Material for aluminum alloy forging, aluminum alloy forged product and method for producing the same

Abstract

To provide a material for aluminum alloy forging with superior mechanical properties at room temperature, an aluminum alloy forged product and a method for producing the same.SOLUTION: An aluminum alloy forged product has an alloy composition where the ratio (Fe / Mn) of Fe content to Mn content is from 0.3 to 1.2 in mass ratio, with the balance being Al and unavoidable impurities. When the crystal grain size of the longitudinal center of a long part is defined as S1 and the crystal grain size of the longitudinal boundary between the long part and a connection part is defined as S2, the value of S1 / S2 ranges from 0.7 to 1.0.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an aluminum alloy material for forging, an aluminum alloy forging, and a method for producing the same. [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, high-tensile steel has traditionally been used for automobile suspension and bumper parts, but in recent years high-strength aluminum alloy materials have come to be used.

[0003] In addition, while iron-based materials have been used exclusively for automobile parts, particularly long parts such as suspension arms, in recent years, they have been increasingly replaced by aluminum materials or aluminum alloy materials, mainly 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, especially A6061, are widely used as aluminum alloy materials. 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 materials as processing materials.

[0005] Recently, due to the need to reduce costs, suspension parts have begun to be put into practical use in which the cast parts are used as they are without extrusion, and then subjected to 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] In recent years, there has been a trend toward making automobiles lighter in order to reduce CO2 emissions, and the demand for aluminum is on the rise. However, as an alternative to steel, aluminum needs to be stronger. On the other hand, one method of increasing the strength of aluminum is known to be suppressing the formation of recrystallized structures during the plastic processing and solution treatment processes, and refining the grain size.

[0008] 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 a sufficiently high strength. Therefore, some alloys contain zirconium (Zr) to prevent recrystallization and prevent the generation of coarse recrystallized grains (see, for example, the above-mentioned Patent Documents 1 and 2).

[0009] Although the addition of Zr is effective in preventing recrystallization, it has the following problems. (1) The addition of Zr weakens the grain refining effect of the Al-Ti-B alloy, coarsening the grains of the casting itself, and leads to a decrease in the strength of the processed product (forged product) after plastic working. (2) The effect of refining the crystal grains of the casting itself is weakened, so that the casting is more likely to crack, has more internal defects, and reduces the yield. (3) Zr forms compounds with Al-Ti-B alloys. These compounds accumulate at the bottom of the furnace in which the molten alloy is stored, contaminating the furnace. In addition, these compounds crystallize out as coarse particles in the resulting castings, reducing their strength.

[0010] Thus, although the addition of Zr is effective in preventing recrystallization, it is difficult to maintain the stability of strength. The present invention has been made in consideration 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 manufacturing method thereof. [Means for solving the problem]

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

[0012] (1) Cu in the range of 0.30 mass% or more and 1.0 mass% or less, Mg in the range of 0.80 mass% or more and 1.8 mass% or less, Si in the range of 0.90 mass% or more and 1.9 mass% or less, Mn in the range of 0.30 mass% or more and 1.2 mass% or less, Fe in the range of 0.20 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 an aluminum alloy forging material having an alloy composition containing, in a range of 0.0010% by mass or more and 0.030% by mass or less, B in a 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) of less than 1.4 in terms of mass ratio, with the balance being Al and unavoidable impurities, and wherein the number density of precipitates containing Mn within a range of 1.5 μm including the grain boundaries in the alloy structure after forging is 4 precipitates / μm 2 The following are aluminum alloy forging materials.

[0013] (2) 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 an aluminum alloy forging material having an alloy composition containing, in the range of 0.0010% by mass or more and 0.030% 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) being 0.3 to 1.2 in mass ratio, with the balance being Al and unavoidable impurities, and wherein the number density of precipitates containing Mn within a range of 1.5 μm including the grain boundaries in the alloy structure after forging is 4 precipitates / μm 2 The following are aluminum alloy forging materials.

[0014] (3) 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 0.61 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 an aluminum alloy forging material having an alloy composition containing, in the range of 0.0010% by mass or more and 0.030% 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) being 0.3 to 1.2 in mass ratio, with the balance being Al and unavoidable impurities, and wherein the number density of precipitates containing Mn within a range of 1.5 μm including the grain boundaries in the alloy structure after forging is 4 precipitates / μm 2 The following are aluminum alloy forging materials.

[0015] (4) The aluminum alloy forging material according to any one of (1) to (3) above, wherein the size of the precipitates containing Mn is 0.2 μm or less.

[0016] (5) An aluminum alloy forging having a long portion and a connecting portion, comprising: Cu in the range of 0.30 mass% to 1.0 mass%, Mg in the range of 0.80 mass% to 1.8 mass%, Si in the range of 0.90 mass% to 1.9 mass%, Mn in the range of 0.30 mass% to 1.2 mass%, Fe in the range of 0.20 mass% to 0.65 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 0.20 mass% to 0.65 mass%, 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 0.20 mass% to 0.65 mass%. an aluminum alloy forging having an aluminum alloy composition containing 0.0010% by 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, a ratio of the Fe content to the Mn content (Fe / Mn) being less than 1.4 by mass, with the remainder being an alloy composition consisting of Al and unavoidable impurities, wherein S1 is a crystal grain size at a central portion in the longitudinal direction of the long portion, and S2 is a crystal grain size at a boundary portion in the longitudinal direction between the long portion and the connecting portion, and the value of S1 / S2 is in the range of 0.7 or more and 1.0 or less.

[0017] (6) An aluminum alloy forging having a long portion and a connecting portion, comprising: 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; 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. an aluminum alloy forging comprising: at least one long portion having a grain size S1 within a range of 0.0010% by mass or more and 0.030% by mass or less; at least one Zr within a 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 being 0.3 to 1.2 in mass ratio, with the balance being Al and unavoidable impurities; and wherein, when a grain size S1 is a grain size S1 at a center portion in the longitudinal direction of the long portion and a grain size S2 is a grain size S2 at a boundary portion in the longitudinal direction between the long portion and the connecting portion, the value of S1 / S2 is in the range of 0.7 to 1.0.

