JPH0941065A - High strength magnesium alloy and its production - Google Patents

Abstract

PURPOSE: To produce an Mg alloy high in strength and specific strength by preparing an Mg alloy composed of specified ratios of Mg, Ca, Zn, Y or the like and having a structure in which intermetallic compounds of Mg-Ca series or the like are finely dispersed into fine crystalline Mg mother phases. CONSTITUTION: In a fine Mg mother phase having a compsn. shown by the general formula: Mg100-a-b-c Caa Znb Xc [where X denotes one or >= two kinds of elements selected from Y, Ce, La, Nd, Pr, Sm and Mm (misch metal), and 0.5<=a<=5 atomic %, 0<b<=5 atomic %, 0<c<3 atomic % and 1<=a+b+c<=5 atomic %], and in which, in a fine Mg mother phases having 100 to 500nm average grain size blonging to nano crystals, one or >= two kinds among finer Mg-Ca series, Mg-Zn series and Mg-X series intermetallic compounds are uniformly dispersed is prepd. Thus, the Mg alloy small in grain size after plastic deformation can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high strength magnesium alloy and a method for producing the same, and more specifically to a technique for increasing the specific strength of a microcrystalline magnesium alloy.

[0002]

2. Description of the Related Art In JP-A-6-25805 and European Patent Publication 0503880, Mga Mb Alc X is disclosed.
d Ze (where M is La, Ce, and / or Mm (Misch metal), X is Ni and / Cu, Z is Mn, Z
n, Zr and / or Ti, a = 70 to 90 at%, b =
2-15 at%, d = 2-15 at%, e = 0.1-8
A high-strength heat-resistant amorphous magnesium alloy having a composition of at%, a + b + c + d + e = 100 at%) has been proposed. The tensile strength of this alloy is about 800-1000MP
It is a and has much higher strength than the conventional magnesium alloy. However, since the above magnesium alloy has an amorphous structure, its form is limited to foil and the like, and there is a problem in terms of practical use as various parts.

Further, Japanese Patent Application Laid-Open No. 4-99244 discloses a high strength magnesium alloy having a mixed phase structure of amorphous and crystalline. The alloy composition is X component (C
u, Ni, Sn, Zn, two or more kinds of elements selected as basic components, and M components (Al, Si, C) as optional components.
1 or 2 or more elements selected from a), Ln component (1 or 2 selected from Y, La, Ce, Nd, Sm)
More than one element or misch metal). In the Mga Xc Md Lne system, which is one of the composition systems, the content of each element is a = 40 to 95 at% and c = 1 to 35a.
t%, d = 1 to 25 at% and e = 3 to 25 at%. Since this alloy partially contains an amorphous structure, there are restrictions on processing into various parts, and there is a problem of embrittlement due to temperature.

A fine crystalline magnesium alloy containing no amorphous phase has been proposed in JP-A-3-47941. The alloy of this publication has a magnesium matrix (α
Phase) has a structure in which a stable or metastable intermetallic compound is uniformly and finely dispersed, and its composition is X component (Cu,
Ni (Sn, Zn, two or more elements selected from the basic elements), M (one or more elements selected from Al, Si, Ca), Ln (Y, La, Ce, Nd,
One or two or more kinds of elements selected from Sm) are arbitrarily added elements. Here, in the Mga Xc Md Lne system,
a = 40 to 95%, c = 1 to 35 at%, d = 1 to 25
at% and e = 3 to 25 at%.

The above-mentioned JP-A-3-47941 and JP-A-4-4791.
In JP 99244, the strength of a rapidly solidified ribbon is measured. On the other hand, although the bulk material is mentioned, the strength is not measured. On the other hand, Japanese Patent Laid-Open No. 3-9
The strength of the extruded material of the magnesium alloy proposed in Japanese Patent No. 0530 has been measured. In this example, Mg76
Proof strength of Al7 Zn1.5 Ca4.5 Nd1 alloy (0.2
%) Is 535 MPa, the tensile strength is 574 MPa, and the elongation is 4.7%. This alloy consists of Al2Ca, Mg22 (Al, Zn) in a matrix with an average grain size of 3μm or less.
Intermetallic compounds such as 49 are dispersed.

