting point and performing plastic working to obtain a forged product; and a forging step of heating the obtained forged product from 20°C to 500°C at a heating rate of 5.0°C / min or more and then heating the product at 530 to 560°C for 0.3 to 3 hours. the quenching step in which the entire surface of the forged product is brought into contact with quenching water within 5 to 60 seconds after the solution treatment and the forged product is quenched in a water tank for more than 1 minute but not exceeding 40 minutes; and the aging step in which the forged product is heated at a temperature of 180°C to 220°C for 0.5 to 8 hours to undergo aging treatment, wherein the split time between the quenching step and the aging step is 2 hours or less.

[0016] Aspect 5 of the present invention is a method for producing an aluminum alloy forged product according to either Aspect 2 or Aspect 3, comprising the steps of: a molten metal forming step of obtaining a molten aluminum alloy; a casting step of obtaining a cast product by casting the obtained molten metal; a forging step of heating the cast product at a temperature of 500°C to the melting point and performing plastic working to obtain a forged product; and a forging step of heating the obtained forged product from 20°C to 500°C at a heating rate of 5.0°C / min or more and then heating the product at 530 to 560°C for 0.3 to 3 hours. the forged product is heated at a temperature of 180°C to 220°C for 0.5 to 8 hours to undergo aging treatment; and in the casting step, the time required for passing through a temperature range of 650 to 600°C during casting solidification is kept within 20 seconds.

[0017] A sixth aspect of the present invention is a method for producing an aluminum alloy forging material according to the first aspect, comprising a molten metal forming step of obtaining a molten aluminum alloy, and a casting step of obtaining a cast product by casting the obtained molten metal, in which a homogenization treatment is not performed after the casting step.

[0018] According to the present invention, it is possible to provide an aluminum alloy forging material, an aluminum alloy forging product, and a method for manufacturing the same, which have excellent mechanical properties at room temperature.

[0019] FIG. 1 is a perspective view showing an example of an aluminum alloy forging according to one embodiment of the present invention. FIG. 2 is a plan view showing another example of an aluminum alloy forging according to one embodiment of the present invention. FIG. 3 is a perspective view showing yet another example of an aluminum alloy forging according to one embodiment of the present invention. FIG. 4 is a cross-sectional view showing an example of the vicinity of a mold of a horizontal continuous casting apparatus for producing an aluminum alloy forging according to one embodiment of the present invention. FIG. 5 is an enlarged cross-sectional view of a main portion of the horizontal continuous casting apparatus shown in FIG. 4 near a cooling water cavity. FIG. 6 is an explanatory view illustrating the heat flux of a cooling wall portion of the horizontal continuous casting apparatus. FIG. 7 is a plan view showing the sampling position of a central portion sampled from the aluminum alloy forging obtained in this example for use in preparing a test piece for evaluating mechanical properties. FIG. 8 is a plan view showing a test piece for evaluating mechanical properties prepared in this example.

[0020] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings used in the following description may show characteristic portions enlarged for convenience in order to make the features easier to understand, and the dimensional ratios of each component may not necessarily be the same as those in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited thereto. Appropriate changes can be made within the scope that does not change the effects of the present invention.

[0021] [Aluminum alloy forging material] First, an aluminum alloy forging material according to one embodiment of the present invention will be described. The aluminum alloy forging material of this embodiment contains Cu in the range of 0.25% by mass to 0.55% by mass, Mg in the range of 0.85% by mass to 1.25% by mass, Si in the range of 1.02% by mass to 1.4% by mass, Mn in the range of 0.55% by mass to 1.0% by mass, Fe in the range of 0.32% by mass to 0.65% by mass, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass to 0.30% by mass, Ti in the range of 0.01% by mass to 0.1% by mass, The aluminum alloy forging material contains B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less, the ratio of the Fe content to the Mn content (Fe / Mn) is 0.3 to 1.1 by mass, and the balance is Al and unavoidable impurities, and in a thermal analysis curve obtained by carrying out differential thermal analysis (DSC), exothermic (precipitation) peaks occur between 200 and 300°C and between 400 and 500°C.

[0022] (Exothermic (precipitation) peaks in thermal analysis curves obtained by differential thermal analysis) It is known that exothermic peaks appearing in thermal analysis curves (DSC curves) obtained by performing differential thermal analysis on metal materials correspond to the formation of predetermined precipitates. In the aluminum alloy forging material according to this embodiment, one exothermic peak is obtained between 200 and 300°C and one between 400 and 500°C in the DSC curve. The exothermic peaks between 200 and 300°C correspond to the formation of β'-Mg ２ The exothermic peak corresponds to the formation of β-Mg ２ This corresponds to the production of Si.

[0023] [Aluminum Alloy Forging] Next, an aluminum alloy forging according to one embodiment of the present invention will be described. FIG. 1 is a perspective view of an aluminum alloy forging according to one embodiment of the present invention. As shown in FIG. 1, an aluminum alloy forging 1a has a long portion 2 and connecting portions 4a, 4b connected to both ends of the long portion 2 in the longitudinal direction. The long portion has a rectangular cross section. Each of these two connecting portions 4 may be provided with a through hole. An aluminum alloy forging 1a having this shape can be used, for example, as an I-type suspension arm.

[0024] The aluminum alloy forged product of this embodiment contains Cu in the range of 0.25 mass% or more and 0.55 mass% or less, Mg in the range of 0.85 mass% or more and 1.25 mass% or less, Si in the range of 1.02 mass% or more and 1.4 mass% or less, Mn in the range of 0.55 mass% or more and 1.0 mass% or less, Fe in the range of 0.32 mass% or more and 0.65 mass% or less, Zn in the range of 0.25 mass% or less, Cr in the range of 0.050 mass% or more and 0.30 mass% or less, and % by mass or less, Ti in the range of 0.01% by mass or more and 0.1% by mass or less, B in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr in the range of 0.0010% by mass or more and 0.050% by mass or less, a ratio of the Fe content to the Mn content, Fe / Mn, in mass ratio, of 0.3 or more and 1.1 or less, the balance being Al and unavoidable impurities, and after conducting a corrosion resistance test in accordance with JIS H8502, 1999, the corrosion rate is 0.045% or less and the corrosion area rate is 3[% / 1.05E+0.9μm 2 ] or less, and the corrosion depth is 300 μm or less.

[0025] The aluminum alloy forging material and aluminum alloy forgings of the above-described embodiments correspond to 6000 series aluminum alloys in that they contain Mg and Si.