[0018] (7) An aluminum alloy forging having a long portion and a connecting portion, comprising: 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 0.61% 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; 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. an aluminum alloy forging comprising: at least one long portion having a grain size S1 within a range of 0.0010% by mass or more and 0.030% by mass or less; at least one Zr within a 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 being 0.3 to 1.2 in mass ratio, with the balance being Al and unavoidable impurities; and wherein, when a grain size S1 is a grain size S1 at a center portion in the longitudinal direction of the long portion and a grain size S2 is a grain size S2 at a boundary portion in the longitudinal direction between the long portion and the connecting portion, the value of S1 / S2 is in the range of 0.7 to 1.0.

[0019] (8) An aluminum alloy forged product according to any one of (5) to (7) above, which is used for a suspension arm.

[0020] (9) A method for producing an aluminum alloy forging according to any one of (5) to (7) above, comprising: a molten alloy forming step of forming an aluminum alloy molten having the same alloy composition as the aluminum alloy forging; a casting step of cooling and solidifying the aluminum alloy molten obtained in the molten alloy forming step to form an aluminum alloy casting; a forging step of forging the aluminum alloy casting obtained in the casting step at a heating temperature of 450°C or higher and 560°C or lower; and a forging step of forging the forging obtained in the forging step. A method for manufacturing an aluminum alloy forged product, comprising: a solution treatment step in which a solution treatment is performed at a treatment temperature of 530°C to 560°C and held for 0.3 to 3 hours; a quenching treatment step in which the entire surface of the forged product is brought into contact with quenching water within a range of 5 to 60 seconds after completion of the solution treatment step, and quenched in a water tank for 1 to 30 minutes; and an aging treatment step in which the forged product after the quenching treatment step is subjected to aging treatment at a heating temperature of 170°C to 210°C for 0.5 to 7 hours.

[0021] (10) The method for producing an aluminum alloy forged product according to (9) above, further comprising a homogenization heat treatment step between the casting step and the forging 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. Effect of the Invention

[0022] According to the present invention, it is possible to provide an aluminum alloy material for forging, an aluminum alloy forging, and a method for producing the same, which have excellent mechanical properties at room temperature. [Brief description of the drawings]

[0023] [Figure 1] 1 is a perspective view showing an example of an aluminum alloy forging according to an embodiment of the present invention. FIG. [Diagram 2] FIG. 4 is a plan view showing another example of an aluminum alloy forged product according to an embodiment of the present invention. [Diagram 3] FIG. 2 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. [Diagram 5] 5 is an enlarged cross-sectional view of a main portion near a cooling water cavity of the horizontal continuous casting machine shown in FIG. 4. [Figure 6] FIG. 2 is an explanatory diagram illustrating a heat flux in a cooling wall portion of a horizontal continuous casting apparatus. [Figure 7A] FIG. 2 is a plan view showing the positions at which the center and boundary portions were sampled from the aluminum alloy forging obtained in this example for preparing test pieces for evaluating mechanical properties. [Figure 7B] FIG. 2 is a plan view showing a test piece for evaluating mechanical properties produced in this example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, the 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 parts in an enlarged scale for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of each component may not necessarily be the same as in reality. In addition, the materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not necessarily limited to them, and may be appropriately modified and implemented within a range that does not change the effects of the present invention.

[0025] [Aluminum alloy materials] First, the aluminum alloy material of the present invention will be described.

[0026] In one embodiment of the present invention, Cu is in the range of 0.30 mass% or more and 1.0 mass% or less, Mg is in the range of 0.80 mass% or more and 1.8 mass% or less, Si is in the range of 0.90 mass% or more and 1.9 mass% or less, Mn is in the range of 0.30 mass% or more and 1.2 mass% or less, Fe is in the range of 0.20 mass% or more and 0.65 mass% or less, Zn is in the range of 0.25 mass% or less, Cr is in the range of 0.050 mass% or more and 0.30 mass% or less, Ti is in the range of 0.01 mass% or more and 0.1 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 in mass ratio, with the balance being Al and unavoidable impurities, and the number density of precipitates containing Mn within a range of 1.5 μm including grain boundaries in the alloy structure after forging is 4 precipitates / μm 2 It is stated as follows.

[0027] In another embodiment of the present invention, an aluminum alloy material 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, Ti in the range of 0.01 mass% or less, and an aluminum alloy forging material having an alloy composition containing at least one of 0.01% by mass and 0.1% by mass or less, at least one of 0.0010% by mass and 0.030% by mass or less, at least one of 0.0010% by mass and 0.050% by mass or less, a ratio of Fe to Mn (Fe / Mn) being at least 0.3 and at most 1.2 by mass, with the balance being Al and unavoidable impurities, and wherein the number density of precipitates containing Mn within a range of 1.5 μm including grain boundaries in the alloy structure after forging is 4 precipitates / μm 2 It is stated as follows.

[0028] Moreover, it is sufficient if the size of the precipitates containing Mn described above is 0.2 μm or less.

[0029] The aluminum alloy material of this embodiment corresponds to a 6000 series aluminum alloy in that it contains Mg and Si.

[0030] (In the forged alloy structure, the number density of precipitates containing Mn within a range of 1.5 μm including the grain boundary is 4 / μm 2 below) The number density of precipitates containing Mn within a 1.5 μm range including the grain boundaries is 4 / μm 2 If the number density of precipitates containing Mn within a range of 1.5 μm including the grain boundary in the alloy structure after forging is more than 4 / μm, the workability may decrease due to the decrease in toughness and impact resistance caused by the increase in deformation resistance. 2 The range is as follows:

[0031] In yet another embodiment of the aluminum alloy material of the present invention, Cu is in the range of 0.25 mass% or more and 0.55 mass% or less, Mg is in the range of 0.85 mass% or more and 1.25 mass% or less, Si is in the range of 1.02 mass% or more and 1.4 mass% or less, Mn is in the range of 0.61 mass% or more and 1.0 mass% or less, Fe is in the range of 0.32 mass% or more and 0.65 mass% or less, Zn is in the range of 0.25 mass% or less, Cr is in the range of 0.050 mass% or more and 0.30 mass% or less, Ti is 0.01 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 the Fe content to the Mn content (Fe / Mn) is 0.3 to 1.2 in mass ratio, with the balance being Al and unavoidable impurities, and the number density of precipitates containing Mn within a range of 1.5 μm including grain boundaries in the alloy structure after forging is 4 precipitates / μm 2 It is stated as follows.

