JP2003183756A - Aluminum alloy for semi-solid molding - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aluminum alloy for semi-solid metal molding which yields a cast product having an excellent strength at elevated temperature and little shrinkage cavity. <P>SOLUTION: The aluminum alloy for semi-solid molding contains 4.0-7.9 mass% Si, 2.0-7.0 mass% Cu, 1.5-3.5 mass% Mg, 0.03-0.30 mass% Ti, if required, 0.001-0.01 mass% B, and/or at least one of 0.2-1.0 mass% Fe, 0.2-1.0 mass% Mn and 0.5-2.5 mass% Ni, and the balance being Al and unavoidable impurities. The aluminum alloy is subjected to metal molding in a solid-liquid state achieved by cooling an alloy having a crystal nucleus at right above or below the melting point. The solid-liquid state having a crystal nucleus is achieved by cooling (at an average cooling rate of 0.01-1°C/s) a liquid-state alloy having a crystal nucleus at a temperature equal to or higher than the liquidus, or a solid-liquid-state alloy having a crystal nucleus at a temperature below liquidus and equal to or higher than the molding temperature, to reach the molding temperature in a retainer. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an aluminum alloy for semi-solid forming which is excellent in castability and heat resistance.

[0002]

2. Description of the Related Art As one of the methods for improving the quality of a cast product, a semi-solid forming method for forming a metal in a solid-liquid coexisting state at a predetermined temperature obtained by lowering a temperature from a liquid, and a method for forming a once solidified metal Attention has been paid to a semi-melt forming method for forming a solid-liquid coexisting metal obtained by raising the temperature to a target temperature.
In particular, the semi-solidification molding method, which has a low cost for casting products, is for pressure-molding a semi-solidified metal having spherical crystals whose temperature is lowered directly from a liquid to reach a target temperature in a mold. This is a method that is expected to diversify.

When a heat-resistant casting is produced by this semi-solid forming method, AC is usually used for JIS casting alloys.
8A, AC8B, and AC8C alloys are used.
In all of these alloys, Si exceeds 8.5% and the upper limit values are 13.0%, 10.5%, and 1 respectively.
It shows a high value of 0.0%.

[0004]

However, the above-mentioned method has some problems. First, when the semi-solidified metal of the heat-resistant alloy is discharged from the holding container, it is difficult to discharge it with an alloy having a high Si, and therefore it cannot be adopted as a rheocast method that requires continuous operation. This is because an alloy having a high Si causes skin-forming type solidification, so that the solidified shell is formed near the wall surface of the holding container, and at the same time, the temperature at the upper portion where the temperature tends to decrease decreases.

Second, in order to prevent the formation of solidified shells,
If the amount of Si is simply suppressed, the high temperature strength will decrease and it will be unsuitable as a heat resistant alloy, and in relation to the required mechanical properties,
The amount of Si cannot be simply reduced.

[0006]

In order to solve such a problem, in the present invention, in the first invention, the content of Si is reduced, and in accordance with the reduction, other elements are added. An aluminum alloy, the content of which is adjusted, and the alloy immediately above and below the melting point having crystal nuclei is cooled and then subjected to mold forming in a solid-liquid coexisting state, in a mass ratio of Si: 4.0 to 4.0.
7.9%, Cu: 2.0 to 7.0%, Mg: 1.5 to
The aluminum alloy for semi-solid forming was characterized by 3.5%, Ti: 0.03 to 0.30%, the balance being Al and unavoidable impurities.

Regarding the solid-liquid coexistence state of the aluminum alloy, in the second invention mainly based on the first invention, the solid-liquid coexistence state obtained after cooling the alloy just above and just below the melting point having the crystal nucleus is obtained. Aluminum alloy is a liquid state aluminum alloy having crystal nuclei above the liquidus temperature, or a solid-liquid coexisting aluminum alloy having crystal nuclei below the liquidus temperature above the forming temperature in a holding container. It was characterized by being cooled to a temperature.