[0006]

The properties of the conventionally proposed fine crystalline high strength magnesium alloy are insufficient in the following points. (A) The content of elements such as Y, La and Nd is at least 3 at
%, The specific gravity of the magnesium alloy becomes large, and the advantage of magnesium that it is a light metal cannot be utilized (JP-A-3-47941). (B) A suitable composition for producing a bulk material is not shown (Japanese Patent Laid-Open No. 3-47941). That is,
If a large amount of Y, La, Nd, etc. is added, the workability deteriorates as the strength increases, so it is difficult to obtain the desired shape, and the total amount of heat applied during processing increases and crystal grain growth easily occurs. Become. (C) The average particle size of the bulk material matrix is 3 μm at maximum.
And is a coarse-grained material (JP-A-3-90530). Therefore, the strength is low and the elongation is low. (D) In a magnesium alloy (Japanese Patent Laid-Open No. 3-90530) that uses Al and Ca as intermetallic compound-forming elements, Mg-Al-based intermetallic compounds are formed.
The effect of improving strength is small. An object of the present invention is to provide a fine crystalline magnesium alloy that can solve these problems (a) to (d) individually or as a whole and a method for producing the same.

[0007]

The high strength magnesium alloy according to the present invention has the general formula: Mg100-abc Caa Zn
b Xc, where X is Y, Ce, La, Nd, Pr, Sm,
One or more elements selected from the group consisting of Mm (Misch metal), 0.5 ≦ a ≦ 5 atomic%, 0 <b ≦
5 atom%, 0 <c <3 atom%, 1 ≦ a + b + c ≦ 1
A structure in which one or more kinds of Mg-Ca-based, Mg-Zn-based, and Mg-X-based intermetallic compounds are finely dispersed in a matrix phase having a composition of 1 atomic% and having a fine crystalline structure. It is characterized by having.

The reasons for limiting the composition of the magnesium alloy of the present invention will be described below. Ca forms an intermetallic compound with Mg, and the compound uniformly finely disperses in a fine Mg mother phase to refine the crystal grains, and enhances strength and specific strength without impairing toughness. Since Mg has a lower specific gravity than Ca, it is particularly effective in maintaining high specific strength. C
If the content (a) of a is less than 0.5%, the effect of improving the specific strength is small, and if it exceeds 5 atomic%, alloying with Mg becomes difficult and embrittlement occurs. Therefore, the Ca content (b) must be in the range of 0.5 to 5 atomic%. The preferable Ca content is 1.0 to 3.0 atom%.

Zn contributes to the strength by forming a solid solution in the Mg crystal to strengthen the matrix solid solution and to form an age hardening precipitate such as Mg-Zn. When the Zn content (b) exceeds 5 atomic%, coarsening of precipitates occurs,
Since the strength decreases, it is necessary to make the content 5 atomic% or less.
The preferable Zn content (b) is 1 to 4 atomic%.

The X component makes the matrix phase of Mg fine and the intermetallic compound formed with Mg is fine Mg.
It is finely dispersed uniformly in the mother phase to enhance the strength without impairing the toughness, and further serves to maintain the fine grain size by fixing the grain boundaries during molding at high temperature. Among the X components, Ce and Y are particularly preferable. If the X component exceeds 3 atomic%, the specific gravity increases and the material tends to become brittle. Further, it becomes difficult to alloy with Mg and it is difficult to maintain a uniform structure of the rapid solidifying agent, so the X component needs to be less than 3 atomic%. The preferable content (c) of the X component is 0.
It is 5 to 2.5 atom%.

Other than the above components are impurities, particularly Cu,
Since the corrosion resistance of Ni, Fe, etc. is remarkably deteriorated, their amounts should be reduced as much as possible.

