JP6900199B2 - Manufacturing method of aluminum alloy for casting, aluminum alloy casting products and aluminum alloy casting products - Google Patents

Description

The present invention relates to an aluminum alloy for casting, an aluminum alloy casting product, and a method for manufacturing an aluminum alloy casting product.

Among the aluminum alloys for casting, Al—Si alloys having good castability such as AC4CH and ADC12 specified in JIS are often used, but the ductility is particularly low because brittle eutectic Si crystallizes. .. Therefore, in some Al—Si alloys, eutectic Si is finely granulated by heat treatment to improve ductility. However, in addition to the increase in energy consumption and cost due to heat treatment, there are also problems that thermal strain occurs in thin-walled products and blister due to gas or the like caught in the product occurs.

On the other hand, Al—Mg-based alloys such as AC7A and ADC5 defined in JIS have excellent ductility without heat treatment, but their strength is not sufficient. It also has the drawback of poor castability. Here, poor castability means that the liquidus temperature is high, the specific heat and latent heat of solidification are small, so the solidification time is short, the fluidity of the molten metal is inferior, and the amount of solidification shrinkage is larger than that of Al—Si alloys. That is, shrinkage cavities are likely to occur, and solidification cracks are likely to occur on the surface of the casting.

Although not specified in the current JIS, AC7B containing about 10% by mass of Mg has been established in the past. By subjecting this alloy to solution heat treatment to dissolve the β phase (Al ₃ Mg ₂ ) as a solid solution, it was possible to obtain strength and ductility superior to that of AC7A containing about 4% by mass of Mg. However, the ductility of this alloy sharply decreases due to aging due to the progress of natural aging after solution heat treatment. Further, there is a problem that stress corrosion cracking is likely to occur. Due to such circumstances, AC7B was hardly produced and was deleted from JIS revised in 1992.

By the way, from the viewpoint of global environmental conservation, all industries are required to save resources and energy. For example, the automobile industry has many problems such as low fuel consumption and measures for recycling. Among them, the reduction of exhaust gas, which is directly linked to global warming, is a major issue, and we are focusing on the development of technology to achieve low fuel consumption, that is, improved fuel consumption. Weight reduction is one of the major factors that improve fuel efficiency. Research is being actively conducted to convert iron-based materials, which have been mainly used in the past, into aluminum alloys, magnesium alloys, carbon materials, etc. as lighter materials. Among them, aluminum alloy is excellent not only in lightness but also in strength, processability, corrosion resistance, thermal conductivity and recyclability, and is expected as a material for promoting weight reduction of automobiles.

Aluminum alloys as automobile materials have already been widely used in engines, wheels, heat exchangers, etc., but application to vehicle body structural members that require high strength and shock absorption is AA standard A365 alloys, etc. Limited to some die-cast aluminum alloys. With reference to Non-Patent Document 1, the target characteristics are a proof stress of 150 MPa or more and an elongation of 20% or more, but the target characteristics cannot be achieved with the above-mentioned practical alloys such as AC7A and AC7B, and for castings to be put into practical use. Aluminum alloys are required to have good castability. That is, even if the casting method does not require pressurization, there is no aluminum alloy for casting that can realize the target characteristics as it is as-cast without heat treatment.

A high-strength, high-toughness aluminum alloy that can be used as it is without heat treatment has been proposed (Patent Document 1). The aluminum alloy proposed in Patent Document 1 has Mn: 0.5 to 2.5% and Mg: 2.5 to 7% in weight%, at least Ti: 0.15 to 0.5%, and Zr: 0. .15-0.5%, B: 0.01-0.1%, and at least Sb: 0.01-0.5%, Bi: 0.01-0.5% Manufacture of a high-strength, high-toughness aluminum alloy member, which comprises melting the raw material so that the balance is substantially aluminum, and solidifying the molten metal of the raw material at a cooling rate of 0.5 ° C./sec or more. The method and the aluminum alloy for casting used for this. It is said that this alloy can obtain a high-strength and high-toughness aluminum alloy member having a tensile strength of 30 kgf / mm ² or more, a 0.2% proof stress of 15 kgf / mm ^{2 or more, and an elongation of 20% or more.}

