U.S. patent application number 13/510989 was filed with the patent office on 2013-07-18 for non-flammable magnesium alloy with excellent mechanical properties, and preparation method thereof.
This patent application is currently assigned to KOREA INSTITUTE OF MACHINERY & MATERIALS. The applicant listed for this patent is Ha Sik Kim, Young Min Kim, Chang Dong Yim, Bong Sun You. Invention is credited to Ha Sik Kim, Young Min Kim, Chang Dong Yim, Bong Sun You.
Application Number | 20130183193 13/510989 |
Document ID | / |
Family ID | 44957671 |
Filed Date | 2013-07-18 |
United States Patent
Application |
20130183193 |
Kind Code |
A1 |
Kim; Young Min ; et
al. |
July 18, 2013 |
NON-FLAMMABLE MAGNESIUM ALLOY WITH EXCELLENT MECHANICAL PROPERTIES,
AND PREPARATION METHOD THEREOF
Abstract
A magnesium alloy that has excellent ignition resistance and is
excellent in both strength and ductility. The magnesium alloy
includes, by weight, 1.0% or greater but less than 7.0% of Al,
0.05% to 2.0% of Ca, 0.05% to 2.0% of Y, greater than 0% but not
greater than 6.0% of Zn, and the balance of Mg, and the other
unavoidable impurities. The total content of the Ca and the Y is
equal to or greater than 0.1% but less than 2.5% of the total
weight of the magnesium alloy. The Mg alloy forms a dense composite
oxide layer that acts as a protective film. Thus the Mg alloy has
very excellent oxidation resistance and ignition resistance, can be
melted, cast and machined in the air or a common inert atmosphere
(Ar or N.sub.2), and can reduce the spontaneous ignition of chips
that are accumulated during the process of machining.
Inventors: |
Kim; Young Min; (Changwon,
KR) ; Kim; Ha Sik; (Changwon, KR) ; You; Bong
Sun; (Changwon, KR) ; Yim; Chang Dong;
(Changwon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kim; Young Min
Kim; Ha Sik
You; Bong Sun
Yim; Chang Dong |
Changwon
Changwon
Changwon
Changwon |
|
KR
KR
KR
KR |
|
|
Assignee: |
KOREA INSTITUTE OF MACHINERY &
MATERIALS
Daejeon
KR
|
Family ID: |
44957671 |
Appl. No.: |
13/510989 |
Filed: |
October 4, 2011 |
PCT Filed: |
October 4, 2011 |
PCT NO: |
PCT/KR11/07298 |
371 Date: |
May 21, 2012 |
Current U.S.
Class: |
420/409 ; 164/46;
164/462; 164/473; 164/57.1; 420/408 |
Current CPC
Class: |
C22C 1/02 20130101; C22C
23/02 20130101; B22D 21/04 20130101; C22C 23/00 20130101; C22C
23/04 20130101; C22C 1/03 20130101; C22F 1/06 20130101; C22C 23/06
20130101 |
Class at
Publication: |
420/409 ;
420/408; 164/57.1; 164/473; 164/462; 164/46 |
International
Class: |
C22C 23/04 20060101
C22C023/04; C22C 23/02 20060101 C22C023/02; C22C 1/02 20060101
C22C001/02; C22C 23/00 20060101 C22C023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 2010 |
KR |
10-2010-96709 |
Mar 16, 2011 |
KR |
10-2011-23260 |
Claims
1. A magnesium alloy manufactured by melt casting, the magnesium
alloy comprising, by weight, 1.0% or greater but less than 7.0% of
Al, 0.05% to 2.0% of Ca, 0.05% to 2.0% of Y, greater than 0% but
not greater than 6.0% of Zn, a balance of Mg, and other unavoidable
impurities, wherein a total content of the Ca and the Y is equal to
or greater than 0.1% but less than 2.5% of a total weight of the
magnesium alloy.
2. The magnesium alloy of claim 1, wherein a content of the Ca
ranges, by weight, from 0.2% to 1.5%.
3. The magnesium alloy of claim 1, wherein a content of the Y
ranges, by weight, from 0.1% to 1.5%.
4. The magnesium alloy of claim 1, wherein contents of the Ca and
the Y range from 0.3% to 2.0% of a total weight of the magnesium
alloy.
5. The magnesium alloy of claim 1, further comprising, by weight,
greater than 0% but not greater than 1.0% of Mn.
6. The magnesium alloy of claim 1, further comprising, by weight,
0.1% to 1.0% of Zr.
7. A method of manufacturing a magnesium alloy, comprising: forming
a magnesium alloy molten metal, which contains Mg, Al and Zn;
adding raw materials of Ca and Y into the magnesium alloy molten
metal; producing a magnesium alloy cast material from the magnesium
alloy molten metal, in which the raw materials of Ca and Y are
added, using a fusion casting method, wherein a magnesium alloy,
which is produced by the above process, comprises, by weight, 1.0%
or greater but less than 7.0% of Al, 0.05% to 2.0% of Ca, 0.05% to
2.0% of Y, greater than 0% but not greater than 6.0% of Zn, a
balance of Mg, and other unavoidable impurities.
8. The method of claim 7, wherein adding the raw materials of Ca
and Y into the magnesium alloy molten metal comprises adding the
raw materials of Ca and Y at a temperature higher than 800.degree.
C.
9. A method of manufacturing a magnesium alloy, comprising: forming
a magnesium alloy molten metal, which contains Mg, Al and Zn;
forming a master alloy ingot, which contains Mg, Al, Zn, Ca and Y,
and is soluble at 750.degree. C. or lower; inputting the master
alloy ingot, which is soluble at 750.degree. C. or lower, into the
magnesium alloy molten metal; and producing a magnesium alloy cast
material from the molten metal, which contains the master alloy
ingot, using a fusion casting method, wherein a magnesium alloy
produced as described above comprises, by weight, 1.0% or greater
but less than 7.0% of Al, 0.05% to 2.0% of Ca, 0.05% to 2.0% of Y,
greater than 0% but not greater than 6.0% of Zn, a balance of Mg,
and other unavoidable impurities.
