Manufacturing method for aluminum alloy forgings

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. The cross section of the longitudinal boundary between a long part and a connection part is free of AIFeSi(Mn) compounds with average crystal grain sizes in the alloy structure ranging from 5 μm to 60 μm and average particle sizes of at least 2.0 μm. For fatigue characteristics at room temperature, the fatigue limit at 107 cycles of fracture repetition is at least 150 MPa.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This invention ,a Forged from aluminum alloy Product Regarding the manufacturing method. [Background technology]

[0002] In recent years, aluminum alloys have seen increasing use as structural components in various products due to their lightweight properties. For example, high-tensile steel has traditionally been used in automotive undercarriages and bumper parts. However, in recent years, high-strength aluminum alloys have come into use.

[0003] Furthermore, in the automotive parts, particularly long components such as suspension arms, iron-based materials were traditionally used exclusively. However, in recent years, with the primary objective of weight reduction, these parts have increasingly been replaced with aluminum or aluminum alloy materials.

[0004] Because these automotive parts require excellent corrosion resistance, high strength, and superior workability, Al-Mg-Si alloys, particularly A6061, are frequently used as aluminum alloy materials. Furthermore, to improve the strength of such automotive parts, aluminum alloy materials are manufactured using forging, a type of plastic deformation process, as the processing material.

[0005] Furthermore, in recent years, due to the need to reduce costs, suspension parts obtained by forging cast components directly without extrusion, followed by solution treatment and artificial aging treatment (T6 treatment), have begun to be put into practical use. To further reduce weight, development of high-strength alloys to replace the conventional A6061 is underway (see, for example, Patent Documents 1-3). [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 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In recent years, with the need to reduce CO2 emissions, there has been a growing demand for lighter automobiles, and consequently, the demand for aluminum is on the rise. However, further increases in strength are necessary to replace steel. One known method for increasing the strength of aluminum is to suppress the formation of a recrystallized structure during plastic deformation and solution treatment processes, thereby refining the grain size.

[0008] However, the aforementioned Al-Mg-Si high-strength alloys had a problem in that the processed structure recrystallized during the forging and heat treatment processes, resulting in the generation of coarse crystal grains, which prevented them from achieving sufficient high strength. Therefore, some alloys have Zr (zirconium) added to prevent the formation of coarse recrystallized grains (see, for example, the above-mentioned Patent Documents 1 and 2).

[0009] However, while adding Zr is effective in preventing recrystallization, it had the following problems. (1) The addition of Zr weakens the grain refinement effect of Al-Ti-B alloys, resulting in coarser grains in the casting itself and a decrease in the strength of the processed product (forged product) after plastic deformation. (2) The grain refinement effect of the casting itself is weakened, making the casting more prone to cracking, increasing internal defects, and worsening yield. (3) Zr forms compounds with Al-Ti-B alloys, and these compounds accumulate at the bottom of the furnace where the molten alloy is stored, contaminating the furnace. In addition, these compounds crystallize coarsely in the manufactured castings, reducing their strength.

[0010] Thus, while the addition of Zr was effective in preventing recrystallization, it was difficult to maintain strength stability. The present invention has been made in view of such a technical background, and an object thereof is to provide a material for aluminum alloy forging, a forged product made of aluminum alloy, and a method for manufacturing the same, which have excellent mechanical properties at normal temperature.

Means for Solving the Problems

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

[0012] (1) An aluminum alloy forging material having an alloy composition in which Cu is in the range of 0.30% by mass or more and 1.0% by mass or less, Mg is in the range of 0.80% by mass or more and 1.8% by mass or less, Si is in the range of 0.90% by mass or more and 1.9% by mass or less, Mn is in the range of 0.30% by mass or more and 1.2% by mass or less, Fe is in the range of 0.20% by mass or more and 0.65% by mass or less, Zn is in the range of 0.25% by mass or less, Cr is in the range of 0.050% by mass or more and 0.30% by mass or less, Ti is in the range of 0.01% by mass or more and 0.1% by mass or less, B is in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr is in the range of 0.0010% by mass or more and 0.050% by mass or less, the ratio Fe / Mn of the content of Fe to the content of Mn is less than 1.4 in terms of mass ratio, and the balance consists of Al and unavoidable impurities, and the average crystal grain size of the alloy structure after forging is in the range of 50 μm or more and 120 μm or less, and the average crystal grain size of the AIFeSi(Mn) - based compound present at the crystal grain boundaries is 3.0 μm or less.

[0013] (2) An aluminum alloy forging stock having an 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, wherein the ratio Fe / Mn of the content of Fe to the content of Mn is 0.3 or more and 1.2 or less in terms of mass ratio, and the balance consists of Al and unavoidable impurities, and the average crystal grain size of the alloy structure after forging is in the range of 50 μm or more and 120 μm or less, and the average crystal grain size of the AIFeSi(Mn)-based compound present at the grain boundaries is 3.0 μm or less, an aluminum alloy forging stock.

[0014] (3) An aluminum alloy forging stock having an 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 0.61% 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, wherein the ratio Fe / Mn of the content of Fe to the content of Mn is 0.3 or more and 1.2 or less in terms of mass ratio, and the balance consists of Al and unavoidable impurities, and the average crystal grain size of the alloy structure after forging is in the range of 50 μm or more and 120 μm or less, and the average crystal grain size of the AIFeSi(Mn)-based compound present at the grain boundaries is 3.0 μm or less, an aluminum alloy forging stock.

[0015] (4) An aluminum alloy forged product having a long section and a connecting section, wherein Cu is in the range of 0.30 mass% to 1.0 mass%, Mg is in the range of 0.80 mass% to 1.8 mass%, Si is in the range of 0.90 mass% to 1.9 mass%, Mn is in the range of 0.30 mass% to 1.2 mass%, Fe is in the range of 0.20 mass% to 0.65 mass%, Zn is in the range of 0.25 mass%, Cr is in the range of 0.050 mass% to 0.30 mass%, Ti is in the range of 0.01 mass% to 0.1 mass%, and B is 0.0010 mass% The aluminum alloy composition has an alloy composition in which Zr is contained in a range of 0.0010% to 0.050% by mass, the ratio of Fe content to Mn content (Fe / Mn) is less than 1.4 by mass, and the remainder consists of Al and unavoidable impurities, the cross section of the longitudinal boundary between the long portion and the connecting portion has an average grain size of alloy structure in the range of 5 μm to 60 μm, and does not contain AIFeSi(Mn)-based compounds with an average grain size of 2.0 μm or more, and the fatigue properties at room temperature have a fracture cycle count of 10 7 Aluminum alloy forged product with a fatigue limit of 150 MPa or more during the cycle.

[0016] (5) An aluminum alloy forged product having a long section and a connecting section, wherein Cu is in the range of 0.25 mass% to 0.55 mass%, Mg is in the range of 0.85 mass% to 1.25 mass%, Si is in the range of 1.02 mass% to 1.4 mass%, Mn is in the range of 0.55 mass% to 1.0 mass%, Fe is in the range of 0.32 mass% to 0.65 mass%, Zn is in the range of 0.25 mass%, Cr is in the range of 0.050 mass% to 0.30 mass%, Ti is in the range of 0.01 mass% to 0.1 mass%, and B is 0.00 The alloy has an alloy composition in which Zr is contained in the range of 10% to 0.030% by mass, Zr in the range of 0.0010% to 0.050% by mass, the ratio of Fe content to Mn content (Fe / Mn) is 0.3 to 1.2 by mass, and the remainder is Al and unavoidable impurities, the cross section of the longitudinal boundary between the long portion and the connecting portion has an alloy structure with an average grain size in the range of 5 μm to 60 μm, and does not contain AIFeSi(Mn)-based compounds with an average grain size of 2.0 μm or more, and the fatigue properties at room temperature have a fracture cycle count of 10 7 Aluminum alloy forged product with a fatigue limit of 150 MPa or more during the cycle.