Total amount of Ca, Zn and X added (a + b +
When the amount of c) is large, the precipitated intermetallic compound becomes coarse and the material becomes brittle. On the other hand, if the amount is too small, the amount of precipitated intermetallic compound becomes insufficient and the strength of the material becomes insufficient. Therefore, 1 atomic% ≤
It is necessary to make the total amount of Ca, Zn and X components added within the range of a + b + c ≦ 11 atomic%. Preferably 2 atomic% ≤ a
+ B + c ≦ 10 atomic%.

Next, the structure of the magnesium alloy of the present invention will be described. A fine magnesium matrix phase having an average particle size of 100 to 500 nm, which is equivalent to that obtained by the liquid quenching method, preferably belongs to so-called nanocrystals, One or more finely divided Mg-Ca-based, Mg-Zn-based, and Mg-X-based intermetallic compounds are uniformly dispersed.

Further, in order to easily obtain a bulk material, it is desirable that the form of the alloy of the present invention is a powder formed into a desired shape and size. The powder can be made into a high strength material by densifying it to 99% or more of its true density by compression and plastic working.

It is possible to make the rapidly solidified alloy into an amorphous state and to form a microcrystalline structure by hot plastic working above the crystallization temperature, but it is not easy to control the working conditions. Is preferably a condition where the cooling rate is as high as possible so that a microcrystalline structure is substantially or completely obtained, for example, a cooling rate of 10 @ 5 DEG C./s or more.

By the rapid solidification method, an alloy having a fine grain size and a uniformly dispersed intermetallic compound can be obtained. This alloy enables superplastic forming by selecting the deformation conditions that simultaneously realize the combination of low flow stress and high ductility. By utilizing this superplastic deformation, the rapidly solidified Mg alloy can be formed into a complicated shape.

Mg94.5 produced under the conditions of Example 1 described later
The effect of strain rate on the tensile properties of Ca2.5 Zn2.5 Y0.5 extruded alloy was evaluated by a tensile test at a test temperature of 300 ° C. and a strain rate of 2 × 10 −4 to 2 × 10 0 / sec. As shown in FIG. From Figure 1, strain rate 2 x
It can be seen that a high elongation of 100% or more occurs in the range of 10 @ -4 to 2.times.10@0 / sec and exhibits superplastic behavior (elongation> 100%).

[0018]

As described in claim 1, by limiting the Mg, Zn, Ca, and X components and forming a structure in which a specific intermetallic compound is finely dispersed in a fine matrix, high strength and high specific strength magnesium can be obtained. An alloy can be obtained. In particular, by setting the upper limit of the X component to <3 atomic%, it is possible to reduce the specific gravity of the magnesium alloy and provide an alloy having a specific strength (TYS) of 3 or more (problem (a),
(D)).

The average particle size of the mother phase is 100
The strength can be increased by making the thickness to be about 500 nm smaller than that of the prior art (problem (C)).

With the alloy composition of the present invention, it is possible to obtain a bulk material having high strength because crystal grain growth hardly occurs during the production of the bulk material (claim 3, problem (b)).

When the alloy having the microcrystalline structure of the present invention is formed by hot plastic working, a material having high strength and specific strength can be easily manufactured (claims 4 to 8, problem (c)). The present invention will be described below with reference to examples.

[0022]

【Example】

Example A Mg alloy having a chemical composition shown in Table 1 was melted by high frequency in an Ar atmosphere to melt a mother alloy. After melting this mother alloy at 850 ° C. in a high frequency furnace in an Ar atmosphere, Ar gas pressure was set to 9.
Atomized powder made of fine crystalline metal was obtained by a high pressure gas injection method of 8 MPa. A powder obtained by classifying the obtained powder to 25 μm or less, which is more rapidly cooled and has smaller precipitated particles and a larger solute solid solution amount, has a temperature of 250 to 350 ° C.,
Extrusion was carried out at an extrusion ratio of 10: 1, diameter 6 mm, length 27
A 0 mm columnar material was obtained. The atmosphere to which the powder was exposed during the steps from the preparation of the powder to the extrusion was a high cleanliness atmosphere in which both oxygen and water concentrations were 1 ppm or less. X-ray diffraction of the columnar material revealed that the intermetallic compounds shown in Table 1 were Mg.
Observed with phase. Further, the grain size of the Mg mother phase is about 100-
500 nm, particle size of intermetallic compound is about 20 to 100 n
m, and it was observed by TEM that fine intermetallic compounds were dispersed in the fine matrix. Next, the columnar material was subjected to a tensile test by an Instron type tensile tester. The results are shown in Table 2. The tensile strength of the Mg alloy of the present invention is 4 in terms of proof stress.
The strength was 50 MPa or more, which was higher than that of the commercial Mg alloy. Furthermore, in specific intensity (σ 0.2 / ρ), 2.8 × 10
5 N ・ m ・ kg-1 or more, A7075 or Ti-6Al-
The value was higher than 4V.

