JPH10140304A - Heat treatment method of magnesium alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat treatment method for further improving mechanical properties (in particular, creep strength and fatigue strength) of an Mg alloy. SOLUTION: Calcium (Ca): 0.5% by weight%
3.0%, zinc (Zn): 1.0 to 6.0%, zirconium (Zr): 0 to 1.0%, one or more lanthanoids: 1.0 to 5.0%, the balance being Magnesium (M
g) and an unavoidable impurity,
Heat to 30-470 ° C, quench, then 150-2
A heat treatment method for a magnesium alloy, comprising tempering by heating to 50 ° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heat treatment method for further improving the mechanical properties (particularly hardness, creep strength and fatigue strength) of an Mg alloy used as a casting alloy.

[0002]

2. Description of the Related Art Mg-Zn-Ca alloys and Mg-R.
E. FIG. Since the (lanthanoid) -Ca alloy has excellent high-temperature strength, various proposals have been made for the alloys of the above-mentioned system. For example, JP-A-6-25791 discloses that zinc is 3 to 8% by weight, calcium is 0.8 to 5% by weight, and copper is 0 to 0%.
10% by weight, optionally further 2% by weight each
Magnesium alloy containing at least one element selected from the group consisting of the following manganese, zirconium and silicon, and at most 4% by weight of a rare earth element, with the balance being magnesium and unavoidable impurities and excellent in room temperature and high temperature strength. Is described. Similarly, as a magnesium alloy excellent in room temperature and high temperature strength, JP-A-6-200348 discloses (a) 0.5 to 5% by weight of a lanthanoid, (b)
0.5-5% by weight of calcium and 1.5% of manganese
% Or less of zirconium and 1.5% or less of zirconium, and (d) optionally 1 to 9.5% by weight of aluminum, 1 to 7.5% by weight of zinc and 0.5% by weight of silver.
(E) further comprising, if desired, 5.5 wt% or less of yttrium, 1.5 wt% or less of strontium, and 10 wt% or less of scandium. It describes a magnesium alloy containing at least one element selected from the group and the balance consisting of magnesium and unavoidable impurities.

[0003]

Generally, Ca is an element that reduces the elongation of a magnesium alloy to which Ca is added. Therefore, in the alloys described in the above two publications, it is necessary to consider a material that has been subjected to a homogenization treatment. Is being done. Further, in the case of a general Mg—Zn alloy (such as ZE41), the strength is improved by performing only the tempering treatment at a relatively low temperature (T5 treatment). This is because compounds of this system are easily formed at relatively low temperatures. On the other hand, general Mg-R. E. FIG. Since it is difficult to completely perform solution treatment even on a system alloy (such as EZ33), T5 treatment is performed.

However, general magnesium alloys containing no Ca (such as ZE41 and EZ33) cannot provide sufficient high-temperature strength. On the other hand, even with the magnesium alloys described in JP-A-6-25791 and JP-A-6-200348, sufficient studies have not been made on the heat treatment, and the properties thereof have not been sufficiently derived.

The present invention has been made to solve the above-mentioned problems of the prior art.
g-Zn-Ca alloy or Mg-R. E. FIG. (Lanthanoid) Provide selection of additional elements and heat treatment method of the obtained magnesium alloy to further improve mechanical properties such as hardness, creep strength, fatigue strength, etc. of Mg-Ca alloy such as -Ca alloy. Is to do.

[0006]

That is, the heat treatment method for a magnesium alloy according to the present invention is characterized in that calcium (C
a): 0.5-3.0%, zinc (Zn): 1.0-6.
0%, one or more lanthanoids: a magnesium alloy containing 1.0 to 5.0%, with the balance being magnesium (Mg) and unavoidable impurities, or calcium (C
a): 0.5-3.0%, zinc (Zn): 1.0-6.
0%, zirconium (Zr): more than 0%, 1.0% or less, one or more lanthanoids: 1.0 to 5.0%, and the balance is magnesium alloy consisting of magnesium (Mg) and unavoidable impurities. Heated to 430-470 ° C,
It is characterized by quenching and then tempering by heating to 150 to 250 ° C.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A detailed examination of the structural change with respect to temperature of a magnesium alloy (hereinafter referred to as the present alloy) used in the method of the present invention shows that the remelting temperature of the present alloy is the same as that of a conventional Mg-Zn-Ca alloy. It was found to be about 60 ° C. higher than the base alloy. Therefore, utilizing this fact, a study was made to further improve the strength by heat treatment.

