JP2001316753A - Magnesium alloy and magnesium alloy member excellent in corrosion resistance and heat resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a heat resistant magnesium allay and a heat resistant member thereof excellent in strength and corrosion resistance. SOLUTION: This magnesium alloy has a composition containing 6.0 to 8.0% Al, 2.0 to 4.0% Ca, 0.1 to 0.8% Mn, 0.001 to 0.05% Sr, 0 to 0.5% Si and 0 to 0.5% Zn, and the balance Mg with inevitable impurities. The heat resistant member is obtained by subjecting the same to injection molding into a die in a half-melted state with a solid phase ratio of <=50%. In this way, the magnesium alloy having excellent strength and heat resistance equal to those of the conventional material cap be obtained. The alloy is also excellent in castability, and the heat resistant member excellent in those characteristics can easily be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a magnesium alloy having excellent corrosion resistance and heat resistance and good castability, and suitable for various high-pressure casting methods such as metal injection molding, die casting, squeeze casting, and the like. The present invention relates to a magnesium alloy member produced by these high-pressure casting methods using the above method.

[0002]

2. Description of the Related Art Magnesium alloys are lightweight and have excellent strength not only at room temperature but also at high temperatures, and are expected to be applied to various uses. For example, magnesium alloys can be used to manufacture highly corrosion-resistant heat-resistant members, such as transmission cases and oil pans, which are expected to be put to practical use in the automotive field. It can be expected and can contribute to the suppression of global warming. In the field of home appliances, a magnesium alloy housing that requires heat resistance as well as corrosion resistance, such as a liquid crystal projector having a light source inside, can be manufactured, thereby contributing to the expansion of high-strength portable devices. In addition, it is expected to be applied to lightweight members requiring heat resistance as well as corrosion resistance such as electric tools and leisure goods.

Conventionally, as this kind of magnesium alloy,
AS-based alloys (AS41, AS21) and AE-based alloys (AE
42) is representative. Although not put into practical use, the following various alloys have been proposed. In addition, all the component amounts of the following alloys are shown by mass%. (1) Al: 1 to 6%, Ca: 0.5 to 4%, Si:
0.5-1.5%, Mn: 0.15-0.5%, Zn:
Mg alloy containing 0.1 to 0.3% (Japanese Patent Publication No. 3-1789)
No. 0). (2) Al: 2 to 10%, Ca: 1.4 to 10%, Ca
/Al≧0.7, Si, Zn: ≦ 2%, rare earth element: ≦
Mg alloy containing 4% (JP-A-6-25790). (3) Al: 5 to 10%, Si: 0.2 to 1.0%, C
a: Mg containing 0.05 to 0.5%, Sr: ≤0.1%
Alloy (JP-A-9-104942). (4) Al: 2 to 10%, Ca: 1.0 to 10%, S
Mg alloy containing at least one of i, Mn, Zn, and Zr: ≤2% and rare earth element: ≤4% (Japanese Patent Application Laid-Open No. 9-27191)
No. 9). (5) Al: 2 to 6%, Ca: 0.5 to 4%, Ca / A
Mg alloy containing l ≦ 0.8 and Sr: ≦ 0.15% (Japanese Patent Application Laid-Open No. 9-272945).

The actions (reasons for addition) of the component elements in each of the above alloys are generally as follows. Al forms a hard intermetallic compound (Mg ₁₇ Al ₁₂ ) with Mg, and enhances the yield strength and tensile strength of the alloy by its dispersion strengthening.
Ca forms a high melting point intermetallic compound with Al or Mg, and increases tensile strength and creep resistance. Si forms a high-melting intermetallic compound (Mg ₂ Si) with Mg, and increases tensile strength and creep resistance. Zn improves age hardening ability and contributes to improvement in strength. The rare earth element (mainly misch metal) forms an intermetallic compound with Al and improves the elongation at break at high temperature and the creep resistance.

[0005]