In the third invention, which is mainly based on the second invention,
The cooling to the molding temperature is performed at an average cooling rate of 0.01 to 1 ° C./s.

A fourth aspect of the invention, which is the first, second or third invention
In the invention, the molten alloy having a superheat degree with respect to the liquidus temperature of the aluminum alloy of less than 50 ° C. is directly poured into the holding container without using a jig to generate the crystal nuclei. .

Further, regarding the component composition of the aluminum alloy, the fifth invention mainly consisting of the first, second, third or fourth invention is characterized by containing B: 0.001 to 0.01%. Further, in the fifth invention mainly composed of the first, second, third, fourth or fifth invention, Fe: 0.2 to 1.0%, M
One or more of n: 0.2 to 1.0% and Ni: 0.5 to 2.5% are included.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a process of directly forming a semi-solidified aluminum alloy from a molten metal.

According to this process, after the molten aluminum alloy 3 is poured into the holding container 2 from the ladle 1, the upper and lower parts of the holding container are kept warm by the heat insulating material 4, while the outer peripheral portion of the holding container 2 is filled with the air 5. By cooling, the temperature of the alloy in the holding container is made uniform, and finally, in order to facilitate discharge of the alloy from the holding container 2, the temperature is further made uniform by the high frequency induction coil 7. After that, the semi-solidified aluminum alloy 6 is discharged from the holding container 2 into a sleeve, and then molded in a molding die.

At this time, when the Si content in the aluminum alloy becomes 8.0% or more, a solidified shell is formed in the vicinity of the wall surface of the holding container 2, and as a result, the semi-solidified aluminum alloy 6 is removed from the holding container 2. Difficult to discharge.

Therefore, when the aluminum alloy is cooled immediately above and below the melting point having crystal nuclei and then subjected to die molding in the solid-liquid coexisting state, the composition of components is Si: 4.0 to mass ratio. 7.9%, Cu: 2.0 to 7.0
%, Mg: 1.5 to 3.5%, Ti: 0.03 to 0.3
0%, as required, B: 0.001 to 0.01%, and / or Fe: 0.2% to 1.0%, Mn: 0.
2 to 1.0, Ni: 0.5 to 2.5, one or two
When an aluminum alloy containing at least one kind and containing the balance Al and unavoidable impurities is used, it is difficult for a solidified shell to form near the wall surface of the holding container when the temperature of the aluminum alloy held in the container is lowered from the liquid state to the semi-solidified state. As a result, the semi-solidified aluminum alloy can be easily discharged from the holding container.

Therefore, the aluminum alloy for semi-solidification of the present invention (aluminum alloy of the present invention) can be applied to a continuous operation apparatus as a casting alloy, and after being discharged from the holding container, it is pressure-formed in the mold. Manufactured into cast products with excellent shrinkage resistance and almost no shrinkage cavities.

In order to obtain a solid-liquid coexisting aluminum alloy having spherical crystals, an aluminum alloy in the liquid state having a crystal nucleus or higher than the liquidus temperature, or having a crystal nucleus lower than the liquidus temperature and a forming temperature or higher. The aluminum alloy in the solid-liquid coexisting state of is cooled to the forming temperature in the holding container.
At the time of this cooling, it is preferable to set the average cooling rate to 0.01 to 1 ° C./s.

When Ti alone or a combination of Ti and B is added as a method for generating crystal nuclei, a molten metal having a superheat degree of less than 50 ° C. with respect to the liquidus temperature of the alloy is used without using a jig. Then, pour the molten metal directly into the holding container. When pouring directly into a holding vessel without using a jig to generate crystal nuclei, the standard superheat degree to the liquidus temperature of the molten metal is less than 50 ° C., but the spheroidization of the primary crystal is more reliable. In order to achieve this, it is more preferable that the degree of superheat is less than 30 ° C.