[0026] (Cu: 0.25% by mass or more, 0.55% by mass or less) Cu has the effect of finely dispersing Mg-Si compounds in the aluminum alloy and improving the tensile strength of the aluminum alloy by precipitating as Al-Cu-Mg-Si compounds such as the Q phase. By ensuring that the Cu content is within the above range, the mechanical properties of the aluminum alloy forging 1a at room temperature can be improved.

[0027] (Mg: 0.85 mass % or more, 1.25 mass % or less) Mg has the effect of improving the tensile strength of the aluminum alloy. Mg dissolves in the aluminum matrix or forms a Mg-Si compound (Mg ２ Si) or Q phase and other Al-Cu-Mg-Si compounds (AlCuMgSi), which contribute to strengthening the aluminum alloy. ２ Si is the CuAl in the aluminum alloy. ２ It has the effect of suppressing the formation of CuAl phase. ２ By suppressing the formation of the phase, the corrosion resistance of the aluminum alloy forging material and the aluminum alloy forged product using the same is improved. By having the Mg content within the above range, it is possible to improve the corrosion resistance as well as the mechanical properties at room temperature of the aluminum alloy forging material and the aluminum alloy forged product using the same.

[0028] (Si: 1.02% by mass or more, 1.4% by mass or less) Like Mg, Si has the effect of improving the corrosion resistance as well as the mechanical properties of aluminum alloy forging materials at room temperature. However, if excessive Si is added to an aluminum alloy, coarse primary crystal Si grains may crystallize, potentially reducing the tensile strength of the aluminum alloy. By keeping the Si content within the above range, it is possible to suppress the crystallization of primary crystal Si, while improving the corrosion resistance as well as the mechanical properties at room temperature of aluminum alloy forging materials and aluminum alloy forgings made therefrom.

[0029] (Mn: 0.55% by mass or more, 1.0% by mass or less) Mn forms fine granular precipitates containing intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Cr-Fe-Si in the aluminum alloy, thereby improving the tensile strength of the aluminum alloy. When the Mn content is within the above range, the mechanical properties at room temperature of the aluminum alloy forging material and aluminum alloy forgings using the same can be improved.

[0030] (Fe: 0.32% by mass or more, 0.65% by mass or less) Fe crystallizes in the aluminum alloy as fine crystals containing intermetallic compounds such as Al-Mn-Fe-Si, Al-Mn-Cr-Fe-Si, Al-Fe-Si, Al-Cu-Fe, and Al-Mn-Fe, thereby improving the tensile strength of the aluminum alloy. Having the Fe content within the above range can improve the room-temperature mechanical properties of aluminum alloy forging materials and aluminum alloy forgings made therefrom. The Fe / Mn relationship is 0.3 to 1.1. Having the Fe / Mn relationship 0.3 to 1.1 can suppress the crystallization of AlFeSi-based compounds of 2.0 μm or more and can increase the number density of AlMn-based compounds within crystal grains.

[0031] (Cr: 0.050% by mass or more, 0.30% by mass or less) Cr forms fine granular precipitates containing intermetallic compounds such as Al-Mn-Cr-Fe-Si and Al-Fe-Cr in the aluminum alloy, thereby improving the tensile strength of the aluminum alloy. When the Cr content is within the above range, the mechanical properties at room temperature of the aluminum alloy forging material and aluminum alloy forgings using the same can be improved.

[0032] (Ti: 0.01% by mass or more, 0.1% by mass or less) Ti has the effect of refining the crystal grains of an aluminum alloy and improving its wrought workability. If the Ti content is less than 0.01% by mass, the effect of refining the crystal grains may not be sufficient. On the other hand, if the Ti content exceeds 0.1% by mass, coarse crystals may be formed, which may reduce the wrought workability. Furthermore, if a large amount of coarse crystals containing Ti are mixed into an aluminum alloy forging material and an aluminum alloy forged product using the same, the toughness may be reduced. Therefore, the Ti content is set to 0.01% by mass or more, and 0.1% by mass or less. The Ti content is preferably 0.015% by mass or more, and 0.050% by mass or less.

[0033] (B: 0.0010% by mass or more, 0.030% by mass or less) B has the effect of refining the crystal grains of an aluminum alloy and improving its wrought workability. Adding B to an aluminum alloy together with the above-mentioned Ti improves the effect of refining the crystal grains. If the B content is less than 0.0010% by mass, the effect of refining the crystal grains may not be sufficient. On the other hand, if the B content exceeds 0.030% by mass, coarse crystals may be formed and may be mixed as inclusions in the aluminum alloy forging material and aluminum alloy forgings made therefrom. Furthermore, if a large amount of coarse crystals containing B are mixed into the final aluminum alloy product, the toughness may be reduced. Therefore, the B content is set to 0.0010% by mass or more, and 0.030% by mass or less. The B content is preferably 0.0050% by mass or more, and 0.025% by mass or more.

[0034] (Zr: 0.0010 mass % or more, 0.050 mass % or less) When Zr is 0.05 mass % or less, Al ３Precipitation in the form of Zr and Al-(Ti, Zr) contributes to improving the strength of aluminum alloy forging materials and aluminum alloy forgings made therefrom by inhibiting recrystallization and precipitation strengthening. If the Zr content exceeds 0.050% by mass, coarse Zr compounds will crystallize, which may lead to a decrease in the corrosion resistance of the aluminum alloy forging materials and aluminum alloy forgings made therefrom. For this reason, the Zr content is set to 0.050% by mass or less. In addition, in order to obtain the above-mentioned effects of inhibiting recrystallization and improving the strength of forgings through precipitation strengthening, the Zr content is preferably 0.0010% by mass or more.

[0035] (Zn: 0.250 mass% or less) Zn may be 0.250 mass% or less. If the Zn content exceeds 0.250 mass%, MgZn ２ The formation of Zn precipitates from the Al matrix at grain boundaries, causing intergranular corrosion and resulting in a decrease in the corrosion resistance of the aluminum alloy forging material and the aluminum alloy forged product made therefrom. For this reason, the Zn content is preferably 0.250 mass% or less, or is preferably zero.

[0036] (Inevitable Impurities) Inevitable impurities are impurities that are inevitably mixed into the aluminum alloy from raw materials or the manufacturing process. Examples of inevitable impurities include Ni, Sn, and Be. The content of these inevitable impurities preferably does not exceed 0.1 mass%.

