FLAME-RESISTANT MAGNESIUM ALLOY AND METHOD FOR PRODUCING THE SAME

Abstract

Provided are: a flame-retardant magnesium alloy which is prevented from the occurrence of the molten metal combustion during the melting of the alloy in casting; and a method for producing the flame-retardant magnesium alloy. A magnesium alloy containing a specific element in a specified amount and also containing a specific rare earth element (RE) in a specified amount. The magnesium alloy makes it possible to form an oxide film of the rare earth element (RE) which is dense and thin and is rarely cracked on the outermost surface of a molten metal. More specifically a flame-retardant magnesium alloy which contains, in % by mass, less than 9.0% of Ca, 0.5% or more and less than 5.7% of Al, 1.3% or less of Si, 0.4% or more and less than 1.3% of a rare earth element and a remainder made up by Mg and unavoidable impurities, wherein the requirement represented by the formula: Al+8Ca≥20.5% is satisfied.

Claims

1. A flame-resistant magnesium alloy comprising, in terms of % by mass, less than 9.0% of Ca, 0.5% or more but less than 5.7% of Al, 1.3% or less of Si, 0.1% or more and 0.5% or less of Mn, and 0.4% or more but less than 1.3% of a rare. earth element with the remaining consisting of Mg and inevitable impurities Al/Ca is 1.2 or less, and Al+8Ca≥20.5%.

2. (canceled)

3. A flame-resistant magnesium alloy comprising, in terms of % by mass, less than 9.0% of Ca, 0.5% or more but less than 5.7% of Al, 1.3% or less of Si, 0.1% or more and 0.5% or less of Mn, and 0.4% or more but less than 1.3% of a rare earth element with the remaining consisting of Mg and inevitable impurities Al/Ca is 1.2 or less, and having a (Mg, Al).sub.2Ca phase continuous in a three-dimensional mesh shape.

4. A flame-resistant magnesium alloy comprising, in terms of % by mass, less than 9.0% of Ca, 0.5% or more but less than 5.7% of Al, 1.3% or less of Si, 0.1% or more and 0.5% or less of Mn, and 0.4% or more but less than 1.3% of a rare earth element with the remaining consisting of Mg and inevitable impurities, Al/Ca is 1.2 or less, and having a thermal conductivity of 80 W/m.Math.K or higher and a tensile strength at 200° C. of 170 MPa or higher.

5. The flame resistant magnesium alloy according to claim 1, wherein the alloy has a Ca—Mg—Si-based compound phase in a Mg mother phase.

6. The flame-resistant magnesium alloy according to claim 1, wherein a Mg purity in a Mg mother phase is 98.0% or more.

7. The flame-resistant magnesium alloy according to claim 1, wherein the rare earth element is mischmetal.

8. A method for producing a flame-resistant magnesium alloy, the method comprising a cooling step in which a molten metal material is cooled at a rate of less than 10.sup.3 K/second, the flame-resistant magnesium alloy comprising, in terms of % by mass, less than 9.0% of Ca, 0.5% or more but less than 5.7% of Al, 1.3% or less of Si, 0.1% Or more and 0.5% or less of Mn, and 0.4% or more but less than 1.3% of a rare earth element with the remaining consisting of Mg and inevitable impurities, and Al+8Ca≥20.5%.

9. A method for producing the flame-resistant magnesium alloy according to claim 1, the method comprising a crystallization step in which a molten metal material is cooled and a (Mg, Al).sub.2Ca phase continuous in a three-dimensional mesh shape and a Mg mother phase containing a Ca—Mg—Si-based compound phase are crystallized.

10. (canceled)

11. A method for producing a flame-resistant magnesium alloy, the method comprising a cooling step in which a molten metal material is cooled at a rate of less than 10.sup.3 K/second, the flame-resistant magnesium alloy comprising, in terms of % by mass, less than 9.0% of Ca, 0.5% or more but less than 5.7% of Al, 1.3% or less of Si, 0.1% or more and 0.5% or less of Mn, and 0.4% or more but less than 1.3% of a rare earth element with the remaining consisting of Mg and inevitable impurities, and having a (Mg, Al).sub.2Ca phase continuous in a three-dimensional mesh shape.

