Aluminum alloy castings, aluminum alloy forgings, and their manufacturing methods

Abstract

To provide an aluminum alloy forging with superior mechanical properties at room temperature.SOLUTION: An aluminum alloy forging has an alloy composition consisting of Cu: 0.25 mass%-0.55 mass%, Mg: 0.60 mass%-1.25 mass%, Si: 0.90 mass%-1.4 mass%, Mn: 0.35 mass%-0.60 mass%, Fe: 0.15 mass%-0.30 mass%, Zn: 0.25 mass% or less, Cr: 0.050 mass%-0.30 mass%, Ti: 0.01 mass%-0.1 mass% or less, B: 0.0010 mass%-0.030 mass%, and Zr: 0.0010 mass%-0.050 mass%, with the mass ratio of Fe / Mn being less than 1.4, and with the balance being Al and unavoidable impurities. The number density of Mn-containing precipitates within 2.0 μm including grain boundaries is 4 / μm2 or more, the fraction of high-angle grain boundaries with a crystal misorientation of 15° or more is 27% or less, and the impact value at room temperature is 10 J / cm2 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an aluminum alloy casting, an aluminum alloy forging, and a method for manufacturing the same. This application claims priority based on Japanese Patent Application No. 2022-210255, filed on December 27, 2022, the contents of which are incorporated herein by reference. [Background technology]

[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, so Al-Mg-Si alloys, especially A6061, are widely used as aluminum alloy materials. To improve strength, these automobile parts are manufactured by forging, a type of plastic processing, using aluminum alloy materials 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 components are used as raw materials without extrusion, and then subjected to a solution treatment and artificial aging treatment (T6 treatment).In order to further reduce weight, development of high-strength alloys to replace the conventional A6061 is underway (see, for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 5-59477 [Patent Document 2] Japanese Patent Application Publication No. 5-247574 [Patent Document 3] Japanese Patent Application Publication No. 6-256880 Summary of the Invention [Problem to be solved by the invention]

[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 sufficiently high strength. Therefore, some alloys have been modified to prevent recrystallization by adding Zr (zirconium) to prevent the generation of coarse recrystallized grains (see, for example, the above-mentioned Patent Documents 1 and 2).

[0008] Although the addition of Zr is effective in preventing recrystallization, it has the following problems. (1) The addition of Zr weakens the grain refinement effect of Al-Ti-B alloys, coarsening the grains of the ingot itself, resulting in a decrease in the strength of the processed product (forged product) after plastic working. (2) The effect of refining the crystal grains of the ingot itself is weakened, which makes the ingot more susceptible to cracking, increases internal defects, and reduces yield. (3) Zr forms compounds with Al-Ti-B alloys, and these compounds accumulate at the bottom of the furnace storing the molten alloy, contaminating 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. [Means for solving the problem]

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

[0012] A first aspect of the present invention is a composition containing Cu in the range of 0.25 mass% to 0.55 mass%, Mg in the range of 0.60 mass% to 1.25 mass%, Si in the range of 0.90 mass% to 1.4 mass%, Mn in the range of 0.35 mass% to 0.60 mass%, Fe in the range of 0.15 mass% to 0.30 mass%, Zn in the range of 0.25 mass% or less, Cr in the range of 0.050 mass% to 0.30 mass%, Ti in the range of 0.01 mass% to 0.1 mass%, and B in the range of 0.0010 mass% to 0.0010 mass%. % or more and 0.030% or less by mass, Zr or Zr in the range of 0.0010% or more and 0.050% or less by mass, the ratio of the Fe content to the Mn content (Fe / Mn) is less than 1.4 by mass, and the balance is Al and unavoidable impurities, and the aluminum alloy forging material has an electrical conductivity after casting of 25% IACS or more and 35% IACS or less and a Rockwell hardness HRF of 62 or more and 82 or less.

[0013] Aspect 2 of the present invention is a composition containing Cu in the range of 0.25 mass% or more and 0.55 mass% or less, Mg in the range of 0.60 mass% or more and 1.25 mass% or less, Si in the range of 0.90 mass% or more and 1.4 mass% or less, Mn in the range of 0.35 mass% or more and 0.60 mass% or less, Fe in the range of 0.15 mass% or more and 0.30 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 0.0010 mass% or more. and 0.030% by mass or less of Zr, and 0.0010% by mass or more and 0.050% by mass or less of Zr, with the ratio of the Fe content to the Mn content being 0.3 or more and 1.2 or less by mass, and the balance being Al and unavoidable impurities, the aluminum alloy forging material having an alloy composition in which the electrical conductivity after casting is 25% IACS or more and 35% IACS or less and the Rockwell hardness HRF is 62 or more and 82 or less.

