JP2009149952A - Heat-resistant magnesium alloy and producing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat-resistant magnesium alloy which has at the same time high strength and high ductility even under high temperature environment and is also inexpensive, and to provide a production method therefor. <P>SOLUTION: The heat-resistant magnesium alloy comprises, in relation to the total amount of the alloy, 1 to 3 atomic% Zn, 1 to 3 atomic% Y and 0.01 to 0.5 atomic% Zr and the balance Mg with inevitable impurities, wherein composition ratio Zn/Y between Zn and Y falls within the range of 0.6 to 1.3 and also, α-Mg phase and an intermetallic compound Mg<SB>3</SB>Y<SB>2</SB>Zn<SB>3</SB>phase are finely dispersed, and a long period stacking ordered structure phase is formed in three-dimensional network shape. The heat-resistant magnesium alloy can be produced by melting a metal material having the above composition at a temperature within the range of 650 to 900°C and pouring the molten metal material into a mold and cooling the molten metal material at a rate of 10 to 10<SP>3</SP>K/sec. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a heat-resistant magnesium alloy and a method for producing the same.

  Since magnesium is lighter than iron and aluminum, it has been studied to be used as a lightweight substitute material in place of a member made of a steel material or an aluminum alloy material. However, in general magnesium alloys, mechanical properties such as tensile strength and elongation decrease at a high temperature range of 200 to 250 ° C., and high temperatures comparable to heat-resistant aluminum alloys such as cast AC8B-T6 material and forged A4032-T6 material. Can't get strength.

Accordingly, various heat-resistant magnesium alloys that have both high strength and high ductility even under high temperature environments have been proposed. Such a heat-resistant magnesium alloy includes, for example, Zn 1 to 4 atomic%, Y 1 to 4.5 atomic%, and Zr 0.1 to 0.5 atomic% with respect to the total amount, and the balance is inevitable with Mg. A magnesium alloy is known which is formed by casting a Mg alloy having a composition in which Zn / Y is in the range of 0.6 to 1.3, and then plastically working. The heat-resistant magnesium alloy includes an intermetallic compound Mg ₃ Y ₂ Zn ₃ and an alloy structure containing Mg ₁₂ ZnY exhibiting a long-period structure, and obtains high strength and high ductility in a high temperature environment. (See Patent Document 1).

However, the heat-resistant magnesium compound must be further plastically processed after casting, and the plastic processing requires a large amount of energy, which increases the manufacturing cost. Thus, an inexpensive heat-resistant magnesium alloy that has both high strength and high ductility in a high temperature environment is desired.
JP 2006-97037 A

  An object of the present invention is to eliminate such inconveniences and to provide an inexpensive heat-resistant magnesium alloy that has both high strength and high ductility in a high temperature environment.

In order to achieve this object, the heat-resistant magnesium alloy of the present invention contains Zn 1 to 3 atomic%, Y 1 to 3 atomic%, and Zr 0.01 to 0.5 atomic% with respect to the total amount, and the balance. Is composed of Mg and inevitable impurities, the composition ratio Zn / Y of Zn and Y is in the range of 0.6 to 1.3, and the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase are It is characterized by being finely dispersed and having a long-period laminated structure phase formed in a three-dimensional network.

The heat-resistant magnesium alloy of the present invention has the above composition, the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase are finely dispersed, and the long-period laminated structure phase has a three-dimensional network shape. By being formed, even in a high temperature environment of 200 to 250 ° C., it is possible to have both high strength and high ductility. When Zn is less than 1 atomic% or more than 3 atomic% and Y is less than 1 atomic% or more than 3 atomic%, either strength or ductility, or both are insufficient with respect to the total amount of heat-resistant magnesium alloy become.

In addition, the heat-resistant magnesium alloy of the present invention contains Zr in the above range to refine the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase, and the intermetallic compound during casting cooling. The coarsening of Mg ₃ Y ₂ Zn ₃ can be suppressed. When the Zr content is less than 0.01 atomic% with respect to the total amount of the alloy, the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase are refined, and the intermetallic compound Mg ₃ Y ₂ Zn during casting cooling. ₃ cannot be obtained, and if it exceeds 0.5 atomic%, the effect of refining the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ reaches a saturated state.

Furthermore, since the heat-resistant magnesium alloy of the present invention surely includes both the intermetallic compound Mg ₃ Y ₂ Zn ₃ and the long-period stacked structure, the composition ratio Zn / Y of Zn and Y is It must be in the range of 0.6 to 1.3. When the Zn / Y composition ratio Zn / Y is less than 0.6 or exceeds 1.3, any one of the intermetallic compound Mg ₃ Y ₂ Zn ₃ and the long-period stacked structure is included in the heat-resistant magnesium alloy. One or both may not be included.

