JP2002266044A - Magnesium alloy - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnesium alloy having improved strength at room temperature and applicable to a sand mold casting process, a plaster mold casting process, a metal die casting process, and a lost pattern mold casting process in addition to a die casting process. SOLUTION: Solution heat treatment and artificial aging treatment are applied to Mg-5%Al-8%Zn-0.6%Ca-0.3%Mn. The solution heat treatment comprises steps of heating the magnesium alloy, holding it at 380 deg.C for 24 hr, and immediately applying rapid cooling down to 25 deg.C by air-blast cooling. The artificial aging treatment comprises steps of heating the rapidly cooled magnesium alloy, holding it at 150 deg.C for 5.5 hr, and then applying natural cooling. By successively applying the prescribed solution heat treatment and artificial aging treatment to the magnesium alloy in this way, the magnesium alloy having 142 MPa 0.2% proof stress at room temperature and 88 HV Vickers hardness can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnesium alloy, and more particularly, to a magnesium alloy having improved strength at room temperature (such as tensile strength characteristics).

[0002]

2. Description of the Related Art In recent years, magnesium alloys have attracted attention because they belong to the lightest class of metal materials, and have been put to practical use as structural or casting metal materials. Magnesium alloys have come to be widely used, for example, as materials for automobile parts. Here, when casting a magnesium alloy into an automobile part, the magnesium alloy is required to have castability (particularly fluidity during casting). In addition, when an automobile part made of a magnesium alloy is used at a high temperature of, for example, 150 ° C., excellent creep resistance and tensile strength are required to be able to withstand the severe use condition. .

[0003] Therefore, it has been desired to develop a magnesium alloy having all of the above three properties of excellent creep resistance at high temperatures, tensile strength, and castability. Conventionally, as this kind of magnesium alloy, The one described in Japanese Patent Application Laid-Open No. 10-324941 filed by the present applicant is already known. This magnesium alloy is about 2
About 9% by weight of aluminum, about 6 to about 12% by weight of zinc, about 0.1 to about 2% by weight of calcium, with the balance being magnesium and the like.

[0004]

When the magnesium alloy according to the prior art described above is cast by the die casting method and the sand casting method, the 0.2% proof stress at room temperature of the cast magnesium alloy is as follows. The result was as follows. That is, the 0.2% proof stress of the magnesium alloy cast by the die casting method is 150 MPa, but the 0.2% proof stress of the magnesium alloy cast by the sand casting method is:
It was found that the pressure was significantly reduced to 96 MPa (FIG. 1).
reference).

This result is due to the solidification rate of the magnesium alloy after casting. If the solidification rate is low, magnesium crystals (α phase) and magnesium crystals (α phase)
This is because the intermetallic compound (β phase) that precipitates at the crystal grain boundaries becomes coarse and reduces the strength of the magnesium alloy. That is, in the die-casting method with a fast solidification rate,
While magnesium crystals and intermetallic compounds in the magnesium alloy are refined and solid solution strengthening by quenching, sufficient strength of the magnesium alloy is obtained,
In the sand casting method with a slow solidification rate, magnesium crystals and intermetallic compounds in the magnesium alloy are coarsened, and the strength of the magnesium alloy is reduced. Here, as the casting method having a low solidification rate of the magnesium alloy as in the sand casting method, a gypsum casting method, a die casting method, a vanishing model casting method and the like can be mentioned. It goes without saying that the strength at room temperature decreases as in the case of the sand casting method.

[0006] As described above, in the magnesium alloy according to the prior art, the strength may decrease at room temperature after casting. Therefore, the magnesium alloy having a desired strength without decreasing the strength even at room temperature. is necessary. In other words, there is a demand for a magnesium alloy capable of obtaining a desired strength even in a casting method in which the solidification rate of the magnesium alloy is low.

The present invention has been made in view of the above-mentioned circumstances, and its object is to improve the strength at room temperature,
An object of the present invention is to provide a magnesium alloy which can be applied to a sand casting method, a gypsum casting method, a mold casting method, and a disappearing model casting method other than the die casting method.

[0008]

The present inventors have conducted intensive studies in view of the above-mentioned circumstances, and as a result, have found that 2 to 9% by weight of aluminum, 6 to 12% by weight of zinc, 0.1 to 2. If a magnesium alloy containing 0% by weight of calcium (as required, 0.2 to 0.5% by weight of manganese) and a balance of magnesium and unavoidable impurities is subjected to a two-stage heat treatment or the like, They found that the strength of the magnesium alloy at room temperature was improved, and completed the magnesium alloy of the present invention.