However, in the method for producing a high-strength and high-toughness aluminum alloy member proposed in Patent Document 1 and the aluminum alloy for casting used for the method, only examples in the range of Mg: 4.4 to 4.7% by weight%. Not shown. It is known that when the Mg content exceeds 5%, coarse Al-Mg-based crystallized products are crystallized and the elongation is significantly reduced. Patent Document 1 shows a solution thereof. It has not been. Further, in order to obtain the tensile properties, it is necessary to substantially set the cooling rate to 5 ° C./sec or more, and when solidified at a cooling rate of less than 5 ° C./sec, the elongation may be less than 20%. It is shown by an embodiment.

The cooling rate of casting varies depending on the casting temperature, mold material / temperature, wall thickness of cast products, etc., but in general, it is 0.05 to 1 ° C / sec for sand casting and 1 to 5 ° C for die casting. It is said that the temperature is 1 to 10 ° C./sec for pressure casting, and 100 ° C./sec or more for die casting. In Patent Document 1, an aluminum alloy member is obtained by a kind of pressure casting called a high pressure casting method. In general, pressure casting and die casting have a high cooling rate and a fine solidified structure can be obtained, so that it is possible to produce a casting having excellent strength and elongation. However, since high pressure is applied to the molten metal to fill the mold, the precision of the mold is strict and equipment costs such as mold costs are high, and inclusions such as air and oxides are easily caught in the product, resulting in strength and strength. There are drawbacks such as reduced elongation.

Shuichiro Watanabe, "New Uses with New Aluminum Materials", Elementary Materials, General Incorporated Association Elementary Materials Center, December 2009, Vol. 50, No. 9, p. 23-29

Japanese Unexamined Patent Publication No. 6-330202

In view of the above circumstances, the development of aluminum alloys, aluminum alloy casting products, and aluminum alloy casting products that can be manufactured by an inexpensive method with a resistance of 150 MPa or more and an elongation of 20% or more without heat treatment has been developed. It has been demanded.

In order to solve the above-mentioned problems, the present inventor has focused on a method of obtaining high yield strength while maintaining high elongation in the untreated as-cast state by variously changing the composition of the Al—Mg-based alloy for casting. I studied. As a result, by optimizing the amounts of Mg, Mn, Ti, B and Zr, high elongation and high strength can be obtained as-cast without heat treatment, and aluminum alloys for casting, aluminum alloy products and aluminum alloys can be obtained. We have realized a method for manufacturing cast products.

The aluminum alloy for casting of the present invention has Mg: 5.0 to 8.0%, Mn: 0.5 to 2.0%, and at least Ti: 0.05 to 0.25%, B: 0 in mass%. It is an aluminum alloy for casting, which contains one of .05 to 0.15% and Zr: 0.05 to 0.25%, and the balance is composed of aluminum and unavoidable impurities.

Further, the average size of the crystallized product composed of the Al-Mg-based crystallized product and the Al-Mn-based crystallized product is 30 μm or less, and the area ratio is 5% or less. 5.0 to 8.0%, Mn: 0.5 to 2.0%, at least Ti: 0.05 to 0.25%, B: 0.05 to 0.15%, Zr: 0.05 to It is an aluminum alloy casting product produced from an aluminum alloy for casting, which contains one of 0.25% and the balance is aluminum and unavoidable impurities.

Further, the average size of the Al-Mg-based crystallized product, which is characterized by having a withstand capacity of 150 MPa or more and an elongation of 20% or more, is 30 μm or less, and the area ratio of the crystallized product is 5% or less by mass%. Mg: 5.0 to 8.0%, Mn: 0.5 to 2.0%, at least Ti: 0.05 to 0.25%, B: 0.05 to 0.15%, Zr: 0. It is an aluminum alloy casting product produced from an aluminum alloy for casting, which contains one of 05 to 0.25% and the balance is aluminum and unavoidable impurities.

