U.S. patent application number 11/235229 was filed with the patent office on 2006-03-30 for magnesium alloy and production process thereof.
This patent application is currently assigned to Kumamoto University. Invention is credited to Yuuichi Ienaga, Yoshihito Kawamura, Ei Kozono, Takeshi Yamaguchi.
Application Number | 20060065332 11/235229 |
Document ID | / |
Family ID | 35063037 |
Filed Date | 2006-03-30 |
United States Patent
Application |
20060065332 |
Kind Code |
A1 |
Ienaga; Yuuichi ; et
al. |
March 30, 2006 |
Magnesium alloy and production process thereof
Abstract
Provided are a magnesium alloy which is inexpensive, can be
produced at a high yield, and has both high strength and high
ductility; and a production process of the magnesium alloy. The
magnesium alloy contains from 1 to 4 atomic % of Zn and from 1 to
4.5 atomic % of Y at a Zn/Y composition ratio ranging from 0.6 to
1.3, and contains both an intermetallic compound
Mg.sub.3Y.sub.2Zn.sub.3, and Mg.sub.12YZn having a long period
structure. It may contain from 2 to 3.5 atomic % of Zn and from 2
to 4.5 atomic % of Y at a Zn/Y composition ratio falling within a
range of from 0.8 to 1.2. It may contain from 1 to 4 atomic % of
Zn, from 1 to 4.5 atomic % of Y and from 0.1 to 0.5 atomic % of Zr
and contains, as a remaining portion, Mg and inevitable impurities.
An alloy structure having both an intermetallic compound
Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn having a long period
structure is available by casting an Mg alloy containing from 1 to
4 atomic % of Zn and from 1 to 4.5 atomic % of Y at a Zn/Y
composition ratio ranging from 0.6 to 1.3, followed by plastic
processing.
Inventors: |
Ienaga; Yuuichi; (Wako-shi,
JP) ; Kawamura; Yoshihito; (Kumamoto-shi, JP)
; Kozono; Ei; (Tamana-gun, JP) ; Yamaguchi;
Takeshi; (Hiroshima-shi, JP) |
Correspondence
Address: |
ARENT FOX PLLC
1050 CONNECTICUT AVENUE, N.W.
SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
Kumamoto University
Honda Motor Co., Ltd.
Kyushu Fujisash Co., Ltd.
The Japan Steel Works, Ltd.
|
Family ID: |
35063037 |
Appl. No.: |
11/235229 |
Filed: |
September 27, 2005 |
Current U.S.
Class: |
148/557 ;
148/667; 420/411 |
Current CPC
Class: |
C22C 23/06 20130101;
C22F 1/06 20130101; C22C 23/04 20130101 |
Class at
Publication: |
148/557 ;
148/667; 420/411 |
International
Class: |
C22C 23/04 20060101
C22C023/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2004 |
JP |
2004-280878 |
Claims
1. A magnesium alloy, which comprises, based on a total alloy
amount, from 1 to 4 atomic % of Zn and from 1 to 4.5 atomic % of Y
at a Zn/Y composition ratio falling within a range of from 0.6 to
1.3, and includesv an intermetallic compound
Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn having a long period
structure.
2. A magnesium alloy according to claim 1, which comprises at least
3 atomic % of Zn and at least 3 atomic % of Y, each based on a
total alloy amount, and as a remaining portion Mg and inevitable
impurities.
3. A magnesium alloy according to claim 1, which comprises from 2
to 3.5 atomic % of Zn and from 2 to 4.5 atomic % of Y, each based
on a total alloy amount, at a Zn/Y composition ratio falling within
a range of from 0.8 to 1.2.
4. A magnesium alloy according to claim 3, which comprises at least
3 atomic % of Zn and at least 3 atomic % of Y, each based on a
total alloy amount, and as a remaining portion Mg and inevitable
impurities.
5. A magnesium alloy according to claim 1, which comprises from 1
to 4 atomic % of Zn, from 1 to 4.5 atomic % of Y, and from 0.1 to
0.5 atomic % of Zr, each based on a total alloy amount, and as a
remaining portion Mg and inevitable impurities.