In order to generate crystal nuclei, a method of using a cooling plate before pouring the molten metal into a holding container, or a method of bringing the molten metal into contact with a vibrating rod after or during pouring is also possible. It can be applied to the alloy of the present invention. Molding is carried out in a mold, but the method of molding is to transfer the semi-solidified aluminum alloy to a sleeve once, and then to fill in the mold and perform pressure molding. It is also applicable to a method of placing a semi-solidified aluminum alloy and then press-molding or forging, or an extrusion molding method.

Here, the reasons for limiting the contents of various elements constituting the aluminum alloy of the present invention and the effect of addition will be described in detail. In the following, "%" means mass ratio.

Si is an important component for improving the castability and mechanical properties of the alloy and lowering the coefficient of thermal expansion.
When the content is less than 4.0%, the coefficient of thermal expansion important for the piston is large. On the other hand, if it is 8% or more, it becomes difficult to discharge the semi-solidified metal produced in the holding container from the container. Therefore, the Si content is set to 4.0 to 7.9%. It is preferably 6.0 to 7.5%.

Cu forms a solid solution in the aluminum matrix, and when it coexists with Ni, it becomes a fine refractory crystallized substance such as Al ₃ Ni (Cu) ₂ and is an important component for improving the high temperature strength. . Further, Cu precipitates as Al ₂ Cu in the aging treatment to improve the material strength, but if the content thereof is less than 2.0%, the above strength improving effect cannot be sufficiently obtained and the high temperature strength is insufficient. Is. On the other hand, if it exceeds 7.0%, shrinkage cavities are likely to occur even in the semi-solidification molding method,
In addition, since segregation increases during casting, it cannot form a solid solution even after heat treatment, resulting in a marked decrease in mechanical properties. Therefore, the content of Cu is set to 2.0 to 7.0%. It is preferably 3.0 to 6.0%.

Since Mg precipitates Mg ₂ Si by aging treatment when coexisting with Si, Mg is an important component for improving the high temperature strength, but if the content thereof is less than 1.5%, the above strength is improved. The effect is not sufficiently obtained and the high temperature strength is insufficient. On the other hand, if it exceeds 3.5%, shrinkage cavities are likely to occur even in the semi-solidification molding method, and coarse Mg ₂ Si crystallizes during casting and segregation increases, so a solid solution can be obtained even by heat treatment. However, the mechanical properties will be significantly reduced. Therefore, the content of Mg is 1.5 to 3.5%
And It is preferably 1.5 to 3.0%.

Ti is an important component for producing a semi-solidified metal having spherical crystals, but a molten metal having a superheat degree of less than 30 ° C. with respect to the liquidus temperature of the alloy is used without using a jig.
When pouring directly into the holding container, the content is 0.03
If it is less than%, a semi-solidified metal having fine spherical crystals cannot be obtained. On the other hand, if it exceeds 0.30%, a coarse Ti compound is formed and the mechanical properties are remarkably deteriorated.
Therefore, the Ti amount is set to 0.03 to 0.30%. Preferably, it is 0.08 to 0.20%.

B is an important component in combination with Ti for producing a semi-solidified metal having finer spherical crystals than Ti alone. However, the superheat degree with respect to the liquidus temperature of the alloy is less than 50 ° C. When pouring the molten metal of No. 3 directly into a holding container without using a jig, if the content is less than 0.001%, a semi-solid metal having fine spherical crystals is obtained as compared with the case of using Ti alone. Absent. Further, even if the content exceeds 0.01%, improvement of the miniaturization effect cannot be expected. For this reason,
The content of B was 0.001 to 0.01%. Preferably, it is 0.001 to 0.005%.

Fe is not a plate-like compound in conventional semi-solid moldings but a lump compound instead of a plate-like compound, and is a component having an effect of improving high temperature strength without extremely deteriorating mechanical properties. If the content is less than 0.2%, the improvement in high temperature strength is insufficient. On the other hand, if it exceeds 1.0%, a coarse Fe compound is formed at the time of casting, resulting in a marked decrease in mechanical properties. Therefore, the content of Fe is set to 0.2 to 1.0%. Preferably 0.2
Is 0.50%.