12. A method for producing a flame-resistant magnesium alloy, the method comprising a cooling step in which a molten metal material is cooled at a rate of less than 10.sup.3 K/second. the flame-resistant magnesium alloy comprising, in terms of % by mass, less than 9.0% of Ca, 0.5% or more but less than 5.7% of Al, 1.3% or less of Si, 0.1% or more and 0.5% or less of Mn, and 0.4% or more but less than 1.3% of a rare earth element with the remaining consisting of Mg and inevitable impurities, and having a thermal conductivity of 80 W/m.Math.K or higher and a tensile strength at 200° C. of 170 MPa or higher.

13. The method for producing a flame-resistant magnesium alloy according to claim 8, further comprising a heat treatment step in which a heat treatment is carried out at 150 to 500° C.

Description

EXAMPLES

[0058] Next, the present invention will be described in more detail based on Examples, but the present invention is not limited thereto. Incidentally, unless specifically described otherwise, “ppm” described in Examples and Comparative Examples indicates “ppm by mass”.

Example 1

[Preparation of Molten Metal]

[0059] A metal material having 4.5% by mass of Al, 4.0% by mass of Ca, 0.3% by mass of Si, 0.3% by mass of Mn, and 0.6% by mass of mischmetal (Mm) added to Mg was injected to a crucible, subjected to high frequency induction melting under Ar atmosphere, and melt at a temperature of 750 to 850° C. to obtain a molten alloy (molten metal).

[Production of Cast Product]

[0060] Subsequently, the obtained molten alloy (molten metal) was cast by injection into a mold, and according to die cast (DC) casting, an engine block was produced.

[0061] Subsequently, the obtained engine block was subjected to a heat treatment at 300° C. for 4 hours to obtain a heat-treated engine block.

[0062] For the obtained engine block and heat-treated engine block, the thermal conductivity (room temperature) and the tensile strength (200° C.) were measured. The results are shown in Table 1.

TABLE-US-00001 TABLE 1 Thermal conductivity Tensile strength Example 1 (at room temperature) (at 200° C.) Engine block 82.2 W/m .Math. K 188 MPa Heat-treated 98.6 W/m .Math. K 174 MPa engine block

Comparative Example 1

[0063] A molten alloy (molten metal) was obtained in the same manner as in Example 1, except that the mischmetal (Mm) wad not added, and an engine block was produced from the obtained molten alloy (molten metal).

Comparative Example 2

[0064] A molten alloy (molten metal) was obtained in the same manner as in Example 1, except that Y was added at 0.3% instead of the mischmetal (Mm), and an engine block was produced from the obtained molten alloy (molten metal).

<Evaluatlon>

[0065] For Examples and Comparative Examples, the following evaluations were carried out.

[Presence or Absence of Combustion of Molten Metal]

[0066] For the molten alloys (molten metals) obtained from Examples and Comparative Examples, presence or absence of combustion of molten metal was observed at the time of melting (in a static state), during die cast (DC) casting (in a stirring state), and in a static state after the die cast (DC). Furthermore, the oxide film formed on a surface of the molten metal after the die cast was picked up and observed by visual inspection. The results are shown in Table 2.

[Seizure Resistance]

[0067] For the obtained engine block, presence or absence of seizure was checked by visual inspection. The results are shown in Table 1. From the engine block obtained in Example 1, seizure was not observed even in the area near a melt exit in which the temperature increases during casting. On the other hand, the engine blocks obtained in Comparative Example 1 and Comparative Example 2, seizure was observed near the melt exit.

[0068] It is recognized that the engine block obtained in Example 1 has an oxide film of a rare earth element (RE), which does not react with iron as a mold material, formed on a surface thereof, and the seizure is suppressed even in the area near a melt exit with high temperature. On the other hand, the engine blocks obtained in Comparative Example 1 and Comparative Example 2 has a surface formed of a calcium oxide film, and due to this reason, a reaction with iron as a mold occurred to yield an occurrence of seizure.

TABLE-US-00002 TABLE 2 Presence or absence of combustion of molten metal At the time of melting During die cast (DC) After die cast (DC) Oxide film of (In static state) (In stirring state) (In static state) molten metal Seizure resistance Example 1 No combustion No combustion No combustion Thin Without seizure Comparative Combustion was shown, Combustion Combustion continued Thick With seizure Example 1 but self-extinguished after 4 minutes Comparative Combustion was shown, No combustion Combustion was shown, Thin With seizure Example 2 but self-extinguished but self-extinguished