10. The method of claim 9, wherein the master alloy ingot, which
contains Mg, Al, Zn, Ca and Y, is soluble at 750.degree. C. or
lower, and is input into the magnesium alloy molten metal at a
temperature lower than 750.degree. C.
11. A method of manufacturing a magnesium alloy, comprising:
forming a magnesium alloy molten metal, which contains Mg, Al and
Zn; adding a Ca compound and a Y compound into the magnesium alloy
molten metal; and producing a magnesium alloy cast material from
the magnesium alloy molten metal, in which the Ca compound and the
Y compound are added, using a fusion casting method, wherein a
magnesium alloy produced by the above process comprises, by weight,
1.0% or greater but less than 7.0% of Al, 0.05% to 2.0% of Ca,
0.05% to 2.0% of Y, greater than 0% but not greater than 6.0% of
Zn, a balance of Mg, and other unavoidable impurities.
12. The method of claim 7, wherein inputting the raw materials of
Ca and Y, the master alloy ingot, which contains Mg, Al, Zn, Ca and
Y, or the Ca compound and the Y compound into the magnesium alloy
molten metal further comprises periodically stirring the magnesium
alloy molten metal.
13. The method of claim 7, wherein the casting method comprises one
selected from the group consisting of mold casting, sand casting,
gravity casting, squeeze casting, continuous casting, strip
casting, die casting, precision casting, lost foam casting, spray
casting, and semi-solid casting.
14. The method of claim 7, further comprising carrying out hot
working on the magnesium alloy cast material produced by the
casting method.
15. The method of claim 9, wherein inputting the raw materials of
Ca and Y, the master alloy ingot, which contains Mg, Al, Zn, Ca and
Y, or the Ca compound and the Y compound into the magnesium alloy
molten metal further comprises periodically stirring the magnesium
alloy molten metal.
16. The method of claim 9, wherein the casting method comprises one
selected from the group consisting of mold casting, sand casting,
gravity casting, squeeze casting, continuous casting, strip
casting, die casting, precision casting, lost foam casting, spray
casting, and semi-solid casting.
17. The method of claim 9, further comprising carrying out hot
working on the magnesium alloy cast material produced by the
casting method.
18. The method of claim 11, wherein inputting the raw materials of
Ca and Y, the master alloy ingot, which contains Mg, Al, Zn, Ca and
Y, or the Ca compound and the Y compound into the magnesium alloy
molten metal further comprises periodically stirring the magnesium
alloy molten metal.
19. The method of claim 11, wherein the casting method comprises
one selected from the group consisting of mold casting, sand
casting, gravity casting, squeeze casting, continuous casting,
strip casting, die casting, precision casting, lost foam casting,
spray casting, and semi-solid casting.
20. The method of claim 11, further comprising carrying out hot
working on the magnesium alloy cast material produced by the
casting method.
Description
TECHNICAL FIELD
[0001] The present invention relates to a magnesium alloy having
excellent ignition resistance or nonflammability, and more
particularly, to a magnesium alloy that can be melted and cast in
the air as well as in a common inert atmosphere due to the presence
of a stable protective film formed on the surface of the molten
metal, has excellent ignition resistance or nonflammability in
order to prevent spontaneous ignition of chips, and is excellent in
both strength and ductility.
BACKGROUND ART
[0002] Magnesium alloys, which have a high specific strength, are
the lightest of alloys, are applicable in a variety of casting and
machining processes, and have a wide range of application, and are
thereby used in almost all fields in which light weight is
required, such as parts for vehicles and electronic parts. However,
magnesium (Mg) is a metallic element that has a low electrochemical
potential and is very active. Mg still has limitations in terms of
the stability and reliability of the material, since it undergoes a
strong reaction when it comes into contact with oxygen or water,
and sometimes causes fires. Therefore, the fields in which Mg can
be applied are still limited compared to its potential
applicability. In particular, it cannot be used in applications in
which safety is important.
[0003] Because of this activity of Mg alloys, it is necessary to
create an inert atmosphere using an inert mixture gas, such as a
flux or CO.sub.2+SF.sub.6. Since the flux that is used in melting
and refining is a chlorinated substance, there is a problem in that
chlorine atoms reside inside a material, thereby significantly
decreasing corrosion resistance when the conditions for processing
the molten metal are not fulfilled. In order to solve this problem,
it is effective to perform melting and casting in an atmosphere in
which SF.sub.6, CO.sub.2 and air are mixed, instead of using the
flux. However, SF.sub.6 is classified as a greenhouse gas, the
global-warming potential (GWP) of which is 24 times that of
CO.sub.2, so that the use thereof is expected to be regulated in
the future time.
[0004] In order to more fundamentally solve this problem, studies
for improving the oxidation resistance of Mg alloys, in particular,
studies intended to increase the ignition temperature of Mg alloys
by adding Ca, Be or rare-earth metals, have been carried out.
Traditionally, Ca has been a main choice among the alloying
elements that are added to Mg alloys that are oxidation resistant
because Ca is cheaper than other rare-earth metals, is nontoxic,
and greatly increases the ignition temperature in consideration of
the amount that is added.
[0005] According to previous studies on magnesium alloys that
contain Ca, it is known that the ignition temperature increases by
about 250.degree. C. when 3wt % or greater of Ca is added.