That is, the magnesium alloy according to the first aspect of the present invention comprises 2 to 9% by weight of aluminum, 6 to 12% by weight.
A magnesium alloy containing 0.1% to 2.0% by weight of zinc, 0.1 to 2.0% by weight of calcium, and the balance consisting of magnesium and unavoidable impurities was subjected to a solution treatment and an artificial aging treatment in that order, and then room temperature. Sometimes at least 140MPa
The gist is to have a 0.2% proof stress and a Vickers hardness of 65 HV or more.

Here, the reason why the content of aluminum in the magnesium alloy is set to be in the range of 2 to 9% by weight is that when the aluminum is less than 2% by weight, the castability and room temperature strength of the magnesium alloy are satisfied. May not be able to be performed, and when aluminum exceeds 9% by weight,
Aluminum has a low melting point (473 ° C) intermetallic compound (Mg17Al12) that combines with magnesium to adversely affect the high-temperature properties (high-temperature strength and creep resistance) of magnesium alloys
Is formed in a large amount.

The reason why the content of zinc in the magnesium alloy is set in the range of 6 to 12% by weight is that when zinc is less than 6% by weight or exceeds 12% by weight, This is because there is a possibility that the properties and room temperature strength cannot be improved, or the high temperature strength and creep resistance of the magnesium alloy cannot be satisfied.

Furthermore, the reason why the content of calcium in the magnesium alloy is set to be in the range of 0.1 to 2.0% by weight is that when the calcium is less than 0.1% by weight, the high temperature strength of the magnesium alloy If the calcium content exceeds 2.0% by weight, the castability of the magnesium alloy deteriorates (decreases).
It is because there is a possibility that it may fall into a state where casting is impossible.

[0013] The "0.2% proof stress" means that when a tensile load is applied, a material (such as a test piece) exceeds its elastic limit and begins to elongate permanently.
The value obtained by dividing the load P0.2 at 2% by the original cross-sectional area A0 (cross-sectional area before applying a tensile load) of the parallel portion of the material (proof stress σ0.2 = P0.2 / A0) [JIS Z2
241 (metallic material tensile test method) and ASTM B55
7]. “Room temperature” refers to a temperature of 5 to 35 ° C.

According to the first aspect of the present invention, when a magnesium alloy containing the above-described predetermined amounts of the respective components is cast, for example, the intermetallic compound (β-phase) is formed at the crystal grain boundary of the magnesium crystal (α-phase). Is obtained. Then, the cast magnesium alloy is subjected to a solution treatment to form an intermetallic compound (alloy component).
Is diffused into the magnesium crystal to obtain a magnesium alloy which is rounded and reduced without the intermetallic compound becoming coarse. Here, when the intermetallic compound in the magnesium alloy is refined without being coarsened, a decrease in the elongation of the magnesium alloy is prevented. Next, an artificial aging treatment is applied to the magnesium alloy that has been subjected to the solution treatment, whereby a magnesium alloy in which an intermetallic compound is precipitated in magnesium crystals and is strengthened (hardened) is obtained.

As described above, the magnesium alloy subjected to the solution treatment and the artificial aging treatment in order has a 0.2% proof stress of at least 140 MPa at room temperature, and
It has Vickers hardness of 5 HV or more, and the strength at room temperature is improved. The practical upper limit of 0.2% proof stress of this magnesium alloy is about 170 MPa. A realistic upper limit of the Vickers hardness is about 95 HV.

The magnesium alloy according to the second aspect of the present invention comprises 2 to 9% by weight of aluminum, 6 to 12% by weight of zinc, 0.1 to 2% by weight of calcium, 0.2 to 0.5% by weight. A magnesium alloy containing manganese and the balance being magnesium and unavoidable impurities, having a solution treatment and an artificial aging treatment in that order, having a 0.2% proof stress of at least 140 MPa at room temperature, and , 65
The gist is to have a Vickers hardness of HV or more.

Here, the respective contents of aluminum, zinc and calcium in the magnesium alloy are set within the above ranges for the same reason as in the magnesium alloy according to the first aspect. The reason why 0.2 to 0.5% by weight of manganese is blended in the magnesium alloy is to improve (improve) the corrosion resistance of the magnesium alloy.

According to the second aspect of the present invention, similarly to the magnesium alloy according to the first aspect, the magnesium alloy which has been subjected to the solution treatment and the artificial aging treatment in order is at least 140 MPa at room temperature. It has a 0.2% proof stress and a Vickers hardness of 65 HV or more, so that the strength at room temperature is improved. In addition, by blending (containing) the predetermined amount of manganese, the corrosion resistance of the magnesium alloy is improved (improved). The practical upper limit of 0.2% proof stress of this magnesium alloy is about 170 MPa. Also. A practical upper limit for Vickers hardness is about 95 HV.