[0014] A third aspect of the present invention is a composition containing Cu in the range of 0.25% by mass to 0.55% by mass, Mg in the range of 0.60% by mass to 1.25% by mass, Si in the range of 0.90% by mass to 1.4% by mass, Mn in the range of 0.35% by mass to 0.60% by mass, Fe in the range of 0.15% by mass to 0.30% 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 0.15% by mass, % 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, the ratio of the Fe content to the Mn content (Fe / Mn) is less than 1.4 by mass, and the balance is Al and unavoidable impurities, and the number density of precipitates containing Mn within 2.0 μm including the grain boundary is 4 precipitates / μm 2 The ratio of high-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less, and the impact value at room temperature is 10 J / cm 2 This is the aluminum alloy forging.

[0015] A fourth aspect of the present invention is the aluminum alloy forged product of the third aspect, wherein the size of the precipitates is 0.5 μm or less.

[0016] A fifth aspect of the present invention is a composition containing Cu in the range of 0.25% by mass to 0.55% by mass, Mg in the range of 0.60% by mass to 1.25% by mass, Si in the range of 0.90% by mass to 1.4% by mass, Mn in the range of 0.35% by mass to 0.60% by mass, Fe in the range of 0.15% by mass to 0.30% 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, and 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, Zr in the range of 0.0010% by mass to 0.050% by mass, a ratio of Fe to Mn (Fe / Mn) in mass ratio of 0.3 to 1.2, and the balance consisting of Al and unavoidable impurities, wherein the number density of precipitates containing Mn within 2.0 μm including grain boundaries is 4 precipitates / μm 2 The ratio of high-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less, and the impact value at room temperature is 10 J / cm 2 This is the aluminum alloy forging.

[0017] A sixth aspect of the present invention is the aluminum alloy forged product of the fifth aspect, wherein the size of the precipitates is 0.5 μm or less.

[0018] A seventh aspect of the present invention is a method for producing an aluminum alloy forging according to any one of the third to sixth aspects, comprising the following steps: a molten metal forming step of obtaining a molten metal of the aluminum alloy; a casting step of casting the obtained molten metal to obtain a casting; a forging step of heating the obtained casting at a temperature of 500°C to the melting point and plastically processing it to obtain a forging; a solution treatment step of heating the obtained forging from 20°C to 500°C at a heating rate of 5.0°C / min or more and holding it at 530-560°C for 0.3 to 3 hours; a quenching step of contacting the entire surface of the forging with quenching water within 5 to 60 seconds after the solution treatment and quenching it in a water tank for more than 1 minute but not more than 40 minutes; and an aging treatment step of heating the forged product that has undergone the quenching treatment step at a temperature of 180°C to 220°C for 0.5 to 8 hours to perform aging treatment.

[0019] An eighth aspect of the present invention is the method for producing an aluminum alloy forged product of the fourth aspect, further comprising, between the casting step and the forging step, a homogenization heat treatment step in which the aluminum alloy cast product is subjected to homogenization heat treatment by holding the aluminum alloy cast product at a temperature in the range of 370°C to 560°C for 2 hours to 10 hours. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide an aluminum alloy material for forging that has excellent mechanical properties at room temperature. According to the present invention, it is possible to provide an aluminum alloy forged product having excellent mechanical properties at room temperature. Furthermore, according to the present invention, the homogenization process that has been carried out to remove segregation after casting of molten aluminum alloy can be eliminated, thereby providing a low-cost, energy-saving method for manufacturing aluminum alloy forged products. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a perspective view showing an example of an aluminum alloy forged product according to an embodiment of the present invention. [Figure 2]FIG. 2 is a plan view showing another example of an aluminum alloy forged product according to an embodiment of the present invention. [Figure 3] FIG. 10 is a perspective view showing yet another example of an aluminum alloy forged product according to an embodiment of the present invention. [Figure 4] 1 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 forged product according to an embodiment of the present invention. [Figure 5] FIG. 5 is an enlarged cross-sectional view of a main part in the vicinity of a cooling water cavity of the horizontal continuous casting machine shown in FIG. [Figure 6] FIG. 2 is an explanatory diagram illustrating the heat flux of a cooling wall portion of the horizontal continuous casting device. [Figure 7] FIG. 2 is a plan view showing the position where the central portion was sampled from the aluminum alloy forging obtained in this example for preparing a test piece for evaluating mechanical properties. [Figure 8] FIG. 1 is a plan view showing a test piece for evaluating mechanical properties produced in this example. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings used in the following description, characteristic portions may be enlarged for convenience in order to make the features easier to understand, and the dimensional ratios of the components may not be the same as in reality. Furthermore, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited to them, and can be implemented with appropriate changes within the scope that does not change the effects.

[0023] [Aluminum alloy forging materials] First, an aluminum alloy forging material according to one embodiment of the present invention. The aluminum alloy forging material 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 0.60 mass% or more and 1.25 mass% or less, Si in the range of 0.90 mass% or more and 1.4 mass% or less, Mn in the range of 0.35 mass% or more and 0.60 mass% or less, Fe in the range of 0.15 mass% or more and 0.30 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 Ti in the range of 0.01 mass% or more and 0.02 mass% or less. An aluminum alloy forging material containing Fe in the range of 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, the ratio of Fe to Mn (Fe / Mn) being less than 1.4 by mass, and the remainder being Al and unavoidable impurities, and having an alloy composition in which the electrical conductivity after casting is 25% IACS or more and 35% IACS or less, and the Rockwell hardness HRF is 62 or more and 82 or less.

