JP7639320B2 - Aluminum alloy forgings and manufacturing method thereof - Google Patents

Description

The present invention relates to an Al-Mg-Si aluminum alloy forging with excellent mechanical properties at room temperature and a method for manufacturing the same.

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

Since these automobile parts require excellent corrosion resistance, high strength, and excellent workability, Al-Mg-Si alloys, especially A6061, are often used as the aluminum alloy material. In order to improve the strength of these automobile parts, they are manufactured by forging, a type of plastic processing, using the aluminum alloy material as the processing material.

In addition, due to the recent need to reduce costs, suspension parts have begun to be used in which cast parts are used as the raw material for forging without extrusion, and then T6 treatment is applied to obtain them. 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).

Japanese Patent Application Publication No. 5-59477 Japanese Patent Application Publication No. 5-247574 Japanese Patent Application Publication No. 6-256880

However, the above-mentioned high-strength Al-Mg-Si alloys have the problem 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 sufficiently high strength. For this reason, some alloys have been designed to prevent recrystallization by adding Zr to prevent the generation of coarse recrystallized grains (for example, Patent Documents 1 and 2 above).

However, although adding Zr is effective in preventing recrystallization, it has the following problems:

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

(2) The effect of refining the crystal grains of the ingot itself is weakened, making the ingot more susceptible to cracking, increasing internal defects, and reducing yields.

(3) Zr forms compounds with Al-Ti-B alloys, and 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 ingot, reducing its strength.

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

The present invention was made in consideration of this technical background, and aims to provide an aluminum alloy forging that has excellent mechanical properties at room temperature and is less susceptible to recrystallization grains, and a manufacturing method thereof.

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

[1] An aluminum alloy forging containing Cu: 0.15% by mass to 1.0% by mass, Mg: 0.6% by mass to 1.3% by mass, Si: 0.60% by mass to 1.45% by mass, Mn: 0.03% by mass to 1.0% by mass, Fe: 0.2% by mass to 0.4% by mass, Cr: 0.03% by mass to 0.4% by mass, Ti: 0.012% by mass to 0.035% by mass, B: 0.0001% by mass to 0.03% by mass, Zn content is 0.25% by mass or less, Zr content is 0.05% by mass or less, and the balance is Al and inevitable impurities.
An aluminum alloy forging, characterized in that no endothermic peak is detected in a temperature range of −50° C. below the solidus temperature in a differential scanning calorimeter curve obtained by differential scanning calorimeter measurement of the cross section of the forging.

[2] A method for producing an aluminum alloy forged product according to the preceding paragraph 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] 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,
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.

According to the invention of [1], the content of each element is set within a predetermined range, and in the differential scanning calorimetry curve obtained by differential scanning calorimetry of the cross section of the forged product, no endothermic peak is detected within a temperature range of -50°C below the solidus temperature, so that an aluminum alloy forged product can be provided that has excellent mechanical properties at room temperature and is less susceptible to recrystallization grains.

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 process and an aging treatment process, it is possible to manufacture an aluminum alloy forging that has excellent mechanical properties at room temperature and is less susceptible to recrystallization grains.

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

FIG. 1 is a perspective view showing an aluminum alloy forging obtained by the manufacturing method of the present invention.

The aluminum alloy forgings of the present invention and the method for manufacturing the aluminum alloy forgings are described below.

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.

The aluminum alloy forged product 1 of this embodiment contains Cu: 0.15% to 1.0% by mass, Mg: 0.6% to 1.3% by mass, Si: 0.60% to 1.45% by mass, Mn: 0.03% to 1.0% by mass, Fe: 0.2% to 0.4% by mass, Cr: 0.03% to 0.4% by mass, Ti: 0.012% to 0.035% by mass, B: 0.0001% to 0.03% by mass, Zn content is 0.25% or less, Zr content is 0.05% or less by mass, and the balance is Al and unavoidable impurities. The differential scanning calorimetry curve obtained by differential scanning calorimetry of the cross section of this forged product 1 is characterized in that no endothermic peak is detected in a temperature range of -50°C from the solidus temperature.