[0017] (6) An aluminum alloy forged product having a long section and a connecting section, wherein Cu is in the range of 0.25% by mass or more and 0.55% by mass or less, Mg is in the range of 0.85% by mass or more and 1.25% by mass or less, Si is in the range of 1.02% by mass or more and 1.4% by mass or less, Mn is in the range of 0.61% by mass or more and 1.0% by mass or less, Fe is in the range of 0.32% by mass or more and 0.65% by mass or less, Zn is in the range of 0.25% by mass or less, Cr is in the range of 0.050% by mass or more and 0.30% by mass or less, Ti is in the range of 0.01% by mass or more and 0.1% by mass or less, and B is 0.00 The alloy has an alloy composition in which Zr is contained in the range of 10% to 0.030% by mass, Zr in the range of 0.0010% to 0.050% by mass, the ratio of Fe content to Mn content (Fe / Mn) is 0.3 to 1.2 by mass, and the remainder is Al and unavoidable impurities, the cross section of the longitudinal boundary between the long portion and the connecting portion has an alloy structure with an average grain size in the range of 5 μm to 60 μm, and does not contain AIFeSi(Mn)-based compounds with an average grain size of 2.0 μm or more, and the fatigue properties at room temperature have a fracture cycle count of 10 7 Aluminum alloy forged product with a fatigue limit of 150 MPa or more during the cycle.

[0018] (7) A forged aluminum alloy product as described in any one of (4) to (6) above, for use as a suspension arm.

[0019] (8) A method for manufacturing an aluminum alloy forging according to any one of (4) to (7) above, comprising: an alloy molten metal forming step of forming an aluminum alloy molten metal having the same alloy composition as the aluminum alloy forging; a casting step of cooling and solidifying the aluminum alloy molten metal obtained in the alloy molten metal forming step to form an aluminum alloy casting; a forging step of performing forging on the aluminum alloy casting obtained in the casting step at a heating temperature of 450°C or more and 560°C or less; and a forging step of applying to the forging obtained in the forging step A method for manufacturing an aluminum alloy forged product, comprising: a solution treatment step of holding the product at a treatment temperature of 530°C to 560°C for 0.3 hours to 3 hours; a quenching step of bringing all surfaces of the forged product into contact with quenching water for a period of 5 seconds to 60 seconds after the completion of the solution treatment step, and quenching the product in a water bath for 1 minute to 30 minutes; and an aging step of aging the forged product after the quenching step at a heating temperature of 170°C to 210°C for 0.5 hours to 7 hours.

[0020] (9) A method for manufacturing an aluminum alloy forged product according to (8), further comprising a homogenization heat treatment step between the casting step and the forging step, wherein the aluminum alloy casting is subjected to a homogenization heat treatment by holding it at a temperature range of 370°C to 560°C for 2 hours to 10 hours. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide an aluminum alloy forging material, an aluminum alloy forged product, and a method for manufacturing the same, all of which exhibit excellent mechanical properties at room temperature. [Brief explanation of the drawing]

[0022] [Figure 1] This is a perspective view showing an example of an aluminum alloy forged product relating to one embodiment of the present invention. [Figure 2] This is a plan view showing another example of an aluminum alloy forged product relating to one embodiment of the present invention. [Figure 3] This is a perspective view showing yet another example of an aluminum alloy forged product relating to one embodiment of the present invention. [Figure 4] This is a cross-sectional view showing an example of the area near the mold of a horizontal continuous casting apparatus for manufacturing aluminum alloy forgings according to one embodiment of the present invention. [Figure 5] Figure 4 is an enlarged cross-sectional view of the main part near the cooling water cavity of the horizontal continuous casting apparatus shown. [Figure 6] This is an explanatory diagram illustrating the heat flux in the cooling wall section of a horizontal continuous casting apparatus. [Figure 7A] This is a plan view showing the sampling locations of the central and boundary portions taken from the aluminum alloy forging obtained in this embodiment for the preparation of test specimens for mechanical property evaluation. [Figure 7B] This is a plan view showing the test specimen for mechanical property evaluation prepared in this embodiment. [Modes for carrying out the invention]

[0023] Embodiments of the present invention will be described in detail below with reference to the drawings. Note that, for the sake of clarity, the drawings used in the following description may show enlarged versions of key features, and the dimensional ratios of each component may not be the same as those in reality. Furthermore, the materials, dimensions, etc., exemplified in the following description are merely examples, and the present invention is not necessarily limited to them. It can be implemented with appropriate modifications without altering its effects.

[0024] [Materials for aluminum alloys] First, the aluminum alloy material according to the present invention will be described. The aluminum alloy material of one embodiment of the present invention contains 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%, 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 An aluminum alloy forging material having an alloy composition in which Zr is contained in the range of 0.0010% by mass or more and 0.030% by mass or less, Zr is contained in the range of 0.0010% by mass or more and 0.050% by mass or less, the ratio of Fe content to Mn content (Fe / Mn) is less than 1.4 by mass, and the remainder consists of Al and unavoidable impurities, wherein the average grain size of the alloy structure after forging is in the range of 50 μm or more and 120 μm or less, and the average grain size of the AIFeSi(Mn) compound present at the grain boundaries is 3.0 μm or less.

[0025] Another embodiment of the present invention provides an aluminum alloy material comprising: Cu in the range of 0.25% to 0.55% by mass, Mg in the range of 0.85% to 1.25% by mass, Si in the range of 1.02% to 1.4% by mass, Mn in the range of 0.55% to 1.0% by mass, Fe in the range of 0.32% to 0.65% by mass, Zn in the range of 0.25% by mass or less, Cr in the range of 0.050% to 0.30% by mass, Ti in the range of 0.01% to 0.1% by mass, and B in the range of 0% by mass. An aluminum alloy forging material having an alloy composition in which Zr is contained 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 content to Mn content (Fe / Mn) is 0.3 or more and 1.2 by mass ratio, and the remainder is Al and unavoidable impurities, wherein the average grain size of the alloy structure after forging is in the range of 50 μm or more and 120 μm or less, and the average grain size of the AIFeSi(Mn) compound present at the grain boundaries is 3.0 μm or less.

[0026] The aluminum alloy material in this embodiment corresponds to a 6000 series aluminum alloy in that it contains Mg and Si.

[0027] (Average grain size of alloy structure after forging: 50 μm to 120 μm) The average grain size of the alloy structure after forging of aluminum alloy forging materials serves as an indicator of the degree of grain refinement. If the average grain size exceeds 120 μm, tensile and fatigue properties may decrease according to the Hall-Petch law. On the other hand, if the average grain size is less than 50 μm, toughness deteriorates and impact resistance decreases, which may reduce workability. For this reason, the average grain size of the alloy structure after forging is set to be in the range of 5 μm or more and 120 μm or less.

[0028] (Average grain size of AIFeSi(Mn) compounds present at grain boundaries: 3.0 μm or less) If a large amount of AIFeSi(Mn)-based compounds are present at the grain boundaries of the alloy structure of aluminum alloy forging materials, there is a risk that the mechanical properties (tensile properties / fatigue properties, etc.) will deteriorate. For this reason, when AIFeSi(Mn)-based compounds are present at the grain boundaries of the alloy structure of aluminum alloy forging materials, the average grain size is set to 3.0 μm or less.

[0029] A further embodiment of the present invention provides an aluminum alloy material comprising: Cu in a range of 0.25% to 0.55% by mass, Mg in a range of 0.85% to 1.25% by mass, Si in a range of 1.02% to 1.4% by mass, Mn in a range of 0.61% to 1.0% by mass, Fe in a range of 0.32% to 0.65% by mass, Zn in a range of 0.25% by mass or less, Cr in a range of 0.050% to 0.30% by mass, Ti in a range of 0.01% to 0.1% by mass, and B An aluminum alloy forging material having an alloy composition in which Zr is contained 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 content to Mn content (Fe / Mn) is 0.3 or more and 1.2 by mass ratio, and the remainder is Al and unavoidable impurities, wherein the average grain size of the alloy structure after forging is in the range of 50 μm or more and 120 μm or less, and the average grain size of the AIFeSi(Mn) compound present at the grain boundaries is 3.0 μm or less.

[0030] [Aluminum alloy forged products] Next, the aluminum alloy forged product according to the present invention will be described. Figure 1 is a perspective view of an aluminum alloy forged product according to one embodiment of the present invention. As shown in Figure 1, the aluminum alloy forged product 1a has a long section 2 and connecting sections 4a and 4b connected to both ends of the long section 2 in the longitudinal direction, respectively. The long section has a quadrilateral cross-section. This shaped aluminum alloy forged product 1a can be used, for example, as an I-shaped suspension arm.