Therefore, in order to realize an ignition temperature of
700.degree. C. or higher, at which casting is possible in the
condition of being exposed to the air without a protective gas, or
an ignition temperature of 650.degree. C. or higher, at which
casting is possible in the condition of including the protective
gas, Ca must be added to Mg alloys, preferably in an amount of 3wt
% or greater, and in a minimum amount of 2wt % or greater. However,
when Ca is added in an amount greater than 2wt %, the tensile
properties of Mg alloys are generally degraded, with the decrease
in elongation being particularly significant. This is because a
great quantity of coarse and brittle eutectic phases is formed,
thereby resulting in cracks. As such, increasing the amount of Ca
that is added has the merit of increasing the ignition resistance,
but also has a drawback in that the tensile properties are
significantly degraded. Therefore, there is the demand for the
development of a magnesium alloy that can satisfy both the ignition
resistance and the tensile properties.
DISCLOSURE
Technical Problem
[0006] Therefore, an object of the present invention is to provide
a magnesium alloy that is intended to solve the foregoing problem
of the related art.
[0007] Specifically, an object of the present invention is to
provide a magnesium alloy that contains Ca therein, and more
particularly, has excellent ignition resistance and excellent
tensile properties.
[0008] In addition, an object of the present invention is to
provide a magnesium alloy that enables an environment-friendly
manufacturing process, which uses a minimum amount of Ca and does
not use a protective gas such as SF.sub.6, which is an
environmental pollutant.
Technical Solution
[0009] In order to realize the foregoing object, according to the
present invention, provided is a magnesium (Mg) alloy, which is
manufactured by melt casting. The Mg alloy includes, by weight,
1.0% or greater but less than 7.0% of Al, 0.05% to 2.0% of Ca,
0.05% to 2.0% of Y, greater than 0% but not greater than 6.0% of
Zn, and the balance of Mg, and the other unavoidable impurities.
The total content of the Ca and the Y is equal to or greater than
0.1% but less than 2.5% of the total weight of the magnesium
alloy.
[0010] In addition, it is preferable that the content of the Ca
range, by weight, from 0.2% to 1.5%.
[0011] Furthermore, it is preferable that the content of the Y
range, by weight, from 0.1% to 1.5%.
[0012] In addition, it is preferable that the contents of the Ca
and the Y range from 0.3% to 2.0% of a total weight of the
magnesium alloy.
[0013] Furthermore, it is preferable that the magnesium alloy
further include, by weight, greater than 0% but not greater than
1.0% of Mn.
[0014] In addition, it is preferable that the magnesium alloy
further include, by weight, 0.1% to 1.0% of Zr.
[0015] According to the present invention, provided is a method of
manufacturing a magnesium alloy. The method includes the following
steps of: forming a magnesium alloy molten metal, which contains
Mg, Al and Zn; adding raw materials of Ca and Y into the magnesium
alloy molten metal; producing a magnesium alloy cast material from
the magnesium alloy molten metal, in which the raw materials of Ca
and Y are added, using a fusion casting method. A magnesium alloy
produced as described above includes, by weight, 1.0% or greater
but less than 7.0% of Al, 0.05% to 2.0% of Ca, 0.05% to 2.0% of Y,
greater than 0% but not greater than 6.0% of Zn, the balance of Mg,
and the other unavoidable impurities.
[0016] In addition, it is preferable that the step of adding the
raw materials of Ca and Y into the magnesium alloy molten metal
include the step of adding the raw materials of Ca and Y at a
temperature higher than 800.degree. C.
[0017] According to the present invention, provided is a method of
manufacturing a magnesium alloy. The method includes the following
steps of: forming a magnesium alloy molten metal, which contains
Mg, Al and Zn; forming a master alloy ingot, which contains Mg, Al,
Zn, Ca and Y, and is soluble at 750.degree. C. or lower; inputting
the master alloy ingot, which is soluble at 750.degree. C. or
lower, into the magnesium alloy molten metal; and producing a
magnesium alloy cast material from the molten metal, which contains
the master alloy ingot, using a fusion casting method. A magnesium
alloy produced as described above includes, by weight, 1.0% or
greater but less than 7.0% of Al, 0.05% to 2.0% of Ca, 0.05% to
2.0% of Y, greater than 0% but not greater than 6.0% of Zn, the
balance of Mg, and the other unavoidable impurities.
[0018] In addition, it is preferable that the master alloy ingot,
which contains Mg, Al, Zn, Ca and Y, is soluble at 750.degree. C.
or lower, and is input into the magnesium alloy molten metal at a
temperature lower than 750.degree. C.
[0019] According to the present invention, provided is a method of
manufacturing a magnesium alloy. The method includes the following
steps of: forming a magnesium alloy molten metal, which contains
Mg, Al and Zn; adding a Ca compound and a Y compound into the
magnesium alloy molten metal; and producing a magnesium alloy cast
material from the magnesium alloy molten metal, in which the Ca
compound and the Y compound are added, using a fusion casting
method. A magnesium alloy produced as described above includes, by
weight, 1.0% or greater but less than 7.0% of Al, 0.05% to 2.0% of
Ca, 0.05% to 2.0% of Y, greater than 0% but not greater than 6.0%
of Zn, the balance of Mg, and the other unavoidable impurities.
[0020] In addition, it is preferable that the step of inputting the
raw materials of Ca and Y, the master alloy ingot, which contains
Mg, Al, Zn, Ca and Y, or the Ca compound and the Y compound into
the magnesium alloy molten metal further include the step of
periodically stirring the magnesium alloy molten metal.
[0021] Furthermore, it is preferable that the casting method be one
selected from the group consisting of mold casting, sand casting,
gravity casting, squeeze casting, continuous casting, strip
casting, die casting, precision casting, lost foam casting, spray
casting, and semi-solid casting.
[0022] In addition, it is preferable that the method further
include the step of carrying out hot working on the magnesium alloy
cast material produced by the casting method.