In the heat-resistant magnesium alloy of the present invention, fine particles of the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase exist between the long-period laminated structure phases formed in a three-dimensional network. It is necessary to provide the alloy structure which is doing. When the particles of the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase are coarsened and the three-dimensional network structure of the long-period laminated structure phase is broken by the coarse particles, the strength is increased in the high temperature environment. And high ductility cannot be obtained.

The heat-resistant magnesium alloy of the present invention having the alloy structure includes Zn 1 to 3 atomic%, Y 1 to 3 atomic%, and Zr 0.01 to 0.5 atomic%, with the balance being Mg. A metal material consisting of unavoidable impurities and having a Zn / Y composition ratio Zn / Y in the range of 0.6 to 1.3 is melted at a temperature in the range of 650 to 900 ° C. and cast into a mold. Can be advantageously produced by a production method of cooling at a rate of 10 to 10 ³ K / sec. When the melting temperature is less than 650 ° C., each metal component constituting the metal material cannot be uniformly melted, and when it exceeds 900 ° C., a part of each metal component is vaporized and lost. Further, when the cooling rate is less than 10 K / sec, the particles of the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase are coarsened, and the three-dimensional network structure of the long-period stacked structure phase is formed. Can't get. On the other hand, it is technically difficult to achieve a cooling rate exceeding 10 ³ K / sec.

  Next, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. 1 is a plan view showing the shape of a cast of the heat-resistant magnesium alloy of the present embodiment, FIG. 2 is a sectional view taken along the line II-II of FIG. 1, and FIG. 3 is an alloy structure of the heat-resistant magnesium alloy of the present embodiment. FIG. 4 is a plan view showing the shape of a test piece cut out from the casting shown in FIGS. 1 and 2 in order to measure mechanical properties. 5 and 6 are backscattered electron images of the alloy structure of the heat-resistant magnesium alloy of the comparative example.

  In this embodiment, first, with respect to the total amount, Zn 1 to 3 atomic%, Y 1 to 3 atomic%, Zr 0.01 to 0.5 atomic%, the balance consists of Mg and inevitable impurities, A metal material having a Zn / Y composition ratio Zn / Y in the range of 0.6 to 1.3 is melted at a temperature in the range of 650 to 900 ° C. to obtain a molten alloy.

Next, the molten alloy is poured into a mold and cast. The casting is performed, for example, by using a mold made of oxygen-free copper (C1020, purity 4N) and casting the molten alloy at a temperature in the range of 800 to 850 ° C. by a gravity casting method. Cooling in the casting is performed at a speed in the range of 10 to 10 ³ K / sec.

As a result, with respect to the total amount, Zn 1 to 3 atomic%, Y 1 to 3 atomic%, Zr 0.01 to 0.5 atomic%, the balance is composed of Mg and inevitable impurities, Zn and Y, The composition ratio Zn / Y is in the range of 0.6 to 1.3, the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase are finely dispersed, and the long-period stacked structure phase is tertiary. A magnesium alloy formed in an original network shape can be obtained. The magnesium alloy is inexpensive because it does not require plastic working after casting, and is a heat-resistant magnesium alloy that combines high strength and high ductility in a high temperature environment of 200 to 250 ° C.

  The heat-resistant magnesium alloy of this embodiment may include a metal selected from the group consisting of Dy, Ho, Er, Gd, Tb, and Tm instead of Y, and Ti or Ti instead of Zr. Hf may be included.

  Next, examples of the present invention, comparative examples, and reference examples are shown.

  In this example, a metal material composed of 2 atomic% Zn, 2 atomic% Y, 0.2 atomic% Zr, and 95.8 atomic% Mg was melted at a temperature of 850 ° C. to obtain a molten alloy. In the molten alloy, the composition ratio Zn / Y between Zn and Y is 1.0.

  Next, the obtained molten alloy was cast into a mold made of oxygen-free copper (C1020, purity 4N) by a gravity casting method to obtain a heat-resistant magnesium alloy casting. The casting was performed while maintaining the molten alloy at a temperature in the range of 800-850 ° C.

As shown in FIG. 1, the casting 1 obtained in this example is rectangular in plan view and has a size of 46 mm × 56 mm. Further, as shown in FIG. 2, the casting 1 has a thickness that gradually changes from t ₁ to t ₄ along the long side, t ₁ = 2 mm (Example 1), t ₂ = 4 mm. (Example 2), t ₃ = 8 mm (Example 3), and t ₄ = 16 mm (Example 4).