Further, in terms of mass%, Mg: 5.0 to 8.0%, Mn: 0.5 to 2.0%, and at least Ti: 0.05 to 0.25%, B: 0.05 to 0.15%. , Zr: Containing one of 0.05 to 0.25%, the balance is substantially composed of aluminum, and the secondary dendrite arm spacing (DASII) of primary crystal α-Al is 55 μm or less. It is an aluminum alloy casting product.

Then, in terms of mass%, Mg: 5.0 to 8.0%, Mn: 0.5 to 2.0%, and at least Ti: 0.05 to 0.25%, B: 0.05 to 0.15%. , Zr: A method for producing an aluminum alloy casting product, which comprises producing a molten metal containing one of 0.05 to 0.25% and having a balance substantially made of aluminum by mold casting.

By mass%, Mg: 5.0 to 8.0%, Mn: 0.5 to 2.0%, and at least Ti: 0.05 to 0.25%, B: 0.05 to 0.15%, Zr. : A method for producing an aluminum alloy casting product, which comprises producing a molten metal containing one of 0.05 to 0.25% and having a balance substantially made of aluminum by gravity mold casting.

By using the aluminum alloy for casting of the present invention, it is possible to obtain an aluminum alloy cast product having a strength of 150 MPa or more and an elongation of 20% or more without heat treatment. The aluminum alloy casting product of the present invention can be manufactured by a manufacturing method such as mold casting, particularly gravity mold casting, which has a relatively low equipment cost.

The figure which shows the microstructure of the aluminum alloy casting of this invention (Example 1) Comparative Example A diagram showing the microstructure of an aluminum alloy casting (Comparative Example 12)

The reason for limiting the manufacturing method of the aluminum alloy for casting, the aluminum alloy casting product, and the aluminum alloy casting product of the present invention will be described. Unless otherwise specified, the content of each alloy element is shown in% by mass.

The content of magnesium (Mg) in the aluminum alloy for casting of the present invention is 5.0 to 8.0%. Mg is dissolved in aluminum to improve strength and proof stress. If the Mg content is less than 5.0%, sufficient proof stress cannot be obtained, and if it exceeds 8.0%, a large amount of Al-Mg-based crystallized products will crystallize and the elongation will be significantly reduced. In this composition range, it is superior to the practical alloy AC7A and has the same fluidity as AC7B, and is less likely to cause casting cracks than AC7A and AC7B. Further, from the viewpoint of preventing stress corrosion cracking, the upper limit of the Mg content is preferably 8.0%. In the range of Mg content of 5.0 to 8.0%, the average size of Al-Mg-based crystals is 30 μm or less, the area ratio is 5% or less, and high elongation is exhibited. When higher strength is required, the Mg content is more preferably 7.0 to 8.0%, and particularly excellent castability is exhibited in this composition range.

20-100 ppm of beryllium (Be) may be added to prevent oxidative depletion of Mg and reaction with the mold.

The content of manganese (Mn) is 0.5 to 2.0%. Mn is dissolved in aluminum to improve strength and proof stress. If the Mn content is less than 0.5%, sufficient proof stress cannot be obtained, and if it exceeds 2.0%, the size and area ratio of Al—Mn-based crystals increase, and the elongation is significantly reduced.

The content of titanium (Ti) is 0.05 to 0.25%. _{Al 3} Ti, which is a compound of Ti and Al, becomes a solidified nucleus of primary crystal α-Al, and the strength, proof stress, and elongation are improved by refining the primary crystal α-Al crystal grains. If the Ti content is less than 0.05%, the above-mentioned effect cannot be obtained, and if it exceeds 0.25%, crystallization increases and elongation decreases.

The content of boron (B) is 0.05 to 0.15%. Similar to Ti, B refines the primary α-Al crystal grains. If the content of B is less than 0.05%, the above-mentioned effect cannot be obtained, and if it exceeds 0.15%, coarse crystallization increases and the elongation decreases.