6. A production process of a magnesium alloy, which comprises
casting an Mg alloy comprising from 1 to 4 atomic % of Zn and from
1 to 4.5 atomic % of Y at a Zn/Y composition ratio falling within a
range of from 0.6 to 1.3; and plastic processing of the cast
product obtained in the above-described step into an alloy
structure containing an intermetallic compound
Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn having a long period
structure.
7. A production process of a magnesium alloy according to claim 6,
which comprises at least 3 atomic % of Zn and at least 3 atomic %
of Y, each based on a total alloy amount, and as a remaining
portion Mg and inevitable impurities.
8. A production process of a magnesium alloy according to claim 6,
which comprises from 2 to 3.5 atomic % of Zn and from 2 to 4.5
atomic % of Y, each based on a total alloy amount, at a Zn/Y
composition ratio falling within a range of from 0.8 to 1.2.
9. A production process of a magnesium alloy according to claim 8,
wherein the magnesium alloy contains at least 3 atomic % of Zn and
at least 3 atomic % of Y, each based on a total alloy amount and
contains as a remaining portion Mg and inevitable impurities.
10. A production process of a magnesium alloy according to claim 6,
wherein the magnesium alloy contains from 1 to 4 atomic % of Zn,
from 1 to 4.5 atomic % of Y and from 0.1 to 0.5 atomic % of Zr,
each based on a total alloy amount and contains as a remaining
portion Mg and inevitable impurities.
11. A production process of a magnesium alloy according to claim 6,
wherein the casting is performed at a cooling rate of 10 K/sec or
less.
12. A production process of a magnesium alloy according to claim 6,
wherein the plastic processing is carried out by extrusion of the
cast product.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a magnesium alloy having
both high strength and high ductility; and a production process
thereof.
[0003] 2. Description of the Related Art
[0004] Since magnesium is lighter in weight than iron or aluminum,
its use as a light-weight substitute for members made of an iron
steel material or aluminum alloy material is under investigation.
Ordinary magnesium alloys have, however, lower strength than the
other metal structure materials such as iron steel, aluminum alloy
and titanium alloy. An AZ91 material for die casting, which is said
to have relatively high strength, has strength as low as 160 MPa.
In addition, industrial parts are required to have, at a moving
part thereof, a percent elongation of at least 4 to 5%, but
ordinary magnesium alloys do not have sufficient ductility. Even
the above-described AZ91 material has a percent elongation of only
about 3%.
[0005] A variety of magnesium alloys equipped with both high
strength and high ductility have so far been proposed.
[0006] For example, known is a magnesium alloy having a composition
represented by the formula: Mg.sub.100-a-b-cCa.sub.aZn.sub.bX.sub.c
(wherein, X represents one or more than one elements selected from
the group consisting of Y, Ce, La, Nd, Pr, Sm and Mm (misch metal);
and 0.5.ltoreq.a.ltoreq.5 atomic %, 0<b.ltoreq.5 atomic %, and
0<c.ltoreq.3 atomic % with the proviso that
1.ltoreq.a+b+c.ltoreq.11 atomic %), and having a structure in which
one or more of Mg--Ca, Mg--Zn and Mg--X intermetallic compounds
have been finely dispersed in a Mg mother phase composed of a fine
crystalline material. The above-described magnesium alloy having
intermetallic compound(s) can be obtained as a high strength
magnesium alloy in the powder form by rapid solidification of a
molten alloy having the above-described composition by atomization
or the like method. It can be molded or formed into even complex
shaped products by hot plastic processing (refer to Japanese Patent
Laid-Open No. 41065/1997).
[0007] Also known is a magnesium alloy having a composition
represented by the formula: Mg.sub.100-a-bLn.sub.aM.sub.b (wherein,
M is one or more elements selected from Al and Zn; Ln is one or
more elements selected from Y, Ce, La, Nd, Pr, Pm, Sm, Eu, Gd, Tb,
Dy, Ho, Er, Tm, Yb, Lu and Mm (misch metal), or a mixture of rare
earth elements; and 0.5.ltoreq.a.ltoreq.5 atomic %, and
0.2.ltoreq.b.ltoreq.4 atomic %, with the proviso that
1.5.ltoreq.a+b.ltoreq.7 atomic %); having a crystal grain size less
than 2,000 nm; and having a long period hexagonal structure in a
part or whole region of the crystals. The above-described magnesium
alloy having a long period hexagonal structure can be prepared as a
high strength and high ductility magnesium alloy in the powder form
by rapid solidification of a molten alloy having the
above-described composition by atomization or the like method. By
subjecting the resulting powder to plastic processing at an
extrusion ratio of from 3 to 20, extrusion goods made of the
magnesium alloy can be obtained (refer to Japanese Patent Laid-Open
No. 2002-256370).