According to a third aspect of the present invention, in the magnesium alloy according to the first or second aspect, an intermetallic compound of Mg-Al-Zn-Ca is precipitated at a crystal grain boundary of the magnesium crystal. Is the gist.

According to the third aspect of the present invention, in addition to the effects of the first and second aspects of the present invention, an intermetallic compound of Mg-Al-Zn-Ca is formed at a crystal grain boundary of a magnesium crystal. Is precipitated, the Mg-Al-Zn-C
The intermetallic compound of a provides high metallic stability of the magnesium alloy at room temperature and high temperature and strengthens the grain boundaries of the magnesium crystal.

According to a fourth aspect of the present invention, in the magnesium alloy according to any one of the first to third aspects, the solution treatment is performed at a temperature of 350 to 380 ° C.
The gist of the invention is that the material is rapidly cooled after being held for up to 70 hours.

Here, the reason why the heating temperature is set in the range of 350 to 380 ° C. is that if the temperature is lower than 350 ° C., the intermetallic compound is hardly diffused into the magnesium crystal, and the coarse intermetallic compound is contained in the crystal grain boundary. This is because there is a possibility that the strength of the magnesium alloy remains to cause a decrease in strength, and when the temperature exceeds 380 ° C., a melting phenomenon of the magnesium alloy itself may occur. In addition, the reason why the heating holding time is set in the range of 20 to 70 hours is that when the heating holding time is less than 20 hours, the intermetallic compound hardly diffuses into the magnesium crystal, and the coarse intermetallic compound remains in the crystal grain boundary. If the strength exceeds 70 hours, the workability deteriorates and the cost may increase, which is not practical. Furthermore, referring to cooling, when the magnesium alloy held by heating is allowed to cool, the alloy component diffused in the magnesium crystal is re-precipitated in the crystal grain boundaries of the magnesium crystal to form a coarse intermetallic compound, so that water cooling is performed. Rapid cooling (rapid cooling) such as cooling or air cooling is required.

According to the fourth aspect of the present invention, since the heating time and the heating holding time are set in a predetermined range, and the magnesium alloy heated and held is rapidly cooled, the heating time and the heating holding time are rapidly cooled. The operation of the invention described in claim 3 is reliably achieved. In addition, workability deterioration and cost increase are suppressed as much as possible.

According to a fifth aspect of the present invention, in the magnesium alloy according to any one of the first to fourth aspects, the artificial aging treatment is performed at a temperature of 150 to 200 ° C. for 0.5 to 10 hours. The gist of the invention is that it is left to cool after being held.

The reason why the heating temperature is set in the range of 150 to 200 ° C. is that if the temperature is lower than 150 ° C. or exceeds 200 ° C., the desired strength of the magnesium alloy may not be obtained. . Further, the heating holding time is set in the range of 0.5 to 10 hours. If the heating holding time is less than 0.5 hours, the strength of the desired magnesium alloy may not be obtained. Although the strength of the magnesium alloy is obtained, it is not practical because the workability deteriorates and the cost increases. Furthermore, when the magnesium alloy heated and held is allowed to cool, the intermetallic compound is easily precipitated in the magnesium crystal and strengthened (hardened), so that the strength of the magnesium crystal, and eventually the magnesium alloy, is more reliably improved.

According to the fifth aspect of the present invention, the heating time and the heating holding time are set within a predetermined range, and the heated and held magnesium alloy is allowed to cool. Accordingly, the effects of the inventions described in the third and fourth aspects are reliably achieved. In addition, workability deterioration and cost increase are suppressed as much as possible.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION The magnesium alloy according to the present invention contains magnesium (Mg) as a main component, 2 to 9 as a main component.
% Aluminum (Al), 6-12% zinc (Zn), 0.1-2.0% calcium (C
a), a very small amount of unavoidable impurities. Further, the magnesium alloy may contain 0.2 to 0.5% by weight of manganese, or may not contain manganese at all. The magnesium alloy according to the present invention,
Has excellent mechanical properties (creep properties, tensile strength properties, etc.) at high temperatures up to 150 ° C, excellent castability,
Moreover, it is practical with an inexpensive alloy.

Further, the magnesium alloy has a 0.2% proof stress of at least 140 MPa at room temperature, and
It has a Vickers hardness of 65 HV or more. In this case, at least 145 MPa, 150 MPa, 155 MPa,
0.2% of 160MPa, 165MPa, 170MPa
It is preferable to have proof stress, 70 HV or more, 75 HV
80 HV or more, 85 HV or more, 88 HV or more, 9
It preferably has a Vickers hardness of 0 HV or more and 95 HV or more. The upper limit of these values is 0.1 MPa of 170 MPa.
It has a 2% proof stress and a Vickers hardness of 95 HV.