[0024] An aluminum alloy material for forging according to another embodiment of the present invention contains Cu in the range of 0.25% by mass to 0.55% by mass, Mg in the range of 0.60% by mass to 1.25% by mass, Si in the range of 0.90% by mass to 1.4% by mass, Mn in the range of 0.35% by mass to 0.60% by mass, Fe in the range of 0.15% by mass to 0.30% by mass, Zn in the range of 0.25% by mass to 0.25% by mass, Cr in the range of 0.050% by mass to 0.30% by mass, and Ti in the range of 0.01% by mass to 0.1% by mass. the aluminum alloy forging material is an aluminum alloy having an alloy composition containing 0.0010% by mass or more and 0.030% by mass or less, 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) is 0.3 or more and 1.2 or less in mass ratio, and the balance is Al and unavoidable impurities, and the aluminum alloy forging material has an electrical conductivity after casting of 25% IACS or more and 35% IACS or less and a Rockwell hardness HRF of 62 or more and 82 or less. The mass ratio of Fe / Mn can be set to 0.3 or more and 1.0 or less, or 0.4 or more and 0.8 or less, or 0.4 or more and 0.7 or less.

[0025] The aluminum alloy forging material of the above embodiment corresponds to a 6000 series aluminum alloy in that it contains Mg and Si.

[0026] (Conductivity: 25%IACS or more and 35%IACS or less) The electrical conductivity of the aluminum alloy forging material of the above embodiment is 25% IACS or more and 35% IACS or less. This electrical conductivity is the electrical conductivity at room temperature, which is approximately 20°C ± 15°C. If the conductivity is less than 25% IACS, the material will be too hard and its workability will decrease, while if it exceeds 35% IACS, the material will be too soft, resulting in poor machinability (ability to separate chips), and the guaranteed strength of the final product may not be met.

[0027] (Rockwell hardness HRF: 62 or more and 82 or less) The Rockwell hardness HRF of the aluminum alloy material for forging of the above embodiment is equal to or greater than 62 and equal to or less than 82. Here, the Rockwell hardness HRF is a value measured in accordance with JIS Z2245:2016 "Rockwell hardness test - Test method." This is because a Rockwell hardness HRF within this range provides good workability. In other words, if the Rockwell hardness HRF is less than 62, the material is too soft, resulting in poor machinability (chip breakability) and the guaranteed strength of the final product may not be met, while if it exceeds 82, the material is too hard and workability is reduced.

[0028] [Aluminum alloy forgings] An aluminum alloy forged product 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 the two connecting portions 4 may have a through-hole. An aluminum alloy forging 1a having this shape can be used, for example, as an I-type suspension arm.

[0029] 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 0.60 mass% or more and 1.25 mass% or less, Si in the range of 0.90 mass% or more and 1.4 mass% or less, Mn in the range of 0.35 mass% or more and 0.60 mass% or less, Fe in the range of 0.15 mass% or more and 0.30 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 Ti in the range of 0.01 mass% or less. 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 Fe to Mn (Fe / Mn) of less than 1.4 by mass, and the balance consisting of Al and unavoidable impurities, wherein the number density of precipitates containing Mn within 2.0 μm including grain boundaries is 4 precipitates / μm 2 The ratio of high-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less. Furthermore, the aluminum alloy forged product of this embodiment has an impact strength of 10 J / cm at room temperature. 2 That is said to be the case.

[0030] For example, the size of precipitates containing Mn contained within 2.0 μm including the grain boundaries is 0.5 μm or less.

[0031] The aluminum alloy forgings of this embodiment correspond to 6000 series aluminum alloy forgings in that they contain Mg and Si.

[0032] (Cu: 0.25 mass% or more, 0.55 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.

[0033] (Mg: 0.60 mass% or more, 1.25 mass% or less) Mg has the effect of improving the tensile strength of the aluminum alloy. Mg contributes to strengthening the aluminum alloy by dissolving in the aluminum matrix or by precipitating as Mg-Si compounds (Mg2Si) such as the β" phase or Al-Cu-Mg-Si compounds (AlCuMgSi) such as the Q phase. Mg2Si also has the effect of suppressing the formation of CuAl2 phase in the aluminum alloy. Suppressing the formation of the CuAl2 phase improves the corrosion resistance of the aluminum alloy forging 1a. When the Mg content falls within the above range, the corrosion resistance as well as the mechanical properties at room temperature of the aluminum alloy forging 1a can be improved.

[0034] (Si: 0.90 mass% or more, 1.4 mass% or less) Like Mg, Si has the effect of improving the corrosion resistance and mechanical properties of the aluminum alloy forging 1a at room temperature. However, if excessive Si is added to the aluminum alloy, coarse primary Si crystal grains may crystallize, which may reduce the tensile strength of the aluminum alloy. By keeping the Si content within the above range, it is possible to improve the corrosion resistance and mechanical properties of the aluminum alloy forging 1a at room temperature while suppressing the crystallization of primary Si crystals.