The casting 1 obtained in this example has a different cooling rate depending on the thickness, and the thickness t ₁ = 2 mm is 668 K / second, and the thickness t ₂ = 4 mm is 166 K / second. The thickness t ₃ = 8 mm was 55 K / second, and the thickness t ₄ = 16 mm was 21 K / second.

The cooling rate was calculated as follows. First, an Al _82.7 Cu _17.3 eutectic alloy was cast in the same manner as in this example except that Al _82.7 atomic% and Cu _17.3 atomic% were used instead of the metal material. Then, the distance between secondary branches (DAS, Dendrite Arm Spacing) of the eutectic alloy was measured. Next, an empirical formula showing the relationship between DAS and cooling rate in the eutectic alloy was obtained. Then, the in empirical formula, and substituting the DAS in the respective thickness part of t ₁ ~t ₄ of heat-resistant magnesium alloy of the present embodiment, to determine the cooling speed of each part.

Next, FIG. 3 shows a backscattered electron image of the alloy structure of the heat-resistant magnesium alloy obtained in this example. FIG. 3A shows a backscattered electron image of the alloy structure at a thickness t ₁ = 2 mm and a cooling rate of 668 K / sec. FIG. 3B shows a portion at a thickness t ₂ = 4 mm and a cooling rate of 166 K / sec. reflection electron image of the alloy structure, FIG. 3 (c), the thickness _t 3 = 8 mm, the reflection electron image of the alloy structure of the portion of the cooling rate of 55K / sec, FIG. 3 (d), the thickness _t 4 = 16 mm The reflected electron images of the alloy structure at the cooling rate of 21 K / second are shown.

From FIG. 3, the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase are present between the long-period laminated structure phases formed in a three-dimensional network for any of the thicknesses t ₁ to t _4. The presence of fine particles was observed.

Next, the test piece 2 having the shape shown in FIG. 4 was cut out from each part of the thicknesses t ₁ to t ₄ of the casting 1 shown in FIGS. 1 and 2, and the mechanical properties of the test piece 2 were evaluated. The test piece has an overall length L = 46 mm, an overall width d = 12 mm, and a thickness of 2 mm, and has a constricted portion with a width of 4 mm at the center. It is affixed.

In this example, the test piece 2 was heated to 200 ° C. and 250 ° C. by induction heating in the atmosphere, and a strain rate of 5 × 10 ⁻⁴ / sec (0. The tensile strength and the elongation were measured at 12 mm / min and a measurement length of 4 mm. The test piece 2 is heated so that the length of the constricted portion in the longitudinal direction of 4 mm is 200 ° C. when heated to 200 ° C., and is heated to 250 ° C. Was controlled to a temperature in the range of 250 ± 2 ° C. The results are shown in Table 1.

In this example, the test piece 2 was heated to 200 ° C. by induction heating in the atmosphere, and the stress ratio was R = −1 (resonance) and the frequency was changed using an electrohydraulic fatigue tester manufactured by MTS. The sine wave was set to 30 to 60 Hz, the life was determined by separation fracture, and the fatigue strength was determined by the stress amplitude at the number of repetitions of 1 × 10 ⁷ times. The heating of the test piece 2 was controlled so that the range of the length of 4 mm in the longitudinal direction of the narrowed portion was 200 ± 2 ° C. when heated to 200 ° C. The results are shown in Table 1.
[Comparative Example 1]
In this comparative example, a magnesium alloy casting was obtained in exactly the same manner as in the above example, except that a metal material composed of 2 atomic% Zn, 2 atomic% Y, and 96 atomic% Mg was used.

The cooling rate of the casting obtained in this comparative example was 21 K / sec at the portion of thickness t ₄ = 16 mm.

Next, FIG. 5 shows a backscattered electron image of the alloy structure of the magnesium alloy obtained in this comparative example. From FIG. 5, it was observed that the particles of the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase are coarsened, and the three-dimensional network structure of the long-period stacked structure phase is broken.

Next, a test piece 2 having the shape shown in FIG. 4 is cut out from a portion of t ₄ = 16 mm of the casting obtained in this comparative example, and the test piece 2 is made exactly the same as the above-described example, and has mechanical properties. Evaluated. The results are shown in Table 1.
[Comparative Example 2]
In this comparative example, a metal material composed of 2 atomic% Zn, 2 atomic% Y, 0.2 atomic% Zr, and 95.8 atomic% Mg was melted at a temperature of 850 ° C. to obtain a molten alloy. In the molten alloy, the composition ratio Zn / Y between Zn and Y is 1.0.