[0008] The above-described magnesium alloys however have a
drawback: a yield at the time of rapid solidification of the molten
alloy is low, which inevitably leads to a cost rise when the powder
obtained by rapid solidification is molded or formed.
[0009] The above-described magnesium alloys each has a percent
elongation not greater than 5%, which is almost a limit value when
they are used for moving portions of industrial parts. Thus, they
do not have sufficient ductility. The industrial parts using the
above-described magnesium alloys therefore have a drawback: design
freedom is greatly limited and they are not suited for practical
use.
[0010] The magnesium alloy having a long period hexagonal
structure, on the other hand, is said so that it could be formed
into a molded product by casting using a copper mold with a large
cooling rate. When the copper mold is used, however, molded
products thus obtained must be relatively small in order to raise
its cooling rate. Thus, this magnesium alloy has a drawback that
any size of a molded product cannot be produced freely.
SUMMARY OF THE INVENTION
[0011] An object of the present invention is to overcome the
above-described drawbacks and provide a magnesium alloy which is
inexpensive, has a good yield, can be molded or formed into any
size, and has both high strength and high ductility; and a
production method of the magnesium alloy.
[0012] With a view to attaining the above-described object, the
magnesium alloy of the present invention comprises from 1 to 4
atomic % of Zn and from 1 to 4.5 atomic % of Y, each based on the
total amount, at a Zn/Y composition ratio falling within a range of
from 0.6 to 1.3, and further comprises Mg.sub.3Y.sub.2Zn.sub.3
which is an intermetallic compound and Mg.sub.12YZn having a long
period structure.
[0013] Since the magnesium alloy according to the present invention
has, as well as the above-described composition, both the
intermetallic compound Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn
having a long period structure, it is able to have both high
strength and high ductility. Either one of or both of strength and
ductility become insufficient when the content of Zn is less than 1
atomic % or exceeds 4 atomic % and that of Y is less than 1 atomic
% or exceeds 4.5 atomic %, based on the total amount of the
magnesium alloy.
[0014] Even if Zn and Y both satisfy the above-described ranges
based on the total amount of the magnesium alloy, either one or
both of strength and ductility becomes insufficient when the
magnesium alloy is free of either one or both of the intermetallic
compound Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn having a long
period structure.
[0015] In addition, the magnesium alloy of the present invention is
required to satisfy the Zn/Y composition ratio which falls within a
range of from 0.6 to 1.3 in order to incorporate both the
intermetallic compound Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn
having a long period structure in the alloy without failure. When
the Zn/Y composition ratio is less than 0.6 or exceeds 1.3, the
magnesium alloy does not always contain either one or both of the
intermetallic compound Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn
having a long period structure.
[0016] It is known in a rapidly solidified Mg--Zn--Y alloy that an
alloy of MgZ.sub.nY.sub.x (X=2 to 4) in which the concentration of
Y>the concentration of Zn has an increased long period structure
as the concentration of Y becomes greater; in the case of an alloy
of MgZn.sub.xY (X=2 to 4) in which the concentration of Zn>the
concentration of Y, heat treatment of it causes precipitation of
the intermetallic compound Mg.sub.3Y.sub.2Zn.sub.3; and an alloy of
MgZn.sub.xY.sub.x (X=1 to 4) in which the concentration of Y=the
concentration of Zn, that is, an equiatomic alloy is heat treated
to generate the long period structure (refer to: Masayuki Nagano,
Minoru Nishida, and Yoshihito Kawamura, "Influences of
concentrations of Zn and Y and heat treatment on the structure
formation of rapidly solidified Mg--Zn--Y alloy", Collected
Abstracts of the 2003 meeting of the Japan Institute of Metals, The
Japan Institute of Metals, p 187).