[0023] The reasons why the content of respective components in the
magnesium alloy of the present invention is limited are as
follows.
[0024] Aluminum (Al)
[0025] Al is an element that increases the strength, flowability
and solidification range of a magnesium alloy, thereby improving
castability. In general, the fraction of the eutectic phase
increases in response to an increase in the content of Al that is
added. In addition, as will be described later, according to the
results of experiments of the present invention, it can be
appreciated that the ignition resistance increases in response to
an increase in the content of Al when Al is added in combination
with other alloying elements. When the content of Al is less than 1
wt %, the effect of the increased strength and ignition resistance
does not occur, and when the content of Al is equal to or greater
than 7 wt %, tensile properties are degraded due to a coarse
Mg.sub.17Al.sub.12 eutectic phase. Therefore, it is preferred that
Al is contained in the range equal to or greater than 1 wt % and
less than 7 wt %.
[0026] Calcium (Ca)
[0027] Ca improves the strength and thermal resistance properties
of a Mg--Al-based alloy by forming an intermetallic compound as
well as reducing the oxidation of a molten metal by forming a thin
and dense oxide layer of CaO on the surface of the molten metal,
thereby improving the ignition resistance of the Mg alloy. However,
when the content of Ca is less than 0.05 wt %, the effect of the
improved ignition resistance is not significant. On the other hand,
when the content of Ca is greater than 2 wt %, the castability of
the molten metal decreases, hot cracking occurs, die sticking
increases, and elongation significantly decreases, which are
problematic. Therefore, in the Mg alloy of the present invention,
Ca is added in an amount ranging preferably from 0.05 wt % to 2.0
wt %, and more preferably from 0.2 wt % to 1.5 wt %.
[0028] Yttrium (Y)
[0029] Y is generally used as an element that increases
high-temperature creep resistance due to precipitation
strengthening, since it has a high solubility limit. When Y is
added in combination with Ca to the magnesium alloy, the fraction
of the coarse Ca-containing eutectic phase decreases. When Y is
added in an amount of 0.5 wt % or greater, there is an effect in
that Al.sub.2Y particles, which form microscopic grains of a cast
material, are formed, thereby improving tensile properties. In
addition, an oxide layer of Y.sub.2O.sub.3 is formed on the surface
of a molten metal to form a mixed layer with MgO and CaO, thereby
increasing ignition resistance. When Y is contained in an amount of
less than 0.05 wt % in the Mg alloy, the increase in the ignition
temperature is not significant. When Y is contained in an amount
greater than 2 wt %, the price of the Mg alloy rises, and the
effect of micronization is lost due to the coarsening of Al.sub.2Y
particles. Therefore, in the Mg alloy of the present invention, Y
is included in an amount ranging preferably from 0.05 wt % to 2.0
wt %, and more preferably from 0.1 wt % to 1.5 wt %.
[0030] Zinc (Zn)
[0031] Zn has an effect of refining grains and increasing strength
when added together with Al. In addition, the maximum solubility
limit of Zn in the Mg alloy is 6.2 wt %. When an amount of Zn
greater than this limit is added, a coarse eutectic phase that is
created during casting weakens the mechanical properties of the
cast material, and a considerable amount of coarse eutectic phase
resides even after homogenization heat treatment, thereby becoming
a factor that weakens the mechanical properties, in particular,
elongation. Therefore, it is preferred that Zn be added in an
amount equal to or less than 6 wt %.
[0032] Manganese (Mn)
[0033] In the Mg--Al-based alloy, Mn improves corrosion resistance
due to its bonding with Fe, which is an impurity element that
impedes corrosion resistance, and increases strength by forming an
Al--Mn intermetallic compound at a rapid cooling speed. However,
when Mn is added in an amount greater than 1.0 wt %, a coarse
.beta.-Mn or Al.sub.8Mn.sub.5 phase is formed in the Mg alloy,
thereby deteriorating the mechanical properties. Therefore, it is
preferred that Mn be included in an amount equal to or less than
1.0 wt %.
[0034] Zirconium (Zr)
[0035] Zr is generally added for the purpose of micronization of
grains due to the non-homogeneous nucleation of Mg crystals in
primary Zr because the primary Zr, the crystal lattice of which is
very similar to Mg crystals, is created during solidification when
Zr is added to a Mg alloy that does not contains some elements,
such as Al and Mn. When Zr is added in an amount less than 0.1 wt
%, its effect is not sufficient. When Zr is added in an amount that
is greater than 1.0 wt %, elongation decreases due to the formation
of the coarse primary Zr. Therefore, it is preferred that Zr be
added in an amount ranging from 0.1 wt % to 1.0 wt %.
[0036] Other Unavoidable Impurities
[0037] The Mg alloy of the present invention may contain impurities
that are unavoidably mixed from raw materials thereof or during the
process of manufacture. Among the impurities that can be contained
in the Mg alloy of the invention, iron (Fe), silicon (Si) and
nickel (Ni) are components that particularly worsen the corrosion
resistance of the Mg alloy. Therefore, it is preferred that the
content of Fe be maintained at 0.004 wt % or less, the content of
Si be maintained at 0.04 wt % or less, and the content of Ni be
maintained at 0.001 wt % or less.