[0023]

[Table 1] Composition Extrusion temperature N0. (At%) (° C) Intermetallic compound phase 1 Mg97.8Ca1 Zn1 Ce0.2 250 Mg2Ca, MgZn, Mg12Ce 2 Mg96.3Ca1 Zn2.5 Ce0.2 250 Mg2Ca, MgZn, Mg12Ce 3 Mg94.5Ca2.5 Zn2.5 Y0.5 250 Mg2Ca, MgZn, Mg24 Y5 4 Mg94.5Ca1 Zn2 Mm2.5 350 Mg2Ca, MgZn, Mg12Ce, Mg17La2, Mg12Nd 5 Mg94Ca2.5 Zn1 Y2.5 300 MgnCa, Mg2Ca, Mg2Ca, Mg2Ca, Mg2Ca , Mg24Y5 6 Mg90Ca2.5 Zn5 Y2.5 300 Mg2Ca, MgZn, Mg24Y5 7 Mg97.5Ca1 Zn1 La0.5 300 Mg2Ca, MgZn, Mg17La2 8 Mg91.5Ca2.5 Z 5 Nd1 300 Mg2Ca, MgZn, Mg9Nd9Mg12Nd 5 Z 5 Pr1 300 Mg2Ca, MgZn, Mg12Pr 10 Mg91.5Ca2.5 Zn5 Sm1 300 Mg2Ca, MgZn, Mg6.2Sm

[0024]

[Table 2] Density Strength yield ratio Specific strength σ0.2 σ0.2 / ρ No. Composition (at%) (ρ) (MPa) (%) ( 105N ・ m ・ kg-1) 1 Mg97.8Ca1Zn1Ce0.2 1.79 510 4.0 2.85 2 Mg96.3Ca1Zn2.5Ce0.2 1.84 540 2.0 2.93 3 Mg94.5Ca2.5Zn2.5Y0.5 1.84 610 1.0 3.32 4 Mg94.5Ca1Zn2Mm2.5 1.99 635 1.0 3.19 5 Mg94Ca2.5Zn1Y2.5 1.86 605 2.0 3.25 6 Mg90Ca2 .5Zn5Y2.5 2.00 625 3.0 3.13

Comparative Example 1 By the same method as in Example 1, No. Table 3 shows the results of measuring the characteristics of the extruded material samples 11 to 17 prepared.

[0026]

[Table 3] Extrusion Density Hardness UTS Elongation Specific Strength Temperature (UTS / No. Composition (at%) (℃) (ρ ) (Hv ) (MPa) ( %) ρ) 11 Mg91.5Ca7.5Zn1 350 1.75 130 380 0 2.17 12 Mg91 .5Ca7.5Y1 350 1.75 160 310 0 1.77 13 Mg85Ca1Zn10Mm4 350 2.39 279 120 0 0.50 14 Mg87Ca7.5Zn2.5Y3 350 1.91 165 280 0 1.47 15 Mg85Ca5Zn5Ce5 350 2.25 220 100 0 0.44 16 Mg84Ca1Zn10Ce5 350 2.46 210 130 0 0.53 17La82Ca1 180 230 0 0.95 Note) Since the material has no elongation, UTS was used to calculate the specific strength.

