JP3107267B2 - Heat resistant magnesium alloy - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a Mg-Al-Zn-R. E. FIG. Related to heat-resistant magnesium alloys.

[0002]

2. Description of the Related Art Magnesium has a specific gravity of 1.74, which is the lightest among metal materials for industrial use, and its mechanical properties are not inferior to those of aluminum alloys. It has attracted attention as a material for fuel efficiency.

[0003] Among the conventional magnesium alloys, Mg-Al
Alloy (ASTM standard-AM60B, AM50A, AM
20A) contains 2 to 12% of Al and a small amount of Mn added thereto. On the Mg side, α-Mg solid solution and β
-A eutectic system of Mg ₁₇ Al ₁₂ compounds,
₁₇ age hardening by the intermediate phase of precipitation of Al ₁₂ occurs. In addition, strength and toughness are improved by solution treatment.

In addition, 5-10% of Al and 1-3% of Zn
Mg-Al-Zn system (ASTM standard-AZ91
D etc.), there is a wide α-solid solution region on the Mg side,
-An Al-Zn-based compound is crystallized. Although as cast, it is tough and excellent in corrosion resistance, but mechanical properties are improved by aging heat treatment, and a pearlite-like compound phase is precipitated at grain boundaries by quenching and tempering.

[0005] In a Mg-Zn alloy, 2%
When Zn is added, the highest strength and elongation can be obtained as cast, but a larger amount of Zn is added in order to improve castability and obtain a sound casting. While tensile in strength of Mg-6% Zn alloy casting is ^two 17 kg / mm, but is improved by the T6 treatment is inferior considerably compared to Mg-Al system. As the Mg-Zn system, for example, Z
CM630A (Mg-6% Zn-3% Cu-0.2M
n).

On the other hand, magnesium alloys having excellent heat resistance and suitable for use at high temperatures have been sought, and rare earth elements (R.
E. FIG. It has been found that the alloys to which (1) is added have mechanical properties at room temperature which are somewhat inferior to those of aluminum alloys, but which are comparable to aluminum alloys at high temperatures up to 250 to 300 ° C. For example, R. E. FIG. As a practical alloy containing Zn, an EK30A alloy containing no Zn (2.5 to
4% R. E. FIG. ZE41A alloy (1% RE, -2.0% Zn-0.6
% Zr) has been put to practical use.

[0007]

Among the above magnesium alloys, Mg-Al alloys or Mg-Al-Zn alloys are inexpensive and can be die-cast, so they are used at low temperatures of at most 60 ° C. However, since the Mg-Al compound has a low melting point and is unstable at high temperatures, the strength and the creep resistance at high temperatures are greatly reduced.

For example, AZ91D is excellent in castability, corrosion resistance and strength from room temperature to 150 ° C., but is inferior in creep resistance at 100 ° C. or higher. If the high-temperature creep characteristic is low, there arises a problem that, for example, when the temperature of the bolted portion increases during use, the tightening force (axial force) decreases. This tendency is particularly remarkable in the case of a die-cast material.

In the solidification process, aluminum in the magnesium alloy forms a crystallized product of Mg ₁₇ Al ₁₂ , but when the cooling rate is high as in the case of die-casting, aluminum before the crystallized material is formed near the grain boundary. A region where the aluminum concentration of the solute atoms is high (dentricixel) is formed. It is considered that due to the presence of the unstable aluminum atoms, grain boundary diffusion in a high-temperature environment becomes active and creep deformation is promoted.

The present invention has been made to solve the above-mentioned problem that the conventional Mg-Al-based die-casting alloy is inferior in creep resistance, and has improved creep characteristics at 150 ° C. It is another object of the present invention to provide a heat-resistant magnesium alloy that secures strength from room temperature to 100 ° C. and improves castability and corrosion resistance.

[0011]

Accordingly, the present inventors have studied the concentration of aluminum that does not form a dendritic cell, and by controlling the aluminum concentration to be 1.0 to 3.0%, the formation of a dendritic cell can be reduced. I found that it could be suppressed. In addition, it has been found that it is effective to add 0.25 to 3.0% of zinc to secure strength and elongation from room temperature to 100 ° C. Further, 0.5 to 4.0 of a rare earth metal or neodymium which forms a crystal having a high melting point is added to the grain boundary to strengthen the grain boundary.
The present invention was completed by adding 2% Mn to improve the corrosion resistance.