In order to improve the high temperature creep strength,
It is advantageous to precipitate the compound after more solute is dissolved in the matrix. Therefore, the alloy is subjected to a solution treatment. The solution treatment temperature is 430 ° C or more and 470 ° C or less. When the temperature is lower than 430 ° C., most of the compounds stop in the form, and the amount of solid solution in the parent phase hardly changes. On the other hand, 470 ° C
When the temperature exceeds, the low melting point portion is re-melted to form a defect. Therefore, the solution treatment temperature needs to be 430 to 470 ° C. In addition, it takes at least 5 hours for the compound to fully dissolve in the parent phase, and almost reaches the solubility limit in 24 hours.
The solution treatment time may be 5 to 24 hours. After this treatment, it is quenched in a suitable medium (for example, hot water, forced air cooling, etc.) so that coarse compounds are not generated in the cooling process.

[0009] The alloy solution-treated as mentioned above is
Tempering by heating to 250 ° C. (hardening by precipitating compound). If the tempering temperature is lower than 150 ° C., it takes a long time to cure. Conversely, when the tempering temperature exceeds 250 ° C., precipitation hardening does not occur significantly. Therefore, the tempering temperature is 150-250 ° C., preferably 150 ° C.
~ 200 ° C. Aging time varies with temperature,
It cures sufficiently in 0.5 to 24 hours. From the viewpoint of temperature control and productivity, the tempering conditions are 180 to 200 ° C, 0.5 to
Two hours is preferred.

In the present alloy, Ca refines precipitates and improves heat resistance. That is, the growth rate of the precipitate is suppressed. This effect becomes significant when Ca is added in an amount of 0.5% or more. If the Ca solubility exceeds the maximum solid solubility limit, the effect of adding Ca saturates, so that there is no significant change even if about 1% or more of Ca is added. Further, the toughness of the alloy decreases as the amount of Ca added increases.
The addition of a is not preferred. Therefore, Ca is 0.1% by weight.
Add 5 to 3.0%. Considering the toughness of the obtained alloy, it is preferable to add 0.5 to 1% of Ca.

In the present alloy, Zn is an element related to solid solution strengthening, precipitation strengthening and castability. In order to strengthen the alloy with Zn, it is necessary to add 1% or more of Zn. However, if Zn is added in excess of 6%, a large amount of the compound will precipitate in the alloy, and the toughness of the alloy will decrease. Therefore, Zn is added in an amount of 1.0 to 6.0% by weight.

In the present alloy, Zr is a crystal grain refining element. However, even if Zr is added in excess of 1%, it is difficult to dissolve Zr in the alloy. Therefore, Zr is added in an amount of 0 to 1.0% by weight. That is, the present alloy may not contain Zr, and when the present alloy contains Zr, Zr is 1
% Or less.

In the present alloy, R.I. E. FIG. (Lanthanoids) improve heat resistance and castability. In order to exhibit this effect remarkably, R. E. FIG. Need to be added. However, R. E. FIG. If the addition ratio exceeds 5%, the effect of improving castability saturates, and a large amount of compounds is generated, thereby reducing the toughness of the alloy. Therefore, R. E. FIG.
Is added in an amount of 1.0 to 5.0% by weight.