[0037] The central portion 2a in the longitudinal direction of the long portion 2 of the aluminum alloy forging 1a of this embodiment is a portion to which the maximum principal stress is applied when the aluminum alloy forging 1a is used, for example, as a suspension arm of a vehicle. The central portion 2a is, for example, a region that is in the range of 1% to 80% of the entire long portion 2, including the longitudinal center of the long portion 2. The aspect ratio of the long portion 2 (longitudinal length / length of the short side perpendicular to the longitudinal direction) is, for example, in the range of 2 to 100. The cross section of the central portion 2a of the long portion 2 is a cross section (hereinafter sometimes referred to as the central cross section) taken along the direction in which pressure is applied when manufacturing the aluminum alloy forging 1a by forging.

[0038] (After the corrosion resistance test, the corrosion rate was 0.045%, and the corrosion area rate was 3% / 1.05E+09μm 2 ] Corrosion depth is 300 μm or less. The corrosion resistance test was carried out in accordance with the method based on JIS H8502,1999.

[0039] The aluminum alloy forging material of this embodiment and aluminum alloy forgings made therefrom have a corrosion rate of 0.045% or less after a corrosion resistance test according to JIS H8502, 1999. The corrosion rate is preferably 0.040% or less. The corrosion rate can be calculated using the following formula: Corrosion rate (%) = (W - W') / W x 100, where W: weight of aluminum product before corrosion, W': weight of aluminum product after corrosion. If the corrosion rate exceeds 0.045%, the corrosion resistance will be so low that it will be difficult to apply the material to automobile undercarriage parts, such as suspension arms.

[0040] The aluminum alloy forging material of this embodiment and the aluminum alloy forging product using the same have a corrosion area ratio of 3% / 1.05E+09 μm after corrosion resistance testing according to JIS H8502, 1999. 2 The corrosion area ratio is 2% / 1.05E+09μm 2 ] or less, and 1.5 [% / 1.05E+09 μm 2 The corrosion area ratio is preferably 1.05 × 10 or less of any of the corroded specimens before and after the corrosion resistance test according to JIS H8502, 1999. ９ μm ２ This can be done by calculating the percentage of the corroded area using image analysis. The corroded area ratio is 3 [% / 1.05E+09 μm 2 If the temperature exceeds 100°C, the corrosion resistance will be low, making it difficult to apply the material to automobile undercarriage parts, such as suspension arms.

[0041] The aluminum alloy forging material of this embodiment and aluminum alloy forgings using the same have a corrosion depth of 300 μm or less after a corrosion resistance test according to JIS H8502, 1999. The corrosion depth is preferably 250 μm or less, and more preferably 210 μm or less. The corrosion depth can be measured, for example, using a one-shot 3D shape measuring instrument (Keyence Corporation, VR6000). The one-shot 3D shape measuring instrument irradiates a striped light onto an object, and the striped pattern distorts depending on the unevenness of the object. The reflected light is received by a CMOS, and the shape of the object is measured from the distortion of the striped pattern using triangulation. If the corrosion depth exceeds 300 μm, the corrosion resistance is low, making it difficult to apply the material to automotive suspension parts, such as suspension arms.

[0042] (Mg ２ In the aluminum alloy forging material and aluminum alloy forging product of this embodiment, Mg ２ The size of the Si compound is 2.5 μm or less. If the size exceeds 2.5 μm, corrosion pits are likely to occur, which may reduce corrosion resistance.

[0043] The aluminum alloy forging material and aluminum alloy forging product of the present embodiment configured as described above are made of the aluminum alloy having the above alloy composition and produced by the method described below. ２ Since the size of the Si compound is controlled to 2.5 μm or less, after the corrosion resistance test according to JIS H8502, 1999, the corrosion rate is 0.045% or less, and the corrosion area rate is 3 [% / 1.05E+09 μm 2 ] or less, the corrosion depth becomes 300 μm or less, and corrosion resistance becomes good.

[0044] The aluminum alloy forging material and aluminum alloy forgings of this embodiment have high strength and durability, good corrosion resistance, and are lightweight, and therefore can be advantageously used for suspension arms of vehicles such as automobiles.

[0045] In the aluminum alloy forging 1a of this embodiment shown in FIG. 1 , one connecting portion 4a is cylindrical with a relatively small diameter, and one connecting portion 4b is cylindrical with a relatively large diameter, and the long portion 2 has a shape in which the width increases from the end edge on the side of one connecting portion 4a toward the end edge on the side of the other connecting portion 4b. However, the shape of the aluminum alloy forging 1a is not limited to this. For example, the one connecting portion 4a and the other connecting portion 4b of the aluminum alloy forging 1a may have the same shape. The width of the long portion 2 may be constant. Furthermore, the long portion 2 may have a curved shape. Three or more connecting portions 4 may be formed.

[0046] Fig. 2 is a plan view of another example of an aluminum alloy forging according to an embodiment of the present invention. The aluminum alloy forging 1b shown in Fig. 2 has three connecting portions 4c, 4d, and 4e. The connecting portions 4c and 4d are connected by a long portion 2, and the connecting portions 4d and 4e are connected by a short portion 5 that is relatively shorter than the long portion 2. A through hole is provided in the connecting portion 4c. This aluminum alloy forging 1b can be used, for example, as an L-shaped suspension arm.

[0047] Fig. 3 is a plan view of yet another example of an aluminum alloy forging according to an embodiment of the present invention. The aluminum alloy forging 1c shown in Fig. 3 has three connecting portions 4f, 4g, and 4h. The connecting portions 4f and 4g are connected by long portions 2, and the connecting portions 4f and 4h are connected by long portions 2. A through hole is provided in the connecting portion 4f. This aluminum alloy forging 1b can be used, for example, as an A-type suspension arm.

[0048] [Methods for manufacturing aluminum alloy forging material and aluminum alloy forgings] Next, a method for manufacturing an aluminum alloy forging material and an aluminum alloy forgings according to one embodiment of the present invention will be described. The method for manufacturing an aluminum alloy forging material and an aluminum alloy forgings according to this embodiment 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.

[0049] (Molten Metal Formation Step) The molten metal formation step is a step of melting raw materials to obtain a molten aluminum alloy having a composition adjusted to include Cu in the range of 0.25% by mass to 0.55% by mass, Mg in the range of 0.85% by mass to 1.25% by mass, Si in the range of 1.02% by mass to 1.4% by mass, Mn in the range of 0.55% by mass to 1.0% by mass, Fe in the range of 0.32% by mass to 0.65% by mass, Zn in the range of 0.25% by mass, and Cr in the range of 0.050% by mass to 0.30% by mass. a molten 6000 series aluminum alloy is obtained by adjusting the alloy composition to have an alloy composition comprising: Ti in the range of 0.01% by mass or more and 0.1% by mass or less; B in the range of 0.0010% by mass or more and 0.030% by mass or less; Zr in the range of 0.0010% by mass or more and 0.050% by mass or less; a ratio of the Fe content to the Mn content, Fe / Mn, in mass ratio, of 0.3 or more and 1.1 or less, with the balance being Al and unavoidable impurities.