The heat-resistant magnesium alloy according to claim 1 of the present invention has a general formula: Mg-a% Al-b% Zn-c% R. E. FIG.
(However, in a magnesium alloy represented by RE rare earth element), 1.0 ≦ a ≦ 3.0 0.25 ≦ b ≦ 3.0 0.5 ≦ c ≦ 4.0, and the weight is Contains Mn; 0.2-0.3% by ratio
When 0.25 ≦ b ≦ 1.0, c ≦ a + 1 and when 1.0 ≦ b ≦ 3.0, c ≦ a + b ≦ 1 / 2c + 4.0 (where a, b, and c are all by weight). The gist is to have satisfactory elongation and excellent strength properties.

Further, in order to further improve the proof stress, the heat-resistant magnesium alloy of the present invention according to claim 1 may further include M
n: 0.1 to 1.0%.

[0014]

The aluminum concentration is limited to 1.0 to 3.0% of the concentration range in which no dendritic cell is formed.
The creep resistance at a temperature of 00 ° C. or higher could be improved. Moreover, since zinc was added in an amount of 0.25 to 3.0%, room temperature to 1% was added.
The strength and elongation up to 00 ° C. were ensured and the castability was improved. 0.5 to rare earth metal or neodymium
Since 4.0% was added, a high-melting-point crystallized substance was formed at the grain boundary, the grain boundary was strengthened, and the creep characteristics at 150 ° C. were improved.

In the present invention, Mn is 0.1 to 1.0%
Since it is contained, the proof stress is improved and the initial decrease in bolt fastening axial force is small. Mn is dissolved in the grains with a small amount of addition, and as a result of solid solution strengthening, the proof stress at room temperature and high temperature is improved. Since the decrease in the initial axial force depends on the proof stress of the material (the object to be fastened), Mn
It is considered that the addition was improved. Furthermore, when Mn was in the range of 0.2 to 0.3%, the corrosion resistance was improved.

In the present invention, the reason for adding the alloy element and the reason for limiting the composition range will be described. Al: 1.0 to 3.0% The axial force retention decreases as the content of Al increases.
1 shows Zn; 2.0%; E. FIG. 2.9%, Mn;
The axial force retention was measured when Al was added at 0 to 4.0% to a 0.2% alloy.
50% was set at 300 ° C. × 300 hours, and the upper limit was 3.0% which satisfied this. FIG. 2 shows the measurement of the rate of occurrence of casting cracks in the same alloy system. If the Al content is less than 1.0%, casting cracks are likely to occur, so the lower limit was set to 1.0%.

Zn: 0.25 to 3.0% Zn: Al; 2.0%; E. FIG. 2.9%, Mn;
As is clear from FIG. 4 showing the tensile strength at room temperature and FIG. 5 showing the tensile elongation at 100 ° C. in the case where Zn is added to the 0.2% alloy in the range of 0 to 4.0%, the addition of 0.25% or more is apparent. Thereby, the room temperature strength is improved, and the tensile elongation at 100 ° C. is also improved. From the viewpoint of room temperature strength, a preferred range is 10% or more. However, as shown in FIG. 3 where the axial force retention of the same alloy system was measured, addition of too much Zn lowers the axial force retention, so that the upper limit is maintained at the target value of 3.0%. And

When a small amount of Zn is added, it is dissolved in the grains and Mg, Al, R.R. E. FIG. And a high melting point compound to improve strength, elongation, and creep resistance. E. FIG. Since low-melting compounds of Mg, Al, and Zn that do not contain Cr are also generated at grain boundaries, creep resistance is deteriorated.

R. E. FIG. 0.5-4.0 R .; E. FIG. Is Al; 2.0%, Zn; 2.0%, Mn;
R. 0.2% alloy E. FIG. As is clear from FIG. 6 showing the axial force retention when 0 to 4.0% is added, the addition of 0.5% or more can greatly improve the axial force retention.
However, FIG. 7 shows the tensile strength of the same alloy system at room temperature.
As is apparent from R. E. FIG. If the added amount exceeds 4.0%, the strength at room temperature is reduced, so the upper limit is set to 4.0%.
And In addition, R. E. FIG. Is preferably a misch metal containing cerium as a main component, but the same effect was obtained when the misch metal was replaced with neodymium.