[0031] The aluminum alloy forged product 1a contains Cu in the range of 0.25% to 0.55% by mass, Mg in the range of 0.85% to 1.25% by mass, Si in the range of 1.02% to 1.4% by mass, Mn in the range of 0.55% to 1.0% by mass, Fe in the range of 0.32% to 0.65% by mass, Zn in the range of 0.25% by mass, Cr in the range of 0.050% to 0.30% by mass, Ti in the range of 0.01% to 0.1% by mass, B in the range of 0.0010% to 0.030% by mass, and Zr in the range of 0.0010% to 0.050% by mass, with a Fe / Mn ratio of 0.3% to 1.2 by mass, and the remainder being Al and unavoidable impurities. Furthermore, the cross-section of the longitudinal boundary portion 2b between the long portion 2 and the connecting portion 4 of the aluminum alloy forged product 1a does not contain AIFeSi(Mn)-based compounds with an average grain size of 5 μm to 60 μm and an average particle diameter of 2.0 μm or more, and the fatigue properties at room temperature show a fracture cycle count of 10 7 The fatigue limit in the cycle is set at 150 MPa or higher.

[0032] The aluminum alloy used as the material for the aluminum alloy forged product 1a in this embodiment corresponds to a 6000 series aluminum alloy in that it contains Mg and Si.

[0033] (Cu: 0.25 mass% or more and 0.55 mass% or less) Cu has the effect of finely dispersing Mg-Si compounds in aluminum alloys and improving the tensile strength of aluminum alloys 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 forged product 1a at room temperature can be improved.

[0034] (Mg: 0.85 mass% or more and 1.25 mass% or less) Mg has the effect of improving the tensile strength of aluminum alloys. Mg contributes to strengthening aluminum alloys by solid dissolving into the aluminum matrix, or by precipitating as Mg-Si compounds such as the β'' phase (Mg2Si), or Al-Cu-Mg-Si compounds such as the Q phase (AlCuMgSi). In addition, Mg2Si has the effect of suppressing the formation of the CuAl2 phase in the aluminum alloy. By suppressing the formation of the CuAl2 phase, the corrosion resistance of the aluminum alloy forged product 1a is improved. By keeping the Mg content within the above range, the corrosion resistance of the aluminum alloy forged product 1a can be improved along with its mechanical properties at room temperature.

[0035] (Si: 1.02 mass% or more and 1.4 mass% or less) Like magnesium, silicon (Si) improves the mechanical properties and corrosion resistance of aluminum alloy forged products 1a at room temperature. However, excessive addition of Si to aluminum alloy may lead to the crystallization of coarse primary Si grains, potentially reducing the tensile strength of the aluminum alloy. By keeping the Si content within the above range, it is possible to suppress the crystallization of primary Si while improving the mechanical properties and corrosion resistance of aluminum alloy forged products 1a at room temperature.

[0036] (Mn: 0.55 mass% or more and 1.0 mass% or less) Mn improves the tensile strength of aluminum alloys 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 having a Mn content within the above range, the mechanical properties of the aluminum alloy forged product 1a at room temperature can be improved.

[0037] (Fe: 0.32 mass% or more and 0.65 mass% or less) Fe crystallizes in aluminum alloys as fine precipitates containing intermetallic compounds such as Al-Mn-Fe-Si, Al-Mn-Cr-Fe-Si, Al-Fe-Si, Al-Cu-Fe, and Al-Mn-Fe, thereby improving the tensile strength of the aluminum alloy. By having a Fe content within the above range, the mechanical properties of the aluminum alloy forged product 1a at room temperature can be improved. Furthermore, the Fe / Mn ratio is between 0.3 and 1.2. A Fe / Mn ratio of 1.2 or less suppresses the crystallization of AlFeSi compounds larger than 2.0 μm, thereby improving mechanical properties.

[0038] (Cr: 0.050 mass% or more, 0.30 mass% or less) Cr improves the tensile strength of aluminum alloys by forming fine granular precipitates containing intermetallic compounds such as Al-Mn-Cr-Fe-Si and Al-Fe-Cr in the aluminum alloy. By having a Cr content within the above range, the mechanical properties of the aluminum alloy forged product 1a at room temperature can be improved.

[0039] (Ti: 0.01 mass% or more, 0.1 mass% or less) Ti has the effect of refining the crystal grains of aluminum alloys and improving their wroughtability. If the Ti content is less than 0.01 mass%, the effect of refining the crystal grains may not be sufficiently obtained. On the other hand, if the Ti content exceeds 0.1 mass%, coarse precipitates may form, which may reduce the wroughtability. In addition, if a large amount of coarse precipitates containing Ti are mixed into the aluminum alloy forged product 1a, the toughness may decrease. Therefore, the Ti content should be between 0.012 mass% and 0.035 mass%. Preferably, the Ti content is between 0.015 mass% and 0.050 mass%.

[0040] (B: 0.0010 mass% or more, 0.030 mass% or less) B has the effect of refining the crystal grains of aluminum alloys and improving their wroughtability. By adding B to aluminum alloys together with Ti as described above, the effect of refining the crystal grains is improved. If the B content is less than 0.0010 mass%, the effect of refining the crystal grains may not be sufficiently obtained. On the other hand, if the B content exceeds 0.030 mass%, coarse precipitates may form and be mixed into the aluminum alloy forged product 1a as inclusions. Furthermore, if a large amount of coarse precipitates containing B are mixed into the final aluminum alloy product, the toughness may decrease. Therefore, the B content should be 0.0010 mass% or more and 0.030 mass%. Preferably, the B content is 0.0050 mass% or more and 0.025 mass%.

[0041] (Zr: 0.0010 mass% or more, 0.05 mass% or less) If the Zr content is 0.05 mass% or less, it precipitates in the form of Al3Zr and Al-(Ti,Zr), contributing to improved strength of the aluminum alloy forged product 1a through recrystallization inhibition and precipitation strengthening. If the Zr content exceeds 0.050 mass%, it may crystallize as coarse Zr compounds, potentially leading to a decrease in the corrosion resistance of the aluminum alloy forged product 1a. Therefore, the Zr content should be 0.050 mass% or less. Furthermore, to obtain the above-mentioned effects of recrystallization inhibition and precipitation strengthening that improve the strength of the forged product, it is preferable that the Zr content be 0.0010 mass% or more.

[0042] (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 formed and precipitates from the Al matrix to the grain boundaries, causing intergranular corrosion and leading to a decrease in the corrosion resistance of aluminum alloy forgings. For this reason, it is preferable that the Zn content be 0.250% by mass or less, or that it be completely absent.

[0043] (Inevitable impurities) Unavoidable impurities are impurities that inevitably become mixed into the aluminum alloy from the raw materials or during the manufacturing process. Examples of unavoidable impurities include Ni, Sn, and Be. It is preferable that the content of these unavoidable impurities does not exceed 0.1% by mass.

[0044] The longitudinal boundary portion 2b between the elongated portion 2 and the connecting portion 4 of the aluminum alloy forged product 1a in this embodiment is the portion where the minimum principal stress is applied, for example, when the aluminum alloy forged product 1a is used as a suspension arm of a vehicle. The cross-section of the longitudinal boundary portion 2b between the elongated portion 2 and the connecting portion 4 is the cross-section in the direction along which pressure was applied when the aluminum alloy forged product 1a was manufactured by forging.

[0045] Here, the grain size was defined as the diameter of a circle with an area equal to that of each grain (equivalent diameter). The grain area was calculated from images of the grains obtained using SEM (Scanning Electron Microscope) or EBSD (Electron Backscatter Diffraction). The average grain size was the average of the equivalent diameters of 420 or more grains. The average grain size may also be calculated using, for example, commercially available image analysis software.

[0046] (Average grain size: 5μm or more, 60μm or less) The average grain size of the alloy structure in the central cross-section of the aluminum alloy forged product 1a serves as an indicator of the degree of grain refinement at the longitudinal boundary 2b between the long section 2 and the connecting section 4 of the aluminum alloy forged product 1a. If the average grain size of the crystal grains in the cross-section of the longitudinal boundary 2b between the long section 2 and the connecting section 4 exceeds 60 μm, the tensile properties and fatigue properties may decrease according to the Hall-Petch law. On the other hand, if the average grain size is less than 5 μm, the toughness may deteriorate and the impact resistance may decrease. For this reason, the average grain size in the cross-section of the longitudinal boundary 2b between the long section 2 and the connecting section 4 is set to be in the range of 5 μm or more and 60 μm or less.

