Aluminum alloy forgings and manufacturing method thereof

Abstract

To provide an aluminum alloy forged article that has excellent mechanical property at ordinary temperature and is less likely to generate recrystallized grain, and to provide a method for producing the same.SOLUTION: An aluminum alloy forged article 1 of the present invention contains Cu: 0.15 mass% to 1.0 mass%, Mg: 0.6 mass% to 1.15 mass%, Si: 0.95 mass% to 1.25 mass%, Mn: 0.4 mass% to 0.6 mass%, Fe: 0.2 mass% to 0.3 mass%, Cr: 0.11 mass% to 0.25 mass%, Ti: 0.012 mass% to 0.035 mass%, and B by 0.0001 mass% to 0.03 mass%, the Zn content is 0.25 mass% or less, the Zr content is 0.05 mass% or less, the balance is Al and unavoidable impurities, and, in the cross-section structure of the forged article 1, the fraction of Mg2Si phase present in the visual field area of 500×500 μm2 as measured by SEM-EBSD method is 0.1% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for producing an Al-Mg-Si aluminum alloy forging having excellent mechanical properties at room temperature. [Background technology]

[0002] In recent years, aluminum alloys have been widely used as structural components for various products, taking advantage of their light weight. For example, high-tensile steel has been used for the suspension and bumper parts of automobiles, but in recent years, high-strength aluminum alloy materials have been used. For automobile parts, such as suspension parts, iron-based materials have been used exclusively, but they are increasingly being replaced by aluminum or aluminum alloy materials, mainly for the purpose of reducing weight.

[0003] These automobile parts require excellent corrosion resistance, high strength, and excellent workability, so Al-Mg-Si alloys, especially A6061, are widely used as aluminum alloy materials. In order to improve the strength of these automobile parts, they are manufactured by forging, which is a type of plastic processing, using aluminum alloy materials as the processing material.

[0004] Recently, due to the need to reduce costs, suspension parts have begun to be put into practical use in which cast parts are used as the raw material without extrusion, and then subjected to T6 treatment. In order to further reduce weight, development of high-strength alloys to replace the conventional A6061 is underway (see Patent Documents 1 to 3 below). [Prior art documents] [Patent documents]

[0005] [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]

[0006] However, the above-mentioned high-strength Al-Mg-Si alloys have a problem in that the processed structure recrystallizes during the forging and heat treatment processes, resulting in the generation of coarse crystal grains, making it impossible to obtain sufficient strength. Therefore, some alloys contain Zr to prevent recrystallization in order to prevent the generation of coarse recrystallized grains (for example, Patent Documents 1 and 2).

[0007] Although the addition of Zr is effective in preventing recrystallization, it has the following problems.

[0008] (1) The addition of Zr weakens the effect of refining the crystal grains of the Al-Ti-B alloy, coarsening the crystal grains of the ingot itself, leading to a decrease in the strength of the processed product (forged product) after plastic processing.

[0009] (2) The effect of refining the crystal grains of the ingot itself is weakened, so that the ingot is more likely to crack, the number of internal defects increases, and the yield decreases.

[0010] (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 also crystallize out as coarse particles in the produced ingots, reducing their strength.

[0011] Thus, although the addition of Zr is effective in preventing recrystallization, it is difficult to maintain the stability of strength.

[0012] The present invention has been made in consideration of the above technical background, and has an object to provide an aluminum alloy forging that has excellent mechanical properties at room temperature and is less susceptible to the generation of recrystallized grains, and a manufacturing method thereof. [Means for solving the problem]

[0013] In order to achieve the above object, the present invention provides the following means.

[0014] [1] An aluminum alloy forging containing 0.15% by mass to 1.0% by mass of Cu, 0.6% by mass to 1.15% by mass of Mg, 0.95% by mass to 1.25% by mass of Si, 0.4% by mass to 0.6% by mass of Mn, 0.2% by mass to 0.3% by mass of Fe, 0.11% by mass to 0.25% by mass of Cr, 0.012% by mass to 0.035% by mass of Ti, 0.0001% by mass to 0.03% by mass of B, a Zn content of 0.25% by mass or less, a Zr content of 0.05% by mass or less, and the balance being Al and unavoidable impurities, In the cross-sectional structure of the forged product, a field area of ​​500 × 500 μm measured by the SEM-EBSD method 2 An aluminum alloy forging, characterized in that the Mg2Si phase fraction present therein is 0.1% or less.