Mn: 0.1 to 1.0% Mn forms a solid solution in the grains, and as a result of solid solution strengthening, the effect of improving the reduction of the initial axial force is obtained. To obtain the above effect, it is necessary to add at least 0.1% or more. The effect of improving the initial axial force reduction is saturated up to 0.4%.
Is increased to exceed 1.0%, Mn-Al-R. E. FIG.
The upper limit is set to 1.0
%. When Mn is added in an amount of 0.2% or more, Mn acts simultaneously with Al to remove Fe which affects corrosion. Even if added in excess of 0.3, no improvement in the corrosion resistance effect is observed, so if it is desired to improve the corrosion resistance, the upper limit is preferably made 0.3%.

In the present invention, Al (a), Zn
(B) and R.I. E. FIG. Regarding (c), c ≦ a + 1 or c ≦ a + b ≦ 1 / 2c + 4.0 is described in R. E. FIG. This is because, if the total amount of Al and Zn is larger than the total amount of Al and Zn, the strength at room temperature is reduced, and the total amount of Al and Zn is (RE) ×
If the amount is more than 1/2 + 4% by weight, the creep property at high temperatures is reduced.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described to clarify the effects of the present invention. (Example 1) Zn; 1.0% containing Al; 0 to 4.0
% And R.C. E. FIG. An alloy containing 0 to 4.0% (hereinafter referred to as alloy system A); Zn; Al containing 2.0%;
0-4.0% and R.I. E. FIG. Alloy containing 0 to 5.0% (hereinafter referred to as alloy system B); Zn containing 3.0% and Al; 0 to 4.0% and R.C. E. FIG. ; 0 to 5.0%
(Hereinafter referred to as alloy system C), Zn;
Al containing 0.25%; 0-4.0% and R.I.
E. FIG. An alloy containing 0 to 5.0% (hereinafter referred to as alloy D) was melted, and the tensile strength at room temperature and the axial force retention at 150 ° C. for 300 hours were measured for each alloy. . The obtained results are shown in FIG. 8 for the alloy system A, FIG. 9 for the alloy system B, FIG. 10 for the alloy system C, and FIG. 11 for the alloy system D. Those with an axial force retention of 50% or less are marked with a cross, those with a tensile strength of 200 MPa or less are marked with black triangles, and those with an axial force retention of 50% or more and a tensile strength of 200 MPa or more. Is shown as ●.

In the alloy system A shown in FIG.
a% Al-b% Zn-c% R. E. FIG. In 1.0 ≦
a ≦ 3.0, 1.0 ≦ b ≦ 3.0, 0.5 ≦ c ≦ 4.
0, the range satisfying c ≦ a + b ≦ 1 / 2c + 4.0 is as follows:
Although the range surrounded by the square abcd in FIG. 8 was outside the range, the composition was x or black triangle, and the axial force retention was 50% or less or the tensile strength was 200 MPa or less.
On the other hand, the compositions in the range surrounded by the square abcd in FIG. 8 are all ●, and the axial force retention is 50% or more and the tensile strength is 200 MPa or more, confirming the effect of the present invention. Was done.

In the alloy system B shown in FIG.
a% Al-b% Zn-c% R. E. FIG. In 1.0 ≦
a ≦ 3.0, 1.0 ≦ b ≦ 3.0, 0.5 ≦ c ≦ 4.
0, the range satisfying c ≦ a + b ≦ 1 / 2c + 4.0 is as follows:
The range surrounded by the hexagonal abcdef in FIG. 9 is a cross or a black triangle with a composition outside this range, and the axial force retention was 50% or less or the tensile strength was 200 MPa or less. On the other hand, the compositions in the range surrounded by the hexagonal abcdef in FIG.
% And the tensile strength was 200 MPa or more, confirming the effect of the present invention.

