WO2005118900A1

WO2005118900A1 - Creep-resistant magnesium alloy

Info

Publication number: WO2005118900A1
Application number: PCT/JP2005/006007
Authority: WO
Inventors: Hiroyuki Omura
Original assignee: Ryobi Ltd.
Priority date: 2004-06-03
Filing date: 2005-03-23
Publication date: 2005-12-15
Also published as: JP2007270159A

Abstract

A creep-resistant magnesium alloy, which has a chemical composition, in mass %, that Al: 2.5 to 6.5 %, Ca: 0.3 to 3.0% , Sn: 0.15 to 3.0 %, Mn: 0.1 to 0.5 % and the balance: Mg and inevitable impurities. Optionally, the magnesium alloy further comprises 0.01 to 0.3 mass % of Sr. The sample 4, which is an embodiment of the above creep-resistant magnesium alloy, has exhibited the creep resistance being superior to those of sample 1 and sample 2 (the alloy-1,2 in JP 2001-316752 A), sample 3 (the alloy in JP 07-3374 A) and sample 9 (AZ91D).

Description

Specification

Creep resistant magnesium alloy

Technical field ·

The present invention relates to a creep-resistant magnesium alloy, and particularly to a creep-resistant magnesium alloy having excellent creep resistance and corrosion resistance required for use in a high-temperature environment and free from structural defects such as structural cracks and excellent die-casting properties. About.

Background art

As an alloy used as a material for automobile parts, an Mg-A1-Ca alloy is known. Recently, an Mg-A 1 -Ca-Sr-Mn alloy has been proposed (for example, see Patent Document 1). This alloy has excellent creep resistance and corrosion resistance, with A1 of 2.0 to 6.0% by mass. & Is 0.3 to 2.0%, 3]: is 0.01 to 1.0%, Mn is 0.1 to 1.0%, and the balance is Mg and impurities. In addition, Si was added to the above alloy in an amount of 0.

Alloys in which 1 to 1.0% or Zn is added in an amount of 0.2 to 1.0% by mass are also proposed.

Further, as an alloy having excellent creep resistance, an Mg-Al-Si-Sn-based alloy has been proposed (for example, see Patent Document 2). This alloy contains 0.01 to 4.0% of A1 by mass, 0.2 to 2.0% of 31 and 6.0 to 20.0% of Sn, and the balance consists of Mg and impurities. Alloy.

Patent document 1: JP 2001-316675A

Patent Document 2: JP-A-7-3374

Disclosure of the invention

Problems to be solved by the invention

However, conventional Mg-A1-Ca-Sr-Mn-based alloys have poor die-casting properties such as seizure to molds due to the inclusion of Ca, and die-casting of actual products It is difficult. In addition, although the effect of preventing cracking is obtained to some extent by adding Sr, the effect on seizure and the like is not obtained. It is conceivable to increase A1 in order to improve the fluidity, but the creep resistance decreases. When Si is added to this alloy, the creep resistance and the corrosion resistance are reduced. In addition, the temperature of the liquidus line increases, and it becomes necessary to raise the temperature of the molten metal. The cause of the decrease in creep resistance is that the thermally unstable Mg ₁₂ Al ₁₇ compound This is because it is easy to crystallize in the world. Also, when Zn is added to this alloy, the creep resistance decreases and cracks occur. Moreover, the corrosion resistance of the Mg-A1-Si-Sn-based alloy is very inferior to that of the Mg-A1-Ca-Sr-Mn-based alloy.

Then, an object of the present invention is to provide a creep-resistant magnesium alloy excellent in creep resistance, corrosion resistance and die-casting property.

Means for solving the problem

In order to achieve the above object, the present invention relates to the following: A1 is 2.5 to 6.5% by mass; Ca is 0.3 to 3.0% by mass; Sn is 0.15 to 3.0% by mass; It provides a creep-resistant magnesium alloy containing 0.1 to 0.5% by mass, with the balance being Mg and unavoidable impurities. By changing the alloy system from an Mg-A1-Ca-Mn-based alloy to an Mg-A1-Ca-Sn-Mn-based alloy, it is possible to improve creep resistance and formability (die-casting properties). It has good corrosion resistance.

Here, the S r 0. from 01 to 0. It preferably contains 3 mass ^_0/0. By adding Sr in an amount of 0.01 to 0.3% by mass, the machinability is further improved, and the effect of preventing machinability cracks and grain boundary cracks is further improved.

Brief Description of Drawings

FIG. 1 (a) is a front view showing the shape of a test piece used for evaluation of cracking performance in experiment 1.