In this way, the content of each element is set within a predetermined range, and no endothermic peak is detected in a temperature range of -50°C below the solidus temperature in the differential scanning calorimetry curve obtained by differential scanning calorimetry of the cross section of the forging 1. This makes it possible to provide an aluminum alloy forging that has excellent mechanical properties at room temperature and is less susceptible to recrystallization grains.

The method for manufacturing an aluminum alloy forged product 1 according to this embodiment involves carrying out a molten metal forming process, a casting process, a homogenizing heat treatment process, a forging process, a solution treatment process, a quenching process, and an aging treatment process in this order to manufacture an aluminum alloy forged product 1, for example, as shown in FIG. 1. Each process will be 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, a molten 6000 series aluminum alloy containing Cu: 0.15% to 1.0% by mass, Mg: 0.6% to 1.3% by mass, Si: 0.60% to 1.45% by mass, Mn: 0.03% to 1.0% by mass, Fe: 0.2% to 0.4% by mass, Cr: 0.03% to 0.4% by mass, Ti: 0.012% to 0.035% by mass, B: 0.0001% to 0.03% by mass, Zn content is 0.25% by mass or less, Zr content is 0.05% by mass or less, and the balance is Al and unavoidable impurities is obtained (prepared). In this molten aluminum alloy, the Zn content may be 0% by mass (Zn-free), and the Zr content may be 0% by mass (Zr-free).

(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.

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

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 then immersed in water (temperature: approximately 20°C) in a water tank where it solidifies completely. This produces long continuous cast material in the shape of a rod, etc.

(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.

In this embodiment, the casting obtained in the casting process is subjected to homogenization heat treatment, in which the casting is held 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 the sufficient strength required for the subsequent aging treatment can be obtained.

(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.

In this embodiment, the ingot after homogenization heat treatment is forged at a heating temperature of 450°C to 560°C to obtain a forged product (such as an automobile suspension arm part). 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.

(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.

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 reached room temperature. The temperature is raised at a rate of at least 5.0°C/min 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.

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.

(Quenching 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.

In this embodiment, the entire surface of the forged product comes into contact with quenching water within 5 to 60 seconds after solution treatment, and the quenching process is carried out in the water tank for more than 5 minutes but not exceeding 40 minutes.

(Aging treatment process)
The aging treatment process is a heat treatment in which the 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.

In this embodiment, the forged product after the quenching process is heated for 0.5 to 1.5 hours at a temperature of 180° C. to 220° C. to perform aging treatment. If the treatment temperature is less than 180° C. or the treatment time is less than 0.5 hours, the Mg ₂ Si-based precipitates that improve the tensile strength do not grow sufficiently, and if the treatment temperature exceeds 220° C., the Mg ₂ Si-based precipitates become too coarse to sufficiently improve the tensile strength.

As described above, the manufacturing method of the aluminum alloy forgings of the present invention sets the content of each element within a predetermined range, and the processing conditions in each processing step are set within a predetermined range, making it 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.

Next, the composition of the "aluminum alloy" in the aluminum alloy forging and manufacturing method thereof according to the present invention will be described in detail below. The aluminum alloy contains Cu: 0.15% to 1.0% by mass, Mg: 0.6% to 1.3% by mass, Si: 0.60% to 1.45% by mass, Mn: 0.03% to 1.0% by mass, Fe: 0.2% to 0.4% by mass, Cr: 0.03% to 0.4% by mass, Ti: 0.012% to 0.035% by mass, B: 0.0001% to 0.03% by mass, Zn content is 0.25% or less, Zr content is 0.05% or less, and the balance is Al and unavoidable impurities.

Si coexists with Mg to form Mg ₂ Si-based precipitates, which contribute to improving the strength of the final product. The Si content is desirably 0.60 mass% or more, since the strength of the final product after aging treatment is further increased by adding Si in excess of the amount that generates Mg ₂ Si relative to the amount of Mg described later. On the other hand, if the Si content exceeds 1.45 mass%, the grain boundary precipitation of Si increases, grain boundary embrittlement is likely to occur, and not only the plastic workability of the ingot and the toughness of the final product are reduced, but the average grain size of the crystallized particles of the ingot may exceed a predetermined upper limit. Therefore, the Si content must be in the range of 0.60 mass% to 1.45 mass%.