[0035] (Mn: 0.35 mass% or more, 0.60 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. By ensuring that the Mn content is within the above range, the mechanical properties of the aluminum alloy forging 1a at room temperature can be improved.

[0036] (Fe: 0.15% by mass or more, 0.30% by mass or less) Fe improves the tensile strength of the aluminum alloy by crystallizing in the aluminum alloy as fine crystals including intermetallic compounds such as Al-Mn-Fe-Si, Al-Mn-Cr-Fe-Si, Al-Fe-Si, Al-Cu-Fe, and Al-Mn-Fe. By ensuring that the Fe content is within the above range, the mechanical properties of the aluminum alloy forging 1a at room temperature can be improved. The Fe / Mn relationship is less than 1.4. By making the Fe / Mn relationship less than 1.4, it is possible to suppress the crystallization of AlFeSi-based compounds having a size of 3.0 μm or more, and to increase the number density of AlMn-based compounds in the crystal grains.

[0037] (Cr: 0.050 mass% or more, 0.30 mass% or less) Cr acts to improve the tensile strength of the aluminum alloy by forming fine granular precipitates containing intermetallic compounds such as Al-Mn-Cr-Fe-Si and Al-Fe-Cr in the aluminum alloy. By ensuring that the Cr content is within the above range, the mechanical properties of the aluminum alloy forging 1a at room temperature can be improved.

[0038] (Ti: 0.01 mass% or more, 0.1 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 the aluminum alloy forging 1a, the toughness may be reduced. Therefore, the Ti content is set to 0.012% by mass or more and 0.035% by mass or less. The Ti content is preferably 0.015% by mass or more and 0.050% by mass or less.

[0039] (B: 0.001 mass% or more, 0.03 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 into the aluminum alloy forging 1a as inclusions. Furthermore, if a large amount of coarse crystals containing B are mixed into the final aluminum alloy product, the toughness may decrease. 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.

[0040] (Zr: 0.0010 mass% or more, 0.05 mass% or less) When Zr is 0.05% by mass or less, it precipitates in the form of AlZr and Al-(Ti,Zr), thereby suppressing recrystallization and contributing to improving the strength of the aluminum alloy forging 1a through precipitation strengthening. If the Zr content exceeds 0.050% by mass, it may crystallize as coarse Zr compounds, which may lead to a decrease in the corrosion resistance of the aluminum alloy forging 1a. For this reason, the Zr content is set to 0.050% by mass or less. Furthermore, in order to obtain the above-mentioned effects of suppressing recrystallization and improving the strength of the forging through precipitation strengthening, the Zr content is preferably 0.0010% by mass or more.

[0041] (Zn: 0.250% by mass or less) The Zn content should be 0.250% by mass or less. If the Zn content exceeds 0.250% by mass, MgZn2 is generated and precipitates from the Al matrix at grain boundaries, causing intergranular corrosion and reducing the corrosion resistance of the aluminum alloy forging. Therefore, it is preferable that the Zn content be 0.250% by mass or less, or that no Zn be included at all.

[0042] (unavoidable 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% by mass.

[0043] The central portion 2a in the longitudinal direction of the long portion 2 of the aluminum alloy forging 1a of this embodiment is the 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 the aluminum alloy forging 1a is manufactured by forging.

[0044] (Does not contain AIFeSi(Mn) compounds with an average particle size of 3.0 μm or more) The alloy structure in the central cross section of the aluminum alloy forging 1a should not contain AIFeSi(Mn)-based compounds with an average particle size of 3.0 μm or more, as the presence of AIFeSi(Mn)-based compounds with an average particle size of 3.0 μm or more may degrade the mechanical properties (tensile properties, fatigue properties, etc.).

[0045] (Impact value 10J / cm 2 (End) The central cross section of the aluminum alloy forged product 1a has an impact value of 10 J / cm at room temperature (20°C). 2 It has mechanical properties of 10 J / cm or more. 2 If it is less than this, the durability of the part may be reduced. In this specification, the term "impact value" refers to the Charpy impact strength measured in accordance with the "Charpy impact test method for metallic materials" specified in JIS Z2242-2005. The test specimen used for the measurement is a cylindrical specimen.

[0046] (The ratio of high-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less) In the central cross section of the aluminum alloy forging 1a, grain boundaries with a crystal orientation difference of 15° or more (high-angle grain boundaries) are an indicator of the degree of recrystallization in the long portion 2 of the aluminum alloy forging 1a. A ratio of these high-angle grain boundaries of 27% or less indicates that recrystallization is sufficiently suppressed. Sufficient suppression of recrystallization improves the mechanical properties of the long portion 2. The ratio of high-angle grain boundaries can be obtained from an EBSD image.