Aluminum is generally known as a metal element that enhances the castability and room-temperature strength of magnesium alloys. On the other hand, aluminum is a factor that adversely affects the creep resistance and tensile strength of magnesium alloys at high temperatures. well known. Therefore, the amount (% by weight) of aluminum contained in the magnesium alloy must be strictly set. The content of aluminum in the magnesium alloy according to the present invention must be set in the range of 2 to 9% by weight, and is preferably set in the range of 3 to 8% by weight.
More preferably, it is set in the range of 5 to 7% by weight.
More preferably, it is set in the range of 6% by weight.

Zinc is used to improve the castability and room temperature strength of the magnesium alloy. Further, in order to obtain the desired high-temperature strength and creep resistance of the magnesium alloy, the content of zinc in the magnesium alloy needs to be set in the range of 6 to 12% by weight, and in the range of 7 to 11% by weight. Is desirably set in the range of 8 to 10% by weight, more preferably 9% by weight.

Of the elements (calcium, silver, rare earth elements (eg, yttrium), etc.) found to improve the high temperature strength and creep resistance of magnesium alloys, calcium is the most economical (low cost). is there. Also, considering the castability of the magnesium alloy, the content of calcium in the magnesium alloy needs to be set in the range of 0.1 to 2.0% by weight, and the content of calcium in the range of 0.3 to 1.8% by weight. Is preferably set in the range of 0.5 to 1.5% by weight or 0.8 to 1.2% by weight, more preferably in the range of 0.9 to 1.0% by weight. Is more preferred.

Inevitable impurities in the magnesium alloy include silicon (Si), iron (Fe), nickel (Ni),
Copper (Cu) is mentioned. Silicon is an impurity element generally contained in commercial pure magnesium ingots used for magnesium alloys. This silicon may be contained up to 0.05% by weight which does not adversely affect the properties of the magnesium alloy according to the present invention.

Of the unavoidable impurities, iron, nickel, and copper are factors that adversely affect the corrosion resistance of the magnesium alloy. Therefore, in magnesium alloy,
0.004% by weight or less of iron, 0.01% by weight of nickel
Hereinafter, it is preferable to prepare copper so as to be 0.008% by weight or less.

In the magnesium alloy according to the present invention,
It has been found that the Mg-Al-Zn-Ca intermetallic compound can be precipitated at the crystal grain boundaries of the magnesium crystal by a predetermined content of aluminum, zinc, and calcium (manganese if necessary) in the alloy. This was confirmed by the results of EDS (energy dispersive spectroscopy) analysis. This M
The g-Al-Zn-Ca intermetallic compound is usually formed along the crystal grain boundary of the magnesium crystal, and enhances the metallic high stability of the magnesium alloy at room temperature or high temperature and the strengthening of the crystal grain boundary of the magnesium crystal. Bring.

To obtain the magnesium alloy according to the present invention, first, 2 to 9% by weight of aluminum, 6 to 12% by weight of zinc, 0.1 to 2.0% by weight of calcium and, if necessary, 0.1 to 2.0% by weight of calcium. A magnesium alloy comprising 2 to 0.5% by weight of manganese, with the balance being magnesium and unavoidable impurities, is prepared.

Then, the prepared magnesium alloy is put into a container made of, for example, stainless steel and heated by a heating device to melt the magnesium alloy. In this case, it is necessary to perform the melting treatment in a gas atmosphere in which the magnesium alloy does not ignite or extremely oxidize. Then, sulfur hexafluoride gas or the like is blown into the molten magnesium alloy to remove oxidized inclusions in the molten material.

Next, the molten material from which oxidized inclusions have been removed is poured into a heated mold, sand mold, gypsum mold, or other mold and cast. Thereafter, a solution treatment is performed on the cast material (cast material). In this case, as the solution treatment, the casting material is 3
It is preferable to cool rapidly after holding at a temperature of 50 to 380 ° C for 20 to 70 hours. Here, as means for rapidly cooling the heated and held cast material, for example, air cooling (forced air cooling), water cooling, or the like can be given. Further, the heating temperature and the heating holding time of the cast material are not particularly limited to the range of 350 to 380 ° C and 20 to 70 hours.

In this case, the heating time is, for example, less than the eutectic temperature, 360-390 ° C., 370-380 ° C., 375-3
The temperature may be set to 85 ° C. or 380 ° C., and the heating holding time may be, for example, 3 to 72 hours, 12 to 60 hours, or 18 to 60 hours.
48 hours, 20-45 hours, 24-40 hours, 28-3
5 hours, 18-25 hours, 20-24 hours, 20 hours,
It may be set to be 24 hours.