[0032] [Aluminum alloy forgings] Next, 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 forged product 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. The aluminum alloy forging 1a having this shape can be used, for example, as an I-shaped suspension arm.

[0033] The aluminum alloy forged product 1a has an aluminum alloy composition containing Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.85% by mass or more and 1.25% by mass or less, Si in the range of 1.02% by mass or more and 1.4% by mass or less, Mn in the range of 0.55% by mass or more and 1.0% by mass or less, Fe in the range of 0.32% by mass or more and 0.65% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% 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, and a ratio of the Fe content to the Mn content, Fe / Mn, is 0.3 to 1.2 in mass ratio, with the balance being Al and unavoidable impurities. In addition, when the crystal grain size in the longitudinal center portion 2a of the long portion 2 of the aluminum alloy forged product 1a is S1 and the crystal grain size in the longitudinal boundary portion between the long portion 2 and the connecting portion 4 is S2, the value of S1 / S2 is 0.7 or more and 1.0 or less.

[0034] The aluminum alloy that is the material of the aluminum alloy forged product 1a of this embodiment corresponds to a 6000 series aluminum alloy in that it contains Mg and Si.

[0035] (Cu: 0.25 mass% or more and 0.55 mass% or less) Cu has the effect of finely dispersing Mg-Si compounds in the aluminum alloy and the effect of improving the tensile strength of the aluminum alloy by precipitating as Al-Cu-Mg-Si compounds including the Q phase. By keeping the Cu content within the above range, the mechanical properties of the aluminum alloy forging 1a at room temperature can be improved.

[0036] (Mg: 0.85 mass% or more and 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 parent phase or 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 CuAl2 phase improves the corrosion resistance of the aluminum alloy forging 1a. By containing Mg 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.

[0037] (Si: 1.02 mass% or more and 1.4 mass% or less) Like Mg, Si has the effect of improving the mechanical properties and corrosion resistance of the aluminum alloy forging 1a at room temperature. However, if excessive Si is added to the aluminum alloy, coarse primary crystal Si 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 mechanical properties and corrosion resistance of the aluminum alloy forging 1a at room temperature while suppressing the crystallization of primary crystal Si.

[0038] (Mn: 0.55 mass% or more and 1.0 mass% or less) Mn has the effect of improving the tensile strength of the aluminum alloy by forming fine granular precipitates including intermetallic compounds such as Al-Mn-Fe-Si and Al-Mn-Cr-Fe-Si in the aluminum alloy. By keeping the Mn content within the above range, the mechanical properties of the aluminum alloy forging 1a at room temperature can be improved.

[0039] (Fe: 0.32 mass% or more, 0.65 mass% or less) Fe acts to improve 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 keeping the Fe content within the above range, the mechanical properties of the aluminum alloy forging 1a at room temperature can be improved. The Fe / Mn relationship is 0.3 or more and 1.2 or less. By keeping the Fe / Mn relationship at 1.2 or less, crystallization of AlFeSi-based compounds having sizes of 2.0 μm or more can be suppressed, and mechanical properties can be improved.

[0040] (Cr: 0.050 mass% or more, 0.30 mass% or less) Cr has the effect of improving 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 keeping the Cr content within the above range, the mechanical properties of the aluminum alloy forging 1a at room temperature can be improved.

[0041] (Ti: 0.01 mass% or more, 0.1 mass% or less) Ti has the effect of refining the crystal grains of the aluminum alloy and improving the wrought workability. If the Ti content is less than 0.01% by mass, the effect of refining the crystal grains may not be sufficiently obtained. On the other hand, if the Ti content exceeds 0.1% by mass, coarse crystallized products may be formed, and the wrought workability may be reduced. In addition, if a large amount of coarse crystallized products containing Ti are mixed into the aluminum alloy forged product 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.

[0042] (B: 0.0010 mass% or more, 0.030 mass% or less) B has the effect of refining the crystal grains of the aluminum alloy and improving the wrought workability. By adding B to the aluminum alloy together with Ti described above, the effect of refining the crystal grains is improved. If the content of B is less than 0.0010% by mass, the effect of refining the crystal grains may not be sufficiently obtained. On the other hand, if the content of B exceeds 0.030% by mass, coarse crystallized products may be formed and may be mixed into the aluminum alloy forged product 1a as inclusions. In addition, if a large amount of coarse crystallized products containing B are mixed into the final product of the aluminum alloy, the toughness may decrease. Therefore, the content of B is set to 0.0010% by mass or more and 0.030% by mass. The content of B is preferably 0.0050% by mass or more and 0.025% by mass.

[0043] (Zr: 0.0010 mass% or more, 0.05 mass% or less) When the Zr content is 0.05% by mass or less, it precipitates in the form of Al3Zr and Al-(Ti,Zr), which contributes to improving the strength of the aluminum alloy forged product 1a by suppressing recrystallization and precipitation strengthening. When the Zr content exceeds 0.050% by mass, it crystallizes as coarse Zr compounds, which may lead to a decrease in the corrosion resistance of the aluminum alloy forged product 1a. For this reason, the Zr content is set to 0.050% by mass or less. In order to obtain the above-mentioned recrystallization suppression effect and the effect of improving the strength of the forged product by precipitation strengthening, the Zr content is preferably 0.0010% by mass or more.

[0044] (Zn: 0.250% by mass or less) The Zn content may 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 to the grain boundaries, causing intergranular corrosion and leading to a decrease in the corrosion resistance of the aluminum alloy forging. For this reason, it is preferable that the Zn content is 0.250% by mass or less, or that it is not contained at all.

[0045] (Inevitable impurities) Inevitable impurities are impurities that are inevitably mixed into the aluminum alloy from the raw materials or manufacturing process. Examples of inevitable impurities include Ni, Sn, Be, etc. The content of these inevitable impurities is preferably not more than 0.1 mass%.

