JP2024088721A - Manufacturing method of aluminum alloy forging - Google Patents

Abstract

The present invention provides a method for producing an aluminum alloy forging material having excellent mechanical properties for use in automobile chassis members.
[Solution] The manufacturing method of the aluminum alloy forging of the present invention includes a quenching process as a heat treatment process, and the quenching process is characterized in that the time from when the forging comes into contact with quenching water to when the entire surface comes into contact with the quenching water is 0.014 sec to 2.20 sec.
[Selected figure] Figure 3

Description

The present invention relates to an aluminum 6000 series alloy forging material suitable for use as a chassis member supporting the body of a transport vehicle, such as a four-wheeled automobile.

In recent years, in response to demands for improved fuel efficiency in the automotive industry, aluminum 6000 series alloys (Al-Mg-Si series), which have high strength, toughness and excellent corrosion resistance, are being used for various components used in automobiles, such as suspension components that support the vehicle body, particularly suspension arms, upper arms, lower arms, tie rod ends, etc., and there is a demand for even lighter automobiles.

To meet these demands, it has become necessary to further improve the strength of JIS 6000 series alloys. In other words, by increasing the strength, it is necessary to make the components thinner. In addition, as suspension components, in addition to strength, further quality improvements are also required in terms of corrosion resistance, such as stress corrosion cracking.

To meet these demands, a proposal has been made to solve the problem by controlling the composition and manufacturing process of a high-strength aluminum 6000 series alloy for use in automobile suspension components, thereby obtaining the required metal structure (see Patent Document 1 below).

JP 2017-179413 A

However, in the manufacturing process, there has been no discussion about the time from when the aluminum alloy forging comes into contact with water until the entire material comes into contact with water during quenching. Conventionally, if this time is not appropriate, air will be entrained during quenching, or the quenching speed will be uneven, making it impossible to obtain the desired quenching speed, resulting in problems with not being able to obtain sufficient mechanical properties, i.e. hardness, which are necessary characteristics for automotive suspension components.

The present invention was made in consideration of this technical background, and aims to provide a method for producing an aluminum alloy forging material with excellent mechanical properties that can impart a sufficient quenching rate by controlling the time from when the material comes into contact with water until the entire material comes into contact with water during quenching.

To achieve the above objective, the present invention provides the following means:

[1] A method for producing an aluminum alloy forging material, comprising a quenching process as a heat treatment process,
The method for producing an aluminum alloy forging, wherein the quenching step is characterized in that the time from when the forging comes into contact with quenching water until the entire surface comes into contact with the quenching water is 0.014 sec to 2.20 sec.

[2] A method for producing an aluminum alloy forging as described in the preceding paragraph 1, in which the aluminum alloy is an Al-Mg-Si alloy.

[3] A method for producing an aluminum alloy forged material according to the preceding paragraphs 1 or 2, in which the solution treatment process is combined with a temperature rise in a hot forging process.

[4] The method for producing an aluminum alloy forging according to any one of the preceding paragraphs 1 to 3, wherein the temperature of the water in the quenching process is 40°C to 90°C.

According to the invention of [1], the time from when the aluminum alloy forging comes into contact with the quenching water until the entire surface comes into contact with the quenching water is 0.014 sec to 2.20 sec in the quenching process, which makes it possible to suppress the entrainment of air during quenching and to impart a uniform and sufficient quenching rate to the aluminum alloy forging, thereby imparting excellent dimensional accuracy and mechanical properties. As a result, it is possible to provide a high-strength aluminum alloy forging suitable for use as automobile suspension components, etc.

According to the invention of [2], by using an Al-Mg-Si alloy as the aluminum alloy, it is possible to provide a high-strength Al-Mg-Si alloy forging material suitable for use as automobile suspension components, etc.

According to the invention [3], since the solution treatment process is combined with the heating process in the hot forging process, it is possible to provide high-strength aluminum alloy forgings suitable for use as automobile suspension parts, etc., at low cost.

According to the invention [4], by setting the water temperature in the quenching process to 40°C to 90°C, it is possible to provide aluminum alloy forgings that are suitable for use as automobile suspension components and have higher quality and strength.

FIG. 1 is an explanatory diagram showing the state of an aluminum alloy forging at the moment when it first comes into contact with quenching water during a quenching process. FIG. 2 is an explanatory diagram showing the state of an aluminum alloy forging at the moment when the entire surface of the aluminum alloy forging comes into contact with quenching water during the quenching treatment process. FIG. 3 is an explanatory diagram showing the locations where the Vickers hardness of an aluminum alloy forging is measured.