Mg coexists with Si to form Mg ₂ Si-based precipitates, which contribute to improving the strength of the final product. If the Mg content is less than 0.6 mass%, the effect of precipitation strengthening may be reduced. On the other hand, if the Mg content exceeds 1.3 mass%, not only will the plastic workability of the ingot and the toughness of the final product decrease, but the average grain size of the crystallized particles in the ingot may exceed a predetermined upper limit. Therefore, the Mg content must be in the range of 0.6 mass% to 1.3 mass%.

Cu increases the apparent supersaturation amount of Mg ₂ Si-based precipitates, and increases the amount of Mg ₂ Si precipitates, thereby significantly promoting the age hardening of the final product. If the Cu content is less than 0.15 mass%, the Q phase (Al-Cu-Mg-Si), which is effective for precipitation strengthening, is difficult to generate, resulting in a decrease in mechanical properties. On the other hand, if the Cu content exceeds 1.0 mass%, the forgeability of the ingot and the toughness of the final product may decrease, and further the corrosion resistance may decrease significantly. Therefore, the Cu content must be in the range of 0.15 mass% to 1.0 mass%.

Mn crystallizes as the AlMnSi phase, and Mn that does not crystallize precipitates and inhibits recrystallization. This effect of inhibiting recrystallization keeps the crystal grains fine even after plastic processing, improving the toughness and corrosion resistance of the final product. If the Mn content is less than 0.03 mass%, the above-mentioned effects may be reduced. On the other hand, if it exceeds 1.0 mass%, giant intermetallic compounds may be formed, and the ingot structure of this invention may not be satisfied. Therefore, the Mn content must be in the range of 0.03 mass% to 1.0 mass%.

Cr also crystallizes as the AlCrSi phase, and Cr that does not crystallize precipitates and inhibits recrystallization. This effect of inhibiting recrystallization keeps the crystal grains fine even after plastic processing, improving the toughness and corrosion resistance of the final product. If the Cr content is less than 0.03 mass%, the above-mentioned effects may be reduced. On the other hand, if it exceeds 0.4 mass%, giant intermetallic compounds may be formed and the ingot structure of this invention may not be satisfied. Therefore, the Cr content must be in the range of 0.03 mass% to 0.4 mass%.

Fe combines with Al and Si in the alloy to crystallize, and prevents grain coarsening. If the Fe content is less than 0.2 mass%, the above effects may not be obtained. Furthermore, if the Fe content exceeds 0.4 mass%, coarse intermetallic compounds may be generated, and plastic workability may deteriorate. Therefore, the Fe content must be 0.2-0.4 mass%.

Zn is treated as an impurity, and if it exceeds 0.25 mass%, it accelerates the corrosion of aluminum itself and deteriorates its corrosion resistance, so it must be kept below 0.25 mass%.

Zr is treated as an impurity, and if its content exceeds 0.05 mass%, the grain refining effect of the Al-Ti-B alloy is weakened, resulting in a decrease in the strength of the processed product after plastic processing, so it must be kept at 0.05 mass% or less.

Ti is an effective alloying element for refining crystal grains, and also prevents the occurrence of ingot cracks in continuously cast rods. If the Ti content is less than 0.012 mass%, the refining effect is not obtained, while if it exceeds 0.035 mass%, coarse Ti compounds may crystallize, causing a deterioration in toughness. Therefore, the Ti content must be in the range of 0.012 mass% to 0.035 mass%.

Like Ti, B is an element that is effective in refining crystal grains, but if it is less than 0.0001 mass%, this effect is not obtained, while if it exceeds 0.03 mass%, there is a risk of deteriorating toughness. Therefore, the B content must be in the range of 0.0001 mass% to 0.03 mass%.