In the alloy system C shown in FIG.
-A% Al-b% Zn-c% R. E. FIG. At 1.0
≦ a ≦ 3.0, 1.0 ≦ b ≦ 3.0, 0.5 ≦ c ≦ 4.
0, the range satisfying c ≦ a + b ≦ 1 / 2c + 4.0 is as follows:
Although the range surrounded by the square abcd in FIG. 10 was outside the range, the composition was x or black triangle, and the axial force retention was 50% or less or the tensile strength was 200 MPa or less. On the other hand, the compositions in the range enclosed by the square abcd in FIG. 10 are all ●, and the axial force retention is 50%.
As described above, the tensile strength was 200 MPa or more, and the effect of the present invention was confirmed.

In the alloy system D shown in FIG.
-A% Al-b% Zn-c% R. E. FIG. At 1.0
≦ a ≦ 3.0, 0.25 ≦ b ≦ 1.0, 0.5 ≦ c ≦
The range that satisfies 4.0 and c ≦ a + 1 is the range surrounded by the square abcd in FIG. 11, but the composition outside this range is × or a black triangle, and the axial force retention is 50%. Or a tensile strength of 200 MPa or less. On the other hand, the compositions in the range surrounded by the square abcd in FIG. 11 are all ●, the axial force retention is 50% or more, and the tensile strength is 200 MPa or more, confirming the effect of the present invention. Was done.

Example 2 A magnesium alloy having the chemical composition shown in Table 1 was melted, and a test piece was cast by cold chamber die casting. In addition, No. Alloy No. 1 is the alloy of the present invention. Alloy No. 2 is a comparative alloy containing Al and Zn in a larger amount than the composition range of the present invention. 3
The alloy is a conventional alloy corresponding to AZ91D.

FIG. 1 2 and 1 3 is a diagram obtained by replicating the optical microscope structure of the present invention alloys and comparative alloys. Comparative alloy, as shown in FIG. 1 2, because the cooling rate is large, there is a high concentration of solute atoms do not form a crystallized substances in the vicinity of the grain boundary region. It is considered that the presence of such a region promotes diffusion in the vicinity of the grain boundary and adversely affects high-temperature creep. In the present invention the alloy as shown in FIG. 1 3, Al and Z
Since such a region does not exist because the concentration of n is low, the high temperature creep characteristics are excellent.

The obtained test pieces were measured for tensile strength at room temperature, and subjected to a bolt loosening test at 150 ° C. for 300 hours. The results obtained are shown in Table 1 and FIG.
The results are shown in FIG.

[0030]

[Table 1]

As shown in Table 1 and FIG. 14, the comparative alloy had a tensile strength of 220 MPa, which is equivalent to that of the conventional alloy, but the bolt loosening caused by high-temperature creep was inferior, and the axial force retention was 30%. Was. AZ9 which is a conventional alloy
Since 1D was also manufactured by die casting, an axial force retention was 30% because there was a region near the grain boundaries where the concentration of solute atoms did not form a crystallized substance.

On the other hand, the alloy of the present invention has a tensile strength at room temperature of 220 MPa, which is almost equal to that of AZ91D, and the axial force retention at 150 ° C. for 300 hours is 70%, impairing the tensile properties. And high temperature creep characteristics could be improved.

Example 3 Mg-2% Al-2% Zn-
3% R. E. FIG. A magnesium alloy having a chemical composition in which the Mn content was changed in the range of 0 to 1.0% with respect to the alloy was melted, and a test piece was cast by cold chamber die casting. The obtained test piece was subjected to a bolt loosening test left in a furnace at 150 ° C. for 1 hour, and an initial axial force retention was measured. The obtained results are shown in FIG. 15 as a relationship diagram with the Mn content.

Next, Mg-2% Al-2% Zn-3%
R. E. FIG. Alloy and Mg-3% Al-2% Zn-3%
R. E. FIG. A magnesium alloy having a chemical composition in which the Mn content is changed in the range of 0 to 1.6% with respect to the alloy is melted, and r =
A casting crack test at 1.0 was performed to measure a casting crack occurrence rate. The obtained results are shown in FIG. 16 as a relationship diagram with the Mn content.

As is clear from the results shown in FIG. 15, the effect of improving the initial axial force reduction can be seen when the Mn content is 0.1% or more. The effect of improving the initial axial force reduction is 0.4%.
%, But as is clear from FIG. 16, when the Mn content further increases, the Mn-Al-R. E. FIG. It was found that a crystallized product was formed and a casting crack occurred. From the above results, it was confirmed that good results were obtained in the composition range of the Mn content of 0.1 to 1.0%.