[0017] According to the investigation by the present inventors,
however, no intermetallic compound Mg.sub.3Y.sub.2Zn.sub.3 exists
in each of the alloy in which the concentration of Y>the
concentration of Z and the equiatomic alloy in which the
concentration of Y=the concentration of Zn, while no long period
structure exists in the alloy in which the concentration of
Zn>the concentration of Y. Accordingly, the long period
structure and intermetallic compound Mg.sub.3Y.sub.2Zn.sub.3 do not
exist simultaneously in the rapidly solidified Mg--Zn--Y alloy.
[0018] The magnesium alloy of the present invention preferably
contains from 2 to 3.5 atomic % of Zn and from 2 to 4.5 atomic % of
Y, each based on the total amount, at a Zn/Y composition ratio
falling within a range of from 0.8 to 1.2, in order to have both
higher strength and higher ductility.
[0019] The magnesium alloy of the present invention may contain
from 1 to 4 atomic % of Zn and from 1 to 4.5 atomic % of Y, based
on the total amount, and contain, as a remaining portion, Mg and
inevitable impurities. Alternatively, it may contain from 0.1 to
0.5 atomic % of Zr, based on the total amount, and contain as a
remaining portion Mg and inevitable impurities.
[0020] Incorporation of Zr in the magnesium alloy of the present
invention within the above-descried range enables to impart a
miniaturized alloy structure to the magnesium alloy.
Miniaturization effect of the alloy structure cannot be attained
when the content of Zr is less than 0.1 atomic % based on the total
alloy amount. On the other hand, when the content of Zr exceeds 0.5
atomic % based on the total alloy amount, formation of the
intermetallic compound Mg.sub.3Y.sub.2Zn.sub.3 is sometimes
disturbed.
[0021] The magnesium alloy of the present invention is able to have
higher strength by the addition, to the above-described
composition, of a small amount of at least one element selected
from the group consisting of La, Ce, Nd, Sm and Yb. Moreover, the
magnesium alloy of the present invention can be obtained as a
composite by adding a reinforcing material such as fibers and
particles.
[0022] The magnesium alloy of the present invention can be produced
by a process comprising casting an Mg alloy containing from 1 to 4
atomic % of Zn and from 1 to 4.5 atomic % of Y, each based on the
total amount, at a Zn/Y composition ratio falling within a range of
from 0.6 to 1.3; and plastic processing of the cast product
obtained in the above-described step into an alloy structure
containing an intermetallic compound Mg.sub.3Y.sub.2Zn.sub.3 and
Mg.sub.12YZn having a long period structure.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Embodiments of the present invention will hereinafter be
described more specifically.
[0024] In this Embodiment, a material containing from 1 to 4 atomic
% of Zn and from 1 to 4.5 atomic % of Y, each based on the total
alloy amount, at a Zn/Y composition ratio falling within a range of
from 0.6 to 1.3, preferably further containing from 0.1 to 0.5
atomic % of Zr and, as a remaining portion, Mg and inevitable
impurities is charged in a carbon crucible. In an argon atmosphere,
the material is melted in a high-frequency melting furnace, for
example, at 700.degree. C. to yield a molten alloy.
[0025] The molten alloy is poured into a mold, followed by casting.
A cooling rate during the casting is preferably 10 K/sec or less.
This cooling rate is much lower than that of atomization method or
twin-roll method employed for rapid solidification, that is,
10.sup.4 K/sec or greater. It is also much lower than that of roll
casting method or quenched copper mold method, that is, 10.sup.3 to
10.sup.2 K/sec. In this Embodiment, ordinarily employed molds such
as metal mold, graphite mold and sand mold can be used for casting
and a copper mold or water-cooled copper mold is not necessary,
which leads to a reduction in the production cost.