  Next, the obtained molten alloy (molten metal) is poured into a mold made of mild steel having an inner diameter of 320 mm and a height of about 1000 mm, and the peripheral speed of the outermost circumference of the molten metal with the vertical axis of the mold as the rotation axis. Rotate in one direction for 5 to 60 seconds and then rotate in the opposite direction for 5 to 60 seconds, and repeat the forward and reverse rotation to solidify the molten metal, and heat resistance A magnesium alloy casting was obtained. The cooling rate of the casting 1 obtained in this comparative example was 1 K / second.

Next, FIG. 6 shows a backscattered electron image of the alloy structure of the magnesium alloy obtained in this comparative example. From FIG. 6, it was observed that the particles of the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase are coarsened, and the three-dimensional network structure of the long-period stacked structure phase is broken.

Next, the test piece 2 having the shape shown in FIG. 4 was cut out from the casting obtained in this comparative example, and the test piece 2 was evaluated in the same manner as in the above example, and the mechanical properties were evaluated. The results are shown in Table 1.
[Reference Example 1]
In this reference example, the tensile strength at 200 ° C. of the magnesium alloy was measured in exactly the same manner as in the above example except that a ZE63A-T6 material, which is a conventionally known magnesium alloy, was used. The results are shown in Table 1.
[Reference Example 2]
In this reference example, the mechanical properties of the aluminum alloy were evaluated in exactly the same manner as in the above example except that the A4032-T6 material, which is a conventionally known aluminum alloy, was used. The results are shown in Table 1.
[Reference Example 3]
In this reference example, the mechanical properties of the aluminum alloy were evaluated in exactly the same manner as in the above example except that the AC8B-T6 material, which is a conventionally known aluminum alloy, was used. The results are shown in Table 1.

  From Table 1, according to each heat-resistant magnesium alloy of an Example, intensity | strength and elongation are large compared with the magnesium alloy of the comparative example 1 and the reference example 1, and high intensity | strength and high in a high temperature environment at 200-250 degreeC. It is clear that it has ductility.

On the other hand, in the heat-resistant magnesium alloy of Comparative Example 2 with a cooling rate of 1 K / second, although the elongation is large, the strength is not sufficient, and the cooling rate is set to 10 to 10 ³ K / second. It is apparent that a heat-resistant magnesium alloy having both high strength and high ductility can be obtained in a high-temperature environment at 200 to 250 ° C. like each of the heat-resistant magnesium alloys.

  Further, from Table 1, according to each heat-resistant magnesium alloy of Example 1, the fatigue strength is comparable to the aluminum alloy A4032-T6 material of Reference Example 2 and surpasses the aluminum alloy AC8B-T6 material of Reference Example 3. It is clear. Also, from Table 1, according to the heat-resistant magnesium alloy of this example, the tensile strength is not greatly reduced between 200 ° C. and 250 ° C. like the aluminum alloys of Reference Examples 2 and 3. At 250 ° C., it is clear that the aluminum alloys of Reference Examples 2 and 3 are greatly exceeded.

The top view which shows the shape of the casting of the magnesium alloy which concerns on this invention. II-II sectional view taken on the line of FIG. The reflection electron image of the alloy structure of the heat-resistant magnesium alloy which concerns on this invention. The top view which shows the shape of the test piece cut out from the casting shown in FIG.1 and FIG.2 in order to measure a mechanical property. The reflection electron image of the alloy structure of the heat-resistant magnesium alloy of a comparative example. The reflection electron image of the alloy structure of the heat-resistant magnesium alloy of a comparative example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Casting, 2 ... Test piece, 3 ... Strain gauge.

Claims (2)

The composition ratio of Zn and Y includes Zn 1 to 3 atomic%, Y 1 to 3 atomic%, and Zr 0.01 to 0.5 atomic% with the balance being Mg and inevitable impurities. Zn / Y is in the range of 0.6 to 1.3, the α-Mg phase and the intermetallic compound Mg ₃ Y ₂ Zn ₃ phase are finely dispersed, and the long-period stacked structure phase is a three-dimensional network. A heat-resistant magnesium alloy characterized in that it is formed. The composition ratio of Zn and Y includes Zn 1 to 3 atomic%, Y 1 to 3 atomic%, and Zr 0.01 to 0.5 atomic% with the balance being Mg and inevitable impurities. A metal material having Zn / Y in the range of 0.6 to 1.3 is melted at a temperature in the range of 650 to 900 ° C., cast into a mold, and cooled at a rate of 10 to 10 ³ K / sec. A method for producing a heat-resistant magnesium alloy.