FIG. 1 (b) is a side view showing the shape of a test piece used in the evaluation of cracking performance in experiment 1.

FIG. 2 is a view showing a measurement result regarding an evaluation of a crack resistance of a creep-resistant magnesium alloy according to an embodiment of the present invention and a comparative material by Experiment 1.

FIG. 3 is a view showing the shape of a test piece used in the creep resistance test in Experiment 2.

FIG. 4 is a side view showing a state of a creep resistance test in Experiment 2.

FIG. 5 is a side view showing a method for measuring the displacement of a test piece in the creep resistance test of Experiment 2.

FIG. 6 is a view showing the measurement results of a creep resistance experiment I of the creep-resistant magnesium alloy and the comparative material according to the embodiment of the present invention.

FIG. 7 is a view showing the measurement results of a creep resistance experiment II of the creep resistant magnesium alloy and the comparative material according to the embodiment of the present invention.

[FIG. 8] Experiment 3 of creep-resistant magnesium alloy and comparative material according to the embodiment of the present invention. The figure which shows the measurement result regarding the corrosion resistance experiment of FIG.

FIG. 9 is a view showing a result of an E PMA analysis of a creep-resistant magnesium alloy according to an embodiment of the present invention.

FIG. 10 is a view showing the measurement results of the creep resistance test of the creep-resistant magnesium alloy according to the embodiment of the present invention and the comparative material in Experiment 4.

FIG. 11 is a microstructure photograph of an Mg—A1-Ca—Mn-based alloy that is a comparative material for a creep-resistant magnesium alloy according to an embodiment of the present invention.

FIG. 12 is a microstructure photograph of a creep-resistant magnesium alloy according to an embodiment of the present invention.

FIG. 13 is a view showing the shape of a test piece used in the creep resistance test in Experiment 5.

FIG. 14 is a view showing a state of a creep resistance test in Experiment 5. '[FIG. 15] Diagrams showing the results of measurements of the creep resistance test of the creep-resistant magnesium alloy and the comparative material in Experiment 5.

BEST MODE FOR CARRYING OUT THE INVENTION

The creep-resistant Mg alloy according to the embodiment of the present invention will be described. In this creep resistant Mg alloy, A 1 (aluminum) has a mass of 2.5 to 6.5 mass ⁰ /. The C a (calcium) is 0.3-3.0 mass ⁰ /. The Sn (tin) is 0.15-3.0 mass ⁰ /. , Mn (manganese) is 0.1 to 0.5 mass ^_0/0, S r (strontium) is included from 01 to 0.3 wt% 0.1, the remainder being unavoidable impurities and Mg (mug Neshiumu). Al, Ca, Sn, Mn, and Mg are essential elements, and Sr is an optional element.

Here, is effective in錄造of such fluidity and cracking resistance The addition of A 1, creep resistance is lowered to crystallize the Mg ₁₇ A 1 i ₂ compound. The amount of A1 added is 6.0 mass. If the ratio exceeds / ₀ , a large amount of the Mg ₁₇ Al ₁₂ compound is crystallized, so that high creep resistance cannot be obtained. Therefore, the amount of A1 added was set to 6.0% by mass or less. On the other hand, if the addition amount of A1 is less than 2.5% by mass, the formability such as the fluidity of the molten metal decreases, and the die casting becomes difficult. Therefore, the amount of A1 added was set to 2.5% by mass or more.

Addition of Ca improves the flame retardancy of the Mg alloy, and enables forging even at a somewhat high melt temperature. However, if it is added too much, it tends to cause structural cracking and seizure, Goods are not obtained. If the added amount of Ca exceeds 3.0% by mass, it is easy to cause cracking and seizure to a mold, and it is not possible to obtain a sound product. Therefore, the addition amount of Ca was set to 3.0 mass ° / ₀ or less. On the other hand, the added amount of Ca was 0.3 mass. If it is less than / ₀ , sufficient creep resistance cannot be obtained. Therefore, the addition amount of Ca was set to 0.3% by mass or more.

In the case of Mg_A 1 _Ca alloy, seizure occurs in the mold only with A 1 and Ca, making die casting difficult. However, adding Sn drastically reduces seizure. Further, the addition of Sn can modify the solidified structure and prevent the thermally unstable Mg ₁₂ A 1 i ₇ compound from crystallizing at the grain boundaries. However, when the added amount of Sn exceeds 3.0% by mass, the corrosion resistance is reduced, and the corrosion resistance equivalent to that of the AZ91D alloy cannot be obtained. Therefore, the amount of Sn added was set to 3.0% by mass or less. On the other hand, if the added amount of 311 is less than 0.15% by mass, it is difficult to produce a sound product because the product tends to crack or seize on the mold. Therefore, the amount of Sn added was 0.15% by mass or more.