[0038] Total Amount of Ca and Y
[0039] When Ca and Y are added in combination, a dense combined
oxide layer of CaO/Y.sub.2O.sub.3 is formed on the surface of a
solid or liquid Mg alloy, so that the ignition resistance of the Mg
alloy is superior to that of a Mg alloy to which Ca or Y is
separately added. In addition, when Ca or Y is separately added, an
amount of 3 wt % or greater is generally added in order to obtain
excellent ignition resistance. In this case, however, there is a
problem in that the tensile properties are greatly degraded because
a coarse intermetallic compound is formed. In contrast, the
addition of Ca and Y in combination can advantageously improve
tensile properties by decreasing the fraction and size of the
intermetallic compound while obtaining excellent ignition
resistance. When Ca and Y are added to the Mg alloy such that the
total content thereof is less than 0.1 wt %, the effect of the
combined addition of Ca and Y does not appear. This results in a
low ignition temperature of 650.degree. C., thereby making it
impossible to perform melting in the air or a common inert gas
atmosphere. In addition, when the total content of Ca and Y is 2.5
wt % or greater, an increase in the cost of the alloy results
without any significant advantage related to the additional
increase in the ignition temperature. Therefore, in the Mg alloy of
the invention, it is preferred that the total content of Ca and Y
that are added be in the range preferably equal to or greater than
0.1 wt % and less than 2.5 wt, and more preferably from 0.2 wt % to
2.0 wt %.
Advantageous Effects
[0040] The Mg alloy according to the invention forms a dense
composite oxide layer that acts as a protective film. Thus the Mg
alloy has very excellent oxidation and ignition resistance, can be
melted, cast and machined in the air or a common inert atmosphere
(Ar or N.sub.2), and can reduce the spontaneous ignition of chips
that are accumulated during the process of machining.
[0041] In addition, the Mg alloy according to the invention is
adapted to reduce costs, protect the health of workers, and prevent
environmental pollution since it does not use a protective gas such
as SF.sub.6.
[0042] Furthermore, the Mg alloy according to the invention is
applicable as a material for structural components, since its
ignition resistance is superior to that of common alloys, with the
ignition temperature thereof being 50.degree. C. higher than the
melting point thereof, and it also has excellent strength and
ductility.
[0043] Moreover, the Mg alloy according to the invention can be
variously used as a processing material or a cast material, and in
particular, can be manufactured as an extruded material, a sheet
material, a forged material, a cast material, and the like, which
can be practically applied to next-generation vehicles, high-speed
rail systems, and the like, in which high-strength, high-elongation
and safety characteristics are required.
DESCRIPTION OF DRAWINGS
[0044] FIG. 1 (a) is a picture showing the surface of an alloy cast
material according to comparative example 1, which is manufactured
in the air according to an exemplary embodiment of the
invention;
[0045] FIG. 1 (b) is a picture showing the surface of an alloy cast
material according to comparative example 2, which is manufactured
in the air according to an exemplary embodiment of the
invention;
[0046] FIG. 2 is a view illustrating a method of measuring the
ignition temperature of a magnesium alloy, which is manufactured
according to an exemplary embodiment of the invention;
[0047] FIG. 3 is a view showing the results of electron probe
micro-analysis (EPMA) on an oxide layer on the surface of a molten
metal after a magnesium alloy according to example 5, which was
cast according to an exemplary embodiment of the invention, was
maintained at 670.degree. C. for 10 minutes;
[0048] FIG. 4 is a view schematically showing the structure of
double composite oxide layers formed on the surface of a solid or
liquid phase in an alloy in which Ca and Y are added in
combination, the double composite oxide layers serving to block the
penetration of external oxygen;
[0049] FIG. 5 (a) is an optical picture showing the microscopic
structure of an alloy of comparative example 3, which is cast
according to an exemplary embodiment of the invention;
[0050] FIG. 5 (b) is an optical picture showing the microscopic
structure of an alloy of example 2, which is cast according to an
exemplary embodiment of the invention;
[0051] FIG. 6 (a) is an optical picture showing the microscopic
structure of an alloy of comparative example 1, which is extruded
according to an exemplary embodiment of the invention;
[0052] FIG. 6 (b) is an optical picture showing the microscopic
structure of an alloy of comparative example 2, which is extruded
according to an exemplary embodiment of the invention;
[0053] FIG. 6 (c) is an optical picture showing the microscopic
structure of an alloy of comparative example 3, which is extruded
according to an exemplary embodiment of the invention;
[0054] FIG. 6 (d) is an optical picture showing the microscopic
structure of an alloy of example 1, which is extruded according to
an exemplary embodiment of the invention;
[0055] FIG. 7 is a picture showing variation in the ignition
temperature depending on the total amount of Ca and Y that is added
in the comparative examples and examples, which are manufactured
according to an exemplary embodiment of the invention; and
[0056] FIG. 8 is a picture showing variations in the value of
tensile strength x uniform elongation depending on the total amount
of Ca and Y that is added in the comparative examples and examples,
which are manufactured according to an exemplary embodiment of the
invention.
BEST MODE
[0057] Reference will now be made in detail to exemplary
embodiments of a Mg alloy and a method of manufacturing the same
according to the present invention. However, it is to be understood
that the following embodiments are illustrative but do not limited
the invention.
[0058] As the results of studies that were carried out on a
thermodynamically calculated alloy design in order to solve the
foregoing problem of the related art and realize the object of the
invention, the inventors of the invention found that, when Ca and Y
are added in combination to a Mg--Al-based alloy or a
Mg--Al--Zn-based alloy, as presented in Table 1 below, the fraction
of a hard eutectic phase (eutectic phase I) significantly decreases
compared to the case in which Ca is added alone, and at the same
time, the formation of a Al.sub.2Y phase, i.e. particles that form
micronized grains, is induced, so that not only ignition resistance
but also tensile strength can be improved.
TABLE-US-00001 TABLE 1 Eutectic Eutectic phase I phase II Al.sub.2Y
(Al.sub.2Ca, Mg.sub.2Ca) (Mg.sub.17CAL.sub.12) Mg--3Al--1Zn--1Ca --
2.241 Mg--3Al--1Zn--2Ca -- 3.733 Mg--3Al--1Zn--1Ca--0.6Y 0.845
2.169 Mg--6Al--1Zn--1Ca -- 2.303 4.183 Mg--6Al--1Zn--2Ca -- 4.600
1.776 Mg--6Al--1Zn--1Ca--0.6Y 0.890 2.272 3.505
[0059] The inventors of the invention manufactured Mg alloys having
a variety of compositions based on the above data. The method of
manufacturing a Mg alloy according to an exemplary embodiment of
the invention is as follows.
[0060] First, raw materials that include Mg (99.9%), Al (99.9%), Zn
(99.99%), Ca (99.9%), Y (99.9%) and selectively Mn (99.9%) were
prepared, and were then melted. Then, Mg alloy cast materials
having the alloy compositions described in example 1 to example 17
and comparative example 1 to comparative example 9 in Table 2 below
were formed from the raw materials using a gravity casting method.
Specifically, the temperature of a molten metal was increased up to
a temperature between 850.degree. C. and 900.degree. C., so that
these elements were completely melted, in order to produce an alloy
by directly inputting Ca and Y, which have high melting points of
842.degree. C. and 1525.degree. C., respectively, into the molten
metal. After that, the molten metal was gradually cooled down to a
casting temperature, and then the Mg alloy cast materials were
produced by casting the molten metal.
[0061] Alternatively, according to an exemplary embodiment of the
invention, it is possible to manufacture a Mg alloy by a variety of
methods in addition to the method in which casting is performed
after a molten metal is formed by simultaneously melting raw
materials including Mg (99.9%), Al (99.9%), Zn (99.99%), Ca (99.9%)
and Y (99.9%). In an example, it is possible to first form a Mg
alloy molten metal using the raw materials of Mg, Al and Zn or
alloys thereof, input the raw materials of Ca and Y, or a Ca
compound and a Y compound into the Mg alloy molten metal, and then
produce a Mg alloy cast material by a suitable casting method. It
is also possible to produce a Mg alloy cast material by preparing a
Mg, Al, Zn, Ca and Y alloy (master alloy ingot) of which the
contents of Ca and Y are higher than final target values, forming a
Mg alloy molten metal using raw materials of Mg, Al and Zn or
alloys thereof, and then inputting the master alloy ingot into the
Mg alloy molten metal. This method is particularly advantageous in
that the master alloy ingot can be input at a temperature that is
lower than the temperature at which the raw materials of Ca and Y
are directly input into the Mg alloy molten metal, since the
melting point of the master alloy ingot is lower than those of the
raw materials of Ca and Y. In addition, the formation of a Mg alloy
according to the invention can be realized by a variety of methods,
and all methods of forming a Mg alloy that are well-known in the
art to which the invention belongs are included as part of the
invention.
[0062] In this embodiment, a graphite crucible was used for
induction melting, and a mixture gas of SF.sub.6 and CO.sub.2 was
applied on the upper portion of the molten metal, so that the
molten metal did not come into contact with the air, in order to
prevent the molten metal from being oxidized before the alloying
process was finished. In addition, after the melting was completed,
mold casting was performed using a steel mold without a protective
gas. A sheet-shaped cast material having a width of 100 mm, a
length of 150 mm and a thickness of 15 mm was manufactured for a
rolling test, a cylindrical billet having a diameter of 80 mm and a
length of 150 mm was manufactured for an extrusion test, and a
cylindrical billet having a diameter of 55 mm and a length of 100
mm was manufactured for an ignition test of the alloy cast
material. Although the Mg alloy was cast by a mold casting method
in this embodiment, a variety of casting methods, such as sand
casting, gravity casting, squeeze casting, continuous casting,
strip casting, die casting, precision casting, spray casting,
semi-solid casting, and the like, may also be used. Although the Mg
alloy according to the invention is not necessarily limited to a
specific casting method, fusion casting is more preferable.
[0063] Afterwards, the slabs that were prepared above were
subjected to homogenization heat treatment at 400.degree. C. for 15
hours. In sequence, the materials of comparative example 1 to
comparative example 6 and example 1 to example 7 in Table 2, which
were subjected to homogenization heat treatment, were machined into
sheet materials having a final thickness of 1 mm via hot working,
in which the respective materials were rolled under conditions of a
roll temperature of 200.degree. C., a roll diameter of 210 mm, a
roll speed of 5.74 mpm, and reduction ratios of each roll of
30%/pass and 72%/pass. Here, when the reduction ratio of each roll
was 30%/pass, rolling was performed a total of 7 times until the
final thickness of 1 mm was realized.
[0064] In addition, in comparative example 7, comparative example 8
and example 8 in Table 2, rod-shaped extruded materials having a
final diameter of 16 mm were manufactured by extruding the
materials that were subjected to homogenization heat treatment
under conditions including an extrusion speed of 5 m/min, an
extrusion ratio of 25:1, and an extrusion temperature of 250. The
extruded materials had a good surface state.
[0065] Although rolling and extrusion were performed after casting
and homogenization heat treatment in this embodiment, the materials
may be manufactured by a variety of machining methods, such as
forging and drawing, without being necessarily limited to a
specific machining method.
Measurement of Ignition Temperature of Mg Alloy
[0066] In order to measure the ignition temperature of the Mg
alloys, chips having a predetermined size were produced by
machining the outer portion of the cylindrical billets, which were
manufactured above, in conditions including a depth of 0.5 mm, a
pitch of 0.1 mm, and a constant speed of 350 rpm. 0.1 g chips that
were produced by the foregoing method were heated by loading them
at a constant speed into a heating furnace, which was maintained at
1000.degree. C. The temperatures at which a sudden rise in
temperature begins during this process were determined as ignition
temperatures, as shown in FIG. 3, and the results are presented in
Table 2.
[0067] As can be seen from comparative example 1 to comparative
example 6 in Table 2, the ignition temperature of Mg alloys
suddenly increases in response to the addition of Ca. When the same
amount of Ca was added, the ignition temperature of the alloys
tends to increase in response to an increase in the content of Al
therein.