[0047] The aluminum alloy forging 1a of this embodiment, which has the above-described structure, is made of an aluminum alloy having the above-described alloy composition, and therefore recrystallization is unlikely to occur during the production of the forging. Therefore, excessively coarse crystal grains are unlikely to be generated. Furthermore, in the cross section of the central portion 2a of the long portion 2 of the aluminum alloy forging 1a of this embodiment, precipitates containing Mn and having a size of 0.5 μm or less are present within 2.0 μm, including the grain boundaries, at a number density of 4 / μm. 2 or more, and has an alloy structure in which the ratio of high-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less. Therefore, the central portion 2a of the long portion 2 has high tensile properties and fatigue properties, excellent toughness, and improved impact resistance.

[0048] The aluminum alloy forged product 1a of this embodiment has high strength and durability in the central portion 2a of the long portion 2, and is lightweight, so that it can be advantageously used as a suspension arm for a vehicle such as an automobile.

[0049] 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, 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.

[0050] FIG. 2 is a plan view of another example of an aluminum alloy forged product 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.

[0051] FIG. 3 is a plan view of yet another example of an aluminum alloy forged product 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.

[0052] In another embodiment of the aluminum alloy forging of the present invention, Cu is contained in a range of 0.25% by mass to 0.55% by mass, Mg is contained in a range of 0.60% by mass to 1.25% by mass, Si is contained in a range of 0.90% by mass to 1.4% by mass, Mn is contained in a range of 0.35% by mass to 0.60% by mass, Fe is contained in a range of 0.15% by mass to 0.30% by mass, Zn is contained in a range of 0.25% by mass, Cr is contained in a range of 0.050% by mass to 0.30% by mass, and Ti is contained in a range of 0.01% by mass to 0.05% by mass. 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 Fe to Mn (Fe / Mn) in mass ratio of 0.3 or more and 1.2 or less, and the balance consisting of Al and unavoidable impurities, wherein the number density of precipitates containing Mn within 2.0 μm including grain boundaries is 4 precipitates / μm 2 The ratio of high-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less. Furthermore, the aluminum alloy forged product of this embodiment has an impact strength of 10 J / cm at room temperature. 2 That is said to be the case. The mass ratio of Fe / Mn can be set to 0.3 or more and 1.0 or less, or 0.4 or more and 0.8 or less, or 0.4 or more and 0.7 or less.

[0053] For example, the size of precipitates containing Mn contained within 2.0 μm including the grain boundaries is 0.5 μm or less.

[0054] [Manufacturing method for aluminum alloy forged products] Next, a method for manufacturing an aluminum alloy forged product according to this embodiment will be described. The method for manufacturing an aluminum alloy forged product of 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.

[0055] (Molten metal forming process) The molten metal forming step is a step in which raw materials are melted to obtain a molten aluminum alloy having a composition adjusted. The composition of the molten aluminum alloy is adjusted to have an alloy composition containing Cu in the range of 0.25% by mass to 0.55% by mass, Mg in the range of 0.60% by mass to 1.25% by mass, Si in the range of 0.90% by mass to 1.4% by mass, Mn in the range of 0.35% by mass to 0.60% by mass, Fe in the range of 0.15% by mass to 0.30% 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 less than 1.4 in mass ratio, and the balance consisting of Al and unavoidable impurities. The Fe / Mn mass ratio may be adjusted to be 0.3 or more and 1.2 or less.

[0056] By carrying out the subsequent processes using molten aluminum alloy with the above composition, it is possible to obtain Al-Mg-Si aluminum alloy forgings that are resistant to recrystallization and have 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 electrorefining.

[0057] Molten aluminum alloys can be obtained by heating and melting an aluminum alloy. Alternatively, aluminum alloys can be formed by melting a mixture containing the elements or compounds containing two or more elements that are the raw materials for the aluminum alloy, in the ratios required to produce the desired aluminum alloy. For example, to control the grain size of the aluminum alloy produced during the casting process, Ti and B can be added as grain refiners, such as Al-Ti-B rods.

[0058] Alternatively, the molten aluminum alloy may be prepared by melting 10% or more of scrap aluminum alloys of the 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 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.

[0059] (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 cast product. The casting process can be carried out by, for example, horizontal continuous casting.

[0060] 4 and 5 show a horizontal continuous casting apparatus that can be used to produce the aluminum alloy cast product of this embodiment. 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 part of the horizontal continuous casting apparatus 10 near the cooling water cavity 24.

[0061] 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 (insulating member) 13 arranged between one end side 12a of the mold 12 and the molten metal receiving portion 11.

[0062] The molten metal receiving portion 11 is composed of a molten metal inlet portion 11a that receives the molten aluminum alloy M obtained in the molten metal forming step, a molten metal holding portion 11b, and an outlet portion 11c into the hollow portion 21 of the mold 12.

[0063] 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.

[0064] 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 body 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.

[0065] 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 synchronous cutter (not shown) that cuts the continuously drawn aluminum alloy rod B to a desired length be installed.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] If the elevation angle is less than 0°, the aluminum alloy rod B may encounter resistance at the other end 12b, which is the mold outlet, when being 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 may not make 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, a remelted skin may appear on the surface of the aluminum alloy rod B, or unsolidified molten aluminum alloy M may erupt from the end of the aluminum alloy rod B, which is undesirable because it may lead to casting problems.