[0046] The central portion 2a in the longitudinal direction of the long portion 2 of the aluminum alloy forging 1a is a portion to which the maximum principal stress is applied when the long aluminum alloy forging 1a is used as, for example, a suspension arm of a vehicle. The boundary portion 2b in the longitudinal direction between the long portion 2 and the connecting portion 4 of the aluminum alloy forging 1a is a portion to which the minimum principal stress is applied when the aluminum alloy forging 1a is used as, for example, a suspension arm of a vehicle. Note that, although the boundary portion 2b in this embodiment indicates the longitudinal boundary portion 2b between the long portion 2 and one connecting portion 4a, it may also be the longitudinal boundary portion between the long portion 2 and the other connecting portion 4b.

[0047] The grain size is an index of the degree of variation in grain size of the aluminum alloy forged product 1a. The closer the grain size ratio is to 1, the smaller the variation. When the grain size in the longitudinal center portion 2a of the long portion 2 of the aluminum alloy forged product 1a is S1 and the grain size in the longitudinal boundary portion 2b between the long portion 2 and the connecting portion 4 is S2, the value of S1 / S2 is 0.7 or more and 1.0 or less.

[0048] The aluminum alloy forged product 1a of this embodiment configured as described above is made of an aluminum alloy having the above-mentioned alloy composition, and when the crystal grain size in the longitudinal center portion 2a of the long portion 2 of the aluminum alloy forged product 1a is S1 and the crystal grain size in the longitudinal boundary portion 2b between the long portion 2 and the connecting portion 4 is S2, the value of S1 / S2 is 0.7 or more and 1.0 or less, and the aluminum alloy forged product 1a has a strength comparable to that of iron-based metallic materials.

[0049] The aluminum alloy forged product 1a of this embodiment has a small crystal grain size ratio between the longitudinal central portion 2a of the long portion 2 and the longitudinal boundary portion 2b between the long portion 2 and the connecting portion 4, and is lightweight, and therefore can be advantageously used as a suspension arm for vehicles such as automobiles.

[0050] In the aluminum alloy forging 1a of this embodiment shown in FIG. 1, one connecting portion 4a is cylindrical with a relatively small diameter, one connecting portion 4b is cylindrical with a relatively large diameter, and the long portion 2 is shaped so that its width increases from the end side of one connecting portion 4a toward the end side of the other connecting portion 4b, but the shape of the aluminum alloy forging 1a is not limited thereto. 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. The long portion 2 may also be curved. Three or more connecting portions 4 may be formed.

[0051] 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 forged product 1b shown in Fig. 2 has three connecting portions 4c, 4d, and 4e. The connecting portion 4c and the connecting portion 4d are connected by a long portion 2, and the connecting portion 4d and the connecting portion 4e are connected by a short portion 5 that is relatively shorter than the long portion 2. This aluminum alloy forged product 1b can be used, for example, as an L-shaped suspension arm.

[0052] FIG. 3 is a plan view of yet another example of an aluminum alloy forged product according to an embodiment of the present invention. An aluminum alloy forging 1c shown in Fig. 3 has three connecting portions 4f, 4g, and 4h. The connecting portions 4f and 4g, and the connecting portions 4f and 4h are each connected by a long portion 2. This aluminum alloy forging 1b can be used as, for example, an A-type suspension arm.

[0053] An aluminum alloy forging according to another embodiment of the present invention is an aluminum alloy forging having a long portion and a connecting portion, and contains Cu in the range of 0.30 mass% or more and 1.0 mass% or less, Mg in the range of 0.80 mass% or more and 1.8 mass% or less, Si in the range of 0.90 mass% or more and 1.9 mass% or less, Mn in the range of 0.30 mass% or more and 1.2 mass% or less, Fe in the range of 0.20 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 less, and the aluminum alloy composition has an alloy composition containing Al and unavoidable impurities, and the aluminum alloy contains at least 0.1% by mass of C, at least 0.0010% by mass of B, at least 0.030% by mass of B, at least 0.0010% by mass of Zr, and a ratio of the Fe content to the Mn content, Fe / Mn, is less than 1.4 in mass ratio, with the remainder being composed of Al and unavoidable impurities, and the value of S1 / S2 is in the range of 0.7 to 1.0, where S1 is the crystal grain size at the center in the longitudinal direction of the long portion and S2 is the crystal grain size at the longitudinal boundary between the long portion and the connecting portion.

[0054] An aluminum alloy forging according to still another embodiment of the present invention is an aluminum alloy forging having a long portion and a connecting portion, and the aluminum alloy forging 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 0.61 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 0.050 mass% or more and 0.050 mass% or less, and Cu in the range of 0.050 mass% or more and 0.050 mass% or less. The alloy contains 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, the ratio of the Fe content to the Mn content Fe / Mn is 0.3 to 1.2 in mass ratio, and the remainder has an alloy composition consisting of Al and unavoidable impurities, and when the crystal grain size at the longitudinal center of the long portion is S1 and the crystal grain size at the longitudinal boundary between the long portion and the connecting portion is S2, the value of S1 / S2 is in the range of 0.7 to 1.0.

[0055] [Manufacturing method for aluminum alloy forgings] Next, a method for manufacturing an aluminum alloy forged product according to this embodiment will be described. The manufacturing method of the aluminum alloy forged product of this embodiment includes, for example, a molten metal forming step, a casting step, a homogenizing heat treatment step, a forging step, a solution treatment step, a quenching treatment step, and an aging treatment step. Among these steps, the solution treatment step may be performed as necessary and is not an essential step.

[0056] (Molten metal formation 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 the same as that of the aluminum alloy forging. That is, a molten 6000 series aluminum alloy is obtained by adjusting the alloy composition to contain 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, B in the range of 0.0010 mass% or more and 0.030 mass% or less, and Zr in the range of 0.0010 mass% or more and 0.050 mass% or less, a ratio of the Fe content to the Mn content (Fe / Mn) being 0.3 to 1.2 in mass ratio, with the remainder being Al and unavoidable impurities. By carrying out the subsequent steps using molten aluminum alloy with the above composition, it is possible to obtain Al-Mg-Si aluminum alloy forgings that are less prone to recrystallization and have excellent mechanical properties at room temperature. Note that virgin aluminum ingot is aluminum with a concentration of 99% or more that is obtained by subjecting alumina produced from minerals to electrolysis, a process known as electrolytic refining.