[0026] The cast product thus obtained is subjected to plastic
processing, whereby a molded or formed product can be obtained. The
molded or formed product is a magnesium alloy containing from 1 to
4 atomic % of Zn and from 1 to 4.5% of Y, based on the total alloy
amount, at a Zn/Y composition ratio falling within a range of from
0.6 to 1.3. Preferably, it further contains from 0.1 to 0.5 atomic
% of Zr and as a remaining portion Mg and inevitable impurities. It
contains both an intermetallic compound Mg.sub.3Y.sub.2Zn.sub.3 and
Mg.sub.12YZn having a long period structure. As a result, the
molded or formed product is able to have both high strength and
high ductility.
[0027] Examples, Comparative examples and Referential Examples of
the present invention will next be described.
EXAMPLES
[0028] In Examples, materials containing, based on the total alloy
amount, from 1 to 4 atomic % of Zn and from 1 to 4.5 atomic % of Y
at a Zn/Y composition ratio falling within a range of from 0.6 to
1.3, preferably further containing from 0.1 to 0.5 atomic % of Zr,
and, as a remaining portion, Mg and inevitable impurities, which
materials were however different from each other with their amounts
of Zn, Y and Zr varied within the above-described ranges were
charged in a carbon crucible. In an argon atmosphere, the materials
were melted in a high-frequency melting furnace, for example, at
700.degree. C. The molten alloys thus obtained were poured into
metal molds, followed by casting at a cooling rate not greater than
10K/sec, whereby rod materials were obtained. The rod materials
were heated to a temperature range of from 350 to 450.degree. C. in
an electric furnace, and then extruded at an extrusion ratio of 10,
whereby extrusion goods were obtained.
[0029] The metal structure of each of the resulting extrusion goods
was identified by X-ray diffraction and transmission electron
microscope, whereby the presence or absence of an intermetallic
compound Mg.sub.3Y.sub.2Zn3 and Mg.sub.12YZn having a long period
structure was confirmed. Test pieces were cut from the extrusion
goods. Their 0.2% proof stress, tensile strength and elongation
were measured by conducting a tensile test on them at normal
temperature. The results are shown in Table 1.
COMPARATIVE EXAMPLES
[0030] In Comparative Examples, in a similar manner to that
employed for the above-described Examples except that materials
containing, each based on the total alloy amount, from 0.5 to 5
atomic % of Zn and from 0.5 to 5 atomic % of Y and containing, as a
remaining portion, Mg and inevitable impurities, which materials
were however different from each other with their amounts of Zn and
Y varied within the above-described ranges were used, rod materials
were obtained. The rod materials were extruded as in the
above-described Examples, whereby extrusion goods were
obtained.
[0031] The metal structure of each of the resulting extrusion goods
was identified by X-ray diffraction and transmission electron
microscope, whereby the presence or absence of an intermetallic
compound Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn having a long
period structure was confirmed. Test pieces were cut from the
extrusion goods. Their 0.2% proof stress, tensile strength and
elongation were measured by conducting a tensile test on them at
normal temperature. The results are shown in Table 1.
REFERENTIAL EXAMPLES
[0032] In Referential Examples, a metal structure of known
magnesium alloys, that is, WE54-T6 material and AZ91 material was
identified by X-ray diffraction and a transmission electron
microscope, whereby the presence or absence of an intermetallic
compound Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn having a long
period structure was confirmed. Test pieces were cut from the
WE54-T6 material and AZ91 material, respectively. Their 0.2% proof
stress, tensile strength and elongation were measured by conducting
a tensile test on them at normal temperature. The results are shown
in Table 1. TABLE-US-00001 TABLE 1 Intermetallic Long-period 0.2%
Proof Tensile Zn Y Zr Extrusion Compound phase stress strength
Elongation (at %) (at %) (at %) Zn/Y at (.degree. C.)