[0036]

As described above, the heat-resistant magnesium alloy of the present invention has the general formula: Mg-a% Al-b% Zn-c
% R. E. FIG. Where 1.0 ≦ a ≦ 3.0, 0.25 ≦
b ≦ 3.0, 0.5 ≦ c ≦ 4.0 and 0.25 ≦ b ≦
1.0 satisfies c ≦ a + 1, and 0.1 ≦ b ≦ 3.
A satisfying c ≦ a + b ≦ 1 / 2c + 4.0 at 0
l, Zn and R.I. E. FIG. The aluminum concentration was limited to 1.0 to 3.0%, which is a concentration range in which no dendritic cell was formed, so that the creep resistance at 100 ° C. or higher could be improved. In addition, since 0.25 to 3.0% of zinc was added, the strength and tensile elongation from room temperature to 100 ° C. were ensured, and the castability was improved. Since 0.5 to 4.0% of the rare earth metal or neodymium was added, a high melting point crystallized substance was formed at the grain boundary, the grain boundary was strengthened, and the creep characteristics at 150 ° C. were improved. Furthermore, since 0.1 to 1.0% of Mn was added, the decrease in initial axial force was improved, and Mn was added to 0.2 to 0.3%.
%, The corrosion resistance was also improved.

[Brief description of the drawings]

FIG. 1 is a diagram showing the relationship between the Al content and the axial force retention in the alloy system of the present invention.

FIG. 2 is a diagram showing the relationship between the Al content and the rate of occurrence of casting cracks in the alloy system of the present invention.

FIG. 3 is a diagram showing the relationship between the Zn content and the axial force retention in the alloy system of the present invention.

FIG. 4 is a diagram showing the relationship between Zn content and tensile strength at room temperature in the alloy system of the present invention.

FIG. 5 is a graph showing the relationship between the Zn content and the tensile strength at 100 ° C. in the alloy system of the present invention.

FIG. 6 is a graph showing R.F. E. FIG. FIG. 3 is a diagram showing the relationship between the content and the axial force retention.

FIG. 7 is a graph showing R.F. E. FIG. It is a diagram which shows the relationship between content and tensile strength.

FIG. 8 is a diagram showing the tensile strength and the axial force holding force of the alloy system of the present invention containing 1.0% Zn.

FIG. 9 is a graph showing the tensile strength and the axial force holding force of the alloy system of the present invention containing 2.0% Zn.

FIG. 10 is a view showing the tensile strength and the axial force holding force of the alloy system of the present invention containing 3.0% of Zn.

FIG. 11 is a view showing the tensile strength and the axial force holding force of the alloy system of the present invention containing 0.25% of Zn.

FIG. 12 is a photomicrograph of a comparative alloy containing Al and Zn in a larger amount than the composition range of the present invention.

FIG. 13 is a simulated view of an optical microscope photograph of the alloy of the present invention.

FIG. 14 is a diagram showing the results of tensile creep tests of the alloys of the present invention, comparative alloys and conventional alloys.

FIG. 15 is a graph showing the relationship between the Mn content and the axial force retention in the alloy system of the present invention.

FIG. 16 is a diagram showing the relationship between the Mn content and the rate of occurrence of casting cracks in the alloy system of the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-33096 (JP, A) JP-A-6-172948 (JP, A) JP-A-62-283446 (JP, A) JP-A-5-83446 171333 (JP, A) WO 91/13181 (WO, A1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 23/00-23/04

Claims (2)

(57) [Claims] 1. General formula, Mg-a% Al-b% Zn-c
% R. E. FIG. (Where RE is a rare earth element): 1.0 ≦ a ≦ 3.0 0.25 ≦ b ≦ 3.0 0.5 ≦ c ≦ 4.0, and Mn; 0.2-0.3% by weight
When 0.25 ≦ b ≦ 1.0, c ≦ a + 1 and when 1.0 ≦ b ≦ 3.0, c ≦ a + b ≦ 1 / 2c + 4.0 (where a, b, and c are all by weight). A heat-resistant magnesium alloy characterized by excellent elongation and excellent strength properties. 2. The heat-resistant magnesium alloy according to claim 1, wherein the heat-resistant magnesium alloy contains 0.1 to 1.0% by weight of Mn.