[0047] In the microstructure of the cross-section of the longitudinal boundary portion 2b between the elongated portion 2 and the connecting portion 4 of the aluminum alloy forged product 1a, the standard deviation of the grain size is not particularly limited, but is preferably 30 or less. This is because suppressing the variation in grain size so that the standard deviation of the grain size is 30 or less increases the impact resistance of the aluminum alloy forged product 1a. The standard deviation of the grain size is more preferably 25 or less, and even more preferably 20 or less.

[0048] (Does not contain AIFeSi(Mn)-based compounds with an average particle size of 2.0 μm or larger) Aluminum alloy forged product 1a The longitudinal boundary portion 2b between the long portion 2 and the connecting portions 4a and 4b The alloy structure in cross-section should not contain AIFeSi(Mn) compounds with an average particle size of 2.0 μm or larger. The presence of AIFeSi(Mn) compounds with an average particle size of 2.0 μm or larger may lead to a decrease in mechanical properties (tensile properties / fatigue properties, etc.).

[0049] (Fatigue limit of 150 MPa or higher in repeated cycles) Aluminum alloy forged product 1a The longitudinal boundary portion 2b between the long portion 2 and the connecting portions 4a and 4b The cross-section shows fatigue characteristics at room temperature (20°C), with a fracture cycle count of 10. 7 The component possesses mechanical properties that result in a fatigue limit of 150 MPa or higher during the cycle. If this fatigue limit is below 150 MPa, there is a risk of reduced component durability.

[0050] (Ratio of large-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 forged product 1a, grain boundaries with a crystal orientation difference of 15° or more (large-angle grain boundaries) serve as an indicator of the degree of recrystallization progress at the longitudinal boundary 2b between the elongated portion 2 and the connecting portion 4 of the aluminum alloy forged product 1a. A ratio of 27% or less of these large-angle grain boundaries indicates that recrystallization is sufficiently suppressed. Sufficient suppression of recrystallization improves the mechanical properties of the elongated portion 2. The ratio of large-angle grain boundaries can be obtained from EBSD images.

[0051] The aluminum alloy forged product 1a of this embodiment, having the above-described alloy composition of the aluminum alloy material, is less prone to recrystallization during the manufacturing of the forged product. Therefore, excessively coarse crystal grains are less likely to form. Furthermore, the cross-section of the longitudinal boundary portion 2b between the long portion 2 and the connecting portion 4 of the aluminum alloy forged product 1a of this embodiment has an alloy structure in which the average crystal grain size is within the range of 5 μm to 60 μm and does not contain AIFeSi(Mn)-based compounds with an average particle diameter of 2.0 μm or more. Therefore, the longitudinal boundary portion 2b between the long portion 2 and the connecting portion 4 has high tensile and fatigue properties, excellent toughness and improved impact resistance. Moreover, the aluminum alloy forged product 1a of this embodiment has a fracture cycle count of 10 7 The fatigue limit during the cycle is 150 MPa or higher, and it has durability comparable to iron-based metal materials.

[0052] The aluminum alloy forged product 1a of this embodiment has high strength and durability at the longitudinal boundary portion 2b between the elongated portion 2 and the connecting portion 4, and is also lightweight, making it advantageous for use as a suspension arm in vehicles such as automobiles.

[0053] In the aluminum alloy forged product 1a of this embodiment shown in Figure 1, one connecting portion 4a is cylindrical with a relatively small diameter, and the other connecting portion 4b is cylindrical with a relatively large diameter. The elongated portion 2 is shaped to widen from the end on the side of one connecting portion 4a to the end on the side of the other connecting portion 4b. However, the shape of the aluminum alloy forged product 1a is not limited to this. For example, one connecting portion 4a and the other connecting portion 4b of the aluminum alloy forged product 1a may have the same shape. The width of the elongated portion 2 may be constant. Also, the elongated portion 2 may have a curved shape. Three or more connecting portions 4 may be formed.

[0054] Figure 2 is a plan view of another example of an aluminum alloy forged product according to one embodiment of the present invention. The aluminum alloy forged product 1b shown in Figure 2 has three connecting parts 4c, 4d, and 4e. Connecting parts 4c and 4d are connected by a long section 2, and connecting parts 4d and 4e are connected by a short section 5 which is relatively shorter than the long section 2. This aluminum alloy forged product 1b can be used, for example, as an L-shaped suspension arm.

[0055] Figure 3 is a plan view of yet another example of an aluminum alloy forged product according to one embodiment of the present invention. The aluminum alloy forged product 1c shown in Figure 3 has three connecting parts 4f, 4g, and 4h. Connecting parts 4f and 4g, and connecting parts 4f and 4h are each connected by an elongated section 2. This aluminum alloy forged product 1b can be used, for example, as an A-type suspension arm.

[0056] An aluminum alloy forged product according to another embodiment of the present invention is an aluminum alloy forged product having a long portion and a connecting portion, wherein the following elements are present: 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%, Cr in the range of 0.050 mass% to 0.30 mass%, and Ti in the range of 0.01 mass% to 0.1 mass. The aluminum alloy composition has an alloy composition in which B is contained in the range of 0.0010% to 0.030% by mass, Zr is contained in the range of 0.0010% to 0.050% by mass, the ratio of Fe content to Mn content (Fe / Mn) is less than 1.4 by mass, and the remainder consists of Al and unavoidable impurities, the cross section of the longitudinal boundary between the long portion and the connecting portion has an alloy structure in the range of 5 μm to 60 μm average grain size of the alloy structure and does not contain AIFeSi(Mn)-based compounds with an average grain size of 2.0 μm or more, and the fatigue properties at room temperature have a fracture cycle count of 10 7 The fatigue limit in the cycle is set at 150 MPa or higher.

[0057] An aluminum alloy forged product according to yet another embodiment of the present invention is an aluminum alloy forged product having a long portion and a connecting portion, wherein Cu is in the range of 0.25 mass% to 0.55 mass%, Mg is in the range of 0.85 mass% to 1.25 mass%, Si is in the range of 1.02 mass% to 1.4 mass%, Mn is in the range of 0.61 mass% to 1.0 mass%, Fe is in the range of 0.32 mass% to 0.65 mass%, Zn is in the range of 0.25 mass%, Cr is in the range of 0.050 mass% to 0.30 mass%, and Ti is in the range of 0.01 mass% to 0.1 mass The alloy has an alloy composition in which, within the range of % or less, B is contained in the range of 0.0010 mass% to 0.030 mass%, Zr is contained in the range of 0.0010 mass% to 0.050 mass%, the ratio of Fe content to Mn content (Fe / Mn) is 0.3 to 1.2 by mass, and the remainder is Al and unavoidable impurities, the cross section of the longitudinal boundary between the long portion and the connecting portion has an alloy structure in which the average grain size of the alloy structure is within the range of 5 μm to 60 μm, and does not contain AIFeSi(Mn)-based compounds with an average grain size of 2.0 μm or more, and the fatigue properties at room temperature have a fracture cycle count of 10 7 The fatigue limit in the cycle is set at 150 MPa or higher.

[0058] [Manufacturing method for aluminum alloy forgings] Next, the manufacturing method for the aluminum alloy forged product of this embodiment will be described. The manufacturing method for aluminum alloy forged products according to this embodiment includes, for example, a molten metal formation step, a casting step, a homogenization heat treatment step, a forging step, a solution treatment step, a quenching step, and an aging treatment step. Of these, the solution treatment step may be performed as needed and is not an essential step.

[0059] (Molten metal formation process) The molten metal formation process is the process of melting raw materials to obtain molten aluminum alloy with a prepared composition. The composition of the molten aluminum alloy is the same as that of the aluminum alloy forged product. Specifically, a molten 6000 series aluminum alloy is obtained by adjusting the alloy composition to contain Cu in the range of 0.25 mass% to 0.55 mass%, Mg in the range of 0.85 mass% to 1.25 mass%, Si in the range of 1.02 mass% to 1.4 mass%, Mn in the range of 0.55 mass% to 1.0 mass%, Fe in the range of 0.32 mass% to 0.65 mass%, Zn in the range of 0.25 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%, B in the range of 0.0010 mass% to 0.030 mass%, and Zr in the range of 0.0010 mass% to 0.050 mass%, with a Fe / Mn ratio of 0.3 to 1.2 mass%, and the remainder consisting of Al and unavoidable impurities. By using the molten aluminum alloy of the above composition for the subsequent processes, it is possible to obtain forged aluminum alloy products of the Al-Mg-Si type that are less prone to recrystallization and have excellent mechanical properties at room temperature. Note that "new aluminum ingot" refers to aluminum with a concentration of 99% or higher obtained by electrolysis, a process called electrolytic refining, on alumina produced from minerals.