[0050] By carrying out the subsequent steps using a molten aluminum alloy of the above composition, it is possible to obtain an Al-Mg-Si aluminum alloy forging that is resistant to recrystallization and has excellent mechanical properties at room temperature. Note that virgin aluminum ingot is aluminum with a concentration of 99% or more, obtained by subjecting alumina produced from minerals to electrolysis, a process known as electrolytic refining.

[0051] A molten aluminum alloy can be obtained by heating and melting an aluminum alloy. Alternatively, the aluminum alloy may be formed by melting a mixture containing the elements or compounds containing two or more elements that are raw materials for the aluminum alloy, in proportions that produce the desired aluminum alloy. For example, to control the grain size of the aluminum alloy produced in the casting process, Ti or B may be mixed as a grain refiner, such as an Al-Ti-B rod.

[0052] Alternatively, the molten aluminum alloy may be prepared by melting 10% or more of scrap aluminum alloys of 1000, 2000, 3000, 4000, 5000, 6000, or 7000 series, with the remainder being new aluminum ingots and the above-mentioned additive elements, to obtain a molten aluminum alloy having a composition adjusted. In this case, an Al-Mg-Si-based aluminum alloy forging can be obtained that is less prone to recrystallization and has excellent mechanical properties at room temperature. Note that new aluminum ingots are aluminum with a purity of, for example, 99% or higher, obtained by subjecting alumina produced from minerals to electrolysis, a process known as electrolytic refining.

[0053] (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. For example, vertical continuous casting or horizontal continuous casting can be used for the casting process. The time required for passing through the temperature range of 650 to 600°C during casting and solidification is controlled to be within 20 seconds.

[0054] 4 and 5 show horizontal continuous casting apparatuses that can be used to produce the aluminum alloy cast product of this embodiment. Fig. 4 is a cross-sectional view showing an example of the vicinity of the mold 12 of the horizontal continuous casting apparatus 10. Fig. 5 is an enlarged cross-sectional view of a main portion of the horizontal continuous casting apparatus 10 near the cooling water cavity 24.

[0055] The horizontal continuous casting apparatus 10 shown in Figures 4 and 5 has a molten metal receiving portion (tundish) 11, a hollow cylindrical mold 12, and a refractory plate-like body (heat insulating member) 13 arranged between one end side 12a of the mold 12 and the molten metal receiving portion 11.

[0056] The molten metal receiving portion 11 is composed of a molten metal inlet portion 11 a that receives the molten aluminum alloy M obtained in the molten metal forming process described above, a molten metal holding portion 11 b, and an outlet portion 11 c that flows into the hollow portion 21 of the mold 12.

[0057] The molten metal receiving portion 11 maintains the upper liquid level of the molten aluminum alloy M at a position higher than the upper surface of the hollow portion 21 of the mold 12, and in the case of multiple casting, stably distributes the molten aluminum alloy M to each mold 12.

[0058] The molten aluminum alloy M held in the molten metal holding portion 11b in the molten metal receiving portion 11 is poured into the hollow portion 21 of the mold 12 through a pouring passage 13a provided in the refractory plate 13. The molten aluminum alloy M supplied into the hollow portion 21 is then cooled and solidified by a cooling device 23 (described later) and drawn out from the other end 12b of the mold 12 as an aluminum alloy rod B, which is a solidified ingot.

[0059] A drawing drive device (not shown) that draws out the cast aluminum alloy rod B at a constant speed may be installed at the other end 12b of the mold 12. It is also preferable that a synchronized cutting machine (not shown) that cuts the continuously drawn aluminum alloy rod B to a desired length be installed.

[0060] The refractory plate 13 is a member that blocks heat transfer between the molten metal receiver 11 and the mold 12, and may be made of materials such as calcium silicate, alumina, silica, a mixture of alumina and silica, silicon nitride, silicon carbide, graphite, etc. Such a refractory plate 13 may also be made up of multiple layers made of different materials.

[0061] In this embodiment, the mold 12 is a hollow cylindrical member made of, for example, one or a combination of two or more materials selected from aluminum, copper, or alloys thereof. The materials for the mold 12 may be selected from an optimum combination in terms of thermal conductivity, heat resistance, and mechanical strength.

[0062] The hollow portion 21 of the mold 12 is formed to have a circular cross section in order to cast the aluminum alloy rod B into a cylindrical rod shape, and the mold 12 is held so that the mold central axis (central axis) C passing through the center of this hollow portion 21 is aligned approximately horizontally.

[0063] The inner peripheral surface 21a of the hollow portion 21 of the mold 12 is formed at an elevation angle of 0° to 3° (more preferably 0° to 1°) with respect to the mold central axis C toward the casting direction of the aluminum alloy bar B (see FIG. 1). That is, the inner peripheral surface 21a is configured in a tapered shape that opens like a cone toward the casting direction. The angle of this taper is the elevation angle.

[0064] If the elevation angle is less than 0°, the aluminum alloy rod B encounters resistance at the other end 12b, which is the mold outlet, when it is drawn out of the mold 12, which may make casting difficult. On the other hand, if the elevation angle exceeds 3°, the inner peripheral surface 21a will not be in sufficient contact with the molten aluminum alloy M, which may reduce the heat transfer effect from the molten aluminum alloy M and the solidified shell formed by cooling and solidifying it to the mold 12, which may result in insufficient solidification. As a result, this is not preferable because it may lead to casting problems such as the formation of a remelted skin on the surface of the aluminum alloy rod B or the ejection of unsolidified molten aluminum alloy M from the end of the aluminum alloy rod B.

[0065] The cross-sectional shape of the hollow portion 21 of the mold 12 (the planar shape when the hollow portion 21 of the mold 12 is viewed from the other end side 21b) may be selected to match the shape of the aluminum alloy rod to be cast, such as a triangular or rectangular cross-sectional shape, a polygonal, semicircular, elliptical, or an irregular cross-sectional shape having no axis or plane of symmetry, in addition to the circular shape of this embodiment.