[0057] The molten aluminum alloy can be obtained by heating and melting the aluminum alloy. Alternatively, the aluminum alloy may be formed by melting a mixture containing the elements or compounds containing two or more elements as raw materials of the aluminum alloy in a ratio that produces the target aluminum alloy. For example, Ti or B may be mixed as a grain refiner such as an Al-Ti-B rod in order to control the grain size of the aluminum alloy produced in the casting process.

[0058] Alternatively, the raw material of the molten aluminum alloy may be 10% or more of scrap material of 1000 series, 2000 series, 3000 series, 4000 series, 5000 series, 6000 series, or 7000 series aluminum alloy, with the remainder being new aluminum ingots and the above-mentioned additive elements, and the molten aluminum alloy may be obtained by melting these to adjust the composition. In this case, it is possible to obtain an Al-Mg-Si-based aluminum alloy forging that is less prone to recrystallization and has excellent mechanical properties at room temperature. Note that the new aluminum ingot is aluminum with a purity of, for example, 99% or more, which is obtained by subjecting alumina produced from minerals to electrolysis, which is called 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, for example, by horizontal continuous casting.

[0060] Here, a horizontal continuous casting apparatus that can be used for producing the aluminum alloy cast product of this embodiment is shown in FIG. 4 and 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.

[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 for receiving the molten aluminum alloy M obtained in the molten metal forming step described above, 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 cooled and solidified by a cooling device 23, which will be described later, and is drawn out from the other end side 12b of the mold 12 as an aluminum alloy rod B, which is a solidified ingot.

[0065] A pull-out drive device (not shown) for pulling out the cast aluminum alloy rod B at a constant speed may be provided at the other end 12b of the mold 12. It is also preferable that a synchronous cutter (not shown) for cutting the continuously pulled aluminum alloy rod B to a desired length is also provided.

[0066] The refractory plate 13 is a member that blocks heat transfer between the molten metal receptacle 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 of multiple layers made of different materials.

[0067] In this embodiment, the mold 12 is a hollow cylindrical member, and is 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 optimal combination in terms of thermal conductivity, heat resistance, and mechanical strength.

[0068] The hollow portion 21 of the mold 12 is formed with a circular cross section in order to cast the aluminum alloy rod B into a cylindrical 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 central axis C of the mold toward the casting direction of the aluminum alloy bar B (see FIG. 4). That is, the inner peripheral surface 21a is tapered so as to open in a cone shape toward the casting direction. The angle of the 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 it is pulled out of the mold 12, which may make casting difficult. On the other hand, if the elevation angle exceeds 3°, the contact of the inner peripheral surface 21a with the molten aluminum alloy M may become insufficient, and the effect of removing heat from the molten aluminum alloy M and its solidified shell to the mold 12 may decrease, which may cause insufficient solidification. As a result, a remelted skin may be formed 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 not preferable.

[0071] In addition, 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 polygon, a semicircle, an ellipse, or an irregular cross-sectional shape having no axis or plane of symmetry, other than the circular shape of this embodiment.

[0072] A fluid supply pipe 22 is disposed at one end side 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 may be any one or more types of lubricating fluid selected from a gas lubricant and a liquid lubricant. When both a gas lubricant and a liquid lubricant are supplied, 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 pumped through the lubricating fluid supply port 22a and supplied to the inner circumferential surface 21a of the mold 12. The liquid lubricant may be heated to decompose into gas and supplied to the inner circumferential surface 21a of the mold 12. Alternatively, a porous material may be disposed in the lubricating fluid 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 accommodates cooling water W for cooling the inner circumferential surface 21a of the hollow portion 21 of the mold 12, and a cooling water injection passage 25 that connects the cooling water cavity 24 and the hollow portion 21 of the mold 12.

[0075] The cooling water cavity 24 is formed in the mold 12 outside the inner circumferential 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 thereto via a cooling water supply pipe .

[0076] As the inner surface 21a of the mold 12 is cooled by the cooling water W contained in the cooling water cavity 24, the heat of the molten aluminum alloy M filling the hollow portion 21 of the mold 12 is removed from the surface in contact with the inner surface 21a of the mold 12, and a solidified shell is formed on the surface of the molten aluminum alloy M.

[0077] The cooling water jet passage 25 sprays cooling water W directly from a shower opening 25a facing the hollow portion 21 toward the aluminum alloy rod B at the other end side 12b of the mold 12 to cool the aluminum alloy rod B. The vertical cross-sectional shape of the cooling water jet passage 25 may be, for example, a semicircular, pear-shaped, or horseshoe-shaped shape other than 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 circumferential 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, it is also possible to configure the cooling water W to be supplied through separate cooling water supply pipes.

[0079] The length from the position where the extension line of the central axis of the shower opening 25a of the cooling water injection passage 25 hits the surface of the cast aluminum alloy bar 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, casting is impossible because a good coating is not formed, and 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 aluminum alloy molten metal M or the aluminum alloy bar B increases, which may cause cracks on the casting surface or tearing inside the mold, making the casting unstable, and is not preferable.

[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 a control signal from a control device (not shown).

[0081] The cooling water cavity 24 is formed such that an inner bottom surface 24a adjacent to the hollow portion 21 of the mold 12 and an inner peripheral surface 21a of the hollow portion 21 of the mold 12 are parallel to each other.

[0082] Note that "parallel" here also includes the case where the inner 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 bottom surface 21a.