[0071] 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 that does not have an axis or plane of symmetry, in addition to the circular shape of this embodiment.

[0072] 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.

[0073] 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. 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.

[0074] 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 stores 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 and the hollow portion 21 of the mold 12.

[0075] The cooling water cavity 24 is formed in the mold 12 outside the inner peripheral surface 21a of the hollow portion 21 and has an annular shape so as to surround the hollow portion 21, and cooling water W is supplied to the cavity 24 via a cooling water supply pipe .

[0076] The inner surface 21a of the mold 12 is cooled by the cooling water W contained in the cooling water cavity 24, thereby removing 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, and forming a solidified shell on the surface of the molten aluminum alloy M.

[0077] Furthermore, 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.

[0078] 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 21a 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 bar B from the cooling water spray passage 25. However, these may also be configured to be supplied by separate cooling water supply pipes.

[0079] 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 aluminum alloy rod B increases, which may cause cracks on the casting surface or tearing inside the mold, making casting unstable.

[0080] 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).

[0081] The cooling water cavity 24 is formed so that an inner bottom surface 24a of the mold 12 near the hollow portion 21 is parallel to the inner peripheral surface 21a of the hollow portion 21 of the mold 12.

[0082] 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 with respect to the inner peripheral surface 21a by more than 0° and up to 3°.

[0083] 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 faces the inner peripheral surface 21a of the hollow portion 21 of the mold 12, has a heat flux value per unit area of ​​10×10 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.

[0084] 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 circumferential 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, and 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.

[0085] In FIG. 4, molten aluminum alloy M in a molten metal receiving portion 11 is supplied through a refractory plate 13 to one end 12a of a mold 12, which is held so that the mold center axis C is substantially horizontal, and is forcibly cooled at the other end 12b of the mold 12 to become an aluminum alloy rod B.

[0086] 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).

[0087] The composition ratio of the cast aluminum alloy rod B can be confirmed, for example, by a method using a photoelectric emission spectrophotometer (eg, PDA-5500 manufactured by Shimadzu Corporation, Japan) as described in "JIS H 1305."

[0088] 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 peripheral 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.

[0089] The liquid lubricant may be a vegetable oil, such as rapeseed oil, castor oil, or salad oil, which are preferred because they have little adverse effect on the environment.

[0090] 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 and leak from the mold 12 due to insufficient lubrication. If the amount of supply is excessive, the excess may be mixed into the aluminum alloy rod B and cause internal defects.

[0091] 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), because a casting speed within this range makes the network structure of crystals formed by casting uniform and fine, which increases the resistance of the aluminum matrix to deformation at high temperatures and improves its high-temperature mechanical strength.

[0092] The amount of cooling water sprayed from the shower openings 25a of the cooling water spray passages 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 not solidify and leak from the mold 12. Also, the surface of the cast aluminum alloy bar B may remelt, forming an uneven structure that may remain as an internal defect. On the other hand, if the amount of cooling water is greater than this range, the mold 12 may lose too much heat, causing it to solidify prematurely.

[0093] 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 crystals may form 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.

[0094] 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 Over 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.

[0095] The cooling wall 27 of the mold 12 receives heat from the molten aluminum alloy M and exchanges this heat by cooling it with the cooling water W contained in the cooling water cavity 24. Regarding the state of this heat exchange, we 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 portion through which heat passes (in this embodiment, the cooling wall portion 27 of the mold 12) T1: low temperature of the location where 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: Length (mm) of the section where heat passes (in this embodiment, the thickness t of the cooling wall portion 27 of the mold 12)

[0096] Good results were obtained even when the amount of lubricant 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:

[0097] To achieve this heat flux range for the cooling wall 27 of the mold 12, the mold 12 should be formed so that the thickness t of the cooling wall 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 27 of the mold 12 should be in the range of 100 W / m K to 400 W / m K.

[0098] 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.

[0099] 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 2The 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.

[0100] 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 cut and remove carbides and the like from the surface of the aluminum alloy rod B, and allows the aluminum alloy rod B to be produced with a high yield.

[0101] The casting process for obtaining a cast product from the molten aluminum alloy M is not limited to the horizontal continuous casting method described above, 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.

[0102] 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 spout 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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 to be produced, and the method is suitable for use with rods with a diameter of 30 to 100 mm.

[0108] (Forging process) The forging process involves cutting the cast aluminum alloy casting to a predetermined size, heating the resulting forging material to a predetermined temperature, and then applying pressure in a press to mold it into a die. In this embodiment, forging is performed without the homogenization treatment that was previously performed after casting to remove segregation. Therefore, the segregation removal that was previously performed in the homogenization treatment must be performed by heating the material during forging, so heating must be performed at a temperature above 500°C and below the melting point. Then, forging is performed to obtain a forged product (e.g., an automobile suspension arm part). If the material heating temperature during forging is below 500°C, compounds such as AlFeSi and MgSi in the alloy structure remain in a segregated state, increasing deformation resistance and preventing sufficient processing, and cracks may occur. Furthermore, if the temperature exceeds the melting point, defects such as eutectic melting may easily occur.