The manufacturing method for the aluminum alloy forging of the present invention will be explained.

Note that the embodiments shown below are merely examples, and the present invention is not limited to these exemplified embodiments, and may be modified as appropriate within the scope of the technical concept of the present invention.

In this embodiment, an aluminum alloy forged product is manufactured by carrying out the following steps in this order: molten metal formation, casting, homogenization heat treatment, hot forging, solution treatment, quenching, and artificial aging hardening. Each of these steps is described below.

(Molten metal forming process)
The molten metal forming step is a step in which raw materials are melted to obtain a molten aluminum alloy having a composition adjusted.

In this embodiment, an Al-Mg-Si alloy molten metal is obtained by dissolving and preparing a composition consisting of 0.80% to 1.40% by mass of Si, 0.15% to 0.50% by mass of Fe, 0.20% to 0.60% by mass of Cu, 0.30% to 0.60% by mass of Mn, 0.50% to 1.20% by mass of Mg, 0.05% to 0.25% by mass of Cr, and the remainder consisting of Al and unavoidable impurities.

(Casting process)
The casting step is a step of obtaining a cast material (a forging billet) by casting the aluminum alloy molten metal obtained in the molten metal forming step.

The casting method is not particularly limited, and any conventionally known method may be used, such as the continuous casting and rolling method or the semi-continuous casting method (DC casting method).

The diameter of the cast material is not particularly limited, but is set to, for example, 30 mm to 80 mm. Furthermore, the cast material may be extruded by an extruder to obtain a forging billet, and in this case, the diameter is also set to, for example, 30 mm to 80 mm.

In addition, during casting, it is preferable to set the cooling rate of the cast material to 10°C/min to 50°C/min. This is because it is possible to manufacture aluminum alloy products with sufficiently high tensile strength at room temperature. In particular, it is preferable to set the cooling rate of the cast material to 15°C/min to 30°C/min.

(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.

By performing this homogenization heat treatment, the size of the intermetallic compounds can be reduced, which suppresses fracture originating from the intermetallic compounds and further improves the tensile strength.

In addition, by performing homogenization heat treatment, each element contained in the intermetallic compound is uniformly diffused into the base material, making it possible to further improve tensile strength through solid solution strengthening and precipitation.

The treatment temperature for 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 deposits in the casting material can be dissolved to achieve sufficient homogenization, while by performing heat treatment at a temperature of 570°C or lower, burning can be prevented.

After this homogenization heat treatment process, the cast material is cut to a specified length to obtain a billet for forging.

(Hot forging process)
The hot forging process is a process in which the forging billet obtained after the homogenization heat treatment process is heated and pressed with a press to form it into a die.

The temperature conditions of the hot forging process are relevant in that they allow the aluminum alloy properties to be expressed more reproducibly. In other words, it is possible to make the microstructure of the aluminum alloy after the solution treatment process described below into equiaxed crystal grains. In particular, it is preferable to perform the hot forging process with a die temperature set to 100°C to 250°C and a material temperature set to 400°C to 550°C. This is because by performing hot forging under such conditions, the tensile strength of the aluminum alloy forging can be further improved.

Next, we will explain the solution treatment process, the quenching process, and the artificial aging hardening process.

(Solution treatment process)
The solution treatment process is a heat treatment in which the aluminum alloy forged material obtained in the hot forging process is held at a high temperature and then rapidly cooled to form a supersaturated solid solution.

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 hours to 6 hours, because such conditions provide a better balance between cost and properties.

The solution treatment process may also be performed in conjunction with the heating process during the hot forging process. In other words, by making the hot forging process a process that also serves as the solution treatment process, the aluminum alloy forged material that has been kept at a high temperature immediately after the hot forging process may be subjected to the quenching process described below to rapidly cool it and form a supersaturated solid solution.

In processes that also include a temperature rise 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, it is possible to achieve a better balance between cost and properties in this process that also includes a temperature rise, just like in the solution treatment process.

By combining this with the heating process in the hot forging process, it is possible to obtain an aluminum alloy of the same quality as in the conventional method of slowly cooling the alloy after the hot forging process, reheating it in a continuous heating furnace or a single furnace, and then carrying out a solution treatment process. This not only saves the energy required for reheating, but also makes it possible to significantly improve manufacturing time.

In addition, it is possible to provide high-strength aluminum alloy forgings suitable for use as automobile suspension components, etc., at low cost.