[0060] Molten aluminum alloy can be obtained by heating and melting an aluminum alloy. Alternatively, it may be formed by melting a mixture containing the elements that are the raw materials for the aluminum alloy, or a compound containing two or more elements, in a proportion that produces the desired aluminum alloy. For example, to control the grain size of the aluminum alloy produced in the casting process, Ti or B may be mixed in as grain refiners such as Al-Ti-B rods.

[0061] Alternatively, molten aluminum alloy may be obtained by using 10% or more of scrap material from 1000, 2000, 3000, 4000, 5000, 6000, and 7000 series aluminum alloys as raw materials, with the remainder being new aluminum ingots and the above-mentioned additive elements, and then melting these to adjust the composition. In this case, Al-Mg-Si aluminum alloy forgings with excellent mechanical properties at room temperature and less susceptible to recrystallization can be obtained. New aluminum ingots refer to aluminum with a purity of 99% or higher, obtained by electrolysis, also known as electrolytic refining, of alumina produced from minerals.

[0062] (Casting process) In the casting process, molten aluminum alloy (liquid phase) is cooled and solidified into a solid (solid phase) to obtain an aluminum alloy casting. For example, a horizontal continuous casting method can be used for the casting process.

[0063] Figures 4 and 5 show a horizontal continuous casting apparatus that can be used to manufacture aluminum alloy castings according to this embodiment. Figure 4 is a cross-sectional view showing an example of the area around the mold 12 of the horizontal continuous casting apparatus 10. Figure 5 is an enlarged cross-sectional view of the main part around the cooling water cavity 24 of the horizontal continuous casting apparatus 10.

[0064] The horizontal continuous casting apparatus 10 shown in Figures 4 and 5 includes a molten metal receiving section (tundish) 11, a hollow cylindrical mold 12, and a refractory plate-like body (insulating member) 13 positioned between one end 12a of the mold 12 and the molten metal receiving section 11.

[0065] The molten metal receiving section 11 consists of a molten metal inlet section 11a for receiving the molten aluminum alloy M obtained in the molten metal forming process described above, a molten metal holding section 11b, and an outlet section 11c for outflow to the hollow section 21 of the mold 12.

[0066] The molten metal receiving section 11 maintains the upper liquid level of the molten aluminum alloy M at a position higher than the upper surface of the hollow section 21 of the mold 12, and in the case of multi-casting, it stably distributes the molten aluminum alloy M to each mold 12.

[0067] The molten aluminum alloy M held in the molten metal holding section 11b within the molten metal receiving section 11 is poured into the hollow section 21 of the mold 12 through the pouring passage 13a provided in the refractory plate-shaped body 13. The molten aluminum alloy M supplied into the hollow section 21 is then cooled and solidified by a cooling device 23 (described later), and is pulled out from the other end 12b of the mold 12 as a solidified ingot, an aluminum alloy rod B.

[0068] The other end 12b of the mold 12 may be equipped with a draw-out drive device (not shown) for drawing out the cast aluminum alloy rod B at a constant speed. It is also preferable to have a synchronized cutting machine (not shown) for cutting the continuously drawn aluminum alloy rod B to any desired length.

[0069] The refractory plate-like body 13 is a member that blocks heat transfer between the molten metal receiving section 11 and the mold 12, and may be composed of materials such as calcium silicate, alumina, silica, a mixture of alumina and silica, silicon nitride, silicon carbide, or graphite. Such a refractory plate-like body 13 can also be composed of multiple layers made of different materials.

[0070] In this embodiment, the mold 12 is a hollow cylindrical member and is formed from one or more materials selected from, for example, aluminum, copper, or alloys thereof. The materials for the mold 12 should be selected in an optimal combination from the viewpoint of thermal conductivity, heat resistance, and mechanical strength.

[0071] 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 shape, and the mold 12 is held such that the mold central axis (central axis) C, which passes through the center of this hollow portion 21, is aligned in a nearly horizontal direction.

[0072] The inner circumferential 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's central axis C, in the casting direction of the aluminum alloy rod B (see Figure 4). In other words, the inner circumferential surface 21a is configured as a tapered shape that opens in a cone shape toward the casting direction. The angle formed by this taper is the elevation angle.

[0073] If the elevation angle is less than 0°, casting may become difficult because the aluminum alloy rod B encounters resistance at the other end 12b, which is the mold exit, when it is pulled out of the mold 12. On the other hand, if the elevation angle exceeds 3°, the contact between the inner circumferential surface 21a and the molten aluminum alloy M becomes insufficient, and the heat dissipation effect from the molten aluminum alloy M and the solidified shell formed therefrom to the mold 12 decreases, which may result in insufficient solidification. As a result, this may lead to casting problems such as the formation of a remelted surface on the surface of the aluminum alloy rod B, or the ejection of unsolidified molten aluminum alloy M from the end of the aluminum alloy rod B, which is undesirable.

[0074] Furthermore, 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 21b) can be selected according to the shape of the aluminum alloy rod to be cast, in addition to the circular shape of this embodiment. For example, it can be a triangular, rectangular, polygonal, semicircular, elliptical, or an irregularly shaped cross-section without an axis of symmetry or plane of symmetry.

[0075] A fluid supply pipe 22 is located at one end 12a of the mold 12 to supply 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 types of lubricating fluid selected from gaseous lubricants and liquid lubricants. When supplying both gaseous and liquid lubricants, it is preferable to provide separate fluid supply pipes for each. The pressurized lubricating fluid supplied from the fluid supply pipe 22 is supplied into the hollow portion 21 of the mold 12 through an annular lubricant supply port 22a.

[0076] In this embodiment, the pressurized lubricating fluid is supplied to the inner circumferential surface 21a of the mold 12 from the lubricant supply port 22a. Alternatively, the liquid lubricant may be heated and decomposed into a gas before being supplied to the inner circumferential surface 21a of the mold 12. Alternatively, a porous material may be placed at the lubricant supply port 22a, allowing the lubricating fluid to seep out onto the inner circumferential surface 21a of the mold 12 through this porous material.

[0077] 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 in this embodiment has a cooling water cavity 24 that contains 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.

[0078] The cooling water cavity 24 is formed in an annular shape inside the mold 12, outside the inner circumferential surface 21a of the hollow portion 21, and cooling water W is supplied via the cooling water supply pipe 26.

[0079] The mold 12 is cooled by the cooling water W contained in the cooling water cavity 24, which removes heat from the molten aluminum alloy M filling the hollow portion 21 of the mold 12 from the surface in contact with the inner surface 21a of the mold 12, causing a solidified shell to form on the surface of the molten aluminum alloy M.

[0080] Furthermore, the cooling water injection passage 25 cools the aluminum alloy rod B by directly applying cooling water W to the aluminum alloy rod B at the other end 12b of the mold 12 from the shower opening 25a facing the hollow portion 21. The longitudinal cross-sectional shape of the cooling water injection passage 25 may be other than the circular shape of this embodiment, for example, a semicircle, a pear shape, or a horseshoe shape.

[0081] In this embodiment, the cooling water W supplied via the cooling water supply pipe 26 is first contained 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 from the cooling water cavity 24 is injected from the cooling water injection passage 25 toward the aluminum alloy rod B. However, it is also possible to configure the system so that these are supplied by separate cooling water supply pipes.

[0082] The effective mold length L is defined as the distance from the point where the extension of the central axis of the shower opening 25a of the cooling water injection passage 25 strikes the surface of the cast aluminum alloy rod B to the contact surface between the mold 12 and the refractory plate-like body 13. This effective mold length L is preferably, for example, 10 mm or more and 40 mm or less. If the effective mold length L is less than 10 mm, casting becomes impossible due to the inability to form a good coating, and if it exceeds 40 mm, the effect of forced cooling decreases, 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 in the casting surface or breakage inside the mold, making casting unstable and therefore undesirable.