[0109] (Solution treatment process) 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.

[0110] In this embodiment, the forged product is solution-treated 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 heating rate from room temperature to the above-mentioned treatment temperature is preferably 5.0°C / min or higher. If the treatment temperature is lower than 530°C, the solute elements may not be dissolved sufficiently. On the other hand, if the treatment temperature exceeds 560°C, the solute elements are more readily dissolved, but eutectic melting and recrystallization may occur. Furthermore, if the heating rate is lower than 5.0°C / min, coarse precipitation of MgSi may occur. On the other hand, if the treatment temperature is lower than 530°C, the solution treatment may not proceed, making it difficult to achieve high strength through aging precipitation.

[0111] (Quenching process) The quenching process is a process in which the forged product in the solid solution state obtained by the solution treatment process is rapidly cooled to form a supersaturated solid solution.

[0112] 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 comes into 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.

[0113] (Aging treatment process) The aging treatment process is a process 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.

[0114] In this embodiment, the forged product after the quenching process is heated to a temperature of 170°C or higher and 210°C or lower and held at that temperature for 0.5 hours or longer and 7 hours or shorter, thereby undergoing aging treatment. If the treatment temperature is lower than 170°C or the holding time is shorter than 0.5 hours, the Mg2Si-based precipitates that improve tensile strength may not grow sufficiently. On the other hand, if the treatment temperature exceeds 190°C or the holding time exceeds 7 hours, the Mg2Si-based precipitates may become too coarse, making it impossible to sufficiently improve tensile strength.

[0115] In another embodiment of the present invention, the method for producing an aluminum alloy forged product further includes, between the casting step and the forging step, a homogenization heat treatment step in which the aluminum alloy cast product is subjected to homogenization heat treatment by holding the aluminum alloy cast product at a temperature in the range of 370°C to 560°C for 2 hours to 10 hours. The method for manufacturing an aluminum alloy forged product of this embodiment differs from the method for manufacturing an aluminum alloy forged product of the above embodiment in that it includes a homogenization heat treatment step. [Example]

[0116] Next, specific examples of the present invention will be described, but the present invention is not particularly limited to these examples.

[0117] [Examples 1 to 8 and Comparative Examples 1 to 3] (Manufacturing of continuous casting products) First, an aluminum alloy was prepared having the alloy composition (the balance being aluminum) shown in Table 1 below. Using the prepared aluminum alloy, a continuous cast product having a circular cross section and a diameter of 82 mm was produced.

[0118] [Table 1]

[0119] (Manufacturing of aluminum alloy forged products) Next, the obtained continuous cast product was subjected to a homogenization heat treatment step (only Comparative Examples 1 to 3), 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 forged product 1a having the shape shown in Fig. 1. The conditions for the homogenization heat treatment step (only Comparative Examples 1 to 3), the forging step, the solution treatment step, the quenching treatment step, and the artificial aging treatment step are shown in Table 2 below.

[0120] [Table 2]

[0121] [evaluation] The following evaluations were carried out 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 3 obtained as described above. The evaluation results of the central portion 2a of the long portion 2 are shown in Table 3 below.

[0122] <fe mn> The Fe / Mn ratio was adjusted to 0.3 or more and 1.2 or less in the examples, and to more than 1.2 in the comparative examples. "Good": Between 0.3 and 1.2. "×": Over 1.2.

[0123] <Conductivity (%IACS)> The electrical conductivity of the obtained continuous cast product was measured at room temperature. (Judgment criteria) "Good": 25% IACS or more and 35% IACS or less. "×": Less than 25% IACS or more than 35% IACS.

[0124] <Rockwell hardness (HRF)> The Rockwell hardness (HRF) of the obtained continuous cast product was measured in accordance with JIS Z2245:2016 "Rockwell hardness test - Test method." (Judgment criteria) "〇": Between 62 and 82. "×": Less than 62 or more than 82.

[0125] <Mechanical property (impact property) evaluation> The central portion 2a of the long portion 2 of the aluminum alloy forged product 1a was cut as shown in Figure 7 to obtain a rectangular column for preparing a test specimen for evaluating mechanical properties (impact properties). The obtained rectangular column was processed to prepare a cylindrical test specimen for evaluating mechanical properties as shown in Figure 8. The parallel portion diameter A of the test specimen for evaluating mechanical properties was 8.0 mm, and the gauge length G was 30.0 mm. The test specimen for evaluating mechanical properties was subjected to a Charpy impact test at room temperature (25°C) in accordance with JIS Z2242 to measure the impact value. The obtained impact value was evaluated based on the following criteria. (Judgment criteria) "Good": Impact value is 10J / cm at room temperature 2 That's all. "X": Impact value is 10J / cm at room temperature 2 is less than.