However, in the above-mentioned conventional magnesium alloy, the composition is adjusted in order to improve the strength and the creep characteristics, but on the other hand, either the strength or the creep characteristics, This results in adverse effects on castability and corrosion resistance. For example, in the alloy, but contain a Al and Zn in order to improve the strength, the addition number of Al, in order to increase the Mg ₁₇ Al _{1 2} a low melting point and and brittle intermetallic compound, the toughness The creep resistance decreases with the decrease.
Also, when a large amount of Zn is added, the creep resistance is reduced and the casting cracking sensitivity is increased. Further, while rare earth elements are effective in improving creep characteristics, they raise the material cost and are liable to be oxidized, so that they tend to seize into a mold. Although Ca and Si have the effect of improving the creep characteristics together with the tensile strength, the addition of a large amount of Ca lowers the toughness and increases the casting crack susceptibility.
Further, the corrosion resistance rapidly deteriorates with an increase in the amount of addition.
In particular, Mg-Al-Ca alloy is expected as a low-cost heat-resistant alloy containing no rare earth element. However, if it contains 2% by mass or more of Ca necessary for obtaining sufficient creep characteristics, the corrosion resistance is significantly deteriorated. There is a disadvantage that. In addition, Si easily forms a compound with Ca,
Since a large amount of crystallization occurs during melting to lower the melting yield, the above-mentioned effects (the effects of improving the tensile strength and creep characteristics) cannot be obtained effectively. As described above, conventional magnesium alloys do not have satisfactory characteristics in any of tensile strength, high-temperature creep characteristics, corrosion resistance, and castability, and thus do not sufficiently satisfy the required characteristics in the above-mentioned applications. Has not been reached. Further, since the conventional alloy generally has a high melting point, it is necessary to raise the melting temperature, so that the molten metal is liable to burn. Also, since the solidus temperature is high, the flowability of the molten metal is poor, and casting defects are likely to occur. Therefore, it did not function as a practical part.

The present invention has been made to solve the above-mentioned problems of the conventional alloys. In particular, the present invention focuses on corrosion resistance, which has hardly been studied in the past, and designs alloys so that soundness can be maintained even at a low melting temperature. It is an object of the present invention to provide a magnesium alloy having excellent castability and excellent creep resistance at high temperatures, and a heat-resistant member manufactured using the same.

[0007]

Means for Solving the Problems In order to solve the above problems, the first invention of the magnesium alloy excellent in corrosion resistance and heat resistance according to the present invention is: Al: 6.0 to 8.0 mass%, Ca: 2.0 to 4.0% by mass, Mn: 0.1 to 0.
8% by mass, Sr: 0.001 to 0.05% by mass, Si:
0-0.5% by mass, Zn: 0-0.5% by mass,
The balance consists of Mg and unavoidable impurities.

[0008] The magnesium alloy having excellent corrosion resistance and heat resistance according to the second invention is the magnesium alloy according to the first invention, wherein at least one of Cu, Ni, Fe, and Cl among the unavoidable impurities has a Cu content of 0.01% by mass. Hereinafter, Ni: 0.001% by mass or less, Fe: 0.004% by mass or less, Cl: 0.00
It is characterized in that the allowable content is 3% by mass or less.

A magnesium alloy member having excellent corrosion resistance and heat resistance according to a third aspect of the present invention is made of the magnesium alloy according to the first or second aspect of the present invention, and is a mold in a completely molten or semi-molten state having a solid fraction of 50% or less. And molded by injection.

The function of the magnesium alloy component of the present invention and the reason for limiting the content will be described below. In addition, the content of each component is shown by mass%. Al: 6.0
-8.0% Al hardly forms a solid solution in the Mg matrix,
g is concentrated on the solidification front of primary crystals, resulting in Mg or Ca
Good fluidity is obtained until a eutectic compound is formed. At this time, if Al is less than 6%, the melting point is high at the time of melting the alloy or at the time of casting, since the melting point is high, and the workability is reduced. On the other hand, if it exceeds 8%, the intermetallic compound increases, so that the toughness decreases and the casting cracking susceptibility increases. For this reason, the Al content is reduced to 6.0 to 8.0%.
To the range.

Ca: 2.0-4.0% Ca forms an intermetallic compound with Mg and Al,
It is mainly crystallized in the form of a network at the crystal grain boundaries, and this acts as an obstacle to the dislocation ascending movement, improving the tensile strength and increasing the resistance to creep deformation. At this time, Ca
If the content is less than 2%, the effect is not sufficient, while 4%
If it exceeds 300, casting cracks are likely to occur, and the corrosion resistance also decreases. For this reason, the content of Ca is limited to 2.0 to 4.0%.

Mn: 0.1-0.8% Mn combines with Al to form an intermetallic compound, and suppresses the deterioration of corrosion resistance by forming a solid solution of Fe as an impurity element. At this time, if the content is less than 0.1%, the effect is not sufficient, while if it exceeds 0.8%, the dissolution yield is deteriorated. For this reason, the content of Mn is limited to 0.1 to 0.8%. For the same reason, it is desirable to limit the lower limit to 0.15% and the upper limit to 0.75%.