[0066] A fluid supply pipe 22 is disposed at one end 12a of the mold 12 to supply a lubricating fluid into the hollow portion 21 of the mold 12. The lubricating fluid supplied from the fluid supply pipe 22 can be one or more lubricating fluids selected from a gas lubricant and a liquid lubricant. When supplying both a gas lubricant and a liquid lubricant, it is preferable to provide separate fluid supply pipes for each. The lubricating fluid supplied under pressure from the fluid supply pipe 22 is supplied into the hollow portion 21 of the mold 12 through an annular lubricant supply port 22a.

[0067] In this embodiment, the lubricating fluid is supplied under pressure from the lubricant supply port 22a to the inner circumferential surface 21a of the mold 12. Note that the liquid lubricant may be heated to decompose into a gas and then supplied to the inner circumferential surface 21a of the mold 12. Alternatively, a porous material may be disposed in the lubricant supply port 22a, and the lubricating fluid may be allowed to seep out onto the inner circumferential surface 21a of the mold 12 through the porous material.

[0068] A cooling device 23, which is a cooling means for cooling and solidifying the molten aluminum alloy M, is formed inside the mold 12. The cooling device 23 of this embodiment has a cooling water cavity 24 that accommodates cooling water W for cooling the inner circumferential surface 21 a of the hollow portion 21 of the mold 12, and a cooling water injection passage 25 that connects the cooling water cavity 24 with the hollow portion 21 of the mold 12.

[0069] The cooling water cavity 24 is formed in a ring shape surrounding the hollow portion 21 outside the inner circumferential surface 21 a of the hollow portion 21 inside the mold 12 , and cooling water W is supplied to the cavity 24 via a cooling water supply pipe 26 .

[0070] The inner surface 21a of the mold 12 is cooled by the cooling water W contained in the cooling water cavity 24, which removes heat from the molten aluminum alloy M filling the hollow portion 21 of the mold 12 from the surface in contact with the inner surface 21a of the mold 12, forming a solidified shell on the surface of the molten aluminum alloy M.

[0071] The cooling water jetting passages 25 spray cooling water W directly from shower openings 25a facing the hollow portion 21 toward the aluminum alloy rods B at the other end 12b of the mold 12 to cool the aluminum alloy rods B. The vertical cross-sectional shape of the cooling water jetting passages 25 may be, for example, semicircular, pear-shaped, or horseshoe-shaped, in addition to the circular shape of this embodiment.

[0072] In this embodiment, the cooling water W supplied through the cooling water supply pipe 26 is first stored in the cooling water cavity 24 to cool the inner peripheral surface 21 a of the hollow portion 21 of the mold 12, and then the cooling water W in the cooling water cavity 24 is sprayed toward the aluminum alloy rod B through the cooling water spray passage 25. However, it is also possible to configure these to be supplied by separate cooling water supply pipes.

[0073] The length from the position where the extension of the central axis of the shower opening 25a of the cooling water injection passage 25 hits the surface of the cast aluminum alloy rod B to the contact surface between the mold 12 and the refractory plate 13 is called the effective mold length L, and this effective mold length L is preferably, for example, 10 mm or more and 40 mm or less. If this effective mold length L is less than 10 mm, a good coating cannot be formed, making casting impossible. If it exceeds 40 mm, the effect of forced cooling is reduced, solidification by the mold wall becomes dominant, and the contact resistance between the mold 12 and the molten aluminum alloy M or the aluminum alloy rod B increases, which may cause cracks on the casting surface or tearing inside the mold, making casting unstable.

[0074] It is preferable that the supply of the cooling water W to the cooling water cavity 24 and the spray of the cooling water W from the shower opening 25a of the cooling water spray passage 25 can be controlled by control signals from a control device (not shown).

[0075] The cooling water cavity 24 is formed so that an inner bottom surface 24 a near the hollow portion 21 of the mold 12 is parallel to the inner peripheral surface 21 a of the hollow portion 21 of the mold 12 .

[0076] Note that "parallel" here also includes the case where the inner peripheral surface 21a of the hollow portion 21 of the mold 12 is formed at an elevation angle of 0° to 3° relative to the inner bottom surface 24a of the cooling water cavity 24, i.e., the case where the inner bottom surface 24a is inclined from 0° to 3° relative to the inner peripheral surface 21a.

[0077] As shown in FIG. 4 , the cooling wall portion 27 of the mold 12, which is the portion where the inner bottom surface 24 a of the cooling water cavity 24 faces the inner peripheral surface 21 a of the hollow portion 21 of the mold 12, has a heat flux value per unit area of ​​10×10 20 from the molten aluminum alloy M in the hollow portion 21 to the cooling water W in the cooling water cavity 24. ５ W / m ２ That's it, 50 x 10 ５ W / m ２ It is formed so as to fall within the following range.

[0078] The mold 12 may be formed so that the thickness t of the cooling wall portion 27 of the mold 12, i.e., the distance between the inner bottom surface 24a of the cooling water cavity 24 and the inner peripheral surface 21a of the hollow portion 21 of the mold 12, is within a range of, for example, 0.5 mm to 3.0 mm, preferably 0.5 mm to 2.5 mm. The material for forming the mold 12 may be selected so that the thermal conductivity of at least the cooling wall portion 27 of the mold 12 is within a range of 100 W / m·K to 400 W / m·K.

[0079] In FIG. 4 , molten aluminum alloy M in a molten metal receiving portion 11 is supplied through a refractory plate 13 to one end 12 a of a mold 12, which is held so that the central axis C of the mold is substantially horizontal, and is forcibly cooled at the other end 12 b of the mold 12 to form an aluminum alloy rod B.

[0080] The aluminum alloy rod B is drawn out at a constant speed by a drawing drive device (not shown) installed near the other end 12b of the mold 12, and is continuously cast to form a long aluminum alloy rod B. The drawn aluminum alloy rod B is then cut to a desired length by, for example, a synchronous cutting machine (not shown).

[0081] The composition ratio of the cast aluminum alloy rod B can be confirmed, for example, by a method using a photoelectric emission spectrophotometer (e.g., PDA-5500 manufactured by Shimadzu Corporation, Japan) as described in "JIS H 1305".

[0082] The difference in height between the liquid level of the molten aluminum alloy M stored in the molten metal receiver 11 and the upper inner circumferential surface 21a of the mold 12 is preferably 0 mm to 250 mm (more preferably 50 mm to 170 mm). By setting the difference in height within this range, the pressure of the molten aluminum alloy M supplied into the mold 12 and the lubricating oil and the gas produced by vaporizing the lubricating oil are suitably balanced, resulting in stable castability.