Finally, by subjecting the material subjected to the solution treatment to artificial aging treatment, magnesium having a 0.2% proof stress of at least 140 MPa at room temperature and a Vickers hardness of 65 HV or more. An alloy is obtained. In this case, as the artificial aging treatment, it is preferable that the material subjected to the solution treatment is kept at a temperature of 150 to 200 ° C. for 0.5 to 10 hours and then cooled. After the heating and holding, the cooling may be performed rapidly without cooling.
The heating temperature and the heating holding time of the material subjected to the solution treatment are not particularly limited to the ranges of 150 to 200 ° C. and 0.5 to 10 hours.

In this case, the heating temperature is set to, for example, 100 to 30.
0 ° C, 150-350 ° C, 200-400 ° C, 130-
230 ° C., 150 ° C., and 200 ° C. may be set.
~ 37 hours, 1 ~ 24 hours, 1.5 ~ 20 hours, 2-1
It may be set to 6 hours, 3 to 14 hours, 4 to 10 hours, 5.5 to 9 hours, 5 to 6 hours, and 5.5 hours.

[0041]

(Embodiment 1) A first embodiment of the present invention will be described below.

First, about 400 g of Mg-5% Al-8%
Zn-0.6% Ca-0.3% Mn (where "%"
(Meaning "% by weight") was placed in a stainless steel container and heated to 680 ° C. in an electric furnace to dissolve it. This dissolution treatment was performed in a sulfur hexafluoride gas atmosphere. Thereafter, sulfur hexafluoride gas was blown into the molten magnesium alloy to remove oxidized inclusions in the molten material.

Next, a silicon carbide mold (thickness 6 mm × height 90 mm × width 1) heated to a temperature of 150 ° C.
The molten material from which the oxidized inclusions have been removed is poured into a casting (having a cavity of 80 mm) and cast. Then, the cast material (cast material) was heated and maintained at a temperature of 380 ° C. for 24 hours, and then immediately cooled by air (forced air cooling) to a temperature of 25 ° C. In this heat treatment, 200 ° C. to 380 ° C.
Was 5 ° C./min.

Then, the rapidly cooled (solution-treated) cast material was heated and maintained at a temperature of 150 ° C. for 5.5 hours, then allowed to cool, and subjected to an artificial aging treatment. Then, the magnesium alloy was taken out of the mold, and the magnesium alloy was processed to obtain a test piece (Example 1).

Then, in order to investigate the tensile strength characteristics of this test piece (Example 1) at room temperature (25 ° C.), a tensile test was performed according to ASTM specification E8-96. The result is shown in FIG. The Vickers hardness of the test piece (Example 1) was also measured. The result is shown in FIG.
Shown in Note that this test piece (Example 1) was
When analyzed by (energy dispersive spectroscopy), it was confirmed that Mg-Al-Zn-Ca intermetallic compound was precipitated at the crystal grain boundary of the magnesium crystal.

(Comparative Examples 1 and 2) Next, Comparative Example 1
And Comparative Example 2 will be described.

In Comparative Examples 1 and 2, about 400 g of Mg-5% Al-8% Zn-
0.6% Ca-0.3% Mn (where "%" means "% by weight") was prepared. Then, put the prepared magnesium alloy in a stainless steel container and place it in an electric furnace for 6 hours.
Heated to a temperature of 80 ° C. to dissolve. This dissolution process
The test was performed in a sulfur hexafluoride gas atmosphere. Thereafter, sulfur hexafluoride gas was blown into the molten magnesium alloy to remove oxidized inclusions in the molten material.

Next, in Comparative Example 1, as in the case of Example 1, oxidation was performed on a silicon carbide mold (having a 6 mm thick × 90 mm high × 180 mm wide cavity) heated to a temperature of 150 ° C. The molten material from which inclusions have been removed is poured and cast. In this case, the magnesium alloy poured into the mold was allowed to cool (as cast). afterwards,
A magnesium alloy was taken out of the mold, and the magnesium alloy was processed to obtain a test piece (Comparative Example 1). Then, in order to investigate the tensile strength characteristics of this test piece (Comparative Example 1) at room temperature, a tensile test was performed according to ASTM specification E8-96, as in Example 1. The result is shown in FIG.