Sr: 0.001 to 0.05% Sr to be added in a very small amount significantly improves the corrosion resistance of the crystallized material while maintaining high creep resistance by being dissolved in the crystallized material at the grain boundary. It has an effect of improving and eliminates a decrease in corrosion resistance due to Ca content. At this time, the content of Sr is 0.1.
If it is less than 001%, the corrosion resistance is not sufficient.
Even if it exceeds 5%, the yield of dissolution in the molten metal is lowered and the effect cannot be expected to be improved.
0.05%. For the same reason, the lower limit is set to 0.0
It is desirable to limit the upper limit to 02% and the upper limit to 0.04%.

Si: 0 to 0.5% Zn: 0 to 0.5% Since both Si and Zn lower the melting point, one or both of them can be contained as desired. However, if each content exceeds 0.5%, the creep resistance decreases, so the upper limit is made 0.5%.

Cu: 0.01% by mass or less Ni: 0.001% by mass or less Fe: 0.004% by mass or less Cl: 0.003% by mass or less These elements are treated as inevitable impurities of the magnesium alloy. However, since it is an element that adversely affects the corrosion resistance, it is desirable to reduce the content as much as possible. Considering industrial properties, Cu: 0.01% or less, Ni: 0.0
01% or less, Fe: 0.004% or less, Cl: 0.00
It is desirable that the allowable content is at least one of 3% or less,
Further, it is more desirable that all of these elements satisfy the above-mentioned allowable contents.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION The magnesium alloy of the present invention is smelted with the above component ranges as target values, but the smelting method is not particularly limited as the present invention. Can be adopted. The molten magnesium alloy can be used as a molten metal or once as a slab, and then subjected to a casting process as a subsequent process. As the casting method in the casting process, various generally known methods can be adopted.However, since the magnesium alloy of the present invention has excellent castability, the demand for castability is high, but high quality is required. It is a material suitable for high-pressure casting such as die casting, squeeze casting, and metal injection molding from which a material can be obtained. The conditions in these casting methods are not particularly limited as the present invention, but in semi-solid molding, it is desirable that the solid phase ratio of the molten metal be 50% or less. This is because if the solid phase ratio exceeds 50%, even with the alloy of the present invention having good castability, the fluidity of the molten metal may be low, and good molding may be difficult.

In the above-mentioned high-pressure casting method, the molten alloy (including the case of semi-molten) has high fluidity, so that it can be cast with good flow even when forming into a thin product, and a high product yield can be obtained. . In addition, the obtained member has few defects due to good hot water flow, and excellent characteristics are secured even in a high-strength material. Therefore, the moldable article made of the alloy of the present invention can be used as a member that is lightweight, high-strength, has high-temperature characteristics, and has excellent corrosion resistance in various applications. Therefore, it can be expected to be used for automobile parts and various portable devices that require these characteristics, and also for electric tools and leisure goods. Moreover, these magnesium alloy products are more recyclable than conventional plastic products, and can contribute to the preservation of the global environment.

[0018]

Embodiments of the present invention will be described below. For the casting, a metal injection molding method (a mold clamping force of 450 t), which is one of the high pressure casting methods, was employed. After melting the inventive alloy and the conventional alloy ingot as a comparison, various raw material chips were produced by cutting. Table 1 shows the chemical analysis results and castability of the raw material chips. In the casting, the mold temperature (443
K), while keeping the injection speed (1.7 m / s) constant, the same solid fraction (approximately 0%) according to the components of each test piece.
(853-9)
03K), creep test piece with parallel part diameter 6mm and thickness 2
mm flat plate (salt spray test piece) was prepared.

A salt water spray test was performed on the flat plate,
The corrosion rate was calculated from the weight loss before and after the 0 hour salt spray test. The test was performed three times for each test, and the average value of the resulting corrosion rates is shown in Table 2. 1 to 3 show the upper and lower limits and the average value of the corrosion rate in each test piece.
FIG. 1 shows the relationship between the Ca content and the corrosion rate in a conventional alloy, and shows the effect of the Ca content on corrosion resistance. That is, it is understood that when the Ca amount exceeds 2% by mass, the corrosion resistance is significantly deteriorated, and the conventional alloy cannot secure good corrosion resistance if the Ca amount necessary for improving the creep characteristics is contained. FIG. 2 shows the effect of the amount of Al added on the corrosion resistance. It is known that the corrosion resistance of an Mg-Al alloy containing no Ca improves with an increase in the Al content. However, when about 3% by mass of Ca is present in order to increase the creep resistance, the Al content is reduced. No increase in corrosion resistance is observed even when the amount is increased. That is,
In a conventional material, it is difficult to obtain good corrosion resistance even with an increase in Al in a Ca-containing magnesium alloy that improves creep characteristics. FIG. 3 shows trace elements Sr, Ba, Si, Zn, M in a Ca-containing Mg alloy.
This shows the effect of the addition of m on corrosion resistance. From this figure, it is understood that the addition of a small amount of Sr dramatically improves the corrosion resistance. The addition of expensive Mm is also effective in improving the corrosion resistance as compared with other trace elements, but even with the addition of 1% by mass, the corrosion resistance has not reached a practical level.
The effect was small for the cost, and the phenomenon of seizure to the mold was observed as described above. That is, only in the present invention, good corrosion resistance can be ensured even if Ca is contained at about 3%.