[0015] [2] A method for producing an aluminum alloy forging according to the preceding paragraph 1, comprising the steps of: a molten metal forming step for obtaining a molten metal; a casting step of obtaining a casting by casting the molten metal obtained in the molten metal forming step; a homogenization heat treatment step in which homogenization heat treatment is performed on the casting obtained in the casting step; A forging process for obtaining a forged product by forging the cast product after the homogenization heat treatment process; a solution treatment step of subjecting the forged product obtained in the forging step to a solution treatment; a quenching treatment step of quenching after the solution treatment step; and an aging treatment step of subjecting the forged product after the quenching treatment step to aging treatment.

[0016] [3] The homogenization heat treatment step is a homogenization heat treatment step in which the casting obtained in the casting step is held at a temperature of 370°C to 560°C for 4 hours to 10 hours, The forging process is a process of forging the casting after the homogenization heat treatment process at a heating temperature of 450°C to 560°C. The solution treatment step is a step of heating the forged product obtained in the forging step from 20°C to 500°C at a heating rate of 5.0°C / min or more, and then holding the product at 530°C to 560°C for 0.3 hours to 3 hours. In the quenching treatment process, the entire surface of the forged product is brought into contact with quenching water within 5 to 60 seconds after the solution treatment process, and quenching is performed in a water tank for more than 5 minutes but not exceeding 40 minutes, 3. The method for producing an aluminum alloy forged product according to item 2 above, wherein the aging treatment step comprises heating the forged product after the quenching treatment step at a temperature of 180°C to 220°C for 0.5 hours to 1.5 hours to perform aging treatment. Effect of the Invention

[0017] According to the invention of [1], the content of each element is set within a predetermined range, and in the cross-sectional structure of the forged product, a field area of ​​500 × 500 μm measured by SEM-EBSD method is 2 By controlling the Mg2Si phase fraction in the aluminum alloy to 0.1% or less, it is possible to provide an aluminum alloy forging that has excellent mechanical properties at room temperature and is less susceptible to the generation of recrystallized grains.

[0018] According to the invention of [2], by including a molten metal forming process, a casting process, a homogenization heat treatment process, a forging process, a solution treatment process, a quenching treatment process and an aging treatment process, it is possible to manufacture an aluminum alloy forging having excellent mechanical properties at room temperature and being resistant to recrystallization grains.

[0019] According to the invention [3], by setting the processing conditions in each processing step within a predetermined range, it is possible to produce an aluminum alloy forging that has even better mechanical properties at room temperature and is less susceptible to the generation of recrystallized grains. [Brief description of the drawings]

[0020] [Figure 1] FIG. 1 is a perspective view showing an aluminum alloy forging obtained by the manufacturing method of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] The aluminum alloy forgings and the method for producing the aluminum alloy forgings of the present invention will now be described.

[0022] It should be noted that the embodiments described below are merely examples, and the present invention is not limited to these exemplified embodiments, but may be modified as appropriate within the scope of the technical concept of the present invention.

[0023] The aluminum alloy forged product 1 of this embodiment contains 0.15% by mass to 1.0% by mass of Cu, 0.6% by mass to 1.15% by mass of Mg, 0.95% by mass to 1.25% by mass of Si, 0.4% by mass to 0.6% by mass of Mn, 0.2% by mass to 0.3% by mass of Fe, 0.11% by mass to 0.25% by mass of Cr, 0.012% by mass to 0.035% by mass of Ti, 0.0001% by mass to 0.03% by mass of B, a Zn content of 0.25% by mass or less, a Zr content of 0.05% by mass or less, and the balance being Al and unavoidable impurities. In the cross-sectional structure of this forged product 1, a field area of ​​500 × 500 μm measured by SEM-EBSD method is 2 The content of the Mg2Si phase in the steel sheet is 0.1% or less.

[0024] In this way, the content of each element is set within a predetermined range, and in the cross-sectional structure of the forged product 1, a field area of ​​500 × 500 μm 2 By controlling the Mg2Si phase fraction in the aluminum alloy to 0.1% or less, it is possible to provide an aluminum alloy forging that has excellent mechanical properties at room temperature and is less susceptible to the generation of recrystallized grains.