[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 from the molten aluminum alloy M in the hollow portion 21 to the cooling water W in the cooling water cavity 24 of 10×10 5 W / m 2 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 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. In addition, the material for forming the mold 12 may be selected so that the thermal conductivity of at least the cooling wall 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 a central axis C of the mold is substantially horizontal, and is force-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 cut to a desired length by, for example, a synchronous cutter (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 spectrophotometric analyzer (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 circumferential surface 21a of the mold 12 is preferably 0 mm to 250 mm (more preferably 50 mm to 170 mm). By setting it in 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 appropriately 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 amount is preferably 0.05 mL / min to 5 mL / min (more preferably 0.1 mL / min to 1 mL / min). If the supply amount is too small, the molten aluminum alloy M of the aluminum alloy bar B may not solidify and may leak from the mold 12 due to insufficient lubrication. If the supply amount is too large, the surplus may get mixed into the aluminum alloy bar B and cause internal defects.

[0091] The casting speed, which is the speed at which the aluminum alloy bar 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, at a casting speed within this range, the network structure of the crystals 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.

[0092] The amount of cooling water sprayed from the shower opening 25a of the cooling water spray passage 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 may leak from the mold 12. Also, the surface of the cast aluminum alloy bar B may remelt, forming a non-uniform structure that may remain as an internal defect. On the other hand, if the amount of cooling water is more than this range, the mold 12 may lose too much heat, causing it to solidify midway.

[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 crystallized matter may be formed in the mold 12 or in front of it, and may be incorporated as internal defects inside the aluminum alloy bar B. On the other hand, if the temperature of the molten aluminum alloy M is too high, a large amount of hydrogen gas is likely to be incorporated into the molten aluminum alloy M, which may be incorporated as porosity in the aluminum alloy bar B and cause internal cavities.

[0094] In addition, 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 That's it, 50 x 10 5 W / m 2 By keeping the temperature within the following range, the occurrence of seizure of the aluminum alloy rod B can be prevented.

[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 formula (1) according to Fourier's law. Q = -k × (T1-T2) / L (1) Q: Heat flux k: Thermal conductivity (W / m K) of the part through which heat passes (in this embodiment, the cooling wall 27 of the mold 12) T1: The low-temperature side temperature of the portion through which heat passes (in this embodiment, the inner bottom surface 24a of the cooling water cavity 24) T2: High temperature side temperature of the portion through which heat passes (in this embodiment, the inner peripheral surface 21a of the hollow portion 21 of the mold 12) L: Length of section through which heat passes (mm) (in this embodiment, thickness t of cooling wall portion 27 of 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 x 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 bar B from being burned. 5 W / m 2 It is preferable to do the following:

[0097] In order to set the heat flux value of the cooling wall 27 of the mold 12 within this range, the mold 12 may 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 or more and 3.0 mm or less. Also, the thermal conductivity of at least the cooling wall 27 of the mold 12 may be set in the range of 100 W / m K or more and 400 W / m K or less.

[0098] When producing the aluminum alloy bar B of this embodiment, the above-mentioned horizontal continuous casting apparatus 10 is used to continuously supply the molten aluminum alloy M stored in the molten metal receiving portion 11 into the hollow portion 21 from one end side 12a of the mold 12. 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 of 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 that the wall surface temperature of the cooling wall portion 27 of the mold 12, which is cooled by the cooling water W, is set to 100° C. or lower.

[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, caused by contact between the lubricating oil gas and the molten aluminum alloy M. This makes it unnecessary to cut and remove carbides and the like on the surface of the aluminum alloy bar B, and allows the aluminum alloy bar 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 above-mentioned horizontal continuous casting method, and any known continuous casting method such as a vertical continuous casting method can be used. The vertical continuous casting method is classified into a float method and a hot top method depending on the method of supplying the molten aluminum alloy M to the mold (casting mold 12), and the case where the hot top method is used will be briefly described below.

[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 installed almost horizontally, where it is forcibly cooled and a solidified shell is formed on the outer surface of the molten metal.

[0103] In addition, cooling water is sprayed directly onto the casting product as it is pulled out of the mold, and the solidification of the metal progresses all the way to the inside of the casting product as it is continuously pulled out. Generally, molds are made of metal members with good thermal conductivity and have a hollow structure to allow the introduction of a cooling medium inside.

[0104] The refrigerant to be used may be appropriately selected from those available industrially, 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, in terms of heat transfer performance and durability at the contact portion with the molten metal. The header is generally made of a refractory material and is installed on the upper side of 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 general range 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 the case of medium to large-sized castings. The diameter of the target casting is not particularly limited, and the method is preferably used for rods having a diameter of 30 to 100 mm.

[0108] (Homogenization heat treatment process) The homogenization heat treatment step is a step in which homogenization heat treatment is performed on the aluminum alloy casting obtained in the casting step to homogenize microsegregation caused by solidification, precipitate supersaturated solid solution elements, and change metastable phases to equilibrium phases. Incidentally, such a homogenization heat treatment step may be carried out as necessary, and the forging step may be directly carried out after the casting step.

[0109] In this embodiment, the cast product obtained in the casting process is subjected to homogenization heat treatment by holding it at a temperature of 370° C. or higher and 560° C. or lower for 2 to 10 hours. By performing homogenization heat treatment in this temperature range, the cast product is homogenized and solute atoms are sufficiently dissolved, so that the sufficient strength required for the subsequent aging treatment can be obtained.

[0110] (Forging process) The forging process is a process in which an aluminum alloy casting after casting or after the homogenization heat treatment process is shaped into a predetermined size to obtain a forging material, the obtained forging material is heated to a predetermined temperature, and then pressure is applied in a press to form it into a die.

[0111] In this embodiment, a forged product (such as an automobile suspension arm part) is obtained by forging a forging material at a heating temperature of 450°C or more and 560°C or less. At this time, the starting temperature for forging the forging material is 450°C or more and 560°C or less. If the starting temperature is less than 450°C, the deformation resistance becomes high and sufficient processing cannot be performed, and if it exceeds 560°C, defects such as forging cracks and eutectic melting are likely to occur.

[0112] (Solution treatment process) The solution treatment process is a process in which the forged product obtained in the forging process is heated to bring about a solution, thereby relieving the distortion introduced in the forging process and causing the solute elements to dissolve in solid solution.