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

<Examples 1 to 12>
Continuously cast aluminum alloys having the alloy compositions shown in Table 1 were used to produce continuous cast materials having a circular cross section with a diameter of 54 mm, and were subjected to homogenization heat treatment under the conditions shown in Table 1. The resulting cast materials were subjected to forging under the conditions shown in Table 1 and plastically worked into the shape of an automobile suspension arm part shown in FIG.

Next, the temperature was raised and solution treatment was 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 forging 1.

<Comparative Examples 1 to 5>
Continuously cast aluminum alloys having the alloy compositions shown in Table 2 were used to produce continuous cast materials having a circular cross section with a diameter of 54 mm, which were then subjected to homogenization heat treatment under the conditions shown in Table 2. The resulting cast materials were subjected to forging under the conditions shown in Table 2 and plastically worked into the shape of an automobile suspension arm part shown in FIG.

Next, the temperature was raised and the solution treatment was performed under the conditions shown in Table 2, after which the quenching treatment shown in Table 2 was performed, and then aging treatment was performed to obtain aluminum alloy forging 1.

Also, quenching begins when the entire forged product is submerged in water.

The aluminum alloy forgings obtained as described above were evaluated according to the following evaluation methods.

<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 were evaluated based on the following criteria.

(Judgment criteria)
"◎": Yield strength at room temperature is 360 MPa or more; "◯": Yield strength at room temperature is 340 MPa or more and less than 360 MPa; "△": Yield strength at room temperature is 320 MPa or more and less than 340 MPa; "×": Yield strength at room temperature is less than 320 MPa.

As is clear from Table 1, the aluminum alloy forgings of Examples 1 to 12 manufactured by the manufacturing method of the present invention had excellent yield strength at room temperature.

In contrast, as shown in Table 2, the aluminum alloy forgings of Comparative Examples 1 to 5, which deviate from the range specified by the present invention, had poor yield strength at room temperature.

<Method for measuring the number of endothermic peaks detected in a temperature range of -50°C below the solidus temperature in a differential scanning calorimeter curve of an aluminum alloy forging>
For each aluminum alloy forging, differential scanning calorimetry was performed using a heat flux type differential scanning calorimeter (DSC8231-SL) manufactured by Rigaku Corporation. A plate-shaped body of 4 mm x 4 mm x 1.5 mm thick was taken from the forging and used as a sample for differential scanning calorimetry. The number of endothermic peaks detected in the temperature range of -50°C from the solidus temperature in the obtained differential scanning calorimeter curve was examined, and the presence or absence of the endothermic peaks is shown in Tables 1 and 2.

(Judgment criteria)
"Good": The number of endothermic peaks detected within a temperature range of -50°C from the solidus temperature is zero.
"X": The number of endothermic peaks detected within a temperature range of -50°C from the solidus temperature is one or more.

As shown in Table 1, no endothermic peaks occurred in Examples 1 to 12.

In contrast, as shown in Table 2, it can be seen that one or more endothermic peaks occurred in Comparative Examples 1 to 5.

The forged products obtained by the method for manufacturing aluminum alloy forged products according to the present invention have excellent mechanical strength at room temperature, and are therefore suitable for use as suspension parts such as suspension arm parts for automobiles, but are not limited to such applications.

1: Aluminum alloy forgings

Claims (3)

An aluminum alloy forging containing Cu: 0.15 mass% to 1.0 mass%, Mg: 0.6 mass% to 1.3 mass%, Si: 1.32 mass% to 1.45 mass%, Mn: 0.03 mass% to 1.0 mass%, Fe: 0.2 mass% to 0.4 mass%, Cr: 0.03 mass% to 0.4 mass%, Ti: 0.012 mass% to 0.035 mass%, B: 0.0001 mass% to 0.03 mass%, 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,
An aluminum alloy forging, characterized in that no endothermic peak is detected in a temperature range of −50° C. below the solidus temperature in a differential scanning calorimeter curve obtained by differential scanning calorimeter measurement of the cross section of the forging. 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. 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,
3. The method for manufacturing an aluminum alloy forged product according to claim 2, 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.

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