Addition of Mn has an effect on the corrosion resistance, but if the addition amount of Mn exceeds 0.5% by mass, the die-casting becomes difficult due to deterioration of the formability such as seizure to a mold. Therefore, the added amount of Mn is 0.5 mass. / ₀ or less. On the other hand, if the added amount of Mn is less than 0.1% by mass, the corrosion resistance decreases. Therefore, the added amount of Mn is 0.1 mass. / ₀ or more.

A small amount of Sr has little effect on creep resistance, but the addition of Sr improves the morphology of the Mg alloy and prevents grain boundary cracking and the like. If the added amount of Sr exceeds 0.3% by mass, seizure or the like tends to occur. Therefore, the addition amount of Sr was set to 0.3% by mass or less. On the other hand, the amount of Sr added was 0.01 mass. If the ratio is less than / ₀ , the effect on shrinkage cracks and grain boundary cracks cannot be obtained. Therefore, the amount of Sr added was set to 0.01% by mass or more.

The minimum amount of usually unavoidable impurities present in less than 0.004 wt% e (iron), 0.001 mass ⁰ /. Less than Ni (nickel), 0.08 mass ⁰ /. Cu (copper) below, which is like 0.01 wt ^_0/0 less than Zn (zinc).

Various experiments were performed on the alloy according to the embodiment of the present invention and the comparative material. Table 1 shows the composition ratio of the samples used in the experiment. Here, Sample 1 and Sample 2 are alloys described in JP-A-2001-316752, Sample 3 is an alloy described in JP-A-7-3374, and Samples 4 and 5 are Samples 6 and 7 are alloys according to an embodiment of the invention; Sample 8 is an ADC12 alloy, and Sample 9 is an AZ9 ID alloy, in which the weight percent is outside the scope of the embodiments of the present invention.

table 1

(Experiment 1)

The alloy of the embodiment of the present invention and the comparative material were evaluated for crackability. Sample 1 shown in Table 1 (alloy_1 of JP-A-2001-31 6752), sample 4 (alloy-1 of the present embodiment-1), sample 5 (alloy-1 of the present embodiment 2), sample 6 and Using each of Sample 7 (an alloy in which the added mass% of Sn is out of the range of the present invention) and the four types of manufacturing conditions shown in Table 2, the shapes shown in FIGS. 1 (a) and 1 (b) were used. Specimens were fabricated and the cracking rate was examined. The shape of the specimen 1 in FIGS. 1 (a) and 1 (b) is such that the length of the parallel portion is 105 mm and the corner R of the constrained end has a radius of curvature Omm. Table 2

Cracks were checked visually and by color check. See Table

Ten specimens 1 were prepared under the respective conditions of 2, and the crack occurrence rate was calculated from the number of specimens 1 having cracks after fabrication. Figure 2 shows the results.The results of Condition 1 in Table 2 are shaded, and the results of Condition 2 are shaded. Fruits are white, condition 3 results are black, condition 4 results are gray. In sample 4 (alloy 1 of this embodiment), no cracks occurred under conditions 1, 2, and 4. In sample 5 (alloy-2 of the present embodiment) and sample 7 (adding 0.35% by mass of Sn), cracking did not occur under conditions 1 and 2. ■

In sample 1 (alloy 1 1 of JP-A-2001-316752), cracks occurred in all conditions and in all 10 samples. Accordingly, it can be seen that Sample 4 (alloy-1 of the present embodiment) and Sample 5 (alloy-1 of the present embodiment) to which Sn was added had clearly superior cracking properties. It is probable that Sample 1 (alloy-1 of JP-A-2001-316752) had cracks due to the addition of Ca. In addition, the addition of Ca decreases the die-casting property (especially, the flowability of the hot water and the seizure increase). Specimen 4 (Alloy 1 of this embodiment) and Sample 4

It is considered that cracking was reduced in 5 (Alloy-1 of the present embodiment) by further adding Sn. Also, by adding Sn, the seizure to the mold is reduced. sample

With 6 (Sn 0.1 mass% addition), cracks of 20% or more occurred under all conditions, and the effect of Sn addition was not so much recognized. Sample 7 (adding 0.35% by mass of Sn) was found to be effective in cracking.