[0083] The liquid lubricant may be a vegetable oil, such as rapeseed oil, castor oil, or salad oil.

[0084] The lubricating oil supply rate is preferably 0.05 mL / min to 5 mL / min (more preferably 0.1 mL / min to 1 mL / min). If the supply rate is too low, the molten aluminum alloy M in the aluminum alloy rod B may not solidify due to insufficient lubrication and may leak from the mold 12. If the supply rate is too high, the excess may get mixed into the aluminum alloy rod B and cause internal defects.

[0085] The casting speed, which is the speed at which the aluminum alloy rod B is withdrawn from the mold 12, is preferably 200 mm / min or more and 1500 mm / min or less (more preferably 400 mm / min or more and 1000 mm / min or less). This is because, if the casting speed is within this range, the network structure of the crystallized matter formed by casting becomes uniform and fine, which increases the resistance of the aluminum matrix to deformation at high temperatures and improves the high-temperature mechanical strength.

[0086] The amount of cooling water sprayed from the shower openings 25a of the cooling water spray passages 25 is preferably 10 L / min to 50 L / min (more preferably 25 L / min to 40 L / min) per mold. If the amount of cooling water is less than this range, the molten aluminum alloy M may not solidify and leak from the mold 12. Furthermore, the surface of the cast aluminum alloy rod B may remelt, forming an inhomogeneous structure that may remain as internal defects. On the other hand, if the amount of cooling water is greater than this range, the mold 12 may lose too much heat, causing it to solidify prematurely.

[0087] The average temperature of the molten aluminum alloy M flowing from the molten metal receiver 11 into the mold 12 is preferably, for example, 650°C or higher and 750°C or lower (more preferably 680°C or higher and 720°C or lower). If the temperature of the molten aluminum alloy M is too low, coarse crystallized products may be formed in the mold 12 or before that, and may be incorporated as internal defects inside the aluminum alloy rod B. On the other hand, if the temperature of the molten aluminum alloy M is too high, a large amount of hydrogen gas may be easily incorporated into the molten aluminum alloy M, which may be incorporated as porosity in the aluminum alloy rod B and cause internal cavities.

[0088] In the cooling wall portion 27 of the mold 12, the heat flux value per unit area from the molten aluminum alloy M in the hollow portion 21 to the cooling water W in the cooling water cavity 24 is 10×10 ５ W / m ２ Above 50 x 10 ５ W / m ２ By keeping the temperature within the following range, it is possible to prevent the aluminum alloy rod B from seizing.

[0089] The cooling wall 27 of the mold 12 receives heat from the molten aluminum alloy M and performs heat exchange by cooling this heat with the cooling water W contained in the cooling water cavity 24. Regarding the state of this heat exchange, attention was focused on the heat flux per unit area, as shown in the explanatory diagram in Figure 6. The heat flux per unit area is expressed by the following equation (1) using Fourier's law. Q = -k × (T1 - T2) / L (1) Q: heat flux k: thermal conductivity (W / m·K) of the location through which heat passes (in this embodiment, the cooling wall 27 of the mold 12) T1: low-temperature side temperature of the location through which heat passes (in this embodiment, the inner bottom surface 24 a of the cooling water cavity 24) T2: high-temperature side temperature of the location through which heat passes (in this embodiment, the inner circumferential surface 21 a of the hollow portion 21 of the mold 12) L: section length (mm) of the location through which heat passes (in this embodiment, the thickness t of the cooling wall 27 of the mold 12)

[0090] Good results were obtained even when the amount of lubricating oil was reduced during casting. Based on the mold material, thickness, and temperature measurement data, the heat flux value per unit area was 10 × 10 ５ W / m ２ By configuring the cooling wall portion 27 of the mold 12 so that the heat flux value per unit area is 50×10 or more, it is possible to prevent the cast aluminum alloy rod B from seizing. ５ W / m ２ It is preferable to do the following:

[0091] To set the heat flux value of the cooling wall portion 27 of the mold 12 within this range, the mold 12 may be formed so that the thickness t of the cooling wall portion 27 of the mold 12 is, for example, in the range of 0.5 mm to 3.0 mm. Also, the thermal conductivity of at least the cooling wall portion 27 of the mold 12 may be set in the range of 100 W / m·K to 400 W / m·K.

[0092] When producing the aluminum alloy rod B of this embodiment, the horizontal continuous casting apparatus 10 described above is used to continuously supply the molten aluminum alloy M stored in the molten metal receptacle 11 from one end 12a of the mold 12 into the hollow portion 21. In addition, cooling water W is supplied to the cooling water cavity 24, and a lubricating fluid, for example, lubricating oil, is supplied from the fluid supply pipe 22.

[0093] The molten aluminum alloy M supplied into the hollow portion 21 is cooled to a temperature at which the heat flux value per unit area of ​​the cooling wall portion 27 is 10×10 ５ W / m ２ The aluminum alloy rod B is cooled and solidified under the above conditions to be cast. During casting of the aluminum alloy rod B, it is preferable to set the wall surface temperature of the cooling wall portion 27 of the mold 12, which is cooled by the cooling water W, to 100° C. or less.

[0094] The aluminum alloy rod B thus obtained has a heat flux value per unit area in the cooling wall portion 27 of 10×10 ５ W / m ２ Cooling and solidification under the above conditions suppresses adhesion of reaction products, such as carbides, that occur due to contact between the lubricating oil gas and the molten aluminum alloy M. This eliminates the need to remove carbides and the like from the surface of the aluminum alloy rod B by cutting, and allows the aluminum alloy rod B to be produced with a high yield.

[0095] The casting process for obtaining a cast product from the molten aluminum alloy M is not limited to the above-mentioned horizontal continuous casting method, and known continuous casting methods such as vertical continuous casting can be used. Vertical continuous casting methods are classified into the float method and the hot top method depending on the method of supplying the molten aluminum alloy M to the mold (casting die 12), and the following will briefly explain the case where the hot top method is used.

[0096] The casting equipment used in the hot top method is equipped with a mold, a molten metal receiving vessel (header), etc. The molten metal supplied to the molten metal receiving vessel passes through a tapping port and then through the header, where the flow rate is adjusted, and enters a cylindrical mold placed almost horizontally, where it is forcibly cooled and a solidified shell is formed on the outer surface of the molten metal.

[0097] Furthermore, cooling water is sprayed directly onto the casting as it is pulled out of the mold, allowing the solidification of the metal to progress throughout the casting as it is continuously pulled out. Molds are generally made of metal materials with good thermal conductivity and have a hollow structure to allow the introduction of a coolant inside.