Sample No. Nos. 11 to 12 have a large amount of added Ca and are brittle. Sample No. 13-15 have a melt mass of 12a
Since it is as large as t% or more, the dispersed intermetallic compound is coarsened and becomes brittle. In addition, the sample No. 16 and 17 are materials in which an amorphous phase is partially mixed. In this material, the intermetallic compound becomes coarse after crystallization due to the large amount of melt, and becomes brittle. The materials of Comparative Examples were all very brittle, showing high hardness but not showing plastic elongation.

Table 4 shows the characteristics of typical conventional Mg alloys, Al alloys and Ti alloys.

[0029]

[Table 4] Density Proof strength Elongation ratio Strength σ0.2 σ0.2 / ρ No. Composition (at%) (ρ) (MPa) (%) (105N ・ m ・ kg-1) 18 A791-T6 (Mg alloy) 1.83 130 5.0 0.7 19 A7075-T6 (Al alloy) 2.80 500 9.0 1.8 20 Ti-6Al-4V (Ti alloy) 4.46 1100 10 2.5

Material Database Metallic Materials: Nikkan Kogyo Shimbun (First Edition) (1989) 1571 Light Metal Association, Aluminum Handbook (4th Edition)
Japan Light Metal Society (1990) 35 Japan Institute of Metals, Metal Handbook (Revised 5th Edition) Maruzen (199)
1) 639

[0031]

As described above, according to the present invention, Mg
Ca with lower specific gravity, Y with a lower limit of 3 atomic%
Since it is possible to obtain a microcrystalline magnesium alloy in which an intermetallic compound is finely distributed in a fine Mg matrix phase while strengthening magnesium with an X component such as Zn and Zn, a material having high strength and specific strength is provided, and a bulk material is further provided. It is also easy to

[Brief description of drawings]

[Fig. 1] The relationship between strain rate, flow stress and elongation is Mg9
4 is a graph showing a 4.5Ca2.5 Zn2.5Y0.5 alloy.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 000003207 Toyota Motor Corporation 1 Toyota Town, Toyota City, Aichi Prefecture (72) Inventor Ken Masumoto 3-8-22 Uesugi, Aoba-ku, Sendai City, Miyagi Prefecture (72) Inventor Akihisa Inoue Banuchi, Kawauchi, Aoba-ku, Sendai-shi, Miyagi 11-806 (72) Inventor Hidehiko Horikiri 1-9-9 Yaesu, Chuo-ku, Tokyo Imperial Piston Ring Co., Ltd. (72) Akira Kato Toyota, Aichi Prefecture City Toyota-City, Toyota City

Claims (8)

[Claims] 1. A general formula: Mg100-abc Caa Znb X
c, where X is Y, Ce, La, Nd, Pr, Sm, Mm
One or more elements selected from the group consisting of (Misch metal), 0.5 ≦ a ≦ 5 atomic%, 0 <b ≦ 5 atomic%, 0 <c <3 atomic%, where 1 ≦ a + b + c ≦ One or two or more of Mg-Ca-based, Mg-Zn-based and Mg-X-based intermetallic compounds having a composition of 11 atomic% and finely crystalline matrix are finely dispersed. A high-strength magnesium alloy having the specified structure. 2. The high strength magnesium alloy according to claim 1, wherein the average grain size of the matrix phase is 100 to 500 nm. 3. The high-strength magnesium alloy according to claim 1, wherein the powder is compressed and plastically worked into a bulk material having a density of 99% or more of the true density. 4. A method for producing a high-strength magnesium alloy, which comprises rapidly solidifying a molten alloy having the composition of claim 1 and then subjecting it to hot plastic working. 5. The method for producing a high-strength magnesium alloy according to claim 4, wherein the rapid solidification is carried out under the condition that the solidified alloy is substantially composed of fine crystals. 6. The method for producing a high-strength magnesium alloy according to claim 5, wherein the hot working is performed in a temperature and strain rate range where superplastic deformation is brought about. 7. The method for producing a high-strength magnesium alloy according to claim 4, wherein the rapid solidification is performed by atomizing the molten alloy. 8. A strain rate of 1 × 10 −3 to 5 × 10 2 /
The method for producing a high-strength magnesium alloy according to claim 6, wherein hot working is performed under the condition of s.