A creep test was performed on each creep test piece while changing the applied stress and the test temperature, and the minimum creep rate at that time was determined. Table 2 shows the applied stress of 70
The minimum creep rate at a test temperature of 423K in MPa is shown. FIG. 4 shows the relationship between the minimum creep rate and the applied stress at a test temperature of 423K. Based on this figure, AE42 to which Ca was not added and Ca
%, The two specimens have almost the same creep characteristics on the low stress side, but the specimen containing Ca has more superior creep properties as the applied stress increases. Becomes noticeable. In addition, in the test piece containing Sr, the creep characteristics were not adversely affected by the content of Sr, and the effect of improving the creep characteristics by Ca appeared. FIG. 5 shows the relationship between the minimum creep rate and the test temperature at a load stress of 50 MPa. As is clear from this figure, regardless of the test temperature, each test piece shows the same creep characteristics, and when combined with the results of FIG. 4, the Ca content indicates that the creep characteristics on the high stress side can be improved. That is, it can be seen that there is an effect in improving the creep strength. In the examples, data relating to the metal injection molding method is shown. However, if the solid phase ratio before injection is 50% or less, which ensures sound moldability, other high-pressure casting methods such as die casting and squeeze are used. Also, the alloy of the present invention can be applied.

[0021]

[Table 1]

[0022]

[Table 2]

[0023]

As described above, according to the magnesium alloy of the present invention, Al: 6.0-8.0% by mass, C
a: 2.0 to 4.0% by mass, Mn: 0.1 to 0.8% by mass, Sr: 0.001 to 0.05% by mass, Si: 0 to 0%
Since it contains 0.5% by mass and Zn: 0 to 0.5% by mass and the balance consists of Mg and unavoidable impurities, it has excellent properties in tensile strength, heat resistance and corrosion resistance. In addition, since the castability is good, the production is easy and a cast product can be obtained without casting defects. Further, the magnesium alloy material of the present invention is characterized in that the above alloy has a solid content of 50%.
Since it is obtained by injection molding in which the following semi-molten state is injected into a mold, it has good mechanical properties and can be easily reduced in weight.

[Brief description of the drawings]

FIG. 1 is a graph showing the influence of Ca content on corrosion resistance in a conventional magnesium alloy test piece.

FIG. 2 is a graph showing the effect of Al content on corrosion resistance of a conventional magnesium alloy test piece.

FIG. 3 is a graph showing the influence of the addition of Sr, Ba, Mm, Si, and Zn on the corrosion resistance of a magnesium alloy test piece.

FIG. 4 is a graph showing the relationship between the minimum creep rate and the applied stress at a test temperature of 423 K for a magnesium alloy test piece.

FIG. 5 is a graph showing a relationship between a minimum creep rate and a test temperature at a load stress of 50 MPa for a magnesium alloy test piece.

Claims (3)

[Claims] 1. Al: 6.0 to 8.0 mass%, Ca:
2.0 to 4.0% by mass, Mn: 0.1 to 0.8% by mass,
Sr: 0.001 to 0.05% by mass, Si: 0 to 0.5
% By mass, Zn: 0 to 0.5% by mass, with the balance being Mg
Magnesium alloy excellent in corrosion resistance and heat resistance characterized by being composed of unavoidable impurities 2. Among the unavoidable impurities, Cu, Ni, F
In one or more of e and Cl, the allowable contents are Cu: 0.01% by mass or less, Ni: 0.001% by mass or less, Fe: 0.004% by mass or less, and Cl: 0.003% by mass or less. The magnesium alloy excellent in corrosion resistance and heat resistance according to claim 1, characterized in that: 3. A corrosion-resistant and heat-resistant alloy comprising the alloy according to claim 1 or 2 and being molded by injection into a mold in a completely molten or semi-molten state having a solid fraction of 50% or less. Excellent magnesium alloy members