The content of zirconium (Zr) is 0.05 to 0.25%. Zr has the same effect as Ti and B. If the Zr content is less than 0.05%, the above-mentioned effect cannot be obtained, and if it exceeds 0.25%, coarse crystallization increases and the elongation decreases.

It is known that when DASII is large, that is, when the cooling rate is slow, the elongation is greatly reduced. The aluminum alloy casting product of the present invention has the above-mentioned alloy composition, and DASII is 55 μm or less. When DASII is 55 μm or less, the elongation is high, and when it exceeds 55 μm, the elongation decreases.

In the method for producing an aluminum alloy casting product of the present invention, a molten metal having the above-mentioned alloy composition can be produced by a mold casting, particularly a manufacturing method such as gravity mold casting, which has a relatively low equipment cost.

As described above, by using the aluminum alloy for casting of the present invention, it is possible to obtain an aluminum alloy casting product having a strength of 150 MPa or more and an elongation of 20% or more without heat treatment. The aluminum alloy casting of the present invention can be manufactured by a manufacturing method such as mold casting, particularly gravity mold casting, which has a relatively low equipment cost.

Next, the details of the present invention will be described with reference to the following examples. The examples shown below are for facilitating understanding of aspects of the present invention, and are not limited to these examples.

Table 1 shows the composition of the alloys examined. The rest other than the elements shown in Table 1 is substantially composed of aluminum and unavoidable impurities. For example, it was confirmed that the Si content of all the Example samples was 0.05 to 0.15% and the Fe content was 0.05 to 0.25%, both of which satisfied the standard values of AC7A. .. Similarly, it was confirmed that the other elements also satisfied the standard value of AC7A. The aluminum alloys shown in Table 1 were melted and cast by the gravity mold method to prepare a casting for collecting test materials.

The method of melting and casting the alloy will be described below. Industrial pure aluminum (purity 99.7% or more) was charged into a graphite crucible as a raw material and melted in an air atmosphere using an electric furnace. Manganese mother alloy (Al-75% Mn), zirconium mother alloy (Al-15% Zr), titanium mother alloy (Al-10% Ti) whose mass was adjusted to obtain the desired composition after the pure aluminum had melted down. , Titanium-boron mother alloy (Al-5% Ti-1% B) and metallic magnesium were added. After performing argon gas bubbling for the purpose of removing hydrogen gas and inclusions in the obtained molten metal, the molten metal was sedated to remove slag on the surface of the molten metal and used for casting. The casting temperature was 735 ° C., the mold for collecting the test material was a boat mold based on FIG. 2 of JIS: H5202, and the mold temperature was set to room temperature. Then, it was naturally air-cooled and taken out from the boat mold to obtain a casting for collecting test material.

A JIS No. 4 tensile test piece was prepared from the casting for collecting the test material obtained as described above. In addition, a sample for microstructure observation was cut out from the same casting. Table 2 shows the tensile test results and microstructure observation results of Examples and Comparative Examples. The major axis of the crystallized material existing in the observation field of view was manually specified, and the length was measured with image processing software to obtain the crystallized product size. Further, the outer shell of the crystallized product was manually specified, and the internal area thereof was calculated by image processing software to obtain the crystallized product area. The area ratio was defined as the total area of crystallized substances present in the observation field of view and the value divided by the observation field of view area. DASII was measured based on the line of intersection method described in "Dendrite Arm Spacing Measurement Procedure" (Casting / Solidification Subcommittee, Japan Institute of Light Metals, January 1988, Vol. 38, No. 1, p.54-60).

All of Examples 1 to 8 had a proof stress of 150 MPa or more and an elongation of 20% or more.
As a representative example of Example Samples 1 to 8, FIG. 1 shows the microstructure of the aluminum alloy casting of Example Sample 1. Al ₃ Mg _{2 which is an Al-Mg-based crystallized product and Al 6} Mn which is an Al-Mn-based crystallized product were observed. The average size of the crystallization was 30 μm or less, and the area ratio was 5% or less. DASII was 55 μm or less.