[0083] Preferably, the supply of cooling water W to these cooling water cavities 24 and the injection of cooling water W from the shower openings 25a of the cooling water injection passages 25 can be controlled by control signals from a control device (not shown).

[0084] The cooling water cavity 24 is formed such that the inner bottom surface 24a of the mold 12 near the hollow portion 21 is parallel to the inner circumferential surface 21a of the hollow portion 21 of the mold 12.

[0085] In this context, "parallel" includes cases where the inner circumferential surface 21a of the hollow portion 21 of the mold 12 is formed at an elevation angle of 0° to 3° with respect to the inner bottom surface 24a of the cooling water cavity 24, that is, cases where the inner bottom surface 24a is inclined to the inner circumferential surface 21a at an angle greater than 0° and up to 3°.

[0086] As shown in Fig. 4, the cooling wall portion 27 of the mold 12, which is the portion where the inner bottom surface 24a of the cooling water cavity 24 and the inner peripheral surface 21a of the hollow portion 21 of the mold 12 face each other, has a heat flux value per unit area from the molten aluminum alloy M in the hollow portion 21 towards the cooling water W in the cooling water cavity 24 of 10×10 5 W / m 2 or more and 50×10 5 W / m 2 or less within the following range.

[0087] The thickness t of the cooling wall portion 27 of the mold 12, that is, the distance between the inner bottom surface 24a of the cooling water cavity 24 and the inner peripheral surface 21a of the hollow portion 21 of the mold 12, may be formed so as to be within the range of, for example, 0.5 mm or more and 3.0 mm or less, preferably 0.5 mm or more and 2.5 mm or less. Further, the forming material of 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 the range of 100 W / m·K or more and 400 W / m·K or less.

[0088] In Fig. 4, the molten aluminum alloy M in the molten metal receiving portion 11 is supplied from one end side 12a of the mold 12 held so that the mold central axis C is substantially horizontal through the refractory plate-like body 13, and is forcibly cooled at the other end side 12b of the mold 12 to become the aluminum alloy rod B.

[0089] The aluminum alloy rod B is pulled out at a constant speed by a drawing drive device (not shown) installed near the other end side 12b of the mold 12, so that a long aluminum alloy rod B is continuously cast. The pulled-out aluminum alloy rod B is cut to a desired length by, for example, a synchronous cutting machine (not shown).

[0090] The composition ratio of the cast aluminum alloy rod B can be confirmed by a method using, for example, a photoelectric emission spectroscopic analyzer (device example: PDA - 5500 manufactured by Shimadzu Corporation, Japan) as described in "JIS H 1305".

[0091] The difference in height between the liquid level of the molten aluminum alloy M stored in the molten metal receiving section 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 keeping it 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 the vaporization of the lubricating oil are suitably balanced, resulting in stable castability.

[0092] Liquid lubricants can use vegetable oils as lubricants. Examples include rapeseed oil, castor oil, and salad oil. These are preferable because they have little adverse impact on the environment.

[0093] The lubricating oil supply rate is preferably 0.05 mL / min to 5 mL / min (more preferably 0.1 mL / min or more and 1 mL / min or less). If the supply rate is too low, the molten aluminum alloy M of the aluminum alloy rod B may not solidify due to insufficient lubrication and may leak from the mold 12. If the supply rate is too high, the excess may mix into the aluminum alloy rod B and cause internal defects.

[0094] The casting speed, which is the speed at which the aluminum alloy rod B is drawn out of the mold 12, is preferably 200 mm / min or more and 1500 mm / min or less (more preferably 400 mm / min or more and 1000 mm / min or less). This is because, within this range of casting speeds, the network structure of the precipitates formed during casting becomes uniform and fine, increasing the resistance to deformation of the aluminum material at high temperatures and improving the high-temperature mechanical strength.

[0095] The amount of cooling water sprayed from the shower opening 25a of the cooling water injection passage 25 is preferably 10 L / min or more and 50 L / min or less per mold (more preferably 25 L / min or more and 40 L / min or less). If the amount of cooling water is less than this, the molten aluminum alloy M may not solidify and may leak from the mold 12. In addition, the surface of the cast aluminum alloy rod 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 more than this range, the heat dissipation from the mold 12 may be too great, causing it to solidify prematurely.

[0096] The average temperature of the molten aluminum alloy M flowing from the molten metal receiving section 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 and in front of the mold 12 and be incorporated into the aluminum alloy rod B as internal defects. On the other hand, if the temperature of the molten aluminum alloy M is too high, a large amount of hydrogen gas is easily incorporated into the molten aluminum alloy M, which may be incorporated into the aluminum alloy rod B as porosity and form internal cavities.

[0097] Furthermore, 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 The above 50 x 10 5 W / m 2 By keeping the following range, seizing of aluminum alloy rod B can be prevented.

[0098] The cooling wall portion 27 of the mold 12 receives heat from the molten aluminum alloy M, and this heat is cooled by the cooling water W contained in the cooling water cavity 24, thus performing heat exchange. 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) according to Fourier's law. Q = -k × (T1 - T2) / L ···(1) Q: Heat flux k: Thermal conductivity (W / m·K) of the heat-transmitting portion (cooling wall portion 27 of the mold 12 in this embodiment) T1: Temperature on the lower side of the area 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 area through which heat passes (in this embodiment, the inner circumferential surface 21a of the hollow portion 21 of the mold 12) L: Length of the section through which heat passes (mm) (In this embodiment, the thickness t of the cooling wall portion 27 of the mold 12)

[0099] Based on mold material, thickness, and temperature measurement data that yielded good results even with reduced lubrication oil during casting, 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 as described above, it is possible to prevent the cast aluminum alloy rod B from seizing. In addition, the heat flux value per unit area is 50 × 10 5 W / m 2 The following is preferable:

[0100] To ensure that the cooling wall portion 27 of the mold 12 is within this range of heat flux values, the mold 12 can be formed such that the thickness t of the cooling wall portion 27 of the mold 12 is in the range of, for example, 0.5 mm or more and 3.0 mm or less. In addition, the thermal conductivity of at least the cooling wall portion 27 of the mold 12 should be in the range of 100 W / m·K or more and 400 W / m·K or less.

[0101] In manufacturing the aluminum alloy rod B of this embodiment, the molten aluminum alloy M stored in the molten metal receiving section 11 is continuously supplied to the hollow section 21 from one end 12a of the mold 12 using the horizontal continuous casting apparatus 10 described above. Cooling water W is supplied to the cooling water cavity 24, and a lubricating fluid, such as lubricating oil, is supplied from the fluid supply pipe 22.

[0102] Then, the molten aluminum alloy M supplied into the hollow section 21 is cooled by the cooling wall section 27, where the heat flux per unit area is 10 × 10 5 W / m 2 The aluminum alloy rod B is cast by cooling and solidifying under the above conditions. Furthermore, when casting the aluminum alloy rod B, it is preferable to keep the wall temperature of the cooling wall portion 27 of the mold 12, which is cooled by the cooling water W, below 100°C.

[0103] The resulting aluminum alloy rod B has a heat flux value of 10 × 10 per unit area in the cooling wall portion 27. 5 W / m 2By cooling and solidifying under the above conditions, the adhesion of reaction products, such as carbides, resulting from contact between the lubricating oil gas and the molten aluminum alloy M is suppressed. As a result, there is no need to cut off carbides and other materials from the surface of the aluminum alloy rod B, and the aluminum alloy rod B can be manufactured in high yield.

[0104] The casting process for obtaining a casting from molten aluminum alloy M is not limited to the horizontal continuous casting method described above; known continuous casting methods such as vertical continuous casting can be used. Vertical continuous casting is classified into the float method and the hot-top method depending on the method of supplying the molten aluminum alloy M to the mold (casting mold 12), but the case using the hot-top method will be briefly explained below.

[0105] The casting apparatus used in the hot top method includes a mold, a molten metal receiving container (header), etc. The molten metal supplied to the receiving section passes through a spout and then through the header, where its flow rate is adjusted. It then enters a cylindrical mold that is installed almost horizontally, where it is forcibly cooled and a solidified shell is formed on the outer surface of the molten metal.