(Experiment 2)

Experiments were performed on the creep resistance of the alloy according to the embodiment of the present invention and the comparative material. Displacement was measured by conducting creep resistance experiment I in which a bending load was applied for 43 hours in a 250 ° C temperature atmosphere and creep resistance experiment II in which a bending load was applied for 100 hours in a 200 ° C temperature atmosphere. . In the creep resistance experiment I, sample 1 (alloy 1 1 of JP-A-2001-316752), sample 4

A test piece 2 as shown in FIG. 3 was manufactured using (the alloy 1 of the present embodiment 1) and the sample 8 (ADC 12). In the creep resistance test II, samples 1 and 2 (alloys 1 and 2 of JP-A-2001-3166752), sample 3 (alloy of JP-A-7-3374), and sample 4 (alloys 1 and 2 of this embodiment) were used. ), Sample 8 (ADC 12) and Sample 9 (AZ91D) were used to fabricate a test piece 2 as shown in FIG. Test piece 2 was an ASTM B-85 tensile test piece (parallel diameter 6.35 mm, distance between gauges 57.5 mm, length 21 Omm). Are supported by supports 3a and 3b, the distance between the supports 3a and 3b is 15 Omm, A 2 kg weight 4 was hung at the center of the test piece 2, a load was applied to the test piece 2 for a predetermined time, and a bending displacement was caused in the test piece 2.

Next, a method of measuring the displacement will be described. As shown in FIG. 5, a position 75 mm from the center of the test piece 2 on one end side of the test piece 2 was fixed by the fixing member 5, and the height on the other end side was measured by the height gauge 6 to calculate the displacement. Figure 6 shows the results of creep resistance experiment I, and Figure 7 shows creep resistance experiment II. In the creep resistance experiment II, the displacement of sample 9 (AZ91D) was 35 mm, but in Fig. 7 it is 4.5 mm for the sake of illustration. From FIG. 7, the creep resistance of Sample 4 (Alloy-1 of this embodiment) is superior to that of Sample 1 (Alloy-1 of JP-A-2001-3166752), and Sample 3 (Alloy-1 of JP-A-7-3374) You can see that it is much better than). Sample 4 (alloy 1 of this embodiment) is considered to have improved creep resistance due to the addition of Ca and Sn, and the same creep resistance as sample 8 (ADC 12), which is an aluminum die-cast alloy was gotten.

Sample 2 (alloy No. 1 in JP-A-2001-316752) is considered to have reduced creep resistance due to the addition of Si. Generally, it is known that the addition of Ca and Si improves the creep resistance.However, when both are used together, the effect is not obtained, and conversely, the creep resistance is considered to decrease. . In addition, even if Si is added, the solid solution range for Mg is extremely narrow, so that it does not form a solid solution, but Sn dissolves well in Mg and forms a solid solution with Mg,

The solid solution strengthening of the Mg alloy by 5n-added kama can be expected.

(Experiment 3)

For the alloy and the comparative material according to the embodiment of the present invention, an experiment on corrosion resistance was performed by a salt spray test (JISZ2371). FIG. 8 shows the results. The corrosion resistance of Sample 4 (alloy-1 of the present embodiment) and Sample 5 (alloy-1 of the present embodiment) was as shown in Sample 2 (Japanese Unexamined Patent Publication No. 2001-31).

It can be seen that it is superior to the alloy of No. 6752-2) and the sample 3 (the alloy of JP-A No. 7-3374). The reason why the corrosion resistance of Sample 3 (Alloy-1 of JP-A No. 7-3374) is lowered is that Sn and Si, which reduce the corrosion resistance, are added. It is generally known that the addition of Sn decreases the corrosion resistance. However, the corrosion resistance of Sample 4 (alloy 1-1 of the present embodiment) and Sample 5 (alloy-2 of the present embodiment) are , Equivalent to Sample 9 (AZ 91D) and corrosion resistant No decrease was seen.

This is because, in the range of addition of Sn in the present embodiment, the solid solution of Sn in the Mg matrix to form a solid solution increases the potential of the entire Mg matrix, and the Mg matrix and the intermetallic compound. This is probably because the potential difference with the precipitates such as is reduced, and local corrosion is not promoted. In addition, by rapidly cooling the die cast from a high temperature where the solid solution area of Sn to Mg is wide, a solid solution that does not affect the corrosion resistance or a solid solution that is somewhat effective in the corrosion resistance can be obtained and an intermetallic compound that reduces the corrosion resistance can be obtained. It is considered that precipitates are not generated much. However, the corrosion resistance of sample 7 (adding 0.35% by mass of Sn) was inferior to that of sample 5 (alloy No. 2 of the present embodiment), and the amount of Sn added exceeded 3.0%. The corrosion resistance is expected to decrease. This is thought to be due to the crystallization of intermetallic compounds that adversely affect corrosion resistance.