[0113] In this embodiment, the forged product is subjected to solution treatment by holding it at a treatment temperature of 530°C or more and 560°C or less for 0.3 to 3 hours. The heating rate from room temperature to the above-mentioned treatment temperature is preferably 5.0°C / min or more. If the treatment temperature is less 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, but eutectic melting and recrystallization may occur easily. In addition, if the heating rate is less than 5.0°C / min, Mg2Si may precipitate coarsely. On the other hand, if the treatment temperature is less than 530°C, the solution treatment may not proceed, making it difficult to achieve high strength by aging precipitation.

[0114] (Hardening process) The quenching process is a process in which the forged product in the solid-solution state obtained in the solution treatment process is rapidly cooled to form a supersaturated solid solution.

[0115] In this embodiment, the forged product is put into a water tank that stores 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 put into the water tank after the 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 forged product, but is, for example, between more than 1 minute and 30 minutes.

[0116] (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 the elements that are supersaturated in solid solution, thereby imparting an appropriate hardness.

[0117] In this embodiment, the forged product after the quenching process is heated to a temperature of 170°C or more and 210°C or less, and is held at that temperature for 0.5 hours or more and 7 hours or less to perform aging treatment. If the treatment temperature is less than 170°C or the holding time is less than 0.5 hours, the Mg2Si-based precipitates that improve the 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 to sufficiently improve the tensile strength. EXAMPLES

[0118] Next, specific examples of the present invention will be described, but the present invention is not particularly limited to these examples.

[0119] [Examples 1 to 23 and Comparative Examples 1 to 3] (Manufacturing of continuous casting products) First, an aluminum alloy forging material having the alloy composition shown in Table 1 below (the balance being aluminum) was prepared. Continuously cast products having a circular cross section and a diameter of 82 mm were produced using the prepared aluminum alloy forging material. The continuous cast products of Examples 1 and 5, the continuous cast products of Examples 2 and 6, the continuous cast products of Examples 3 and 7, and the continuous cast products of Examples 4 and 8 each have the same alloy composition, but the conditions of the treatment process for producing the aluminum alloy forged products are different. Moreover, in Examples 9 to 23, the homogenization heat treatment process was not performed.

[0120] [Table 1]

[0121] (Manufacture of aluminum alloy forgings) Next, the obtained continuous cast product was subjected to a homogenization heat treatment step (none in Examples 9 to 23), a forging process step, a solution treatment process step, a quenching process step, and an artificial aging process step in this order to obtain an aluminum alloy forged product 1a having the shape shown in Fig. 1. The conditions of the homogenization heat treatment step, the forging process step, the solution treatment process step, the quenching process step, and the artificial aging process step are shown in Table 2 below.

[0122] [Table 2]

[0123] [evaluation] The aluminum alloy forging materials of Examples 1 to 23 and Comparative Examples 1 to 3 and the boundary portion 2b in the longitudinal direction of the long portion 2 in the aluminum alloy forging 1a were evaluated as follows. The evaluation results are shown in Table 3 below. For the refinement evaluation of the forging material and the forged product, a plate-shaped body (7mm x 7mm x 2mm thick) for preparing the evaluation test specimen was used as the evaluation test specimen. The average crystal grain size and standard deviation of the crystal grain size were measured for the surface of the evaluation test specimen taken using SEM-EBSD (scanning electron microscope-electron backscatter diffraction). The obtained average crystal grain size and standard deviation of the crystal grain size were judged based on the following criteria to evaluate the refinement of the crystal grains and the recrystallization / coarsening of the crystal grains. The measurement conditions for SEM-EBSD were an acceleration voltage of 15kV, a measurement pitch of 0.5μm / px, and an analysis area of ​​500×500μm. 2 The grain boundary definition angle was set to 15°.

[0124] <Component: Fe / Mn ratio> An evaluation was conducted to see whether the Fe / Mn ratio of aluminum alloy forging materials was within the range of 0.3 to 1.2. (Judgment criteria) "Good": Fe / Mn ratio is within the range of 0.3 or more and 1.2 or less. "X": The Fe / Mn ratio is outside the range of 0.3 or more and 1.2 or less.

[0125] <Forging material: Number density of precipitates containing Mn> The number density of precipitates containing Mn within a range of 1.5 μm including the grain boundaries was measured. (Judgment criteria) "Good": The number density of precipitates containing Mn is 4 / μm 2 The following is the result. "×": The number density of precipitates containing Mn is 4 / μm 2 exceeds.

[0126] <Evaluation of grain size ratio (S1 / S2)> The aluminum alloy forged product 1a was cut perpendicularly to the surface at the center of the long part and at the boundary between the long part and the connecting part, and a plate-like body (2 mm thick) was taken as a test piece for measuring grain size. The obtained plate-like body was cut into 7 mm squares to obtain a test piece for measuring grain size of 7 mm x 7 mm x 2 mm thick. The average grain size was measured on the surface (cross section) of the test piece for evaluating grain size taken using SEM-EBSD (scanning electron microscope-electron backscatter diffraction). The grain size of the center of the long part was S1, and the grain size of the boundary between the long part and the connecting part in the longitudinal direction was S2. The grain size ratio was evaluated by judging the value of S1 / S2 based on the following criteria. The measurement conditions of SEM-EBSD 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) "O": 0.7 or more and 1.0 or less. “×”: Less than 0.7. [Table 3]

[0127] As shown in Table 3, by manufacturing an aluminum alloy forging by containing Zr and Zn, setting the content of each element within a prescribed range, and carrying out each of the molten metal formation process, casting process, homogenization heat treatment process, forging process, solution treatment process, quenching treatment process and aging treatment process under prescribed processing conditions within each process, it was confirmed that when the crystal grain size at the longitudinal center of the long portion is S1 and the crystal grain size at the longitudinal boundary between the long portion and the connecting portion is S2, the crystal grain size ratio represented by S1 / S2 can be reduced, and an aluminum alloy forging can be obtained having a metal structure with little variation at room temperature. [Explanation of symbols]

[0128] 1a, 1b, 1c...Aluminum alloy forgings 2...Long section 2a…Central part 2b…boundary part 4,4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h...Connection part 5…Short section 10...Horizontal continuous casting equipment 11...Molten metal receiving part (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 (insulating material) 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 aluminum alloy W…Cooling water