In Comparative Example 2, a mold heated to a temperature of 150 ° C. (thickness 6 mm × height 90 mm × width 180 mm)
The molten material from which the oxidized inclusions had been removed was cast in a hot chamber die casting machine by a die casting method. In this case, the magnesium alloy poured into the mold was allowed to cool (as cast). Thereafter, the magnesium alloy was taken out of the mold, and the magnesium alloy was processed to obtain a test piece (Comparative Example 2). Then, in order to investigate the tensile strength characteristics of this test piece (Comparative Example 2) at room temperature, a tensile test was performed in accordance with ASTM specification E8-96 in the same manner as in Example 1 and Comparative Example 1. Was. The result is shown in FIG.

As can be understood from FIG. 1, the 0.2% proof stress of the magnesium alloy of Example 1 is 142 MPa, and the 0.2% proof stress of the magnesium alloy of Comparative Example 1 is 9 MPa.
6 MPa, which is 0.2% of the magnesium alloy of Comparative Example 2.
The% yield strength was found to be 150 MPa.

From the comparison between Example 1 and Comparative Example 1, it was found that the magnesium alloy according to the prior art was subjected to the solution treatment and the artificial aging treatment in order, so that the 0.2% proof stress of the magnesium alloy at room temperature was improved. It was found that 46 MPa was also improved. From the comparison between Example 1 and Comparative Example 2,
It was also found that even in the case of the casting method in which the solidification rate of the magnesium alloy is low, it is possible to provide the same 0.2% proof stress as in the case of the die casting method in which the solidification rate of the magnesium alloy is high.

As can be understood from FIG. 5, the Vickers hardness of the magnesium alloy of Example 1 was found to be 88 HV.

According to this embodiment, the following effects can be obtained.

According to the magnesium alloy of this embodiment,
The strength at room temperature can be improved as compared with the magnesium alloy according to the related art.

Since the strength of the magnesium alloy of this embodiment at room temperature can be improved, the magnesium alloy of this embodiment can be manufactured by sand casting, plaster casting, die casting, vanishing model casting other than die casting. It can be applied to law.

According to this embodiment, since 0.3% by weight of manganese is mixed in the magnesium alloy, the corrosion resistance of the magnesium alloy can be improved (improved).

According to the present embodiment, the Mg-Al-Zn-Ca intermetallic compound is precipitated at the crystal grain boundary of the magnesium crystal. High metallic stability of the magnesium alloy at room temperature or high temperature and strengthening of the grain boundary of the magnesium crystal can be obtained.

According to the present embodiment, since the heating holding time required for the solution treatment and the artificial aging treatment is set to be relatively short at 29.5 hours, deterioration of workability and increase in cost are suppressed as much as possible. Can be.

Here, in order to mainly confirm the treatment state (solution treatment and artificial aging treatment) of the magnesium alloy according to the first embodiment, the following experiment was conducted. Various experimental results are shown in FIGS.

(Degree of Solution of Intermetallic Compound in Magnesium Alloy) First, Mg-5 before heat treatment used in Example 1 was used.
% Al-8% Zn-0.6% Ca-0.3% Mn (where "%" means "% by weight") with two heating temperatures and various heating holding times. Were subjected to solution treatment. The heating temperature is 350 ° C., 380 ° C., and the heating holding time is 3 hours, 12 hours, 18 hours, 2 hours.
0 hours, 24 hours, 28 hours, 45 hours, 48 hours, 7
2 hours. Note that experiments were not performed for all combinations of the heating time and the heating holding time. After the heating and holding, it is rapidly cooled by air cooling (forced air cooling).

The Vickers hardness of each of the magnesium alloys subjected to the solution treatment under various conditions was measured. The result is shown in FIG. Here, the relationship between the heating holding time and the Vickers hardness is represented as (heating holding time (hour), Vickers hardness (HV)) below. For example, the heating holding time is 1 hour, and the Vickers hardness is 50.
If it is HV, it will be (1,50).

As shown in FIG. 2, at a heating temperature of 350 ° C., (12,58.1), (18,58.3),
(20,59.3), (24,59.6), (48,5
9.8) and (72, 61.2), indicating that a Vickers hardness of 61.2 HV can be obtained in a heating holding time of 72 hours.

At a temperature of 380 ° C., (3,60.
1), (20, 62.0), (24, 62.0), (2
8,60.5) and (45,59.4), indicating that a Vickers hardness of 62.0 HV, which is the maximum value, can be obtained when the heating and holding time is 20 hours and 24 hours.

Next, FIGS. 3 and 4 show photographs of the magnesium alloy having the highest Vickers hardness at each of the above-mentioned temperatures, with the structure of the alloy enlarged 400 times. FIG. 3 is a photograph showing a microstructure of a magnesium alloy that has been subjected to a solution treatment at a temperature of 350 ° C. and a heating holding time of 72 hours. Also, FIG.
5 is a photograph showing the microstructure of a magnesium alloy that has been subjected to a solution treatment at a temperature of 24 hours and a heat holding time of 24 hours.