(Quenching process)
Next, the quenching process, which is a feature of the present invention, is a heat treatment for rapidly cooling the solid solution state obtained in the solution treatment process to form a supersaturated solid solution.

The quenching process of the present invention is carried out after the solution treatment process or after the hot forging process which also serves as the solution treatment, so that the time from when the aluminum alloy forged material first comes into contact with the quenching water until the entire surface comes into contact with the quenching water (hereinafter referred to as the "immersion time") is 0.014 sec to 2.20 sec.

If the submersion time is less than 0.014 seconds, air (air bubbles) will be trapped on the upper surface (water surface side) of the aluminum alloy forging when it is submerged, and the presence of these air bubbles on the surface of the aluminum alloy forging will act as an insulating layer, slowing down the cooling rate.

On the other hand, if the submersion time exceeds 2.20 seconds, the parts of the aluminum alloy forging that are not yet submerged will be cooled due to heat conduction from the parts that are already submerged to the parts that are not yet submerged. Also, the parts that are cooled by contact with the quenching water will have a high cooling rate and therefore a high tensile strength, but the parts that are cooled by the above-mentioned heat conduction will have a low cooling rate and therefore a low tensile strength. In this way, parts with high tensile strength and parts with low tensile strength coexist in the aluminum alloy forging, resulting in parts with large differences in tensile strength within a single aluminum alloy forging.

In this embodiment, quenching is performed so that the time from when one end of the aluminum alloy forging (L-shaped arm) 1 first comes into contact with the water surface H of the quenching water W, as shown in FIG. 1, until the entire surface of the aluminum alloy forging 1 comes into contact with the quenching water W, as shown in FIG. 2, is 0.014 sec to 2.20 sec.

In addition, in this embodiment, when the aluminum alloy forgings are placed in a wire cage and submerged in water by a crane, the submersion time of the aluminum alloy forgings is controlled by adjusting the lowering speed of the crane.

Also, depending on the shape of the aluminum alloy forging, there may be orientations that make it easier or harder to sink, so the submersion time of the aluminum alloy forging may be controlled by immersing it in the quenching water in an appropriate orientation so that the submersion time is between 0.014 sec and 2.20 sec.

In addition, in the quenching process of this embodiment, it is preferable to perform rapid cooling (water quenching) with water at 40°C to 90°C.

In this way, by rapidly cooling with water at 40°C to 90°C, it is possible to provide aluminum alloy forgings that are of higher quality and strength and are suitable for use as automobile suspension components, etc.

In this way, the quenching process of the present invention has a time of 0.014 to 2.20 seconds from when the aluminum alloy forging comes into contact with the quenching water until the entire surface comes into contact with the quenching water, which makes it possible to suppress the entrainment of air during quenching and to impart a uniform and sufficient quenching rate to the aluminum alloy forging, thereby imparting excellent dimensional accuracy and mechanical properties. This makes it possible to provide a high-strength aluminum alloy forging suitable for use as automobile suspension components, etc.

(Artificial age hardening treatment process)
The artificial age hardening process is a heat treatment for imparting an appropriate hardness to an aluminum alloy forging by heating and holding the aluminum alloy forging at a relatively low temperature to precipitate elements that are in a supersaturated solid solution.

In this embodiment, it is preferable to set the heating temperature to 160°C to 250°C and the holding time to 10 minutes to 8 hours. This is because such conditions provide a better balance between cost and properties.

In this embodiment, by carrying out the above-mentioned heat treatments (solution treatment process, quenching treatment process, and artificial aging hardening treatment process), it is possible to obtain an aluminum alloy forging material in which fine precipitates are uniformly dispersed and which has a high balance of strength, ductility, and toughness.

Aluminum alloy products (castings, forgings, etc.) manufactured in this way have excellent mechanical properties at room temperature, making them ideal for use as materials for automobile suspension parts (suspension arms, upper arms, lower arms, tie rod ends, etc.).

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

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 a molten aluminum alloy, and the molten aluminum alloy was then continuously cast to obtain a continuous cast material. The obtained continuous cast material was subjected to a homogenization heat treatment and then air-cooled.

Then, the air-cooled continuous cast material was hot forged at a material temperature of 530°C and a die temperature of 180°C. The resulting forged material was solution treated at 530°C, quenched in water at 50°C, and then heated at 180°C for 6 hours for artificial aging hardening, resulting in a forged product.

When performing this water quenching, the submersion time was set to 0.2 seconds.

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 remainder being Al and unavoidable impurities, was heated to obtain a molten aluminum alloy, and the molten aluminum alloy was then continuously cast to obtain a continuous cast material. The obtained continuous cast material was subjected to a homogenization heat treatment and then air-cooled.

Next, the air-cooled continuous cast material was hot forged at a material temperature of 530°C and a die temperature of 180°C, and immediately after forging, it was placed in water at 50°C for water quenching, and then heated at 180°C for 6 hours for artificial aging hardening treatment to obtain a forged product.

When performing this water quenching, the submersion time was set to 0.2 seconds.

Example 3
A forged product was obtained in the same manner as in Example 1, except that the submersion time was 1.0 sec.

Example 4
A forged product was obtained in the same manner as in Example 2, except that the submersion time was 1.0 sec.

Example 5
A forged product was obtained in the same manner as in Example 1, except that the submersion time was set to 2.0 seconds.

Example 6
A forged product was obtained in the same manner as in Example 2, except that the submersion time was set to 2.0 seconds.

<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 a molten aluminum alloy, and the molten aluminum alloy was then continuously cast to obtain a continuous cast material. The obtained continuous cast material was subjected to a homogenization heat treatment and then air-cooled.

Then, the air-cooled continuous cast material was hot forged at a material temperature of 530°C and a die temperature of 180°C. The resulting forged material was solution treated at 530°C, quenched in water at 50°C, and then heated at 180°C for 6 hours for artificial aging hardening, resulting in a forged product.

When performing this water quenching, the submersion time was set to 0.013 seconds.

<Comparative Example 2>
A forged product was obtained in the same manner as in Comparative Example 1, except that the submersion time was set to 2.3 seconds.

<Comparative Example 3>
A forged product was obtained in the same manner as in Comparative Example 1, except that the submersion time was set to 3.0 seconds.

<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 a molten aluminum alloy, and the molten aluminum alloy was then continuously cast to obtain a continuous cast material. The obtained continuous cast material was subjected to a homogenization heat treatment and then air-cooled.

Next, the air-cooled continuous cast material was hot forged at a material temperature of 530°C and a die temperature of 180°C, and immediately after forging, it was placed in water at 50°C for water quenching, and then heated at 180°C for 6 hours for artificial aging hardening treatment to obtain a forged product.

When performing this water quenching, the submersion time was set to 0.013 seconds.

<Comparative Example 5>
A forged product was obtained in the same manner as in Comparative Example 4, except that the submersion time was set to 2.3 seconds.

<Comparative Example 6>
A forged product was obtained in the same manner as in Comparative Example 4, except that the submersion time was set to 3.0 seconds.

Each forged product obtained as described above was evaluated according to the following methods.

<Hardness measurement>
Hardness measurements were performed on each of the forged products of Examples 1 to 6 and Comparative Examples 1 to 6. Specifically, the forged products were cut into 10 mm squares, filled with resin, and the target surface was polished to #2000 with emery paper, and then the Vickers hardness was measured using a Vickers hardness tester. The load for the Vickers hardness measurement was 10 g, and 10 points were measured for one sample, and the average Vickers hardness was calculated.

The Vickers hardness measurements were performed at measurement points P1 to P5 of the L-shaped arm shown in Figure 3. The results of the Vickers hardness measurements are shown in Table 1. The criteria for judgment in Table 1 were: ◯ if the error (hardness difference) in the measurement results at the five points was 5HV or less, and × if it was 6HV or more.

From Table 1, it can be seen that there is almost no error (hardness difference) in Examples 1 to 6, and sufficient mechanical properties are obtained.

On the other hand, in Comparative Examples 1 to 6, there is an error (hardness difference), and it is clear that sufficient mechanical properties are not obtained.

The forged products for undercarriages obtained by the manufacturing method of the present invention have high strength and are therefore suitable for use as materials for, for example, suspension arms, upper arms, lower arms, tie rod ends, etc., of the undercarriages of automobiles, but are not limited to such uses.

1: Aluminum alloy forging material W: Quenching water

Claims (1)

A method for producing an aluminum alloy forging material, comprising a quenching process as a heat treatment process,
In the quenching process, the time from when the forged material comes into contact with the quenching water to when the entire surface comes into contact with the quenching water is 0.014 sec to 2.20 sec,
A method for producing an aluminum alloy forging, characterized in that the solution treatment step is performed in combination with a temperature rise in a hot forging step.

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