Method for manufacturing aluminum alloy forging material

Abstract

To provide a manufacturing method of an aluminum alloy forging material having a mechanical characteristic excellent in an automobile undercarriage member.SOLUTION: A manufacturing method of an aluminum alloy forging material includes a hardening treatment process as a heat treatment process. In the hardening treatment process, a time from the beginning of contact of the forging material with hardening water until complete contact of the whole surface with hardening water is 0.014 sec-2.20 sec.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a forged material of an aluminum 6000 series alloy suitable as a chassis member for supporting the body of a transportation machine typified by, for example, a four-wheel vehicle.

Background Art

[0002] In recent years, due to the demand for improved fuel efficiency in the automotive industry, various members used in automobiles, such as chassis members for supporting the body, particularly automotive chassis members used for suspension arms, upper arms, lower arms, tie rod ends, etc., an aluminum 6000 series alloy (Al-Mg-Si series) having high strength, high toughness, and excellent corrosion resistance has been used, and among them, further weight reduction of automobiles has been required.

[0003] In order to meet this requirement, it has become necessary to further improve the strength of JIS standard 6000 series alloys. That is, it is necessary to make the members thinner by increasing the strength. In addition to strength, further quality improvement is required in terms of corrosion resistance such as stress corrosion cracking for chassis members.

[0004] In order to meet such requirements, as a high-strength aluminum 6000 series alloy for automotive chassis members, proposals have been made to obtain a required metal structure by controlling its composition and manufacturing process to solve the problems. (See Patent Document 1 below)

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the manufacturing process, there has been no discussion regarding the time from when the aluminum alloy forging comes into contact with water until the entire forging comes into contact with water during quenching. Conventionally, if this time is not appropriate, air is entrapped during quenching, or unevenness occurs in the quenching rate and the desired quenching rate cannot be obtained, resulting in a problem that sufficient mechanical properties, namely hardness, which are required characteristics for automotive underbody members, cannot be achieved.

[0007] The present invention has been made in view of such a technical background, and an object thereof is to provide a method for manufacturing an aluminum alloy forging having excellent mechanical properties by controlling the time from when the forging comes into contact with water until the entire forging comes into contact with water during quenching, thereby providing a sufficient quenching rate.

Means for Solving the Problems

[0008] In order to achieve the above object, the present invention provides the following means.

[0009] [1] A method for manufacturing an aluminum alloy forging including a quenching treatment step as a heat treatment step, wherein in the quenching treatment step, the time from when the forging comes into contact with quenching water until all surfaces come into contact with the quenching water is 0.014 sec to 2.20 sec. A method for manufacturing an aluminum alloy forging characterized by this.

[0010] [2] The method for manufacturing an aluminum alloy forging according to item 1 above, wherein the aluminum alloy is an Al-Mg-Si based alloy.

[0011] [3] The method for manufacturing an aluminum alloy forging according to item 1 or 2 above, wherein the solution treatment step combines heating during the hot forging step.

[0012] [4] The method for manufacturing an aluminum alloy forging according to any one of items 1 to 3 above, wherein the temperature of the water in the quenching treatment step is 40°C to 90°C.

Effects of the Invention

[0013] According to the invention of [1], in the quenching process, the time from when the aluminum alloy forging comes into contact with the quenching water until all its surfaces come into contact with the quenching water is 0.014 sec to 2.20 sec. Thus, air entrainment during quenching can be suppressed, and a uniform and sufficient quenching rate can be imparted to the aluminum alloy forging. Therefore, excellent dimensional accuracy and mechanical properties can be achieved. For this reason, it is possible to provide a high-strength aluminum alloy forging suitable for automotive underbody members and the like.

[0014] According to the invention of [2], by using an Al-Mg-Si series alloy as the aluminum alloy, it is possible to provide a high-strength Al-Mg-Si series alloy forging suitable for automotive underbody members and the like.

[0015] According to the invention of [3], since the solution treatment process uses the temperature increase during the hot forging process in combination, it is possible to inexpensively provide a high-strength aluminum alloy forging suitable for automotive underbody members and the like.

[0016] According to the invention of [4], by setting the temperature of the water in the quenching process to 40°C to 90°C, it is possible to provide an aluminum alloy forging suitable for higher-quality and higher-strength automotive underbody members and the like.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0018] A method for manufacturing an aluminum alloy forging material of the present invention will be described.

[0019] Note that the following embodiments are merely illustrative, and the present invention is not limited to these illustrated embodiments, and can be appropriately modified without departing from the technical idea of the present invention.

[0020] In this embodiment, an aluminum alloy forging is manufactured by performing a molten metal forming step, a casting step, a homogenization heat treatment step, a hot forging step, a solution treatment step, a quenching treatment step, and an artificial aging hardening treatment step in this order. Hereinafter, each of these steps will be described.

[0021] (Molten Metal Forming Step) The molten metal forming step is a step of obtaining an aluminum alloy molten metal in which raw materials are melted and the composition is adjusted.

[0022] In this embodiment, an Al-Mg-Si alloy molten metal is obtained by melting and preparing a composition having Si: 0.80% by mass to 1.40% by mass, Fe: 0.15% by mass to 0.50% by mass, Cu: 0.20% by mass to 0.60% by mass, Mn: 0.30% by mass to 0.60% by mass, Mg: 0.50% by mass to 1.20% by mass, Cr: 0.05% by mass to 0.25% by mass, and the balance being Al and unavoidable impurities.

[0023] (Casting Step) The casting step is a step of obtaining a casting material (forging billet) by casting the aluminum alloy molten metal obtained in the molten metal forming step.

[0024] The method of casting is not particularly limited, and a conventionally known method is used. For example, a continuous casting and rolling method or a semi-continuous casting method (DC casting method) can be mentioned.

[0025] Also, the diameter of the casting material is not particularly limited, but is set to, for example, 30 mm to 80 mm. Further, the casting material may be extruded by an extruder to obtain a forging billet, and in this case as well, it is set to, for example, 30 mm to 80 mm.

[0026] In addition, in the casting process, it is preferable to set the cooling rate of the casting material to 10°C / min to 50°C / min. This is because by doing so, aluminum alloy products with a sufficiently large tensile strength at room temperature can be manufactured. In particular, it is preferable to set the cooling rate of the casting material to 15°C / min to 30°C / min.

[0027] (Homogenization heat treatment process) The homogenization heat treatment process is a process of performing homogenization heat treatment on the casting material obtained in the casting process to homogenize the microsegregation caused by solidification, precipitate supersaturated solid solution elements, and change metastable phases to equilibrium phases.

[0028] By performing this homogenization heat treatment, the intermetallic compound can be made smaller, the fracture starting from the intermetallic compound can be suppressed, and the tensile strength can be further improved.

[0029] In addition, by performing homogenization heat treatment, each element contained in the intermetallic compound is uniformly diffused into the base material, and further improvement of the tensile strength by solid solution strengthening and precipitation becomes possible.

[0030] In addition, the treatment temperature in the homogenization heat treatment is preferably set in the range of 450°C to 570°C. By performing heat treatment at a temperature of 450°C or higher, intermetallic compounds such as crystallized products of the casting material can be dissolved and sufficiently homogenized, and by performing heat treatment at a temperature of 570°C or lower, burning can be prevented.

[0031] After performing such a homogenization heat treatment process, the casting material is cut into a predetermined length to obtain a forging billet.

[0032] (Hot forging process) The hot forging process is a process of heating the forging billet obtained after the homogenization heat treatment process and applying pressure with a press to perform die forming.

[0033] The temperature conditions in the hot forging process are related in terms of more reproducibly expressing the characteristics of the aluminum alloy. That is, it becomes possible to make the microstructure of the aluminum alloy after the solution treatment process described later into equiaxed crystal grains. In particular, in the hot forging process, it is preferable to set the die temperature to 100°C to 250°C and the material temperature to 400°C to 550°C. By performing hot forging under such conditions, the tensile strength of the aluminum alloy forged material can be further improved.

[0034] Next, the solution treatment process, quenching process, and artificial aging hardening process will be described.

[0035] (Solution Treatment Process) The solution treatment process is a heat treatment that holds the aluminum alloy forged material obtained in the hot forging process at a high temperature and then rapidly cools it to form a supersaturated solid solution.

[0036] In the solution treatment process, it is preferable to set the heating temperature to 500°C to 560°C and the holding time to 0.5 hour to 6 hours. By setting such conditions, the balance between cost and characteristics can be made better.

[0037] Also, the solution treatment process may be a process that combines the temperature increase in the hot forging process. That is, by making the hot forging process also serve as a solution treatment process, the aluminum alloy forged material held at a high temperature immediately after the hot forging process can be directly subjected to the quenching process described later, and rapid cooling can be performed to form a supersaturated solid solution.

[0038] In the process that combines the temperature increase in the hot forging process, it is preferable to set the temperature immediately after the hot forging process to 500°C to 560°C and the time from immediately after the hot forging process to quenching to 1 second to 30 seconds. By setting such conditions, similar to the solution treatment process, in this process that combines the temperature increase, the balance between cost and characteristics can be made better.

[0039] By using the combined heating during the hot forging process in this way, compared with the case where the aluminum alloy is slowly cooled once after the conventional hot forging process and then reheated in a continuous heating furnace or a single furnace for solution treatment, aluminum alloys of the same quality can be obtained. Moreover, not only can the energy required for reheating be saved, but the manufacturing time can also be significantly improved.

[0040] Furthermore, a high-strength aluminum alloy forging material suitable for automotive underbody members and the like can be provided at low cost.

[0041] (Quenching process) Next, the quenching process, which is a feature of the present invention, is a heat treatment that rapidly cools the solid solution state obtained by the solution treatment process to form a supersaturated solid solution.

[0042] In the quenching process of the present invention, after the solution treatment process or after the hot forging process that also serves as the solution treatment, the time from when the aluminum alloy forging material first contacts the quenching water until all surfaces come into contact with the quenching water (hereinafter referred to as the "immersion time") is set to be 0.014 sec to 2.20 sec for quenching.

[0043] If the immersion time is less than 0.014 sec, when immersed, air (bubbles) is entrapped on the upper surface side (water surface side) of the aluminum alloy forging material, and the presence of these bubbles on the surface of the aluminum alloy forging material serves as a heat insulation layer, reducing the cooling rate.

[0044] On the other hand, if the immersion time exceeds 2.20 sec, due to the heat conduction from the already immersed part to the non-immersed part of the aluminum alloy forging material, the non-immersed part will be cooled. Also, the part cooled by contact with the quenching water has a high cooling rate, so the tensile strength increases, but the part cooled by the above heat conduction has a low cooling rate, so the tensile strength decreases. In this way, parts with high and low tensile strengths will coexist in the aluminum alloy forging material, resulting in a large difference in tensile strength within a single aluminum alloy forging material.

[0045] In this embodiment, as shown in FIG. 1, after one end of the aluminum alloy forging (L-shaped arm) 1 first contacts the water surface H of the quenching water W, as shown in FIG. 2, quenching is performed such that the time from when one end of the aluminum alloy forging 1 first contacts the water surface H of the quenching water W until all surfaces of the aluminum alloy forging 1 contact the quenching water W is 0.014 sec to 2.20 sec.

[0046] Further, in this embodiment, when the aluminum alloy forging is placed in the wire cage and submerged in water by the crane, the immersion time of the aluminum alloy forging is controlled by adjusting the lowering speed of the crane.

[0047] Also, depending on the shape of the aluminum alloy forging, there is a direction in which it sinks easily or a direction in which it sinks difficultly. Therefore, the immersion time of the aluminum alloy forging may be controlled by immersing it in the quenching water in an appropriate direction so that the immersion time is 0.014 sec to 2.20 sec.

[0048] Further, in the quenching treatment step of this embodiment, it is preferable to perform rapid cooling (water quenching treatment) with water at 40°C to 90°C.

[0049] This is because by rapidly cooling with water at 40°C to 90°C, it is possible to provide an aluminum alloy forging suitable as a higher-quality and higher-strength automotive underbody member or the like.

[0050] Thus, in the quenching treatment step of the present invention, since the time from when the aluminum alloy forging contacts the quenching water until all surfaces contact the quenching water is 0.014 sec to 2.20 sec, it is possible to suppress the entrainment of air during quenching and to give the aluminum alloy forging a uniform and sufficient quenching rate. Therefore, excellent dimensional accuracy and mechanical properties can be given. For this reason, it is possible to provide a high-strength aluminum alloy forging suitable as an automotive underbody member or the like.

[0051] (Artificial aging hardening treatment step) The artificial age hardening treatment process is a heat treatment for heating and holding an aluminum alloy forging at a relatively low temperature to precipitate elements in supersaturated solid solution and impart appropriate hardness.

[0052] In this embodiment, it is preferably carried out by setting the heating temperature to 160°C to 250°C and the holding time to 10 minutes to 8 hours. This is because such conditions result in a better balance between cost and properties.

[0053] In this embodiment, by performing the above heat treatment (solution treatment process, quenching treatment process, and artificial age hardening treatment process), a forging material of an aluminum alloy with fine precipitates uniformly dispersed and highly balanced strength, ductility, and toughness can be obtained.

[0054] The aluminum alloy products (castings, forgings, etc.) manufactured in this way have excellent mechanical properties at room temperature, and are therefore suitably used as materials for, for example, automotive underbody parts (suspension arms, upper arms, lower arms, tie rod ends, etc.).

Example

[0055] Next, specific examples of the present invention will be described, but the present invention is not particularly limited to these examples.

[0056] <Example 1> An aluminum alloy containing 1.10% by mass of Si, 0.25% by mass of Fe, 0.40% by mass of Cu, 0.50% by mass of Mn, 0.85% by mass of Mg, and 0.15% by mass of Cr, with the balance being Al and unavoidable impurities, was heated to obtain an aluminum alloy melt, and then a continuous casting material was obtained by performing continuous casting using the aluminum alloy melt. After subjecting the obtained continuous casting material to homogenization heat treatment, it was air-cooled.

[0057] Subsequently, the continuously cast material after air cooling was subjected to hot forging at a material temperature of 530°C and a die temperature of 180°C. The obtained forged material was solution-treated at 530°C, quenched in water at 50°C, and then heated at 180°C for 6 hours to perform artificial aging hardening treatment, obtaining a forged product.

[0058] When performing this quenching, the immersion time was set to 0.2 seconds and quenching was carried out.

[0059] <Example 2> An aluminum alloy containing 1.10% by mass of Si, 0.25% by mass of Fe, 0.40% by mass of Cu, 0.50% by mass of Mn, 0.85% by mass of Mg, and 0.15% by mass of Cr, with the balance being Al and unavoidable impurities, was heated to obtain an aluminum alloy melt, and then a continuously cast material was obtained by performing continuous casting using the aluminum alloy melt. After performing homogenization heat treatment on the obtained continuously cast material, it was air cooled.

[0060] Subsequently, the continuously cast material after air cooling was hot forged at a material temperature of 530°C and a die temperature of 180°C, quenched in water at 50°C immediately after forging, and then heated at 180°C for 6 hours to perform artificial aging hardening treatment, obtaining a forged product.

[0061] When performing this quenching, the immersion time was set to 0.2 seconds and quenching was carried out.

[0062] <Example 3> A forged product was obtained in the same manner as in Example 1 except that the immersion time was set to 1.0 second.

[0063] <Example 4> A forged product was obtained in the same manner as in Example 2 except that the immersion time was set to 1.0 second.

[0064] <Example 5> A forged product was obtained in the same manner as in Example 1 except that the immersion time was set to 2.0 seconds.

[0065] <Example 6> A forged product was obtained in the same manner as in Example 2 except that the immersion time was set to 2.0 sec.

[0066] <Comparative Example 1> An aluminum alloy containing 1.10% by mass of Si, 0.25% by mass of Fe, 0.40% by mass of Cu, 0.50% by mass of Mn, 0.85% by mass of Mg, and 0.15% by mass of Cr, with the balance being Al and unavoidable impurities, was heated to obtain an aluminum alloy melt. Then, a continuously cast material was obtained by performing continuous casting using the aluminum alloy melt. After performing a homogenization heat treatment on the obtained continuously cast material, it was air-cooled.