[0098] The refrigerant to be used may be selected from among those that are industrially available, but water is recommended from the viewpoint of ease of use.

[0099] The mold used in this embodiment is appropriately selected from metals such as copper and aluminum, or graphite, from the viewpoint of heat transfer performance and durability at the contact point with the molten metal. The header is generally made of a refractory material and is installed above the mold. The material and size of the header may be appropriately selected depending on the composition range of the alloy to be cast and the dimensions of the cast product, and are not particularly limited.

[0100] The average cooling rate during casting may be appropriately selected from a generally recommended range, such as 10 to 300°C / sec. The casting speed may be appropriately selected from a range generally used in horizontal continuous casting, such as 200 to 600 mm / min.

[0101] The casting method described above makes it possible to obtain a uniform metal structure even in medium to large castings. There are no particular restrictions on the diameter of the castings, and the method is suitable for use with rods with diameters of 30 to 100 mm.

[0102] (Forging Process) The forging process is a process in which the cast aluminum alloy casting is cut to a predetermined size, the obtained forging material is heated to a predetermined temperature, and then pressure is applied in a press to form it into a die. In this embodiment, the forging process is carried out without carrying out the homogenization process that has conventionally been carried out after casting to remove segregation. Therefore, since the segregation removal that was carried out by the homogenization process must be carried out by heating the material during forging, the heating must be carried out at a temperature of 500°C or higher and below the melting point. Then, a forging process is carried out to obtain a forged product (for example, an automobile suspension arm part). If the material heating temperature during forging is lower than 500°C, the AlFeSi system and Mg ２The Si-based compounds remain in a segregated state, which increases the deformation resistance, making it impossible to perform sufficient processing, and causes cracks. Furthermore, when the melting point is exceeded, defects such as eutectic melting are likely to occur.

[0103] (Solution Treatment Step) The solution treatment step is a step in which the forged product obtained in the forging step is heated to bring about a solution, thereby alleviating the strain introduced in the forging step and causing the solute elements to dissolve.

[0104] In this embodiment, the forged product is subjected to solution treatment by holding it at a treatment temperature of 530°C or higher and 560°C or lower for a period of 0.3 to 3 hours. The temperature rise rate from room temperature to the above-mentioned treatment temperature is preferably 5.0°C / min or higher. If the treatment temperature is lower than 530°C, the solute elements may not be dissolved sufficiently. On the other hand, if the treatment temperature exceeds 560°C, the solute elements may be dissolved more easily, but eutectic melting or recrystallization may occur. Furthermore, if the temperature rise rate is lower than 5.0°C / min, the Mg ２ On the other hand, if the treatment temperature is less than 530°C, the solution treatment does not proceed well, and it may be difficult to achieve high strength by aging precipitation.

[0105] (Quenching Treatment Step) The quenching treatment step is a step in which the forged product in the solid solution state obtained by the solution treatment step is rapidly cooled to form a supersaturated solid solution.

[0106] In this embodiment, the forged product is placed in a water tank containing water (quenching water) and quenched by submerging the forged product. The water temperature in the water tank is preferably 20°C or higher and 60°C or lower. The forged product is preferably placed in the water tank after solution treatment for 5 seconds or higher and 60 seconds or lower so that the entire surface of the forged product is in contact with water. The submersion time of the forged product varies depending on the size of the casting, but is, for example, between 1 minute and 30 minutes.

[0107] The split time between the quenching treatment step and the subsequent aging treatment step is set to within 2 hours.

[0108] (Aging Treatment Step) The aging treatment step is a step in which the forged product is heated and held at a relatively low temperature to precipitate supersaturated solid-solution elements, thereby imparting an appropriate hardness.

[0109] In this embodiment, the forged product after the quenching treatment step is heated to a temperature of 170°C or higher and 210°C or lower, and is then held at that temperature for 0.5 hours or longer and 7 hours or shorter to undergo aging treatment. If the treatment temperature is lower than 170°C or the holding time is shorter than 0.5 hours, the Mg content, which improves the tensile strength, is reduced. ２ On the other hand, if the treatment temperature exceeds 190°C or the holding time exceeds 7 hours, Mg ２ There is a risk that the Si-based precipitates will become too coarse and the tensile strength will not be improved sufficiently.

[0110] As mentioned above, the split time between the quenching treatment step and the subsequent aging treatment step is set to within 2 hours. The split time is the time from the solution treatment and water quenching to the artificial aging treatment. By setting the split time to within 2 hours, Mg ２ The size of the Si compound can be controlled to 2.5 μm or less.

[0111] [Method for manufacturing a material for aluminum alloy forging] A method for manufacturing a material for aluminum alloy forging according to one embodiment of the present invention will be described. The method for manufacturing a material for aluminum alloy forging according to this embodiment includes a molten metal forming step for obtaining a molten aluminum alloy, and a casting step for obtaining a cast product by casting the obtained molten metal, and does not perform a homogenization treatment after the casting step.

[0112] According to the manufacturing method of the aluminum alloy forging material of this embodiment, it is possible to manufacture an aluminum alloy forging material having a Rockwell hardness [HRF] of 60 or more and 78 or less, and having 200 or more chips per 1 g when cut.

[0113] Next, specific examples of the present invention will be described, but the present invention is not particularly limited to these examples.

[0114] [Examples 1 to 8 and Comparative Examples 1 to 4] (Production of Continuously Cast Products) First, aluminum alloys were prepared having the alloy compositions (the balance being aluminum) shown in Table 1 below. Continuously cast products having a circular cross section and a diameter of 82 mm were produced using the prepared aluminum alloys.

[0115]

[0116] (Manufacturing of Aluminum Alloy Forgings) Next, the obtained continuous cast product was subjected to a homogenizing heat treatment step (only Comparative Examples 1 to 4), a forging step, a solution treatment step, a quenching treatment step, and an artificial aging treatment step in this order to obtain an aluminum alloy forging 1a having the shape shown in Fig. 1. The conditions for the homogenizing heat treatment step (only Comparative Examples 1 to 4), the forging step, the solution treatment step, the quenching treatment step, and the artificial aging treatment step are shown in Table 2 below.

[0117]

[0118] [Evaluation] The following evaluations were performed on the central portion 2a in the longitudinal direction of the long portion 2 in the aluminum alloy forgings 1a of Examples 1 to 8 and Comparative Examples 1 to 4 obtained as described above. The evaluation results of the central portion 2a of the long portion 2 are shown in Table 3 below.