As shown in FIG. 2, at a heating temperature of 350 ° C., the Vickers hardness tends to increase as the heating time increases, but it takes 72 hours to reach the maximum Vickers hardness. It is considered that a longer heating and holding time is required, and it can be said that the treatment time is too long to make the solution treatment sufficient, which is not practical. FIG.
In the magnesium alloy subjected to the solution treatment at a heating temperature of 350 ° C. and a heating holding time of 72 hours, the Mg—Al—Zn precipitated at the crystal grain boundary of the magnesium crystal shown in FIG.
In a state where the intermetallic compound of -Ca is slightly coarsened,
It is observed that the solution treatment is slightly insufficient, but this is acceptable.

As shown in FIG. 2, at the heating temperature of 380 ° C., the Vickers hardness reached the maximum value when the heating time was 20 hours and 24 hours, and when the heating time exceeded 24 hours, the Vickers hardness was increased. Tends to decrease. Further, in the case of the magnesium alloy subjected to the solution treatment at a heating temperature of 380 ° C. and a heating holding time of 24 hours as shown in FIG. 3, Mg-Al-Z precipitated at the crystal grain boundary of the magnesium crystal.
It is observed that the n-Ca intermetallic compound is rounded and small (fine), without coarsening, and that the solution treatment is sufficient.

That is, at the heating temperature of 380 ° C., until the Vickers hardness reaches the maximum value, the intermetallic compound of Mg—Al—Zn—Ca diffuses into the magnesium crystal, and the solution treatment (solution treatment) is performed. Degree) progresses toward a good state, but if the heating and holding time exceeds 24 hours, the intermetallic compound present in the magnesium crystal will diffuse, conversely, causing the strength of the magnesium crystal itself to decrease. It is presumed from FIG. 2 that the magnesium alloy lowers the Vickers hardness. From the above, at the heating temperature of 380 ° C., the heating holding time is 20 to 24.
The solution heat treatment time was the best, and it was confirmed that the solution treatment of the magnesium alloy according to Example 1 was sufficient.

(Strength of magnesium alloy) First, the above-mentioned (solution degree of intermetallic compound in magnesium alloy)
, An artificial aging treatment was further performed on the magnesium alloy that had been subjected to the solution treatment at a temperature of 380 ° C. and a heating and holding time of 24 hours by further combining two heating temperatures and various heating and holding times. The heating temperature is 150 ° C, 200
° C, and the heating holding time is 0.1 hour, 0.5 hour,
1 hour, 1.5 hours, 2 hours, 3 hours, 4 hours, 5.5
Hours, 6 hours, 9 hours, 10 hours, 14 hours, 16 hours, 20 hours, 24 hours and 37 hours. Note that experiments were not performed for all combinations of the heating time and the heating holding time. After the heating and holding, it is left to cool to room temperature.

Then, the Vickers hardness of the magnesium alloy subjected to the artificial aging treatment under various conditions was measured. The result is shown in FIG. Here, the relationship between the heating holding time and the Vickers hardness is represented as (heating holding time (hour), Vickers hardness (HV)) below.

As shown in FIG. 5, at a heating temperature of 150 ° C., (0.1,58.8), (1,67.3),
(2,72.1), (4,79.4), (5.5,8)
8.0), (9,84.3), (16,80.8),
(24,81.5), and it was found that a Vickers hardness of a maximum value of 88.0 HV was obtained when the heating holding time was 5.5 hours.

At a temperature of 200 ° C., (0.1,5
8.8), (0.5,78.1), (1,77.5),
(1.5, 81.6), (2,78.1), (3,7)
4.2), (6,73.4), (10,71.4),
(14,72.6), (20,74.0), (24,7)
2.5) and (37,70.8), and it was found that a Vickers hardness of the maximum value of 81.6 HV was obtained when the heating holding time was 1.5 hours.

As shown in FIG. 5, when the heating temperature is 150
It can be seen that, in both cases of C and 200 C, after the Vickers hardness reaches the maximum value, the Vickers hardness tends to decrease even if the heating holding time is lengthened. Therefore, when the Vickers hardness reaches the maximum value, the time for further heating and holding is wasteful and undesirable. As is clear from FIG. 5, at a heating temperature of 150 ° C., the artificial aging treatment with a heating holding time of 5.5 hours was the best, and it was confirmed that the magnesium alloy according to Example 1 had sufficient strength. (At a heating temperature of 200 ° C., the artificial aging treatment with a heating holding time of 1.5 hours is the best).