[0067] Next, the continuously cast material after air-cooling was hot forged at a material temperature of 530°C and a die temperature of 180°C. The obtained forged material was solution-treated at 530°C, quenched in water at 50°C, and then heated at 180°C for 6 hours to perform artificial aging hardening treatment to obtain a forged product.

[0068] When performing this quenching, the immersion time was set to 0.013 sec and quenching was performed.

[0069] <Comparative Example 2> A forged product was obtained in the same manner as in Comparative Example 1 except that the immersion time was set to 2.3 sec.

[0070] <Comparative Example 3> A forged product was obtained in the same manner as in Comparative Example 1 except that the immersion time was set to 3.0 sec.

[0071] <Comparative Example 4> An aluminum alloy containing 1.10% by mass of Si, 0.25% by mass of Fe, 0.40% by mass of Cu, 0.50% by mass of Mn, 0.85% by mass of Mg, and 0.15% by mass of Cr, with the balance being Al and unavoidable impurities, was heated to obtain an aluminum alloy melt. Then, a continuously cast material was obtained by performing continuous casting using the aluminum alloy melt. After performing a homogenization heat treatment on the obtained continuously cast material, it was air-cooled.

[0072] Subsequently, the continuously cast material after air cooling was subjected to hot forging at a material temperature of 530°C and a die temperature of 180°C, and immediately after forging, it was immersed in water at 50°C for water quenching. Then, it was heated at 180°C for 6 hours for artificial aging hardening treatment to obtain a forged product.

[0073] When performing this water quenching, the immersion time was set to 0.013 sec for quenching.

[0074] <Comparative Example 5> A forged product was obtained in the same manner as in Comparative Example 4 except that the immersion time was set to 2.3 sec.

[0075] <Comparative Example 6> A forged product was obtained in the same manner as in Comparative Example 4 except that the immersion time was set to 3.0 sec.

[0076]

Table 1

[0077] For each of the forged products obtained as described above, various evaluations were performed based on the following evaluation methods.

[0078] <Hardness measurement> Hardness measurements were performed on the forged products of Examples 1 to 6 and Comparative Examples 1 to 6. Specifically, the forged products were cut out into 10 mm squares, resin-embedded, and the target surface was polished with emery paper up to #2000. Then, the Vickers hardness was measured using a Vickers hardness tester. The load during Vickers hardness measurement was 10 g, and 10 measurements were taken for each sample to calculate the average Vickers hardness.

[0079] Also, the Vickers hardness was measured at the measurement points P1 to P5 of the L-shaped arm shown in Figure 3. The Vickers hardness measurement results are shown in Table 1. The judgment criteria in Table 1 were ○ when the error (hardness difference) of the five measurement results was 5 HV or less, and × when it was 6 HV or more.

[0080] From Table 1, it can be seen that in Examples 1 to 6, almost no error (hardness difference) occurred, indicating that sufficient mechanical properties were obtained.

[0081] On the other hand, it can be seen that errors (hardness differences) occur in Comparative Examples 1 to 6 and sufficient mechanical properties are not obtained.

Industrial Applicability

[0082] Since the forging for the wheel area obtained by the manufacturing method of the present invention has high strength, for example, it is suitably used as a material for suspension arms, upper arms, lower arms, tie rod ends, etc. for the wheel area of automobiles, but it is not particularly limited to such applications.

Explanation of Signs

[0083] 1: Aluminum alloy forging W: Quenching water

Claims

【Claim 1】 A method for manufacturing an aluminum alloy forging material including a quenching treatment step as a heat treatment step, wherein, in the quenching treatment step, the time from when the forging material comes into contact with quenching water until all surfaces come into contact with the quenching water is 0.014 sec to 2.20 sec, the solution treatment step uses the temperature rise during the hot forging step in combination, the aluminum alloy is an Al-Mg-Si based alloy, and a method for manufacturing an aluminum alloy forging material, characterized in that the temperature of the water in the quenching treatment step is 40°C to 90°C.

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