[0025] The method for manufacturing an aluminum alloy forging 1 according to the present embodiment involves carrying out 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 in this order to manufacture an aluminum alloy forging 1 as shown in Fig. 1, for example. Each step will be described below.

[0026] (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.

[0027] In this embodiment, a molten 6000 series aluminum alloy containing Cu: 0.15 mass% to 1.0 mass%, Mg: 0.6 mass% to 1.15 mass%, Si: 0.95 mass% to 1.25 mass%, Mn: 0.4 mass% to 0.6 mass%, Fe: 0.2 mass% to 0.3 mass%, Cr: 0.11 mass% to 0.25 mass%, Ti: 0.012 mass% to 0.035 mass%, B: 0.0001 mass% to 0.03 mass%, Zn content is 0.25 mass% or less, Zr content is 0.05 mass% or less, and the balance is Al and inevitable impurities is obtained (prepared). In this molten aluminum alloy, the Zn content may be 0 mass% (Zn not contained), and the Zr content may be 0 mass% (Zr not contained).

[0028] (Casting process) The casting step is a step of obtaining a casting by casting the aluminum alloy molten metal obtained in the molten metal forming step.

[0029] The continuous casting method for obtaining a cast product is not particularly limited, and various known continuous casting methods (vertical continuous casting method, horizontal continuous casting method, etc.) can be mentioned. As the vertical continuous casting method, a hot top casting method, etc. is used. Below, a brief description will be given of a case where an aluminum alloy continuous cast material is produced by a hot top casting method using a hot top casting device as an example of a continuous casting method (i.e., a case where an aluminum alloy continuous cast material is produced by continuously casting a molten aluminum alloy by the hot top casting method).

[0030] The hot top casting device is equipped with a mold, a molten metal receiving vessel (header), etc. The mold is cooled by cooling water that fills its interior. The receiving vessel is generally made of refractory material and is installed above the mold. The molten aluminum alloy in the receiving vessel is poured downward into the cooled mold, and is cooled and solidified at a predetermined cooling rate by the cooling water sprayed from the mold, and is further immersed in water (temperature: about 20°C) in a water tank where it solidifies completely. This produces long continuous cast material in the shape of a rod or the like.

[0031] (Homogenization heat treatment process) The homogenization heat treatment process is a process in which the cast material obtained in the casting process is subjected to homogenization heat treatment to homogenize microsegregations caused by solidification, precipitate supersaturated solid solution elements, and transform metastable phases into equilibrium phases.

[0032] In this embodiment, the casting obtained in the casting process is subjected to homogenization heat treatment by holding it at a temperature of 370° C. to 560° C. for 4 to 10 hours. By carrying out homogenization heat treatment in this temperature range, the ingot is homogenized sufficiently and solute atoms are sufficiently dissolved, so that sufficient strength required for the subsequent aging treatment can be obtained.

[0033] (Forging process) The forging step is a step in which the forging billet obtained after the homogenization heat treatment step is heated and pressed with a press to form it into a die.

[0034] In this embodiment, the ingot after the homogenization heat treatment is forged at a heating temperature of 450°C to 560°C to obtain a forged product (such as a suspension arm part for an automobile). At this time, the starting temperature for forging the forging material is 450°C to 560°C. If the starting temperature is less than 450°C, the deformation resistance becomes high and sufficient processing becomes impossible, and if it exceeds 560°C, defects such as forging cracks and eutectic melting are likely to occur.

[0035] (Solution treatment process) The solution treatment process is a process for relieving the strain introduced in the forging process and for dissolving the solute elements.

[0036] In this embodiment, the temperature of the forged product after the forging process is lowered to 20°C, and then heating begins once it has returned to room temperature. The temperature is increased at a rate of 5.0°C / min or higher throughout the entire temperature range from 20°C to 500°C, and the product is held at 530°C to 560°C for 0.3 to 3 hours to perform solution treatment.

[0037] If the heating rate is less than 5.0°C / min, coarse Mg2Si precipitates, and if the treatment temperature is less than 530°C, the solution treatment does not progress and high strength through aging precipitation cannot be achieved. If the treatment temperature exceeds 560°C, although the solid solution of the solute elements is further promoted, eutectic melting and recrystallization are likely to occur.

[0038] (Hardening process) The quenching process is a heat treatment for forming a supersaturated solid solution by rapidly cooling the solid solution state obtained by the solution treatment process.

[0039] In this embodiment, the entire surface of the forged product is brought into contact with quenching water within 5 to 60 seconds after the solution treatment, and quenching is performed in the water tank for more than 5 minutes and up to 40 minutes.

[0040] (Aging treatment process) The aging treatment process is a heat treatment in which an aluminum alloy forged product is heated and held at a relatively low temperature to precipitate elements that are supersaturated in solid solution, thereby imparting an appropriate hardness.

[0041] In this embodiment, the forged product after the quenching process is heated at a temperature of 180°C to 220°C for 0.5 to 1.5 hours to perform aging treatment. If the treatment temperature is less than 180°C or the treatment time is less than 0.5 hours, the Mg2Si-based precipitates that improve the tensile strength do not grow sufficiently, and if the treatment temperature exceeds 220°C, the Mg2Si-based precipitates become too coarse to sufficiently improve the tensile strength.

[0042] As described above, in the manufacturing method of aluminum alloy forgings of the present invention, the content of each element is set within a prescribed range, and the processing conditions in each processing step are set within prescribed ranges, so that it is possible to manufacture aluminum alloy forgings that have even better mechanical properties at room temperature and are less susceptible to the generation of recrystallized grains. EXAMPLES

[0043] Next, specific examples of the present invention will be described, but the present invention is not particularly limited to these examples.

[0044] <Examples 1 to 13> A continuous cast material with a circular cross section and a diameter of 54 mm was produced from an aluminum alloy having the alloy composition shown in Table 1, and was subjected to homogenization heat treatment under the conditions shown in Table 1. The obtained cast material was forged under the conditions shown in Table 1 and plastically processed into the shape of an automobile suspension arm part shown in Figure 1.

[0045] Next, heating and solution treatment were performed under the conditions shown in Table 1, followed by quenching treatment as shown in Table 1, and then aging treatment to obtain aluminum alloy forgings 1.

[0046] <Comparative Examples 1 to 9> A continuous cast material with a circular cross section and a diameter of 54 mm was produced from an aluminum alloy having the alloy composition shown in Table 2, and was subjected to homogenization heat treatment under the conditions shown in Table 2. The obtained cast material was forged under the conditions shown in Table 2 and plastically processed into the shape of an automobile suspension arm part shown in Figure 1.

[0047] Next, heating and solution treatment were performed under the conditions shown in Table 2, followed by quenching treatment as shown in Table 2, and then aging treatment to obtain aluminum alloy forgings 1.

[0048] In addition, quenching begins when the entire forged product is immersed in water.

[0049] [Table 1]

[0050] [Table 2]

[0051] Each of the aluminum alloy forged products obtained as described above was evaluated according to the following evaluation methods.

[0052] <Method for evaluating strength at room temperature> Tensile test pieces having a gauge length of 25.4 mm and a parallel part diameter of 6.4 mm were taken from the obtained aluminum alloy forgings, and the tensile test pieces were subjected to a room temperature (25°C) tensile test to measure the yield strength and evaluate it based on the following criteria.

[0053] (Judgment criteria) "〇": The strength at room temperature is 370 MPa or more. "△": The yield strength at room temperature is 360MPa or more but less than 370MPa. "X": The yield strength at room temperature is less than 360 MPa.

[0054] As is clear from Table 1, the aluminum alloy forged products of Examples 1 to 13 produced by the production method of the present invention were excellent in yield strength at room temperature.

[0055] In contrast, as shown in Table 2, the aluminum alloy forged products of Comparative Examples 1 to 9, which deviate from the range specified by the present invention, were inferior in yield strength at room temperature.

[0056] <Measuring method for Mg2Si phase fraction in aluminum alloy forgings obtained by SEM-EBSD method> The Mg2Si phase fraction was measured for each aluminum alloy forging using a SEM-EBSD device. A plate of 10 mm x 10 mm x 2 mm thickness was taken from the forging and used as the SEM-EBSD measurement sample. The measurement conditions were an acceleration voltage of 15 kV, a measurement pitch of 0.5 μm / px, and an analysis area of ​​500 × 500 μm. 2 and the grain boundary definition angle was 15°. The results are shown in Tables 1 and 2.