Mn is a component having the effect of improving the high temperature strength without extremely deteriorating the mechanical properties, but if the content of Mn is less than 0.2%, the improvement of the high temperature strength is insufficient. On the other hand, if it exceeds 1.0%, a coarse Mn compound is formed at the time of casting, resulting in a marked decrease in mechanical properties. Therefore, the Mn content is 0.2 to 1.0%.
And It is preferably 0.2 to 0.50%.

Ni is solid-dissolved in an aluminum matrix and crystallizes as an intermetallic compound stable at high temperature such as Al ₃ Ni, Al ₃ Ni ₂ and Al ₃ Ni (Cu) _{2 to} form a massive crystallized substance. Therefore, it is an important component for improving the high temperature strength, but if the content is less than 0.5%, a sufficient amount of crystallized substances cannot be obtained, and the high temperature strength is insufficient. On the other hand, 2.5
If it exceeds%, shrinkage cavities are likely to occur even in the semi-solidification molding method, and a coarse Ni compound is formed during casting, resulting in a marked decrease in mechanical properties. Therefore, the Ni content is set to 0.5 to 2.5%. It is preferably 0.8 to 2.0%.

Since the cooling rate during solidification is high in the semi-solidification molding method, addition of an improving element is usually unnecessary, but in the case of a product with a large product thickness, it is improved for the purpose of refining eutectic Si. Since any one of the elements Sr, Na, and Sb can be added to suppress the variation in elongation value and improve the elongation value, these elements can be added as necessary. In addition to the addition of Ti and B for the purpose of refining the crystal grains, Zr can be added to obtain a similar spherical microstructure.

Examples of the present invention will be described below, but the conditions used in the examples are mere examples, and the aluminum alloy of the present invention is not limited to these conditions.

(Examples) Alloys having the chemical components shown in Table 1 were melted, and each alloy was 490 ° C. × 6 h → 60 WQ → 1.
A tensile test was performed by performing T6 treatment at 80 ° C. × 6 h, then performing heat treatment at 200 ° C. for 100 h, and then heating and holding at 200 ° C. for 30 minutes. The results obtained are
It is also shown in the table.

[0031]

[Table 1]

Comparative alloys 1 and 2 are AC8A and AC8C alloys obtained by gravity casting. These alloys have high high-temperature strength of 150 MPa or more (see "σB" column in Table 1). However, even if a semi-solid metal is produced in the holding container, these alloys cannot be discharged from the holding container when the liquidus rate most suitable for molding is around 50% (Table 1). (See "Slurry discharge" column). Therefore, the alloy of AC8A and AC8C is not suitable for the semi-solid forming method.

In Comparative Alloy 3, it was difficult to show a spherical structure completely because of a small amount of Ti, and as a result, a non-uniform structure was shown at the time of molding (see "Primary crystal α" column in Table 1).

In Comparative Alloy 4, since the amount of Ti was large, a coarse Ti compound was generated, and the strength and elongation were lowered (Table 1
(See columns "σB" and "δ"). In Comparative Alloy 5, Cu
Due to the small amount, it exhibits lower high temperature strength than the conventional heat-resistant alloy AC8C. In Comparative Alloy 6, since the amount of Cu was large, segregation was likely to occur, the solution treatment could not be completely performed even by heat treatment, and both strength and elongation were low.

In Comparative Alloy 7, since the amount of Mg was small, even if the amount of Cu for improving the strength was increased, high strength could not be obtained. In Comparative Alloy 8, since the Mg content was too large, high strength equivalent to that of the conventional heat-resistant alloys AC8A and AC8C was obtained, but shrinkage cavities were likely to occur.

In Comparative Alloy 9, the high temperature strength was low because the amount of Si was too small. In Comparative Alloy 10, the semi-solid metal was not discharged from the holding container because the amount of Si was too large. In Comparative Alloy 11, since the Fe content was large, a coarse Fe compound was generated, the high temperature strength and the elongation were lowered, and shrinkage cavities were generated.