[0106] Furthermore, cooling water is directly sprayed onto the casting as it is removed from the mold, allowing the metal to solidify inside the casting as it is continuously removed. Generally, molds are made of metal materials with good thermal conductivity and have a hollow structure to introduce a coolant into the interior.

[0107] The refrigerant used can be selected from industrially available options, but water is recommended for its ease of use.

[0108] The mold used in this embodiment is appropriately selected from metals such as copper or aluminum, or graphite, from the viewpoint of heat transfer performance and durability at the contact area with the molten metal. The header is generally made of refractory material and is installed on the upper side of the mold. The material and size of the header can be appropriately selected depending on the composition range of the alloy to be cast and the dimensions of the casting, and are not particularly restricted.

[0109] The average cooling rate during casting should be appropriately selected from a generally recommended range, such as 10 to 300°C / second. The casting speed should be appropriately selected from a range common in horizontal continuous casting, such as 200 to 600 mm / min.

[0110] The casting method described above allows for the acquisition of a uniform metallic structure even in medium to large castings. There are no particular restrictions on the diameter of the castings to be used, and it is suitably applied to rods with a diameter of 30 to 100 mm.

[0111] (Homogenization heat treatment process) The homogenization heat treatment process involves applying a homogenization heat treatment to the aluminum alloy casting obtained in the casting process. This process homogenizes the microsegregation caused by solidification, precipitates supersaturated solid solution elements, and transforms the metastable phase into an equilibrium phase. Furthermore, these homogenization heat treatment processes can be performed as needed, and it is also possible to proceed directly to the forging process after the casting process.

[0112] In this embodiment, the casting obtained in the casting process is subjected to a homogenization heat treatment, held at a temperature of 370°C or higher and 560°C or lower for 2 to 10 hours. By performing the homogenization heat treatment within this temperature range, the casting is sufficiently homogenized and solute atoms are sufficiently dissolved, so that sufficient strength required by the subsequent aging treatment can be obtained.

[0113] (Forging process) The forging process involves shaping an aluminum alloy casting, either after casting or after a homogenization heat treatment, to a predetermined size to obtain a material for forging. This material is then heated to a predetermined temperature and subsequently molded using a press.

[0114] In this embodiment, a forging process is performed on a forging material at a heating temperature of 450°C or higher and 560°C or lower to obtain a forged product (for example, an automobile suspension arm part). At this time, the starting temperature for forging of the forging material is set to 450°C or higher and 560°C or lower. This is because if the starting temperature is below 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.

[0115] (Solution treatment process) The solution treatment process involves heating the forged product obtained in the forging process to induce a solution state, thereby easing the strain introduced during the forging process and enabling the solid solution of solute elements.

[0116] In this embodiment, the forged product is subjected to solution treatment by holding it at a treatment temperature of 530°C or higher and 560°C or lower for 0.3 to 3 hours or less. 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 below 530°C, the solid solution of the solute element may be insufficient. On the other hand, if it exceeds 560°C, the solid solution of the solute element is further promoted, but eutectic melting and recrystallization may occur more easily. Also, if the heating rate is less than 5.0°C / min, coarse precipitation of Mg2Si may occur. On the other hand, if the treatment temperature is below 530°C, solution treatment may not progress, making it difficult to achieve high strength through age precipitation.

[0117] (Heat treatment process) The quenching process involves rapidly cooling the forged product, which is in a solid solution state obtained through the solution treatment process, to form a supersaturated solid solution.

[0118] In this embodiment, the forging is quenched by immersing it in a tank of water (quenching water). The water temperature in the tank is preferably between 20°C and 60°C. The forging is preferably placed in the tank of water for 5 seconds to 60 seconds after the solution treatment so that all surfaces of the forging come into contact with the water. The immersion time of the forging varies depending on the size of the forging, but is, for example, between 1 minute and 30 minutes.

[0119] (Statute of Limitations Process) The aging process involves heating and holding the forged product at a relatively low temperature to precipitate supersaturated dissolved elements, thereby imparting appropriate hardness.

[0120] 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 then aged by holding it at that temperature for 0.5 hours or higher and 7 hours or lower. If the treatment temperature is below 170°C or the holding time is less than 0.5 hours, there is a risk that the Mg2Si-based precipitates that improve tensile strength will not grow sufficiently. On the other hand, if the treatment temperature exceeds 190°C or the holding time exceeds 7 hours, there is a risk that the Mg2Si-based precipitates will become too coarse, and it will not be possible to sufficiently improve the tensile strength. [Examples]

[0121] Next, specific embodiments of the present invention will be described, but the present invention is not particularly limited to those embodiments.

[0122] [Examples 1-23 and Comparative Examples 1-3] (Manufacturing of continuously cast products) First, the aluminum alloy with the alloy composition shown in Table 1 below (the remainder being aluminum) composition I prepared the aluminum. composition Using this method, a continuous casting with a circular cross-section and a diameter of 49 mm was produced. The continuous castings of Examples 1 and 5, Examples 2 and 6, Examples 3 and 7, and Examples 4 and 8 all have the same alloy composition, but the processing conditions for manufacturing the aluminum alloy forgings differ. In addition, Examples 9 to 23 did not undergo a homogenization heat treatment process.

[0123] [Table 1]

[0124] (Manufacturing of aluminum alloy forgings) Next, the obtained continuous castings were subjected to a homogenization heat treatment process (omitted in Examples 9-23), a forging process, a solution treatment process, a quenching process, and an artificial aging process in this order to obtain an aluminum alloy forged product 1a with the shape shown in Figure 1. The conditions for the homogenization heat treatment process, forging process, solution treatment process, quenching process, and artificial aging process are shown in Table 2 below.

[0125] [Table 2]

[0126] [evaluation] The aluminum alloy forging materials of Examples 1-23 and Comparative Examples 1-3, and the longitudinal boundary portion 2b of the long portion 2 in the aluminum alloy forged product 1a were evaluated as follows. The evaluation results are shown in Table 3 below. For the evaluation of the refinement of forging materials and forged products, plate-like specimens (7 mm × 7 mm × 2 mm thick) used for preparing evaluation specimens were used. The average grain size and standard deviation of the grain size were measured on the surface of the collected evaluation specimens using a SEM-EBSD (Scanning Electron Microscope-Electron Backscatter Diffraction). The obtained average grain size and standard deviation were evaluated based on the following criteria to assess grain refinement and recrystallization / coarsening. The SEM-EBSD measurement conditions were: acceleration voltage of 15 kV, measurement pitch of 0.5 μm / px, and analysis area of ​​500 × 500 μm. 2 The grain boundary definition angle was set to 15°.

[0127] <Component: Fe / Mn ratio> We evaluated whether the Fe / Mn ratio of the aluminum alloy forging material was within the range of 0.3 to 1.2. (Judgment criteria) "〇" ... The Fe / Mn ratio is within the range of 0.3 to 1.2. "×" - The Fe / Mn ratio is outside the range of 0.3 to 1.2.

[0128] <Forging material: average grain size> We evaluated whether the average grain size of the aluminum alloy forging material was within the range of 50 μm to 120 μm. (Judgment criteria) "〇" ... The average crystal grain size is within the range of 50 μm to 120 μm. "×" - The average crystal grain size is outside the range of 50 μm to 120 μm.

[0129] <Forging material: Average crystal grain size of AIMnFeSi compound> We evaluated whether the average grain size (size) of the AIFeSi compound used as a material for aluminum alloy forging was within the range of 3.0 μm or less. (Judgment criteria) "〇" - The average crystal grain size (size) of the AIMnFeSi compound is 3.0 μm or less. "×" - The average crystal grain size (size) of the AIMnFeSi compound exceeds 3.0 μm.

[0130] <Forged products: Number of AIMnFeSi compounds with a size of 2.0 μm or larger> The number of AIMnFeSi compound particles with a size of 2.0 μm or larger was measured in aluminum alloy forged products. (Judgment criteria) "〇" ... No AIMnFeSi compound particles larger than 2.0 μm are present (0 particles). "×" ... At least one AIMnFeSi compound particle larger than 2.0 μm is present.

[0131] <Forged products: Average grain size and standard deviation of alloy structure> The average grain size and its standard deviation were measured for aluminum alloy forged products. (Judgment criteria: average grain size) "〇" ... The average grain size of the alloy structure is within the range of 5 μm to 60 μm. "×" - The average grain size of the alloy structure is outside the range of 5 μm to 60 μm. (Judgment criteria: standard deviation) "〇" ... The standard deviation of the average crystal grain size is 15 or less. "×" ... The standard deviation of the average crystal grain size exceeds 15.