In addition, technical ideas that are not described in the claims and that are grasped from the embodiment and the examples are described below together with their effects.

(A) The magnesium alloy according to any one of claims 1 to 3, wherein the solution treatment is performed at a temperature of 380 ° C. for 24 hours and then quenched, and the artificial aging treatment is performed. Is 5.5 at a temperature of 150 ° C.
A magnesium alloy which is left to cool after being held for a time.

With this configuration, the effects of the first, second, and third aspects of the invention can be reliably achieved.

(B) 2 to 9% by weight of aluminum, 6
Performing a solution treatment on a magnesium alloy containing up to 12% by weight of zinc and 0.1 to 2.0% by weight of calcium and the balance of magnesium and unavoidable impurities, and then performing an artificial aging treatment A heat treatment method for a magnesium alloy, comprising:

In this way, at least one room temperature
A magnesium alloy having a 0.2% proof stress of 40 MPa and a Vickers hardness of 65 HV or more can be obtained. Further, a magnesium alloy having the effects of the invention described in claim 1 is obtained.

(C) 2 to 9% by weight of aluminum, 6
~ 12 wt% zinc, 0.1-2 wt% calcium,
A magnesium alloy containing 0.2 to 0.5% by weight of manganese, with the balance being magnesium and unavoidable impurities, being subjected to a solution treatment and then an artificial aging treatment. Heat treatment method.

In this way, at least one room temperature
A magnesium alloy having a 0.2% proof stress of 40 MPa and a Vickers hardness of 65 HV or more can be obtained. Further, a magnesium alloy having the effects of the invention described in claim 2 is obtained.

[0080]

As described above in detail, according to the first to fifth aspects of the present invention, the strength of the magnesium alloy at room temperature is improved, and the sand casting method and the gypsum casting method other than the die casting method are used. , A magnesium alloy applicable to die casting and vanishing model casting.

According to the second aspect of the present invention, the corrosion resistance of the magnesium alloy can be improved (improved). Furthermore, according to the third aspect of the present invention, it is possible to obtain high metallic stability of the magnesium alloy at room temperature or high temperature and strengthen the grain boundary of the magnesium crystal. In addition, according to the invention described in claim 4 and claim 5, deterioration of workability and increase in cost can be suppressed as much as possible.

[Brief description of the drawings]

FIG. 1 is a graph showing 0.2% proof stress of Mg alloys of Examples and Comparative Examples.

FIG. 2 is a graph showing a relationship between a heating holding time and a Vickers hardness in a solution treatment of a magnesium alloy.

FIG. 3 is a photograph showing a state in which the structure of the Mg alloy is magnified 400 times.

FIG. 4 is a photograph showing a state in which the structure of the Mg alloy is magnified 400 times.

FIG. 5 is a graph showing a relationship between a heating holding time and a Vickers hardness for an artificial aging treatment of a magnesium alloy.

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[Procedure amendment]

[Submission date] March 9, 2001 (2001.3.9)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

[Correction contents]

FIG. 3

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Fig. 4

[Correction method] Change

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Claims (5)

[Claims] 1 to 9% by weight of aluminum, 6 to 12%
A magnesium alloy containing 0.1% to 2.0% by weight of zinc and 0.1% to 2.0% by weight of calcium, with the balance being magnesium and unavoidable impurities, being subjected to solution treatment and artificial aging treatment in order, and Sometimes at least 140MPa
A magnesium alloy having a 0.2% proof stress and a Vickers hardness of 65 HV or more. 2. 2 to 9% by weight of aluminum, 6 to 12% by weight.
Wt% zinc, 0.1-2 wt% calcium, 0.2
A magnesium alloy containing ０．５0.5% by weight of manganese, with the balance being magnesium and unavoidable impurities, in a state where a solution treatment and an artificial aging treatment are sequentially performed,
A magnesium alloy having a 0.2% proof stress of at least 140 MPa at room temperature and a Vickers hardness of 65 HV or more. 3. The magnesium alloy according to claim 1, wherein Mg is present at a crystal grain boundary of the magnesium crystal.
-A magnesium alloy, wherein an intermetallic compound of Al-Zn-Ca is precipitated. 4. The magnesium alloy according to claim 1, wherein the solution treatment comprises:
A magnesium alloy which is rapidly cooled after being maintained at a temperature of 350 to 380 ° C for 20 to 70 hours. 5. The magnesium alloy according to claim 1, wherein the artificial aging treatment is carried out at a temperature of 150 to 200 ° C. for 0.5 to 10 hours, followed by cooling. A magnesium alloy, characterized in that: