U.S. patent application number 10/748166 was filed with the patent office on 2004-08-12 for high strength mg based alloy and mg based casting alloy and article made of the alloy.
Invention is credited to Abe, Teruyoshi, Hirane, Teruo, Nakamura, Kiyomi, Uchida, Toshio.
Application Number | 20040154703 10/748166 |
Document ID | / |
Family ID | 18367490 |
Filed Date | 2004-08-12 |
United States Patent
Application |
20040154703 |
Kind Code |
A1 |
Nakamura, Kiyomi ; et
al. |
August 12, 2004 |
High strength Mg based alloy and Mg based casting alloy and article
made of the alloy
Abstract
A high strength Mg based alloy and a Mg based casting alloy
having a good fluidity and a good mechanical property, and are used
to provide a molded article using the alloy. A high strength Mg
based alloy, which contains 12 to 20% of Al by weight; 0.1 to 10%
of Zn; 0.1 to 15% of Sn; and 0.05 to 1.5% of Mn is used by being
injection molded.
Inventors: |
Nakamura, Kiyomi; (Hitachi,
JP) ; Hirane, Teruo; (Hitachinaka, JP) ;
Uchida, Toshio; (Hitachinaka, JP) ; Abe,
Teruyoshi; (Hitachi, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
18367490 |
Appl. No.: |
10/748166 |
Filed: |
December 31, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10748166 |
Dec 31, 2003 |
|
|
|
09727535 |
Dec 4, 2000 |
|
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Current U.S.
Class: |
148/420 ;
148/538 |
Current CPC
Class: |
C22C 23/02 20130101;
C22C 23/00 20130101; C22C 23/04 20130101; C22C 1/005 20130101 |
Class at
Publication: |
148/420 ;
148/538 |
International
Class: |
C22C 023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 3, 1999 |
JP |
11-344210 |
Claims
What is claimed:
1. A method for using a high strength Mg based casting alloy which
contains, by weight, more than 12%, and up to 17%, of Al; 0.1 to
10% of Zn; 1 to 10%, of Sn; and 0.05 to 1.5% of Mn, said method
comprising the step of injection molding the Mg based casting
alloy.
2. A method for using a high strength Mg based casting alloy which
contains, by weight, more than 12%, and up to 20%, of Al; 0.1 to
10% of Zn; 1 to 10%, of Sn; and 0.05 to 1.5% of Mn, and has crystal
size of 10 to 30 .mu.m, said method comprising the step of
injection molding the Mg based casting alloy using a metal
mold.
3. A method for using a high strength Mg based casting alloy which
contains, by weight, 18 to 20% of Al; 0.1 to 5% of Zn; 1 to 10%, of
Sn; and less than 1.5% of Mn, and has a tensile strength (x) at
20.degree. C. larger than 240 MPa; and an elongation (y) larger
than 0.5% and at the same time larger than a value calculated by
y=-0.295x+78, said method comprising the step of injection molding
the Mg based casting alloy using a metal mold.
4. A method for using a high strength Mg based casting alloy, which
is injection molded using a metal mold, and which contains, by
weight, 12 to 15% of Al; 0.1 to 5% of Zn; 1 to 10% of Sn; 0.1 to
0.5% of Mn, and the remainder contains Mg more than 75%, said
method comprising the step of injection molding the Mg based
casting alloy using a metal mold.
5. A method for using a high strength Mg based casting alloy which
contains, by weight, 12 to 15% of Al; 0.1 to 5% of Zn; 1 to 10% of
Sn; 0.1 to 0.5% of Mn; at least one element selected from the group
consisting of Ca, Si and rare-earth elements of which the total
content is less than 5%; at least one kind of element selected from
the group consisting of Sr and Sb of which the total content is
less than 1%; and the remainder which is consisting essentially of
Mg, said method comprising the step of injection molding the Mg
based casting alloy using a metal mold.
6. A method for using a Mg based casting alloy, which contains, by
weight, 12 to 20% of Al; and 1 to 10%, of Sn, said method
comprising the step of injection molding the Mg based casting alloy
using a metal mold.
7. A method for using a Mg based casting alloy, which contains, by
weight, 12 to 20% of Al; 1 to 10%, of Sn; and less than 1.5% of Mn,
said method comprising the step of injection molding the Mg based
casting alloy using a metal mold.
8. A method for using a high strength Mg based casting alloy, which
contains, by weight, 12 to 15% of Al; 1 to 3% of Zn; 1.5 to 4.5% of
Sn; 0.05 to 0.5% of Mn; and the remainder which is consisting
essentially of Mg, said method comprising the step of injection
molding the Mg based casting alloy using a metal mold.
9. A method for using high strength Mg based alloy according to any
one of claims 1 to 4, wherein the Mg based casting alloy contains
one kind or more than two kinds of elements selected from the group
consisting of Ca, Si and rare-earth elements of which the total
content is less than 5% by weight; and at least one kind of element
selected from the group consisting of Sr and Sb of which the total
content is less than 1%.
10. A method for using a Mg based casting alloy according to any
one of claims 6 to 8, wherein the Mg based casting alloy contains
one kind or more than two kinds of elements selected from the group
consisting of Ca, Si and rare-earth elements of which the total
content is less than 5% by weight; and at least one kind of element
selected from the group consisting of Sr and Sb of which the total
content is less than 1%.
11. A die cast article produced by the method for using a Mg-based
casting alloy according to any one of claims 1 to 8.
12. A die cast article produced by the method for using a Mg-based
casting alloy according to claim 9.
13. A die cast article produced by the method for using a Mg-based
casting alloy according to claim 10.
14. The method for using a Mg-based casting alloy according to any
one of claims 2, 6 and 7, wherein the alloy includes 12%-17%
Al.
15. A method for using a Mg-based casting alloy according to any
one of claims 1, 2, 6, and 7, wherein the Mg based casting alloy is
molded using a semi-melted state where a solid phase and a liquid
phase of an alloy are mixed.
16. A method for using a high strength Mg based casting alloy,
which contains, by weight, more than 10%, and up to 17%, of Al; 0.1
to 10% of Zn; 1 to 10%, of Sn; and 0.05 to 1.5% of Mn, whose
surface is covered with an oxide film which contains Mg of 15 to
35% by atoms, said method comprising the step of injection molding
the Mg based casting alloy using a metal mold.
17. A method for using a high strength Mg based casting alloy
according to claim 16, wherein said oxide film further includes an
oxide of Al of less than 15% by atoms.
18. A method for using a high strength Mg based casting alloy which
contains, by weight, more than 10%, and up to 17%, of Al; 0.1 to
10% of Zn; 1 to 10%, of Sn; and 0.05 to 1.5% of Mn, whose surface
is covered with an inert oxide film having a natural immersion
electric potential, 30 minutes after immersing into an aqueous
solution of 0.01 mol Na.sub.2B.sub.4O.sub.7, pH of 9.2 and a
temperature of 25.degree. C., which is greater than -1500 mV, said
method comprising the step of injection molding the Mg based
casting alloy using a metal mold.
19. A method for using a high strength Mg based casting alloy
according to any one of claims 1 to 4, wherein the Mg based casting
alloy consists essentially of the Al, the Zn, the Sn, the Mn and
Mg.
20. A method for using a high strength Mg based casting alloy
according to claim 5, wherein the Mg based casting alloy consists
essentially of the Al, the Zn, the Sn, the Mn, the at least one
element selected from the group consisting of Ca, Si and rare-earth
elements, and the at least one element selected from the group
consisting of Sr and Sb, and the Mg.
21. A method for using a high strength Mg based alloy, which
contains, 12 to 20% of Al by weight, 0.1 to 10% of Zn by weight,
0.5 to 10% of Sn, and 0.05 to 1.5% of Mn; and the remainder which
is consisting essentially of Mg, the method comprising the step of
injection molding the Mg based casting alloy using a metal
mold.
22. A method for using a high strength Mg based casting alloy which
contains, by weight, 12 to 15% of Al; 0.1 to 5% of Zn; 1 to 10% of
Sn; 0.1 to 0.5% of Mn; at least one element selected from the group
consisting of Ca, Si and rare-earth elements of which the total
content is less than 5%; at least one kind of element selected from
the group consisting of Sr and Sb of which the total content is
less than 1%; and the remainder which is consisting essentially of
Mg, whose surface is covered with an oxide film which contains Mg
of 15 to 35% by atoms, said method comprising the step of injection
molding the Mg based casting alloy using a metal mold.
23. A method for using a high strength Mg based casting alloy which
contains, by weight, 12 to 20% of Al; and 1 to 10%, of Sn, whose
surface is covered with an oxide film which contains Mg of 15 to
35% by atoms, said method comprising the step of injection molding
the Mg based casting alloy using a metal mold.
24. A method for using a high strength Mg based casting alloy which
contains, by weight, 2 to 20% of Al; 1 to 10%, of Sn; and less than
1.5% of Mn, whose surface is covered with an oxide film which
contains Mg of 15 to 35% by atoms, said method comprising the step
of injection molding the Mg based casting alloy using a metal
mold.
25. A method for using a high strength Mg based casting alloy which
contains, by weight,12 to 15% of Al; 0.1 to 5% of Zn; 1 to 10% of
Sn; 0.1 to 0.5% of Mn; at least one element selected from the group
consisting of Ca, Si and rare-earth elements of which the total
content is less than 5%; at least one element selected from the
group consisting of Sr and Sb of which the total content is less
than 1%; and the remainder which is consisting essentially of Mg,
whose surface is covered with an inert oxide film having a natural
immersion electric potential, 30 minutes after immersing into an
aqueous solution of 0.01 mol Na.sub.2B.sub.4O.sub.7, pH of 9.2 and
a temperature of 25.degree. C., which is greater than -1500 mV,
said method comprising the step of injection molding the Mg based
casting alloy using a metal mold.
26. A method for using a high strength Mg based casting alloy which
contains, by weight, 12 to 20% of Al; and 1 to 10%, of Sn, whose
surface is covered with an inert oxide film having a natural
immersion electric potential, 30 minutes after immersing into an
aqueous solution of 0.01 mol Na.sub.2B.sub.4O.sub.7, pH of 9.2 and
a temperature of 25.degree. C., which is greater than -1500 mV,
said method comprising the step of injection molding the Mg based
casting alloy using a metal mold.
27. A method for using a high strength Mg based casting alloy which
contains, by weight, 2 to 20% of Al; 1 to 10%, of Sn; and less than
1.5% of Mn, whose surface is covered with an inert oxide film
having a natural immersion electric potential, 30 minutes after
immersing into an aqueous solution of 0.01 mol
Na.sub.2B.sub.4O.sub.7, pH of 9.2 and a temperature of 25.degree.
C., which is greater than -1500 mV, said method comprising the step
of injection molding the Mg based casting alloy using a metal
mold.
28. A method for using a high strength Mg based casting alloy
according to any one of claims 1, 2, 4, 5, 6, 7 and 8, wherein said
alloy has an elongation (y) larger than 0.5%.
29. A method for using a high strength Mg based casting alloy
according to any one of claims 1 to 8, wherein said alloy has an
elongation (y) larger than 3.5%.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation application of U.S. Ser.
No. 09/727,535, filed Dec. 4, 2000, the contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a novel Mg based alloy and
a novel Mg casting alloy capable of mass producing OA parts, car
parts, electric appliance parts and so on through die casting,
injection molding or the like, and relates to articles mold-cast
using the alloy.
[0004] 2. Description of the Prior Art
[0005] The casting Mg alloys practically used in present time are
as follows:
[0006] (1) AZ, AM alloys (Mg--Al--(Zn)--Mn system, for example,
ASTM: AZ91D);
[0007] (2) AS alloy (Mg--Al--Si--Mn system, for example, ASTM:
AS41); and
[0008] (3) AE, QE, WE alloys (an alloy group containing one or more
kinds of REM, Ag, Y).
[0009] The alloy (1) is most commonly used as the die casting and
the injection molding Mg alloy, and particularly the AZ91D is good
in die-castability and in corrosion resistance and widely applied
to car parts and electric appliance parts. The alloys (2), (3) are
alloys improving the mechanical properties such as the creep
property and the high temperature strength. As the prior art in
regard to these alloys, various kinds of alloys are disclosed in
the following patent gazettes.
[0010] For example, Japanese Patent Application Laid-Open No.
6-330216 discloses an Mg based alloy containing Ca, Si, Al, Zn and
Mn, Japanese Patent Application Laid-Open No. 9-104942 discloses an
Mg based alloy containing 5 to 10 of Al, 0.2 to 1 of Si and 0.05 to
0.5 of Cu, and Japanese Patent Application Laid-Open No. 10-147830
discloses an Mg based alloy containing 1 to 6 of Gd and 6 to 12 of
Y.
[0011] With growing needs of thin thickness and high precision of
parts in order to reduce in weight and size of potable devices,
high fluidity alloys have been required. The alloy (1) of AZ91D
described above is comparatively high in the fluidity, but the
molding yield in injection molding is not always sufficiently
high.
[0012] The alloy groups (2), (3) are prior to AZ91D in the
mechanical properties such as creep property, strength at high
temperature. However, because of the bad fluidity, the alloy groups
(2), (3) are apt to cause casting cracks in the molding method of
high speed cooling such as the injection molding method and are bad
in castability.
[0013] The fluidity may be improved by raising the temperature of
molten alloy. However, raising of the molten alloy temperature has
problems in oxidation of the molten alloy and in shortening of
durable lifetime of the production machines. Therefore, it is
necessary to improve the fluidity by the other method.
[0014] It is known that the solidification structure of AZ91D
becomes dendritic when it is cooled in a comparatively slow speed
such as at ingot casting. As described above, the alloy is designed
by placing special emphasis on the molten fluidity, and in regard
to the properties after solidification, the alloy is designed so
that the various kinds of properties such as the mechanical
properties are optimized on the premise that the structure of AZ91D
becomes dendritic.
[0015] However, in the cases of die casting and injection molding
to which the alloy is widely applied, it is known that the
structure after solidification becomes the cellular structure not
the dendritic structure because the cooling rate is very fast.
Therefore, it is required to change the designing method of the
conventional alloying composition.
SUMMARY OF THE INVENTION
[0016] An object of the present invention is to provide a high
strength Mg based alloy and a Mg based casting alloy having a good
fluidity and a good mechanical property, and a cast article using
the alloy.
[0017] As a result of various kinds of studies in order to solve
the problems described above, it is found that the melting point of
the alloy is lowered and the fluidity is improved by adding
appropriate amounts of Al, Sn and Zn to a magnesium alloy, and the
present invention is established.
[0018] The present invention is characterized by a high strength Mg
based alloy, which contains 2 to 20% of Al by weight; 0.1 to 10% of
Zn; 0.1 to 15% of Sn; and 0.05 to 1.5% of Mn, or preferably the
remainder which is consisting essentially of Mg.
[0019] The present invention is characterized by a high strength Mg
based alloy, which contains 2 to 20% of Al by weight; 0.1 to 10% of
Zn; 0.1 to 15% of Sn; and 0.05 to 1.5% of Mn, and has crystal size
of 10 to 300 .mu.m, or preferably the remainder which is consisting
essentially of Mg.
[0020] The present invention is characterized by a high strength Mg
based alloy, which contains 8 to 20% of Al by weight; 0.1 to 5% of
Zn; 0.1 to 10% of Sn; and less than 1.5% of Mn, and has a tensile
strength (x) at 20.degree. C. larger than 240 MPa; and an
elongation ratio (y) larger than 0.5% and at the same time larger
than a value calculated by y=-0.295x+78, or preferably the
remainder which is consisting essentially of Mg.
[0021] The present invention is characterized by a high strength Mg
based alloy, which contains 12 to 15% of Al by weight; 0.1 to 5% of
Zn; 1 to 10% of Sn; 0.1 to 0.5% of Mn, and the remainder contains
Mg more than 75%, or preferably the remainder which is consisting
essentially of Mg.
[0022] The present invention is characterized by a high strength Mg
based alloy, which contains 12 to 15% of Al by weight; 0.1 to 5% of
Zn; 1 to 10% of Sn; 0.1 to 0.5% of Mn; one kind or more than two
kinds of elements selected from the group consisting of Ca, Si and
rare-earth elements of which the total content is less than 5%; at
least one kind of element selected from the group consisting of Sr
and Sb of which the total content is less than 1%; or preferably
the remainder which is consisting essentially of Mg.
[0023] The present invention is characterized by a Mg based casting
alloy, which contains 2 to 20% of Al by weight; and 0.1 to 15% of
Sn; or preferably the remainder which is consisting essentially of
Mg.
[0024] The present invention is characterized by a Mg based casting
alloy, which contains 2 to 20% of Al by weight; 0.1 to 10% of Sn;
and less than 1.5% of Mn, or preferably the remainder which is
consisting essentially of Mg.
[0025] The present invention is characterized by a Mg based casting
alloy, which contains 10 to 15% of Al by weight; 0.5 to 3% of Zn;
1.5 to 4.5% of Sn; 0.05 to 0.5% of Mn, or the remainder which is
consisting essentially of Mg.
[0026] The present invention is characterized by a Mg based casting
alloy which is prepared by that the above-mentioned Mg based
casting alloys are added with one kind or more than two kinds of
elements selected from the group consisting of Ca, Si and
rare-earth elements of which the total content is less than 5% by
weight; and at least one kind of element selected from the group
consisting of Sr and Sb of which the total content is less than 1%,
or the remainder which is consisting essentially of Mg.
[0027] The present invention is characterized by a die cast article
or injection molding article, which is casted using a molten metal
of any one of the alloys is described above.
[0028] The present invention is characterized by a thixotropic mold
article, which is molded using a molten metal of a mixture of
liquid phase and solid phase of any one of the alloys described
above.
[0029] In detail, it is preferable that the magnesium based alloys
described above are formed in desirable shapes through die casting
by injection molding.
[0030] The magnesium alloys in accordance with the present
invention are improved in the fluidity due to lowering of the
melting point particularly by adding a small amount of Sn to the Mg
based alloy containing Al, and accordingly members having less
surface defects can be obtained. Further, since low temperature
molding can be performed and accordingly the contraction at
solidifying is small, members having a high dimensional accuracy
can be obtained. Therefore, the molding yield can be largely
improved.
[0031] Further, since the load to the machines, for example, the
cylinder of an injection molding machine or the like is decreased,
the durable lifetime of the heat resistant materials can be
lengthened.
[0032] Furthermore, the magnesium alloys in accordance with the
present invention are good in mechanical property and corrosion
resistance because of the homogeneous and fine microstructure.
[0033] For the purpose of solid-solution hardening, precipitation
hardening and improvement of fluidity, the element Al is added
above 2%, preferably above 8%, particularly preferable above 12%.
However, an excessive addition exceeding 20% of the element Al
produces a large grain Mg--Al intermetallic compound to
substantially decrease the elongation of the molded products.
Further, in the casting method having a high cooling rate such as
the die casting or the injection molding, the solidified structure
becomes finer as the content of Al is increased, and the Mg--Al
intermetallic compound does not grow large-sized, but is finely
distributed in the crystal grain boundaries. This effect becomes
obvious particularly when Sn is added together. In order to make
the elongation above 3.5% and the tensile strength above 265 MPa,
it is preferable to add 12 to 17% of Al.
[0034] Further, the element Al in the magnesium alloy in accordance
with the present invention is solved in the .alpha.-Mg phase, and
reduce the melting point of the alloy. Further, the element Al is
solid-solved in the .alpha.-Mg phase and crystallizes the Mg--Al
intermetallic compound, with the result that the strength at room
temperature of the alloy is improved. Furthermore, the element Al
suppresses oxidation of the molten alloy, and improves fluidity of
the molten alloy. In order to attain these effects, the Al content
is above 12%, and preferably above 15%.
[0035] The element Sn is solved in the .alpha.-Mg phase, and reduce
the melting point of the alloy with a small amount of nearly 0.1%,
particularly more than 0.5%. Further, the element Sn is solved in
the .alpha.-Mg phase and crystallizes the Mg--Sn intermetallic
compound, as a result the strength at room temperature is improved.
Furthermore, the effect of Sn on lowering the melting point becomes
obvious particularly when Al and Zn are added together, but the
effect is almost saturated when the Sn content becomes 5%. Further,
when the Sn content exceeds 15%, the elongation is largely
decreased, and the density of the alloy becomes large, and lose the
advantage of lightness of the magnesium alloy. Particularly, the Sn
content needs to be lower than 10% in order to keep the elongation
above 3.5%, and the Sn content needs to be preferably lower than 8%
in order to keep the elongation above 4%. When the Sn content is 1
to 7%, it is possible to obtain an alloy having both of high
strength and high elongation.
[0036] The element Zn is added above 0.1% in order to improve the
strength at room temperature and the castability. However, when the
Zn content exceeds 10%, casting cracks are apt to occur. It is
preferable that the Zn content is within a range of 0.1 to 5%,
preferably 1 to 5% in which the strength is high and the casting
cracks do not occur.
[0037] The element Mn improve the corrosion resistance, this is
because Mn forms a intermetallic compound with Al, and fix Fe in
the intermetallic compound, the element Fe being contained in the
alloy as an impurity deteriorate the corrosion resistance. When the
Mn content exceeds 1%, the Al-Mn group intermetallic compound
excessively deposited and cause an evil effect on the mechanical
property, the upper limit of Mn content is set to 1%. Particularly,
for the corrosion resistance, Mn content is effective above 0.05%,
and preferably 0.1 to 0.5%.
[0038] The alloy in accordance with the present invention further
contains at least one element selected from the group consisting of
Ca, Si and rare-earth elements, the content of the one kind or in
total being less than 5%; and at least one element selected-from
the group consisting of Sr and Sb, the content of the one kind or
in total being less than 1%. The elements Ca and Si and rare-earth
elements are effective to lower the melting point because these
elements form eutectic groups with Mg. However, since addition of
these elements deteriorates the casting property, the upper limit
of the content is 5%. Particularly, it is preferable that the
content is above 0.1% and the upper limit is set to 3%.
[0039] The elements Sr and Sb make the metallic structure fine, and
to improve the mechanical properties. The effect of elements Sr and
Sb is increased when the element Si or Ca is added together. The
effect of elements Sr and Sb is increased as the content is
increased, but the effect is saturated when the content exceeds 1%.
Therefore, the upper limit is set to 1%. Particularly, it is
preferable that the content is above 0.03%, and the upper limit is
set to 0.5%.
[0040] The Mg based alloy in accordance with the present invention
is characterized that the surface is covered with an oxide film
which contains Mg of 15 to 35% by atoms; preferably 20 to 30%, and
Mo of 5 to 20%. The Mg based alloy in accordance with the present
invention is characterized that the surface is covered with an
oxide-film which contains Mg of 15 to 35% by atoms; Mo of 5 to 20;
and metallic Al of less than 30%, preferably 10 to 25%. The Mg
based alloy in accordance with the present invention is
characterized that the surface is covered with an oxide film which
contains Mg of 15 to 35% by atoms; Mo of 5 to 20; oxide Al of less
than 15%; and metallic Al of less than 15%, preferably 4 to 12%.
The Mg based alloy in accordance with the present invention is
characterized that the surface is covered with an inert oxide film
of which a natural immersion electric potential 30 minutes after
immersing into an aqueous solution of 0.01 mol
Na.sub.2B.sub.4O.sub.7, pH 9.2, 25.degree. C. is higher than -1500
mV, preferably higher than -1400 mV. The Mg based alloy in
accordance with the present invention is characterized that the
surface is covered with an oxide film of which a natural immersion
electric potential 15 minutes after immersing into an aqueous
solution of 0.01 mol Na.sub.2SO.sub.4, 25.degree. C. is higher than
-1500 mV, preferably higher than -1400 mV. Further, the Mg based
alloy in accordance with the present invention is characterized
that the surface is covered with the above-described oxide film or
a specified oxide film, and a water repellent organic film
containing fluoride is further coated on the oxide film.
BRIEF DESCRIPTION OF DRAWINGS
[0041] FIG. 1 is a cross-sectional view showing the construction of
an injection molding machine used in the present embodiment.
[0042] FIG. 2 is a microscopic photograph showing the metallic
structure of a magnesium based alloy ingot fabricated in the
embodiment 1.
[0043] FIG. 3 is a graph showing the relationship between Sn
content and melting point.
[0044] FIG. 4 is a diagram that shows the relationship between the
cylinder temperature and fluidity lengths for both the
magnesium-based alloy No. 2 in the present invention and an alloy
AZ91D in a prior art.
[0045] FIG. 5 is a graph showing the relationship between Sn
content and Vickers hardness.
[0046] FIG. 6 is a graph showing the relationship between Sn
content and tensile strength.
[0047] FIG. 7 is a graph showing the relationship between Sn
content and elongation ratio.
[0048] FIG. 8 is a graph showing the relationship between Al
content and tensile strength.
[0049] FIG. 9 is a graph showing the relationship between Al
content and elongation.
[0050] FIG. 10 is a SEM photograph showing the metallic structure
of a magnesium based alloy ingot fabricated in the embodiment
2.
[0051] FIG. 11 is a graph showing the relationship between
elongation and tensile strength.
[0052] FIG. 12 is a graph showing the relationship between
elongation and tensile strength.
[0053] FIG. 13 is a graph showing the salt spray test result for
various Mg based alloys.
[0054] FIG. 14 is a perspective view showing a note-shaped personal
computer.
[0055] FIG. 15 is a perspective view showing a mobile type liquid
crystal projector.
[0056] FIG. 16 is a perspective view showing a home electric vacuum
cleaner.
[0057] FIG. 17 is a perspective view showing an impeller.
[0058] FIG. 18 shows a perspective view of a portable telephone
apparatus to which a magnesium-based alloy disclosed in the
embodiment 1 in the present invention is applied.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
[0059] A magnesium chloride type flux was applied on the inner
surface of a melting pot made of casting iron pre-heated in an
electric furnace, and raw materials were put into the melting pot
so as to form an alloy having a composition (weight %) shown in
Table 1 to be melted. After stirring the molten metal at
750.degree. C. and removing slag, the molten metal was cast in a
metal mold of 50 mm.times.50 mm.times.300 mm pre-heated to
150.degree. C. to fabricate a Mg alloy ingot. During melting work,
in order to preventing burning the flux was sprinkled on the molten
alloy surface, if necessary, Mm is a mischmetal (La50 wt %-Ce50 wt
% alloy).
[0060] FIG. 2 shows a typical metallic structure of an alloy
obtained through the method as described above. Mg--Al compound
phase (white portions) are crystallized in a network shape in the
.alpha.-phase grain boundary, and Mg--Sn compound phase (black
portions) are crystallized between the network of the Mg--Al
compound phase.
[0061] FIG. 3 shows measured results of melting points of the
alloys, particularly the relationship between the melting point and
Sn content for the alloys No. 1 to 3 and 11 to 13. The alloy
melting point is decreased as the Sn content is increased, and the
effect of Sn addition on the melting point is saturated when the
its content exceeds 10 Wt %. However, it can be understood that the
melting point of the alloy No. 12 containing Al and Zn contents
less than the specified values of the present invention is small in
the melting point fall from AZ91D alloy (No. 11). Further, as shown
in the figure, the melting point is steeply decreased as the Sn
content is increased up to the Sn content of 2%, but mildly
decrease where the Sn content is above 2%. Further, by making the
Sn content above 0.5%, the melting point is lower than that 596 OC
of AZ91D.
Embodiment 2
[0062] A magnesium chloride type flux was applied, on the inner
surface of a melting pot made of casting iron preheated in an
electric furnace, and raw materials were put into the melting pot
so as to form an alloy having a composition (weight %) shown in
Table 1 to be melted. After stirring the molten metal at
750.degree. C. and removing slag, the molten metal was cast in a
metal mold of 50 mm.times.50 mm.times.300 mm pre-heated to
150.degree. C. to fabricate a Mg alloy ingot. During melting work,
in order to preventing burning the flux was sprinkled on the molten
alloy surface, if necessary. An alloy chip of 2 mm to 10 mm
diameter was fabricated by milling the ingot obtained through the
method as described above, and used as a raw material for injection
molding. A machine having a mold clamping force of 75 t was used
for the injection molding to form an injection molded piece of 120
mm.times.50 mm.times.1 mm thickness. The molding condition was as
follows. A Mm (mischmetal) indicates an alloy containing 50 wt % La
and 50 wt % Ce.
[0063] Injection speed: 1.6 m/s
[0064] Injection pressure: 800 kg/cm.sup.2
[0065] Molten metal temperature: alloy melting point+20.degree.
C.
[0066] Mold temperature: 150.degree. C.
[0067] Strength evaluation tests (hardness, tensile strength,
elongation) were conducted by obtaining the following test pieces
from the molded pieces obtained as described above.
[0068] Test piece: 1 mm thickness, 12 mm gage length, 16 mm length
and 10 mm width of parallel part.
[0069] Tensile test: Using an Instron testing machine, measurement
was performed under the condition of 0.3/mm strain speed and at
25.degree. C.
[0070] The test pieces No. 1 to 10 and 12, 13 are samples each
within the composition range of the embodiment of the present
invention, and the test pieces No. 11, 14 and 15 are comparative
examples out of the composition range of the embodiment of the
present invention (the test piece No. 11 is AZ91D standard
alloy).
1TABLE 1 Alloy No. Al Zn Sn Mn Others Mg 1 12 3 1 0.2 -- bal. 2 12
3 5 0.2 -- bal. 3 12 3 10 0.2 -- bal. 4 12 5 5 0.2 -- bal. 5 15 3 5
0.2 -- bal. 6 18 3 5 0.2 -- bal. 7 20 3 5 0.2 -- bal. 8 12 1 3 0.2
Si: 1, Sr: 0.05 bal. 9 12 1 3 0.2 Ca: 2, Sb: 0.05 bal. 10 12 1 3
0.2 Mm: 2 bal. 11 8.9 0.76 -- 0.24 -- bal. 12 11 0 1 0.2 -- bal. 13
12 3 11 0.2 -- bal. 14 21 3 5 0.2 -- bal. 15 12 3 5 -- -- bal.
[0071] FIG. 1 is a cross-sectional view showing the main portion of
the injection molding machine used in the present embodiment.
[0072] An alloy raw material 1 for injection molding is put into a
hopper 2 to be supplied into a cylinder 4. The raw material is
kneaded and mixed in the cylinder 4 while being transferred toward
a nozzle 6 by a rotating screw 5, and at the same time heated by a
cylinder heater 7. The alloy raw material is injection molded under
a melted state where the heated temperature is higher than the
liquid-phase line temperature, or under a semi-melted state where a
solid phase having a temperature lower than the liquid-phase line
temperature and a liquid phase are mixed. The melted state or
semi-melted state molten metal 10 of the raw alloy material
transferred to the front portion of the screw 5 is filled into a
metal mold 9 though the nozzle 6 by moving the screw forward using
a high speed injection mechanism 8. The pressure in the metal mold
is kept until the molten metal is solidified, and after being
solidified the metal mold 9 is opened to take out the molded
article. Referring to the figure, the screw 5 has a spiral blade 13
on a cylindrical solid based body 14, and the alloy raw material 1
is heated up to a high temperature to be made the melted state or
the semi-melted state depending on the temperature of the heater 7
while being kneaded with the blade 13 by rotation of the screw 5.
The reference character 12 is a backflow preventing ring for the
molten metal 10.
[0073] The alloy raw material 1 used in the present embodiment is
prepared by melting an alloy of each of the compositions under a
non-oxidized atmosphere, and then by cutting the formed alloy into
chips smaller than 10 mm to form grains of the raw material.
[0074] FIG. 4 is a diagram that shows the relationship between the
injection temperature and fluidity lengths for both the
magnesium-based alloy No. 2 in the present invention, an alloy
AZ91D in a prior art. The cylinder temperature is the temperature
at which alloys were molded for their fluidity length verification.
The fluidity length of an alloy is the length for such sound
portion in an injection-molded alloy that has no surface-defects
like crack. The alloy No. 2 is a magnesium-based alloy containing
12% aluminum, 1% zinc, and 5% tin each in weight ratio.
[0075] The fluidity length was verified using a fluidity length
verification metallic mold having a width of 10 mm, a thickness of
1 mm, and an overall length of 380 mm, into which each alloy to be
verified was injection-molded by an injection molding apparatus
shown in FIG. 1 keeping the verification metallic mold constantly
at 200.degree. C.
[0076] As shown in FIG. 4, it is evident that the alloy in the
present invention has higher fluidity length performance than alloy
AZ91D at any temperature in our investigation.
[0077] In contrast to that the fluidity lengths of alloys in a
prior art reaches saturation of about 300 mm at a temperature
600.degree. C., the alloy No. 12 in the present invention that
includes 3% zinc spread its fluidity length to about 350 mm at
570.degree. C. and another alloy in the present invention that
includes 1% zinc also spreads to about 350 mm at 580.degree. C.
[0078] FIG. 5 to FIG. 7 are graphs showing the relationships
between Sn content and test results of hardness and tensile
strength of the injection molded article made of each of the alloys
shown in Table 1. As shown in the graphs, by adding Sn by 1%, both
of the hardness and the tensile strength become above Hv 110 in
hardness and above 269 MPa in tensile strength, respectively. On
the other hand, the elongation ratio is improved until the Sn
content is increased up to 5 wt %, but is decreased when the Sn
content exceeds 5%, and is steeply decreased to a value before
adding Sn when the Sn content exceeds 9%.
[0079] FIG. 8 and FIG. 9 are graphs showing results of tensile test
when the Al content is varied on the basis of the alloy No. 2
(Mg-12A1-3Zn-5Sn). As shown in the graphs, the tensile strength is
improved with increasing the Al content, and the tensile above 279
MPa can be obtained up to 17% of Al content. In regard to the
elongation ratio, the elongation ratio above 1.9% can be obtained
up to 20% of Al content. However, when the Al content exceeds 20%,
the elongation ratio is extremely decreased to a value smaller than
1%, which is impractical.
[0080] As the contents of Al, Zn, Sn in the magnesium alloy are
increased, (Mg--Al group, Mg--Sn group) crystallized in the
.alpha.-phase grain boundaries are increased. Increase in the
amount of the generally causes to lower the elongation. However,
addition of Al, Zn, Sn also has an effect to fine the
.alpha.-phase, and accordingly the relative ratio of the
.alpha.-phase grain boundary volume to the intermetallic compound
amount is not largely changed even if the amount of the
intermetallic compound is increased. Therefore, it can be
considered that large decrease of elongation can be suppressed.
However, it is considered that the fining effect is saturated and
the elongation is steeply decreased at values near the Sn and Al
contents of 10 wt % and 20 wt %, respectively.
[0081] FIG. 10 shows the photograph of the structure of the
injection molded article made of the alloy No. 2. The .alpha.-phase
grains having size of nearly 1 to 20 .mu.m, mainly less than 5
.mu.m and the Mg--Al compound phase crystallized in network shape
in the grain boundaries are observed. White small nodules are the
Mg--Sn compound phase, and it can be understood from this
photograph that the solidification structure is refined, and the
Mg--Al and the Mg--Sn compound phase are uniformly distributed.
[0082] In the case where among the magnesium alloys described
above, the embodiments of the alloys No. 1 to 3 in accordance with
the present invention are injection molded by setting the molten
alloy temperature to the same value (620.degree. C.), surface
defects of the molded articles of the alloys No. 1 to 3 are
substantially decreased compared to those of the molded article of
AZ91D alloy. The reason is that the difference between the molten
alloy temperature and the melting point becomes larger by the
amount of decreasing the melting point, and accordingly the
fluidity is improved.
[0083] Further, in the case where molding was performed by setting
the molten alloy temperature at injection molding to a temperature
lower than the melting point of the alloy by 10.degree. C., that
is, in the case where injection molding was performed under the
semi-solid state that the solid phase and the liquid phase were
mixed, the dimensional accuracy of the molded article made of each
of the alloys was better than that of AZ91D alloy.
[0084] FIG. 11 is a graph showing the relationship between tensile
strength and elongation of the Mg based alloy when the Sn content
is varied to the 12% Al-3% Zn alloy. As shown in the graph,
although the strength and the elongation are increased up to the Sn
content of 5%, the strength is increased but the elongation is
decreased when the Sn content exceeds 5%. However, the elongation
is as high as 0.5% even at the Sn content of 11%.
[0085] The straight line in the graph is expressed by the
elongation (%) (y) and the tensile strength (MPa) (x), the present
embodiment has the elongation higher than the value calculated by
y=-0.295x+78. Further, it is preferable that the tensile strength
and the elongation are higher than values calculated by the
relationships y=-0.295x+82, 85 or 87.
[0086] FIG. 12 is a graph showing the relationship between tensile
strength and elongation of the Mg based alloy when the Al content
is varied to the 3% Zn-5% Sn alloy. As shown in the graph, it can
be understood that the tensile strength having a value higher than
275 MPa can be obtained by increasing the Al content to 12%, and
the elongation having a value higher than 0.5% can be also obtained
when the Al content is less than 20.5%. It is also preferable that
in this graph, the values are set higher than the values calculated
by the above-described relationship expressed by the elongation
ratio (y) and the tensile strength (x).
[0087] FIG. 13 is a graph showing the corrosion rate of injection
molded articles made of the present embodiments of alloys No. 2, 5,
6, 7 and the comparative alloys No. 11, 15 by a salt water spray
test (splaying 5% NaCl aqueous solution for 360 hours) at
20.degree. C. From the graph, it can be understood that all the
alloys of the present embodiment have better corrosion resistance
below corrosion mass loss of 0.1 (mg/cm.sup.2.multidot.day)
compared to that of AZ91D alloy (No. 11). Further, it can be also
understood that the corrosion resistance is more improved as the Al
content is higher. Further, as it is clear from the fact that the
alloy No. 2 added with Mn shows better corrosion resistance
compared to that of the comparative alloy No. 15 not added with Mn,
addition of a very small amount of Mn substantially increase the
corrosion resistance. Further, as shown by the alloys No. 5 and 7,
it can be understood that high corrosion resistance can be obtained
by increasing the Al content.
Embodiment 3
[0088] FIG. 14 is a perspective view showing a notebook-size
personal computer. In a main body 21, there are arranged a keyboard
22 for operating input means and a switch board unit 23 containing
light-emitting diodes (LEDs) for indicators and a main switch. The
exterior of the main body 21 is composed of a main body upper case
26 and main body bottom case 27. The exterior of a display portion
24 is composed of a liquid crystal display (LCD) case 41 and an LCD
front 42. In the LCD front 42, a display window is opened SO that
the display portion of the liquid crystal screen 25.
[0089] Among these components, the LCD front 42 was molded using
the alloy No. 2 by an injection molding machine of 650 t mold
clamping force in order to make the weight light and to improve the
stiffness and the heat dissipation. The injection speed was 3
m/sec, molten alloy temperature was 580.degree. C. and metal mold
temperature was 200.degree. C. The dimension of the molded article
was 230 mm.times.180 mm.times.4 mm, and average thickness of 0.7
mm. The molded article obtained through such a way could be formed
in a good dimensional accuracy without surface defects and with
good yield. Similarly, the bottom case was fabricated.
Embodiment 4
[0090] FIG. 15 is a perspective view showing a mobile type liquid
crystal projector.
[0091] A main body is composed of a switch board unit 32 containing
LEDs for indicators and a main switch and a projection lens 33, and
the exterior is composed of a main body upper case 31 and a main
body bottom case 34.
[0092] Among these components, the main body upper case 31 was
casted using the alloy No. 2 by a hot chamber die-cast machine of
600 t mold clamping force. The molding condition was injection
speed of 2.5 m/sec, molten alloy temperature of 600.degree. C. and
metal mold temperature of 200.degree. C. The dimension of the
molded article was 248 mm.times.330 mm.times.100 mm, and average
thickness of 1.5 mm. Even though the component was comparatively
large, a good molded article could be formed without filling
defects in a thin wall portion nor occurrence of surface
defects.