[0132] <Mechanical properties (fatigue properties) evaluation> As shown in Figure 7A, the longitudinal boundary 2b between the long section 2 and the connecting section 4 of the aluminum alloy forged product 1a was cut to obtain a prismatic body for the preparation of a test specimen for evaluating mechanical properties (fatigue properties). The obtained prismatic body was processed to prepare a cylindrical test specimen for evaluating mechanical properties, as shown in Figure 7B. The parallel section diameter A of the test specimen for evaluating mechanical properties was 8.0 mm, and the gauge length G was 30.0 mm. The fatigue life of the test specimen for evaluating mechanical properties was measured by performing a rotational bending fatigue test at room temperature (25°C). The obtained fatigue life results were evaluated based on the following criteria. (Judgment criteria) "〇" ... Number of repeated fractures: 10 7 The fatigue limit in the cycle is 150 MPa or higher. "×" ... Number of repeated fractures: 10 7 The fatigue limit in the cycle is less than 150 MPa.

[0133] <Overall Rating> The evaluation results for each of the evaluation items described above were evaluated based on the following criteria. (Judgment criteria) "O" ... The result for all evaluation items is "O". "×" - One or more of the evaluation results are "×".

[0134] [Table 3]

[0135] As shown in Table 3, it was confirmed that by setting the content of each element within a predetermined range, and by carrying out each process—molten metal formation, casting, homogenization heat treatment, forging, solution treatment, quenching, and aging—with the processing conditions within a predetermined range, it is possible to produce aluminum alloy forged products in which sufficiently refined crystal grains can be formed in the longitudinal center of the long section with suppressed grain size variation, crystal coarsening due to recrystallization is suppressed, and aluminum alloy forged products with excellent mechanical properties at room temperature can be obtained. [Explanation of symbols]

[0136] 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 apparatus 11…Molten metal receiving section (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-like material (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 section B... Aluminum alloy rod M...Molten aluminum alloy W... Cooling water

Claims

1. A method for manufacturing an aluminum alloy forged product having a long section and a connecting section, A process of forming an alloy molten metal having the same alloy composition as the aforementioned aluminum alloy forged product, A casting process in which the molten aluminum alloy obtained in the molten alloy forming process is cooled and solidified to form an aluminum alloy casting, A forging process is performed on the aluminum alloy casting that has undergone the above casting process, at a heating temperature of 450°C to 560°C. A solution treatment step is performed on the forged product obtained in the forging step, by holding it at a treatment temperature of 530°C to 560°C for 0.3 hours to 3 hours. After the completion of the solution treatment process, the entire surface of the forged product is brought into contact with quenching water for a period of 5 seconds to 60 seconds, and the product is quenched in a water tank for a period of 1 minute to 30 minutes. The process includes an aging treatment step in which the forged product after the quenching treatment is subjected to an aging treatment at a heating temperature of 170°C to 210°C for 0.5 hours to 7 hours. 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%, 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 0.030 mass% The alloy composition has the following characteristics: it contains Zr in the range of 0.0010% by mass or more and 0.050% by mass or less, the ratio of Fe content to Mn content (Fe / Mn) is less than 1.4 by mass, and the remainder consists of Al and unavoidable impurities; the cross section of the longitudinal boundary between the long portion and the connecting portion has an average grain size of the alloy structure in the range of 5 μm or more and 60 μm or less, and does not contain AlFeSi(Mn)-based compounds with an average grain size of 2.0 μm or more; and the fatigue properties at room temperature have a fracture cycle count of 10 ７ A method for manufacturing aluminum alloy forgings, wherein the fatigue limit in the cycle is 150 MPa or higher.

2. A method for manufacturing an aluminum alloy forged product having a long section and a connecting section, A process of forming an alloy molten metal having the same alloy composition as the aforementioned aluminum alloy forged product, A casting process in which the molten aluminum alloy obtained in the molten alloy forming process is cooled and solidified to form an aluminum alloy casting, A forging process is performed on the aluminum alloy casting that has undergone the above casting process, at a heating temperature of 450°C to 560°C. A solution treatment step is performed on the forged product obtained in the forging step, by holding it at a treatment temperature of 530°C to 560°C for 0.3 hours to 3 hours. After the completion of the solution treatment process, the entire surface of the forged product is brought into contact with quenching water for a period of 5 seconds to 60 seconds, and the product is quenched in a water tank for a period of 1 minute to 30 minutes. The process includes an aging treatment step in which the forged product after the quenching treatment is subjected to an aging treatment at a heating temperature of 170°C to 210°C for 0.5 hours to 7 hours. Cu in the range of 0.25% to 0.55% by mass, Mg in the range of 0.85% to 1.25% by mass, Si in the range of 1.02% to 1.4% by mass, Mn in the range of 0.55% to 1.0% by mass, Fe in the range of 0.32% to 0.65% by mass, Zn in the range of 0.25% by mass, Cr in the range of 0.050% to 0.30% by mass, Ti in the range of 0.01% to 0.1% by mass, and B in the range of 0.0010% to 0.030% by mass. Within the range below, the alloy contains Zr in a range of 0.0010% by mass or more and 0.050% by mass or less, the ratio of Fe content to Mn content Fe / Mn is 0.3 or more and 1.2 by mass ratio, and the remainder consists of Al and unavoidable impurities, and the cross section of the longitudinal boundary between the long portion and the connecting portion has an average grain size of the alloy structure in the range of 5 μm or more and 60 μm or less, and does not contain AlFeSi(Mn)-based compounds with an average grain size of 2.0 μm or more, and the fatigue properties at room temperature have a fracture cycle count of 10 ７ A method for manufacturing aluminum alloy forgings, wherein the fatigue limit in the cycle is 150 MPa or higher.

3. A method for manufacturing an aluminum alloy forged product having a long section and a connecting section, A process of forming an alloy molten metal having the same alloy composition as the aforementioned aluminum alloy forged product, A casting process in which the molten aluminum alloy obtained in the molten alloy forming process is cooled and solidified to form an aluminum alloy casting, A forging process is performed on the aluminum alloy casting that has undergone the above casting process, at a heating temperature of 450°C to 560°C. A solution treatment step is performed on the forged product obtained in the forging step, by holding it at a treatment temperature of 530°C to 560°C for 0.3 hours to 3 hours. After the completion of the solution treatment process, the entire surface of the forged product is brought into contact with quenching water for a period of 5 seconds to 60 seconds, and the product is quenched in a water tank for a period of 1 minute to 30 minutes. The process includes an aging treatment step in which the forged product after the quenching treatment is subjected to an aging treatment at a heating temperature of 170°C to 210°C for 0.5 hours to 7 hours. Cu in the range of 0.25% to 0.55% by mass, Mg in the range of 0.85% to 1.25% by mass, Si in the range of 1.02% to 1.4% by mass, Mn in the range of 0.61% to 1.0% by mass, Fe in the range of 0.32% to 0.65% by mass, Zn in the range of 0.25% by mass, Cr in the range of 0.050% to 0.30% by mass, Ti in the range of 0.01% to 0.1% by mass, and B in the range of 0.0010% to 0.030% by mass. Within the range below, the alloy contains Zr in a range of 0.0010% by mass or more and 0.050% by mass or less, the ratio of Fe content to Mn content Fe / Mn is 0.3 or more and 1.2 by mass ratio, and the remainder consists of Al and unavoidable impurities, and the cross section of the longitudinal boundary between the long portion and the connecting portion has an average grain size of the alloy structure in the range of 5 μm or more and 60 μm or less, and does not contain AlFeSi(Mn)-based compounds with an average grain size of 2.0 μm or more, and the fatigue properties at room temperature have a fracture cycle count of 10 ７ A method for manufacturing aluminum alloy forgings, wherein the fatigue limit in the cycle is 150 MPa or higher.

4. A method for manufacturing an aluminum alloy forged product according to any one of claims 1 to 3, further comprising a homogenization heat treatment step between the casting step and the forging step, in which the aluminum alloy casting is subjected to a homogenization heat treatment by holding it at a temperature range of 370°C to 560°C for 2 hours to 10 hours.

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