TABLE-US-00002 TABLE 2 Alloy Alloy Composition (wt %) Ignition Temp
Symbol Al Zn Ca Y Mn Zr (.degree. C.) Test Atm. Comp. Ex. 1 AZ31 3
1 490 Air 554 Air + Ar Comp. Ex. 2 AZX311 3 1 1 708 Air Comp. Ex. 3
AZX312 3 1 2 747 Air Comp. Ex. 4 AZ61 6 1 507 Air 602 Air + Ar
Comp. Ex. 5 AZX611 6 1 1 703 Air Comp. Ex. 6 AZX612 6 1 2 755 Air
Comp. Ex. 7 ZX61 6 1 672 Air Comp. Ex. 8 ZX62 6 2 704 Air Comp. Ex.
9 ZK60 5.5 0.45 553 Air Example 1 Alloy 1 3 0.8 1 1 0.3 807 Air
Example 2 Alloy 2 3 1 1 0.6 768 Air 776 Air + Ar Example 3 Alloy 3
3 1 0.7 0.6 714 Air 707 Air + Ar Example 4 Alloy 4 3 0.8 0.3 0.3
0.25 698 Air 705 Air + Ar Example 5 Alloy 5 6 1 1 0.6 774 Air
Example 6 Alloy 6 6 1 0.7 0.6 745 Air 749 Air + Ar Example 7 Alloy
7 6 1 0.3 0.3 705 Air 717 Air + Ar Example 8 Alloy 8 6 1 0.1 0.1
677 Air Example 9 Alloy 9 6 2 1 0.6 783 Air Example 10 Alloy 10 4 4
0.7 0.6 658 Air 711 Air + Ar Example 11 Alloy 11 4 4 0.1 0.1 771
Air Example 12 Alloy 12 1 6 1 1 653 Air 676 Air + Ar Example 13
Alloy 13 1 6 0.7 0.6 744 Air Example 14 Alloy 14 1 6 1 0.3 689 Air
Example 15 Alloy 15 2 6 1 1 659 Air Example 16 Alloy 16 1 6 0.7 0.6
0.2 755 Air Example 17 Alloy 17 698 Air
[0068] In Table 2, comparing each ignition temperature of example 2
and example 5 with the respective ignition temperature of
comparative example 2 and comparative example 5, it can be
appreciated that the ignition temperature is much higher when Y was
also added to the Mg alloys than when Ca was added alone to the Mg
alloys. This is because a mixed layer of CaO and Y.sub.2O.sub.3 was
formed in the portion that was in contact with molten metal due to
the addition of Y, as can be seen from the result of electron probe
micro-analysis (EPMA) of FIG. 4, and that this layer was able to
effectively reduce the oxygen in the air from penetrating into and
reacting with the molten metal. In addition, a mixed layer of CaO
and MgO was present in the outer portion of the mixed layer of CaO
and Y.sub.2O.sub.3. These double mixed layers help the molten metal
remain stable even at high temperatures.
[0069] In addition, comparing comparative example 3 with example 2
and comparative example 6 with example 5, it can be appreciated
that the ignition temperature was higher when Ca and Y were added
in combination than when Ca was added alone, even though the total
content of Ca and Y was less than the content of Ca. This shows
that a more excellent effect can be realized in terms of increasing
ignition resistance when Ca and Y are added in combination than
when Ca is used alone in order to increase the ignition temperature
of the Mg alloy.
[0070] In addition, Table 2 presents that the Mg alloy according to
example 1 has a very high ignition temperature of 807.degree. C.
This is because Y has a very high content of 1 wt %. Thus, it can
be appreciated that ignition resistance can significantly increase
in response to an increase in the content of Y that is added.
Furthermore, in Table 2, the Mg alloy according to example 8 has a
very high ignition resistance of 811.degree. C. This shows that the
ignition temperature of the Mg alloy, in which 6 wt % of Zn is
added, significantly increases when Ca and Y are added respectively
in an amount of 1 wt %.
Evaluation of Tensile Properties of Mg Alloy
[0071] The sheet materials, which were manufactured by the
above-described method, were heat-treated at 250.degree. C. for 30
minutes, and then sub-size sheet-shaped samples according to the
ASTM-E-8M standard, in which the length of a gauge was 25 mm, were
produced. A tensile test was carried out at room temperature under
a strain of 1.times.10.sup.-3s.sup.-1 using a common tensile
tester, and the results are presented in Table 3.
[0072] In addition, samples of a rod-shaped extruded material, in
which the length of a gauge was 25 mm, were manufactured, and
tensile test was carried out under the same conditions as for the
sheet-shaped samples.
[0073] As presented in Table 3, comparing comparative example 2
with comparative example 3, comparative example 5 with comparative
example 6, and comparative example 7 with comparative example 8, it
can be appreciated that the yield strength and tensile strength
increased but elongation significantly decreased in response to the
increase in the content of Ca from 1 wt % to 2 wt %. This decrease
in the elongation is because the fraction of a microscopic
precipitate phase of Al.sub.2Ca as well as the fraction of a coarse
and hard ternary eutectic phase of Mg--Al--Ca increased, as shown
in FIG. 5 (a), when the content of Ca that was added was increased
to 2 wt %. In contrast, as shown in FIG. 5 (b), when the content of
Ca that was added was 1 wt %, even though 0.6 wt % of Y was
included, no coarse and hard ternary eutectic phase of Mg--Al--Ca
was observed and thus elongation was not decreased. Likewise,
comparing the microscopic structures of the extruded materials of
comparative example 1 to comparative example 3 and example 1 with
reference to FIG. 6, when the content of Ca that was added was
increased to 1 wt % and 2 wt %, large amounts of black second
phases, indicated by the arrows in FIG. 6 (b) and FIG. 6 (c),
respectively, were observed, and elongation decreased since the
hard second phases were vulnerable to defects.