(Experiment 4)

E PMA analysis was performed on the alloy according to the embodiment of the present invention. The composition of the sample analyzed was Mg-4.5% A1-1.7% Ca-0.15% Mn-0.7% Sn, and the results are shown in FIG. As shown in Fig. 9, Sn partially dissolved in the Mg matrix, and Sn was crystallized at the grain boundaries. Also by the addition of S n, at the grain boundaries, not put out Mg Ha Mari crystal, A 1 ₂ C a and S n compounds gave the grain boundary crystallized. In addition, it is a force S, Mg Ca-based compound in which crystallization of Mg is partially observed. Al ₂ Ca was crystallized in the form of links in the matrix, and a structure effective for creep resistance was obtained. Furthermore, there was no Mg A1 compound that was one of the causes of the decrease in creep resistance.

An experiment on creep resistance was performed on the sample and the comparative material. The test method is the same as the creep resistance test I in (Experiment 2). Table 3 shows the samples used in the experiment. Here, Samples 10 and 11 are Mg-A1-Ca-Mn-based alloys as comparative materials, Sample 12 is an alloy having the same composition as the sample subjected to EPMA analysis, and Sample 13 Is an alloy according to an embodiment of the present invention, and Sample 14 is an ADC 12 alloy. Three specimens were prepared for one sample, and all the specimens were tested. Figure 10 shows the displacement of each test piece and the average value of each sample. From Fig. 10, creep resistance of Samples 12 and 13 is better than Samples 10 and 11. You can see that. As described above Mg- Al-Ca-a Mn alloy by the addition of S n, thermally stable A 1 ₂ C a compound is easily crystallized at grain boundaries, thermally labile Mg ₁₂ A it is possible to prevent crystallization of 1 ₁₇ compound, it is believed that the creep resistance is improved. Furthermore, as described above, a part of Sn dissolved in the Mg matrix, and thus it is considered that solid solution strengthening was obtained.

Table 3

FIGS. 11 and 12 show microstructure photographs of Samples 11 and 12, respectively. As shown in FIG. 11, sample 11 has many cracks at the grain boundaries. The Mg_Al-Ca-Mn alloy is considered to have cracked because the grain boundaries are extremely unstable. On the other hand, as shown in FIG. 12, no grain boundary crack was observed in Sample 12, which is the alloy of the present embodiment. The S n added Caro, the modification effect of the grain boundary, such as A 1 ₂ C a crystallizes in the grain boundary was observed.

(Experiment 5)

Experiments were performed on the creep resistance of the alloy according to the embodiment of the present invention and the comparative material. Table 4 shows the samples used in the experiment. Sample 15 is an alloy according to an embodiment of the present invention, Sample 16 is an alloy outside the scope of the present invention, Sample 17 is an ADC12 alloy, and Sample 18 is an AZ91D alloy. . As shown in Fig. 13, the test piece 10 used in the experiment had a parallel part diameter of 6.0 mm, 0.1 mm, a distance between gauge points of 52 mm, and a length of 15 Omm. Specimen 10 was produced by producing under the production conditions shown in Condition 4 of Table 2. Then, as shown in Fig. 14, the test piece was placed in the preheating furnace 11 set at 150 ° C, the strain gauge 12 was fixed to the test piece 10, a load of 35 MPa was applied, and the strain was measured at each elapsed time. did. Table 4

Figure 15 shows the results of the creep test of Experiment 5. As can be seen from the results of Samples 15 and 16, it was recognized that the addition of Sn improved the creep resistance. In addition, it can be seen that the creep resistance of the sample 15 which is the alloy according to the present embodiment is superior to the sample 17 which is the ADC12 alloy. This is believed to thermally From Jona A 1 ₂ C a compound S n addition as described above is because you put the grain boundary crystallized.

The creep-resistant magnesium alloy according to the present invention is not limited to the above embodiment, and various modifications and improvements can be made within the scope described in the claims. '

Industrial applicability

The creep-resistant magnesium alloy of the present invention can be used as an alloy used as a material for automobile parts.

Claims

The scope of the claims

[1] A1 2.5-6.5 mass ⁰ /. , 〇 & 0.3-3.0 mass ⁰ /. , Sn 0.15 to 3.0% by mass, Mn 0.1 to 0.5% by mass. / ₀ , the balance being Mg and unavoidable impurities, characterized by being a creep-resistant magnesium alloy.

[2] The creep-resistant magnesium alloy according to claim 1, wherein Sr is contained in an amount of 0.01 to 0.3% by mass.