[0014]

The present invention will be described in more detail with reference to the following experimental examples. The following experimental examples include examples and comparative examples, but are examination examples of heat treatment conditions, and are all shown by serial numbers as experimental examples. Example 1 I. Manufacture of Magnesium Alloy A magnesium chloride-based flux was applied to the inner surface of a high chromium alloy steel (SUS430) crucible preheated in an electric furnace, and pure magnesium ingot was poured and melted therein.
Metal Ca, Zn, cerium-based misch metal (Mm) was added to the molten metal kept at 700 ° C., and the temperature was further raised to 780 ° C. to add the Mg—Zr alloy, and the molten metal was stirred. After sufficient stirring, it was confirmed that these were completely dissolved, and then refining was performed. After the refining, the temperature was kept at 780 ° C.
During the melting operation, a mixed gas of carbon dioxide gas and SF ₆ gas was blown onto the surface of the molten metal at a flow rate of 0.2 liter / min to prevent combustion, and a flux was sprayed on the surface of the molten metal as appropriate. A boat mold was cast from the molten metal. This alloy composition is Mg-2% Zn-2% Mm-0.6% Ca-0.6%
Zr (% is% by weight).

II. Examination of Solution Treatment Temperature FIGS. 1 to 4 are micrographs of the metal structure when the magnesium alloy is kept at a high temperature in an argon stream and quenched in warm water at about 80 ° C. (solution treatment). FIG. 1 is a micrograph of a solution treatment temperature of 410 ° C. and a solution treatment time of 24 hours (FIG. 1 (a) is 500 times magnification, FIG. 1 (b) is 1000 times magnification: Experimental Example 1), and FIG. Solution treatment temperature 440
At 24 ° C. and a solution treatment time of 24 hours [FIG.
(A) is 500 times magnification, FIG. 2 (b) is 1000 times magnification:
Experimental Example 2], FIG. 3 is a micrograph of a solution treatment temperature of 465 ° C. and a solution treatment time of 24 hours [FIG. 3 (a) is 500 times magnification, FIG. 3 (b) is 1000 times magnification: Experimental Example 3 ],
FIG. 4 is a micrograph of a solution treatment temperature of 480 ° C. and a solution treatment time of 24 hours [FIG.
4 (b) shows a magnification of 1000 times: Experimental Example 4].

There is no significant change in the metal structure of the alloy up to a solution treatment temperature of 410 ° C. (Experimental Example 1), but a solution treatment temperature of 440 ° C. (Experimental Example 2) and a solution treatment temperature of 465 ° C.
In (Experimental example 3), the number of black compounds in the metal structure of the alloy is reduced. This indicates that the black compound was decomposed and the solute was dissolved in the parent phase. However, at the solution treatment temperature of 480 ° C. (Experimental Example 4), the low melting point portion starts remelting, and defects are formed in the alloy.

III. Examination of Tempering Temperature FIG. 5 shows the hardness of the alloy (Vickers hardness: Hv) when the tempering temperature and the tempering time were changed in tempering the alloy of Experimental Example 3 (solution treatment at 465 ° C. for 24 hours). FIG. 4 is a diagram (age hardening curve) showing a change in the curve (age). Tempering temperature is 1
At 00 ° C. (Experimental Example 5), no remarkable curing was observed. When the tempering temperature was 150 ° C. (Experimental Example 6), the hardness increased with time. When the tempering temperature is 200 ° C. (Experimental Example 7), the peak hardness is exhibited in a very short time. Therefore, 2
It can be seen that aging softening occurs in a short time at a tempering temperature of 00 ° C. or higher. On the other hand, in the alloy (Experimental Example 8) simply maintained at room temperature to 465 ° C. after casting, almost no change in hardness was observed.

IV. FIG. 6 shows the effect of quenching and tempering on the tensile strength.
The tensile strength of an alloy tempered at 2 ° C. for 2 hours (Experimental Example 9) and an as-cast alloy without heat treatment (Experimental Example 10) are shown. Due to the heat treatment, the alloy of Experimental Example 9 was replaced with Experimental Example 10
It can be seen that the tensile strength was higher than that of the alloy No.

FIG. 7 shows one of the alloys of Experimental Examples 9 and 10.
It shows the time to reach 0.1% creep elongation at 50 ° C. and 100 MPa. Due to the heat treatment, the alloy of Experimental Example 9 had a longer time to reach 0.1% elongation than the alloy of Experimental Example 10.