[0126] <Refinement evaluation, recrystallization and crystal coarsening evaluation> The central portion 2a of the long portion 2 of the aluminum alloy forging 1a was cut perpendicular to the surface of the central portion 2a to obtain a plate (2 mm thick) for preparing a test piece for refinement evaluation. The obtained plate was cut into a 7 mm square to obtain a 7 mm × 7 mm × 2 mm thick test piece for refinement evaluation. The surface (cross section of the central portion 2a) of the obtained test piece for refinement evaluation was measured using SEM-EBSD (scanning electron microscope-electron backscatter diffraction) to measure the number of AlFeSi-based compounds of 3.0 μm or more and the ratio of high-angle grain boundaries with a crystal orientation difference of 15° or more. The number of AlFeSi-based compounds of 3.0 μm or more and the ratio of high-angle grain boundaries were evaluated based on the following criteria to evaluate the refinement of crystal grains and the recrystallization / crystal coarsening. The SEM-EBSD measurement conditions were an acceleration voltage of 15 kV, a measurement pitch of 0.5 μm / px, and an analysis area of ​​500 × 500 μm. 2 The grain boundary definition angle was set to 15°. (Judgment criteria) (Criteria for determining the number of AlFeSi compounds of 3.0 μm or larger) "O" - if none (0). "×"...if present. (Criteria for determining the ratio of high-angle grain boundaries) "O" is 27% or less. "×": Over 27%.

[0127] <Method for measuring the number density of precipitates containing Mn in aluminum alloy forgings> Furthermore, for each aluminum alloy forging, a field emission scanning electron microscope (FE-SEM) was used to measure the number density of precipitates containing Mn within 2.0 μm, including the grain boundaries. A sample piece for microstructure observation measuring approximately 10 mm x 10 mm x 10 mm was cut from the center 2a of the long portion 2 of the aluminum alloy forging 1a, and this sample piece was polished using a cross-section polisher. FE-SEM (field emission scanning electron microscope) photographs of the polished sample pieces were then taken, and the field of view area in this SEM photograph was 1.5815 mm. 2 Within this range, the number density of precipitates containing Mn within 2.0 μm including the grain boundaries was determined, and the number density was evaluated according to the following criteria. (Number density criteria) "O"...4 pieces / μm 2 That's all. "×"...4 pieces / μm 2 The following is the result.

[0128] <Overall rating> Seven evaluation results, including Fe / Mn ratio, electrical conductivity, Rockwell hardness, impact properties, the number of AlFeSi compounds of 3.0 μm or larger, the number density of AlMn compounds, and the ratio of high-angle grain boundaries with a crystal orientation misorientation of 15° or larger, were evaluated based on the following criteria. (Judgment criteria) "O" - All seven ratings are "O". "X": One or more of the seven ratings are "X".

[0129] [Table 3] [Explanation of symbols]

[0130] 10...Horizontal continuous casting equipment 11...Tundish 11a...Molten metal inlet 11b...Molten metal holding section 11c...Outflow part 12...Mold 12a...One end side 12b…Other end side 13... Refractory plate (heat insulating member) 13a…Pouring passage 21...Hollow part 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 B: Aluminum alloy rod M...molten alloy W...cooling water 100...Aluminum alloy forgings< / fe>

Claims

1. 1. An aluminum alloy forging comprising an aluminum alloy having an alloy composition containing Cu in the range of 0.25 mass% to 0.55 mass%, Mg in the range of 0.60 mass% to 1.25 mass%, Si in the range of 0.90 mass% to 1.4 mass%, Mn in the range of 0.35 mass% to 0.60 mass%, Fe in the range of 0.15 mass% to 0.30 mass%, Zn in the range of 0.25 mass% or less, Cr in the range of 0.050 mass% to 0.30 mass%, Ti in the range of 0.01 mass% to 0.1 mass%, B in the range of 0.0010 mass% to 0.030 mass%, Zr in the range of 0.0010 mass% to 0.050 mass%, and the balance consisting of Al and unavoidable impurities, wherein the number density of precipitates containing Mn within 2.0 μm including grain boundaries is 4 precipitates / μm ２ or more, the ratio of high-angle grain boundaries with a crystal orientation difference of 15° or more is 27% or less, and the impact value at room temperature is 10 J / cm ２ The above-mentioned method for producing an aluminum alloy forged product is as follows: a molten metal forming step for obtaining a molten metal of the aluminum alloy; a casting step of obtaining a casting by casting the obtained molten metal; a forging step in which the casting is heated at a temperature of 500°C to the melting point and subjected to plastic working to obtain a forged product; a solution treatment step in which the obtained forged product is heated from 20°C to 500°C at a heating rate of 5.0°C / min or more and then held at 530 to 560°C for 0.3 to 3 hours; a quenching step in which all surfaces of the forged product are 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 and not more than 40 minutes; an aging treatment step in which the forged product that has undergone the quenching treatment step is heated at a temperature of 180°C to 220°C for 0.5 hours to 8 hours to undergo aging treatment; A method for manufacturing an aluminum alloy forged product, which does not include a homogenization heat treatment step in which homogenization heat treatment is performed between the casting step and the forging step.

2. 2. The method for producing an aluminum alloy forged product according to claim 1, wherein the size of the precipitates is 0.5 μm or less.

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