TABLE-US-00003 TABLE 3 Tensile Properties YS.sup.1) TS.sup.2)
El.sup.3) UEl.sup.4) TS .times. UEl Alloy Symbol (MPa) (MPa) (%)
(%) (MPa %) Remarks Comp. Ex. 1 AZ31 176.4 274.5 25.2 17.4 4788
RAM.sup.5) 176.8 270.4 26.0 15.3 4142 EM.sup.6) Comp. Ex. 2 AZX311
191.1 276.1 24.3 16.9 4658 RAM 239.4 294.5 17.1 11.8 3479 EM Comp.
Ex. 3 AZX312 255.2 303.6 16.5 9.7 2943 RAM 346.0 355.4 9.0 5.8 2045
EM Comp. Ex. 4 AZ61 218.7 324.0 22.0 17.2 5565 RAM 166.5 298.1 26.4
21.1 6292 EM Comp. Ex. 5 AZX611 204.4 306.2 19.7 16.0 4909 RAM
150.8 276.9 21.2 19.3 5337 EM Comp. Ex. 6 AZX612 230.0 321.0 16.7
14.1 4536 RAM 169.9 275.6 19.2 16.4 4533 EM Comp. Ex. 7 ZX61-F
191.4 268.1 25.4 17.2 4606 EM Comp. Ex. 8 ZX62-F 294.9 298.5 13.7
9.4 2791 EM Comp. Ex. 9 ZE60-F 238.4 318.4 24.1 13.5 4298 EM
Example 2 Alloy 2 175.8 265.2 24.7 18.4 4880 RAM Example 3 Alloy 3
171.1 264.3 26.5 18.4 4856 RAM Example 4 Alloy 4 175.1 267.4 27.8
16.8 4483 EM Example 5 Alloy 5 225.7 323.4 19.6 15.5 5020 RAM
Example 8 Alloy 8 156.3 297.6 26.8 22.6 6738 EM Example 9 Alloy 9
242.1 337.0 16.8 15.3 5157 RAM Example 10 Alloy 10 215.1 340.2 21.7
19.5 6633 EM Example 11 Alloy 11 152.0 302.1 33.5 29.1 8780 EM
Example 12 Alloy 12 189.8 323.7 27.3 22.7 7338 EM Example 13 Alloy
13 161.5 276.1 26.8 22.4 6196 RAM Example 14 Alloy 14 165.9 288.3
30.3 25.9 7467 EM Example 15 Alloy 15 167.5 280.8 31.3 23.9 6711 EM
Example 16 Alloy 16 175.3 285.7 26.5 22.3 6363 EM Notes) YS.sup.1):
Yield Strength, TS.sup.2): Tensile Strength, El.sup.3): Elongation,
UEl.sup.4): Uniform Elongation, RAM.sup.5): Rolled and Annealed
Material, EM.sup.6): Extruded Material
[0074] On the other hand, as shown in FIG. 6 (d), no hard second
phase that decreases elongation was observed in the extruded
material of an alloy in which each of Ca and Y was added in an
amount of 1 wt %. This result is more apparent when comparing
example 2 with comparative example 3, example 5 with comparative
example 6, and example 13 with comparative example 8. Specifically,
it can be appreciated that, even though only 1 wt % of Ca and 0.6
wt % of Y were added in example 2 and example 5, their elongation
was very high and their ignition resistance and tensile strength
were at levels similar to those of comparative example 3 and
comparative example 6, in which 2 wt % of Ca was added. Likewise,
in example 13, it can be appreciated that the ignition resistance
was greatly increased and that the tensile properties, particularly
the value of tensile strength x uniform elongation, were greatly
increased when 1 wt % of Ca and 1 wt % of Y were added to the
Mg--6Zn--1Al alloy. That is, due to the addition of a small amount
of Y, it was possible to produce a Mg alloy of this embodiment in
which the content of Ca was maintained low, on the order of 1 wt %,
but in which the fraction of the coarse and hard ternary eutectic
phase was greatly decreased, such that both strength and elongation
were improved.
[0075] In addition, comparing example 2 with comparative example
and example 5 with comparative example 5, it can be appreciated
that example 2 and example 5 contain the same content of Ca that
was added in relation to the addition of Y, and have ignition
resistance that is superior to that of the case in which Y was not
added. At the same time, the value of tensile
strength.times.uniform elongation is further increased.
[0076] This tendency can be appreciated from FIG. 7 and FIG. 8,
which show variations in the ignition temperature and tensile
properties thereof in response to the total amount of Ca and Y that
was added. As shown in FIG. 7, the ignition temperature tends to
gradually increase in response to an increase in the total amount
of Ca and Y that was added. In particular, it can be appreciated
that the slope of the increase in the ignition temperature is
further increased when Y is added than when Y is not added. In
contrast, as shown in FIG. 8, when Ca is added alone, the value of
tensile strength x uniform elongation tends to greatly decrease in
response to an increase in the content of Ca that is added,
irrespective of the type of hot working. However, when both Ca and
Y are added, the mechanical strength thereof is improved more than
that of an alloy in which neither Ca nor Y is added. From these
results, it can be appreciated that the ignition resistance is
greatly increased, and at the same time that tensile properties are
greatly improved due to the addition of a small content of Ca and Y
at the same time.
[0077] The Mg alloy and the method of manufacturing the same
according to exemplary embodiments of the present invention have
been described above in detail with reference to the accompanying
drawings. However, it will be apparent to a person having ordinary
skilled in the art to which the present invention belongs that the
foregoing embodiments are merely examples of the invention and
various modifications and variations are possible. Therefore, it
should be understood that the scope of the invention shall be
defined only by the appended claims.
* * * * *