Embodiment 5
[0093] FIG. 16 is a perspective view showing a home electric vacuum
cleaner having an impeller using the Mg based alloy, in accordance
with the present invention.
[0094] Referring to FIG. 16, the reference character 51 is a vacuum
cleaner main body which contains a control circuit and an electric
drive fan and so on, the reference character 52 is a hose connected
to a suction nozzle portion of the vacuum cleaner main body 51, the
reference character 53 is a hose grip portion, the reference
character 54 is an extension pipe connected to an end (the hose
grip portion 53) of the hose, the reference character 55 is a
nozzle body connected to the extension pipe 54, the reference
character 56 is a switch operating portion arranged in the hose
grip portion 53, the reference character 57 is a first infrared
light emitting portion arranged in the hose grip portion 53, the
reference character 58 is a second infrared light emitting portion
arranged in the hose grip portion 53, and the reference character
59 is an infrared light receiving portion arranged on the upper
surface of the vacuum cleaner main body.
[0095] FIG. 17 is an exploded perspective view showing the
impeller.
[0096] As a molding method of integrating a front plate 61, a rear
plate 62 and blades 63 in one piece, an injection molding method
was employed in the present embodiment. In this method, a light
metal raw material formed in pellets is used similarly to the
injection molding method, and kneaded and melted directly inside an
injection molding machine without using any melting furnace or the
like, and injected into a metal mold to obtain a molded article. In
the present embodiment, the front plate 61, the rear plate 62 and
the blades 63 integrated in one piece are individually formed in
one piece using the magnesium based alloy shown in Embodiment 1.
Solder material layers are provided over all the surfaces of the
front plate 61 and the rear plate 62, and the blades 63 are joined
with the solder material. The reference character 64 is a suction
port. In the present embodiment, the impeller can be obtained by a
mixed molten alloy of liquid phase and solid phase using the
injection molding machine shown in FIG. 1.
[0097] According to the present embodiment, the impeller can be
made light in weight without filling defects even though the wall
thickness is as thin as 0.7 mm, and the air flow resistance can be
reduced. Therefore, the rotating speed of 45000 to 50000 rpm can be
attained at 1 kW consumed electric power, and the suction power can
be attained above 550 W.
Embodiment 6
[0098] FIG. 18 shows a perspective view of a portable telephone
apparatus to which a magnesium-based alloy disclosed in the
embodiment 1 in the present invention is applied. As illustrated in
FIG. 18, the apparatus is comprised of a cover (4) that includes a
number display part (2) and a plurality of keys (3), a retractable
antenna (5), and a case (6).
[0099] Among these parts, the cover (4) and the case (6) were
injection-molded out of the alloy No. 2 for reduce weight, and
improving stiffness, heat dissipation, and electromagnetic
shielding properties using an injection molding apparatus having
mold clamping force of 75 ton. The injection speed was 1 m/s and
the temperature of the molten metal was 580.degree. C. The
dimensions of the molded product were 125 mm by 38 mm by 8 mm and
average wall thickness was 0.5 mm. This alloy has not caused any
filling-defect and surface-defect with acceptable yield in molding
process even in a thin wall product like this embodiment.
Embodiment 7
[0100] A front cabinet of a 21-inch type television set, a steering
wheel core of a vehicle, a case body of a video-camera, a rid of an
MD player and a case body of a compact camera are manufactured by a
mixed molten alloy of liquid phase and solid phase using the
injection molding machine shown in FIG. 1. In these cases, good
molding crystals can be obtained without filling defects even
though the wall thickness is as thin as 0.7 mm.
Embodiment 8
[0101] Oxide films having 0.1 to 3 .mu.m were formed on the
surfaces of the various kinds of the products described in
Embodiments 3 to 6 using the Mg based alloys in accordance with the
present invention by immersing the products into aqueous solutions
of 1M-Na.sub.2MoO.sub.4 and 1M-Na.sub.2SO.sub.4-0.5M.NaF (adjusting
to pH 3.0 with H.sub.2SO.sub.4) at 60.degree. C. for 180 seconds,
respectively. The surface of the product is colored, and the
thickness of the film can be estimated from the tone of the color.
The color is changed from light brown to dark blown, and further to
black depending on the processing time. The obtained film showed
good corrosion resistance, and had such an inert electric potential
that the natural immersion electric potential 30 minutes after
immersing into an aqueous solution of 0.01M-Na.sub.2B.sub.4O.sub.7
(pH 9.18) was higher than -1500 mV. Further, the oxide film was
suitable as a based for coating with paint.
[0102] A water repellent fluoride film was further coated on the
oxide film by being immersed into a solution dissolving
perfluoro-hexane for 24 hours and then by being heated at
150.degree. C. for 10 minutes. The organic film had such a high
water repellence that the contact angle with water was 120 to 130
degrees, and accordingly the durability could be further
improved.
[0103] According to the present invention, it is possible to obtain
an Mg based alloy which is low in melting point, good in fluidity
at molding, and good in mechanical property due to uniform and fine
structure. Further, by reducing number of surface defects by
improving the fluidity and by improving the dimensional accuracy by
low temperature molding, the molding yield can be substantially
improved. Furthermore, by reducing load to the metal members and
the heat resistant members such as the mold and the cylinder of the
injection molding machine, the lifetime of these members can be
extended, and accordingly the production efficiency of the
magnesium based alloy parts can be improved.
[0104] In addition, according to the present invention, by forming
the oxide film containing heavy metals having plural valences and
enriched with Al in the based material on the surface of the Al
containing Mg alloy through process in the solution, the oxide film
can, serve as a paint based having good corrosion resistance.
Further, the film described above can be fabricated without using
any material harmful for the environment.
[0105] By applying a general corrosion preventive paint or a water
repellent paint onto the film, a better corrosion preventive
coating film can be obtained.
* * * * *