Claims

1. 1. An aluminum alloy forging material having an alloy composition comprising Cu in the range of 0.30 mass% or more and 1.0 mass% or less, Mg in the range of 0.80 mass% or more and 1.8 mass% or less, Si in the range of 0.90 mass% or more and 1.9 mass% or less, Mn in the range of 0.30 mass% or more and 1.2 mass% or less, Fe in the range of 0.20 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, B in the range of 0.0010 mass% or more and 0.030 mass% or less, and Zr in the range of 0.0010 mass% or more and 0.050 mass% or less, a ratio of the Fe content to the Mn content (Fe / Mn) being less than 1.4 in mass ratio, with the balance being Al and unavoidable impurities, In the alloy structure after forging, the number density of precipitates containing Mn within a range of 1.5 μm including the grain boundary is 4 / μm ２ The following are aluminum alloy forging materials.

2. 1. An aluminum alloy forging material having an alloy composition comprising Cu in the range of 0.25% by mass or more and 0.55% by mass or less, Mg in the range of 0.85% by mass or more and 1.25% by mass or less, Si in the range of 1.02% by mass or more and 1.4% by mass or less, Mn in the range of 0.55% by mass or more and 1.0% by mass or less, Fe in the range of 0.32% by mass or more and 0.65% by mass or less, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% by mass or more and 0.30% 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, and 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) being 0.3 to 1.2 in mass ratio, with the balance being Al and unavoidable impurities, In the alloy structure after forging, the number density of precipitates containing Mn within a range of 1.5 μm including the grain boundary is 4 / μm ２ The following are aluminum alloy forging materials.

3. 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 is in the range of 0.61 mass% or more and 1.0 mass% or less, Fe is in the range of 0.32 mass% or more and 0.65 mass% or less, Zn is in the range of 0.25 mass% or less, Cr is in the range of 0.050 mass% or more and 0.30 mass% or less, Ti is in the range of 0.01 mass% or more and 0.1 mass% or less, An aluminum alloy forging material having an alloy composition containing 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) being 0.3 to 1.2 in terms of mass ratio, with the balance being Al and unavoidable impurities, In the alloy structure after forging, the number density of precipitates containing Mn within a range of 1.5 μm including the grain boundary is 4 / μm ２ The following are aluminum alloy forging materials.

4. 4. The aluminum alloy material for forging according to claim 1, wherein the size of the precipitates containing Mn is 0.2 μm or less.

5. An aluminum alloy forging having a long portion and a connecting portion, an aluminum alloy composition comprising Cu in the range of 0.30 mass % or more and 1.0 mass % or less, Mg in the range of 0.80 mass % or more and 1.8 mass % or less, Si in the range of 0.90 mass % or more and 1.9 mass % or less, Mn in the range of 0.30 mass % or more and 1.2 mass % or less, Fe in the range of 0.20 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, B in the range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in the range of 0.0010 mass % or more and 0.050 mass % or less, a ratio of the Fe content to the Mn content (Fe / Mn) being less than 1.4 in mass ratio, with the balance being composed of Al and unavoidable impurities; An aluminum alloy forged product in which the value of S1 / S2 is in the range of 0.7 or more and 1.0 or less, where S1 is the grain size at the longitudinal center of the long portion and S2 is the grain size at the longitudinal boundary between the long portion and the connecting portion.

6. An aluminum alloy forging having a long portion and a connecting portion, an alloy composition comprising 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, B in the range of 0.0010 mass% or more and 0.030 mass% or less, and Zr in the range of 0.0010 mass% or more and 0.050 mass% or less, a ratio of the Fe content to the Mn content (Fe / Mn) being 0.3 to 1.2 in mass ratio, with the balance being Al and unavoidable impurities; An aluminum alloy forged product in which the value of S1 / S2 is in the range of 0.7 or more and 1.0 or less, where S1 is the grain size at the longitudinal center of the long portion and S2 is the grain size at the longitudinal boundary between the long portion and the connecting portion.

7. An aluminum alloy forging having a long portion and a connecting portion, an alloy composition comprising 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 0.61 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, B in the range of 0.0010 mass % or more and 0.030 mass % or less, and Zr in the range of 0.0010 mass % or more and 0.050 mass % or less, a ratio of the Fe content to the Mn content (Fe / Mn) being 0.3 to 1.2 in mass ratio, with the balance being Al and unavoidable impurities; An aluminum alloy forged product in which the value of S1 / S2 is in the range of 0.7 or more and 1.0 or less, where S1 is the grain size at the longitudinal center of the long portion and S2 is the grain size at the longitudinal boundary between the long portion and the connecting portion.

8. 8. The aluminum alloy forged product according to claim 5, which is used for a suspension arm.

9. A method for producing an aluminum alloy forged product according to any one of claims 5 to 7, a molten alloy forming step of forming a molten aluminum alloy having the same alloy composition as the aluminum alloy forged product; a casting step of cooling and solidifying the molten aluminum alloy obtained in the molten alloy forming step to form an aluminum alloy casting; a forging step of forging the aluminum alloy casting having undergone the casting step at a heating temperature of 450° C. or more and 560° C. or less; A solution treatment process in which the forged product obtained in the forging process is subjected to solution treatment at a treatment temperature of 530°C to 560°C for 0.3 hours to 3 hours; a quenching process in which the entire surface of the forged product is brought into contact with quenching water within a range of 5 seconds to 60 seconds after the completion of the solution treatment process, and quenched in a water tank for 1 minute to 30 minutes; and an aging treatment step of subjecting the forged product after the quenching treatment step to an aging treatment at a heating temperature of 170°C or higher and 210°C or lower for a period of 0.5 hours or higher and 7 hours or lower.

10. 10. The method for producing an aluminum alloy forged product according to claim 9, further comprising a homogenization heat treatment step between the casting step and the forging step, in which the aluminum alloy cast product is held at a temperature range of 370°C or higher and 560°C or lower for 2 hours or longer and 10 hours or shorter to perform homogenization heat treatment.

Images