FIG. 8 shows the results of a rotary bending fatigue test of the alloys of Experimental Examples 9 and 10. Alloy of Example 9 it can be seen that improved 10 ⁷ times fatigue limit than the alloy of Example 10.

Embodiment 2 I. Production of magnesium alloy A magnesium alloy was produced in the same manner as in Example 1 except that the addition of the Mg-Zr alloy in Example 1 was not performed. The alloy composition is Mg-2% Zn-2% Mm-0.7
% Ca (% is% by weight).

II. Examination of the influence of the presence or absence of heat treatment on the hardness of the alloy The magnesium alloy was heated at 465 ° C for 24 hours, then quenched in warm water, and further tempered at 200 ° C for 2 hours. Thereafter, the Vickers hardness (Hv) of this magnesium alloy was measured. For comparison, Vickers hardness (Hv) was also measured for an as-cast magnesium alloy that was not subjected to the heat treatment. FIG. 9 shows the results. FIG.
It can be seen from the above that the heat treatment improves the hardness of the magnesium alloy.

[0023]

According to the magnesium alloy obtained by the heat treatment method of the present invention, precipitates stable at high temperatures are finely dispersed in α-Mg. Strength and fatigue strength improved.

[Brief description of the drawings]

FIG. 1 shows a solution treatment condition of a magnesium alloy: 410
FIG. 1A is a micrograph of a metal structure when treated at 24 ° C. for 24 hours and then quenched in warm water at about 80 ° C. (FIG. 1A is 500 times magnification, FIG. 1B is 1000 times magnification).

[FIG. 2] Solution treatment condition of magnesium alloy: 440
FIG. 2 (a) is a photomicrograph of the metal structure when treated at 24 ° C. for 24 hours and then quenched in warm water at about 80 ° C. (FIG. 2 (a) is 500 ×, FIG. 2 (b) is 1000 ×).

[FIG. 3] Solution treatment condition of magnesium alloy: 465
FIG. 3A is a micrograph of a metal structure when treated at 24 ° C. for 24 hours and then quenched in warm water at about 80 ° C. (FIG. 3 (a) is 500 times magnification, FIG. 3 (b) is 1000 times magnification).

[FIG. 4] Solution treatment condition of magnesium alloy: 480
FIG. 4A is a micrograph of a metal structure when treated at 24 ° C. for 24 hours and then quenched in warm water at about 80 ° C. [FIG. 4 (a) is 500 times magnification, and FIG. 4 (b) is 1000 times magnification].

FIG. 5 is a diagram (age hardening curve) showing a change in hardness of an alloy when a tempering temperature and a tempering time are changed.

FIG. 6 is a graph showing the tensile strength of a heat-treated alloy and an as-cast alloy without heat treatment.

FIG. 7 is a graph showing the time required to reach 0.1% creep elongation at 150 ° C. and 100 MPa for an alloy subjected to heat treatment and an as-cast alloy not subjected to heat treatment.

FIG. 8 is a diagram showing the results of a rotary bending fatigue test of an alloy subjected to heat treatment and an as-cast alloy not subjected to heat treatment.

FIG. 9 is a diagram showing the hardness of an alloy subjected to heat treatment and an as-cast alloy not subjected to heat treatment.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22F 1/00 691 C22F 1/00 691B 692 692Z

Claims (1)

[Claims] 1. Calcium (Ca) by weight%: 0.5 to
Magnesium alloy containing 3.0%, zinc (Zn): 1.0 to 6.0%, one or more lanthanoids: 1.0 to 5.0%, the balance being magnesium (Mg) and unavoidable impurities Or calcium (Ca) by weight%: 0.5 to
3.0%, zinc (Zn): 1.0 to 6.0%, zirconium (Zr): more than 0% and 1.0% or less, one or more lanthanoids: 1.0 to 5.0% A magnesium alloy consisting of magnesium (Mg) and unavoidable impurities, heated to 430 to 470 ° C., quenched, and then tempered by heating to 150 to 250 ° C. .