The proof stress of Comparative Examples Samples 9, 10 and 15 having a low Mn content did not reach 150 MPa. In Comparative Examples Samples 11 to 13 having low Ti, B and Zr contents, the primary α-Al crystal grains could not be refined, the DASII was 56 μm or more, the proof stress did not reach 150 MPa, and the elongation was less than 20%. It was. The elongation of samples 14 and 16 having a high Mn content did not reach 20%. FIG. 2 shows the microstructure of the aluminum alloy casting of Comparative Example Sample 16. _{It was confirmed that Al 3} Mg _{2, which} is an Al-Mg-based crystallized product, was crystallized along the grain boundaries. The average size of the crystallization was larger than 30 μm and the area ratio exceeded 5%. As described above, when at least one of Mn, Ti, B and Zr is out of the composition range of the present invention, at least one of the yield strength and the elongation does not satisfy the target characteristic.

In order to evaluate the castability of the aluminum alloy for casting of the present invention, a fluidity test was carried out. A MIT type fluidity tester was used for the fluidity test. The test conditions were a decompression degree of 0.0395 MPa and a metal head of 250 mm, and molten aluminum was sucked from one end of an L-shaped glass tube, and the length (flow length) to the position where the flow stopped was measured. The molten metal temperature was set to three levels of 700 ° C., 730 ° C. and 760 ° C., and the test was conducted at each level n = 3 to calculate the average value. Table 3 shows the fluidity test results of Example 8 and the JIS alloy AC7A and the old JIS alloy AC7B.

Example Sample 8 was superior to AC7A and had the same degree of fluidity as AC7B.

In addition, a crack test was conducted as an evaluation of castability. The crack test used the ring-shaped mold described in "Mold Casting Method" (written by Kazunori Kobayashi, Nikkan Kogyo Shimbun, August 27, 1968, p. 30-31). The mold temperature was normal temperature, and the pouring temperature was liquidus temperature + 100 ° C. After cooling the casting, the length of the crack visible on the surface of the crack test piece was measured. The test was conducted at each level n = 4. Table 4 shows the crack test results of Examples 1, 3 and 8 and AC7A which is a JIS alloy and AC7B which is an old JIS alloy.

Immediately after casting the molten metal into the mold for collecting crack test pieces, cracks with an average length of about 6 mm were observed on the surface of the three test pieces in AC7A near the pouring port. Further, when the cracking test piece was removed from the mold, all the test pieces of AC7B cracked in the vicinity of the pouring port, and the test piece broke. On the other hand, no cracks occurred in all the test pieces of Example Samples 1, 3 and 8. Since most of AC7A was cracked immediately after casting, it was not evaluated after it was removed from the mold.

From the results of the fluidity test and the cracking test, it was confirmed that the example sample had good fluidity comparable to that of AC7B and was less crackable than the practical alloys AC7A and AC7B.

Based on the above results, the amounts of Mg, Mn, Ti, B and Zr that obtain high ductility and high strength in the as-cast state without heat treatment were determined, and an aluminum alloy for casting having excellent castability was obtained. Further, by using the aluminum alloy for casting of the present invention, it is possible to obtain an aluminum alloy casting product having a strength of 150 MPa or more and an elongation of 20% or more without heat treatment. The aluminum alloy casting of the present invention can be manufactured by a manufacturing method such as mold casting, particularly gravity mold casting, which has a relatively low equipment cost.

Claims (1)

In terms of mass%, Mg: 7.0 to 8.0%, Mn: 0.5 to 1.7 %, and at least Ti: 0.05 to 0.25%, B: 0.05 to 0.15%, Zr. : Contains one of 0.05 to 0.25%, the balance is composed of aluminum and unavoidable impurities, and the average size of the crystallized product consisting of Al-Mg-based crystallized product and Al-Mn-based crystallized product is 27～30Myuemu, and the area ratio is 5% or less, the secondary dendrite arm spacing (DASII) is 45～55Myuemu, aluminum alloy casting product, characterized in that at least resistant force 150MPa and elongation of 20% or more.

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