[0057] As shown in Table 1, in Examples 1 to 13, the Mg2Si phase fraction was 0.1% or less.

[0058] In contrast, as shown in Table 2, in Comparative Examples 1 to 9, the Mg2Si phase fraction was greater than 0.1%. [Industrial Applicability]

[0059] The forged products obtained by the method for producing aluminum alloy forged products according to the present invention have excellent mechanical strength at room temperature and are therefore suitable for use, for example, as suspension parts such as suspension arm parts for automobiles, although they are not particularly limited to such applications. [Explanation of symbols]

[0060] 1: Aluminum alloy forgings

Claims

1. An aluminum alloy forging containing 0.15 mass% to 1.0 mass% Cu, 0.6 mass% to 1.15 mass% Mg, 0.95 mass% to 1.25 mass% Si, 0.4 mass% to 0.6 mass% Mn, 0.2 mass% to 0.3 mass% Fe, 0.11 mass% to 0.25 mass% Cr, 0.012 mass% to 0.035 mass% Ti, and 0.0001 mass% to 0.03 mass% B, with a Zn content of 0.25 mass% or less, a Zr content of 0.05 mass% or less, and the balance being Al and unavoidable impurities, In the cross-sectional structure of the forged product, a field area of ​​500×500 μm measured by the SEM-EBSD method ２ Mg present in ２ The Si phase fraction is 0.03% or more and 0.1% or less, An aluminum alloy forging having a yield strength of 373 MPa or more.

2. A method for producing an aluminum alloy forged product according to claim 1, a molten metal forming step for obtaining a molten metal; a casting step of obtaining a casting by casting the molten metal obtained in the molten metal forming step; a homogenization heat treatment step in which homogenization heat treatment is performed on the casting obtained in the casting step; A forging process for obtaining a forged product by forging the cast product after the homogenization heat treatment process; a solution treatment step of subjecting the forged product obtained in the forging step to a solution treatment; a quenching treatment step of quenching after the solution treatment step; and an aging treatment step of subjecting the forged product after the quenching treatment step to aging treatment.

3. An aluminum alloy forging containing, by mass, 0.15% to 1.0% Cu, 0.6% to 1.15% Mg, 0.95% to 1.25% Si, 0.4% to 0.6% Mn, 0.2% to 0.3% Fe, 0.11% to 0.25% Cr, 0.012% to 0.035% Ti, 0.0001% to 0.03% B, a Zn content of 0.25% or less, a Zr content of 0.05% or less, and the remainder being Al and unavoidable impurities, A method for producing an aluminum alloy forging, wherein the Mg 2 Si phase fraction present in a field area of ​​500×500 μm 2 measured by a SEM-EBSD method in a cross-sectional structure of the forging is 0.03% or more and 0.1% or less, a molten metal forming step for obtaining a molten metal; a casting step of obtaining a casting by casting the molten metal obtained in the molten metal forming step; a homogenization heat treatment step in which homogenization heat treatment is performed on the casting obtained in the casting step; A forging process for obtaining a forged product by forging the cast product after the homogenization heat treatment process; a solution treatment step of subjecting the forged product obtained in the forging step to a solution treatment; a quenching treatment step of quenching after the solution treatment step; and an aging treatment step for performing aging treatment on the forged product after the quenching treatment step. The homogenization heat treatment step is a homogenization heat treatment step in which the casting obtained in the casting step is held at a temperature of 370°C to 560°C for 4 hours to 10 hours, The forging process is a process of forging the casting after the homogenization heat treatment process at a heating temperature of 450°C to 560°C. The solution treatment step is a step of heating the forged product obtained in the forging step from 20°C to 500°C at a heating rate of 5.0°C / min or more, and then holding the product at 530°C to 560°C for 0.3 hours to 3 hours. In the quenching treatment step, the entire surface of the forged product is brought into contact with quenching water within 5 to 60 seconds after the solution treatment step, and quenching is performed in a water tank for more than 5 minutes but not exceeding 40 minutes. The method for manufacturing an aluminum alloy forged product is characterized in that the aging treatment step involves heating the forged product after the quenching treatment step at a temperature of 180°C to 220°C for 0.5 hours to 1.5 hours to perform aging treatment.

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