[0119] <Fe / Mn> The Fe / Mn ratio was adjusted to 0.3 or more and 1.1 or less in the examples, and less than 0.3 and more than 1.1 in the comparative examples. (Evaluation criteria) "Good": 0.3 or more and 1.1 or less. "Poor": Less than 0.3 and more than 1.1.

[0120] <Corrosion rate is 0.045% or less> After a corrosion resistance test according to JIS H8502, 1999, the corrosion rate is 0.045% or less. (Evaluation criteria) "Good": 0.045% or less. "Poor": More than 0.045%.

[0121] <Corrosion area rate 3 [% / 1.05E+09μm 2 ] or less> After corrosion resistance testing according to JIS H8502, 1999, the corrosion area ratio is 3 [% / 1.05E+09μm 2 ] or less. (Evaluation criteria) "Good"...3 [% / 1.05E+09 μm 2] or less. "×" ... 3 [% / 1.05E+09 μm 2 <Corrosion depth is 300 μm or less> After the corrosion resistance test according to JIS H8502, 1999, the corrosion depth is 300 μm or less. (Evaluation criteria) "Good": 300 μm or less. "Poor": More than 300 μm.

[0122] <Mg ２ The size of Si compounds is 2.5 μm or less (criteria) "Good": Mg ２ All Si compounds are 2.5 μm or less. "X": Mg exceeding 2.5 μm ２ There are Si compounds.

[0123] <Overall evaluation> Fe / Mn ratio, corrosion rate, corrosion area rate, corrosion depth, Mg ２ The five evaluation results of the size of the Si compound were evaluated based on the following evaluation criteria: (Evaluation criteria) "O": All five evaluations were "O". "X": One or more of the five evaluations were "X".

[0124]

[0125] DESCRIPTION OF SYMBOLS 10...Horizontal continuous casting apparatus 11...Molten metal receiving portion (tundish) 11a...Molten metal inlet portion 11b...Molten metal holding portion 11c...Outlet portion 12...Mold 12a...One end side 12b...Other end side 13...Refractory plate-shaped body (heat insulating member) 13a...Molten metal pouring passage 21...Hollow portion 21a...Inner peripheral surface 21b...Other end side 22...Fluid supply pipe 22a...Lubricant supply port 23...Cooling device 24...Cooling water cavity 24a...Inner bottom surface 25...Cooling water injection passage 25a...Shower opening 26...Cooling water supply pipe 27...Cooling wall portion B...Aluminum alloy rod M...Molten alloy W...Cooling water 100...Aluminum alloy forging

Claims

1. An aluminum alloy forging material having an alloy composition containing Cu in the range of 0.25% by mass to 0.55% by mass, Mg in the range of 0.85% by mass to 1.25% by mass, Si in the range of 1.02% by mass to 1.4% by mass, Mn in the range of 0.55% by mass to 1.0% by mass, Fe in the range of 0.32% by mass to 0.65% by mass, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass to 0.30% by mass, Ti in the range of 0.01% by mass to 0.1% by mass, B in the range of 0.0010% by mass to 0.030% by mass, and Zr in the range of 0.0010% by mass to 0.050% by mass, wherein the ratio of the Fe content to the Mn content (Fe / Mn) is 0.3 to 1.1 by mass, and the balance is Al and unavoidable impurities, An aluminum alloy forging material in which exothermic peaks occur between 200 and 300°C and between 400 and 500°C in the thermal analysis curve obtained when differential scanning calorimetry (DSC) is carried out.

2. An aluminum alloy forging having an alloy composition containing Cu in the range of 0.25% by mass to 0.55% by mass, Mg in the range of 0.85% by mass to 1.25% by mass, Si in the range of 1.02% by mass to 1.4% by mass, Mn in the range of 0.55% by mass to 1.0% by mass, Fe in the range of 0.32% by mass to 0.65% by mass, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass to 0.30% by mass, Ti in the range of 0.01% by mass to 0.1% by mass, B in the range of 0.0010% by mass to 0.030% by mass, and Zr in the range of 0.0010% by mass to 0.050% by mass, wherein the ratio of the Fe content to the Mn content (Fe / Mn) is 0.3 to 1.1 in mass ratio, and the balance is Al and unavoidable impurities, as specified in JIS After conducting the corrosion resistance test according to H8502, 1999, the corrosion rate was 0.045% or less, and the corrosion area rate was 3% / 1.05E+09μm 2 ] or less, and the corrosion depth is 300 μm or less.

3. The aluminum alloy forged product according to claim 2, which is used for a suspension arm.

4. A method for producing an aluminum alloy forged product according to claim 2 or 3, comprising: a molten metal forming step of obtaining a molten aluminum alloy; a casting step of casting the obtained molten metal to obtain a cast product; a forging step of heating the cast product at a temperature of 500°C to the melting point and plastically processing it to obtain a forged product; a solution treatment step of heating the obtained forged product from 20°C to 500°C at a heating rate of 5.0°C / min or more to 530-560°C and holding it at 530-560°C for 0.3 to 3 hours; a quenching step of contacting the entire surface of the forged product with quenching water within 5 to 60 seconds after the solution treatment step, and quenching it in a water tank for more than 1 minute but not exceeding 40 minutes; and an aging treatment step of heating the forged product at a temperature of 180°C to 220°C for 0.5 to 8 hours to perform aging treatment. a split time between the quenching step and the aging treatment step being within 2 hours.

5. A method for producing an aluminum alloy forged product according to claim 2 or 3, comprising: a molten metal forming step of obtaining a molten aluminum alloy; a casting step of casting the obtained molten metal to obtain a cast product; a forging step of heating the cast product at a temperature of 500°C to the melting point and plastically working it to obtain a forged product; a solution treatment step of heating the obtained forged product from 20°C to 500°C at a heating rate of 5.0°C / min or more to 530-560°C and holding it at 530-560°C for 0.3 to 3 hours; a quenching step of contacting the entire surface of the forged product with quenching water within 5 to 60 seconds after the solution treatment step, and quenching it in a water tank for more than 1 minute but not exceeding 40 minutes; and an aging treatment step of heating the forged product at a temperature of 180°C to 220°C for 0.5 to 8 hours to perform aging treatment. In the casting step, the time required for passing through a temperature range of 650 to 600°C during casting and solidification is set to within 20 seconds.

6. A method for producing an aluminum alloy forging material according to claim 1, comprising: a molten metal forming step for obtaining a molten aluminum alloy; and a casting step for obtaining a cast product by casting the obtained molten metal, wherein no homogenization treatment is carried out after the casting step.

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