Mg.sub.3Y.sub.2Zn.sub.3 Mg.sub.12YZn (MPa) (MPa) (%) Example 1 2 2
-- 1 350 .smallcircle. .smallcircle. 395 429 10.2 Example 2 2 2 --
1 375 .smallcircle. .smallcircle. 415 446 7.8 Example 3 2 2 0.2 1
350 .smallcircle. .smallcircle. 405 465 8.5 Example 4 2 2 0.2 1 400
.smallcircle. .smallcircle. 425 471 8.5 Example 5 3 3 -- 1 450
.smallcircle. .smallcircle. 430 487 7.5 Example 6 3 3.5 -- 0.86 450
.smallcircle. .smallcircle. 440 492 6 Example 7 3.5 3 -- 1.17 350
.smallcircle. .smallcircle. 425 490 7.5 Example 8 3.5 3.5 -- 1 350
.smallcircle. .smallcircle. 450 523 4.5 Example 9 2.5 3 -- 0.83 350
.smallcircle. .smallcircle. 407 485 9 Example 10 2 3 -- 0.67 350
.smallcircle. .smallcircle. 370 447 8.3 Example 11 2.5 4 -- 0.63
450 .smallcircle. .smallcircle. 370 450 6 Example 12 1.5 1.5 -- 1
350 .smallcircle. .smallcircle. 374 417 7.7 Example 13 1 1 -- 1 350
.smallcircle. .smallcircle. 373 392 10.3 Example 14 2 2 -- 1.3 400
.smallcircle. .smallcircle. 377 402 5.1 Comparative Example 1 0.5 2
-- 0.25 400 x .smallcircle. 278 329 8.2 Comparative Example 2 1 2
-- 0.5 350 x .smallcircle. 375 420 4 Comparative Example 3 1 3 --
0.33 350 x .smallcircle. 418 440 2 Comparative Example 4 4 2 -- 2
450 .smallcircle. x 288 338 10.6 Comparative Example 5 5 3 -- 1.67
450 .smallcircle. x 376 383 2.5 Comparative Example 6 3 5 -- 0.6
450 x .smallcircle. 348 451 2.6 Comparative Example 7 0.5 0.5 -- 1
350 x .smallcircle. 323 341 12 Comparative Example 8 5 5 -- 1 450
.smallcircle. .smallcircle. 457 477 0.3 Referential Example 1
WE54-T6 material -- -- x x 172 250 2 Referential Example 2 AZ91
material -- -- x x 160 230 3 Intermetallic compound
Mg.sub.3Y.sub.2Zn.sub.3: .smallcircle. when it is contained, x when
it is not contained Long-period phase Mg.sub.12YZn: .smallcircle.
when it is contained, x when it is not contained
[0033] From Table 1, it is apparent that the magnesium alloys
obtained in Examples 1 to 14 containing, based on the total alloy
amount, from 1 to 4 atomic % of Zn and from 1 to 4.5 atomic % of Y
at a Zn/Y composition ratio falling within a range of from 0.6 to
1.3, and containing both an intermetallic compound
Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn having a long period
structure have both high strength and high ductility, because they
are markedly superior to known WE54-T6 material and AZ91 material
in each of strength (0.2% proof stress, tensile strength) and
ductility (elongation).
[0034] Compared with the magnesium alloys obtained in Examples,
those obtained in Comparative Examples 1 to 5 containing Zn and Y
at a Zn/Y composition ratio outside the range of from 0.6 to 1.3
have only either one of the intermetallic compound
Mg.sub.3Y.sub.2Zn.sub.3 or Mg.sub.12YZn having a long period
structure, suggesting that they are not equipped sufficiently with
either one or both of strength and ductility. It is apparent that
the magnesium alloy obtained in Comparative Example 6 which
contained Y in an amount exceeding the invention range of from 1 to
4.5 atomic % does not have the intermetallic compound
Mg.sub.3Y.sub.2Zn.sub.3 so that it does not have sufficient
ductility. It is also apparent that the magnesium alloy obtained in
Comparative Example 7 containing Zn in an amount less than the
invention range of from 1 to 4 atomic % and Y in an amount less
than the invention range of from 1 to 4.5 atomic % does not have
the intermetallic compound Mg.sub.3Y.sub.2Zn.sub.3 so that it does
not have sufficient strength. It is also apparent that the
magnesium alloy obtained in Comparative Example 8 containing Zn in
an amount exceeding the invention range of from 1 to 4 atomic % and
Y in an amount exceeding the invention range of from 1 to 4.5
atomic % contains both the intermetallic compound
Mg.sub.3Y.sub.2Zn.sub.3 and Mg.sub.12YZn having a long period
structure but it does not have sufficient ductility.
* * * * *