In Comparative Alloy 12, since the Mn content is large,
Coarse Mn compounds were generated, and high temperature strength and elongation were lowered. In Comparative Alloy 13, since a large amount of Ni was generated, a coarse compound was generated and high strength could not be obtained. In Comparative Alloy 14, the amount of B was large, but there was no difference in the morphology and size of the spherical crystals from the inventive example in which the amount of B was 0.008%.

On the other hand, the alloys 1 to 10 of the present invention are lower Si alloys than the conventional piston alloys, but contain Cu and Mg in a larger amount than the conventional alloys, and if necessary, required amounts of Ni and Mn. , Fe are included, so that high-temperature strength characteristics equivalent to those of conventional ones are exhibited.

[0039]

As is apparent from the above description,
When the aluminum alloy of the present invention is used to lower the temperature of a metal held in a container from a liquid state to a semi-solidified state, a solidified shell is unlikely to be formed in the vicinity of the wall surface of the holding vessel, so the semi-solidified metal is retained from the holding vessel. It becomes easy to discharge. Therefore, the aluminum alloy of the present invention can be applied to a continuous operation device, and can produce a cast product excellent in high-temperature strength with little shrinkage cavities by being pressure-molded in a mold after being discharged.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a process of directly producing a semi-solid metal from a molten aluminum alloy.

[Explanation of symbols]

1 ... Ladle 2 ... Holding container 3 ... Aluminum alloy melt 4 ... Insulation 5 ... Air 6 ... Semi-solidified aluminum alloy 7 ... High frequency induction coil

Continued front page    (72) Inventor Satoshi Satoshi             1980 Okiyama, Ogushi, Obu, Yamaguchi Prefecture             Ube Industries Co., Ltd. (72) Inventor Nobuhiro Ishizaka             Showa Light Alloy Co., Ltd. 2 Yawata Kaigan Dori, Ichihara City, Chiba Prefecture             Inside the company (72) Inventor Shigeo Hirose             Showa Light Alloy Co., Ltd. 2 Yawata Kaigan Dori, Ichihara City, Chiba Prefecture             Inside the company

Claims (6)

[Claims] 1. An aluminum alloy which is subjected to mold forming in a solid-liquid coexisting state after cooling an alloy having crystal nuclei just above and just below a melting point and having a mass ratio of Si: 4.0 to 7.
9%, Cu: 2.0 to 7.0%, Mg: 1.5 to 3.5
%, Ti: 0.03 to 0.30%, the balance Al and unavoidable impurities, and an aluminum alloy for semi-solid forming. 2. A solid-liquid coexisting aluminum alloy obtained by cooling an alloy immediately above and below the melting point having crystal nuclei is a liquid state aluminum alloy having crystal nuclei at a liquidus temperature or higher, or a crystal. The aluminum alloy for semi-solid forming according to claim 1, which is obtained by cooling an aluminum alloy in a solid-liquid coexisting state having a nucleus lower than the liquidus temperature and not less than the forming temperature to the forming temperature in a holding container. . 3. The cooling to the molding temperature is 0.01 to
The aluminum alloy for semi-solid forming according to claim 2, which is performed at an average cooling rate of 1 ° C / s. 4. A molten metal having a superheat degree of less than 50 ° C. with respect to a liquidus temperature of an aluminum alloy, directly without using a jig.
The aluminum alloy for semi-solid forming according to claim 1, 2 or 3, wherein the crystal nuclei are generated by pouring the molten metal into a holding container. 5. The aluminum alloy for semi-solid forming according to claim 1, 2, 3 or 4, wherein B: 0.001 to 0.01% is contained. 6. Fe: 0.2 to 1.0%, Mn: 0.2
.About.1.0%, Ni: 0.5 to 2.5%, and one or more of them are contained.
Or the aluminum alloy for semi-solid forming according to 5.