U.S. patent application number 14/712609 was filed with the patent office on 2015-11-05 for method for manufacturing extruded magnesium alloy and extruded magnesium alloy manufactured thereby.
This patent application is currently assigned to KOREA INSTITUTE OF MACHINERY AND MATERIALS. The applicant listed for this patent is KOREA INSTITUTE OF MACHINERY AND MATERIALS. Invention is credited to Jun Ho BAE, Ha-Sik KIM, Young Min KIM, Byoung-Gi MOON, Sung Hyuk PARK, Chang Dong YIM, Bong Sun YOU.
Application Number | 20150315690 14/712609 |
Document ID | / |
Family ID | 51062293 |
Filed Date | 2015-11-05 |
United States Patent
Application |
20150315690 |
Kind Code |
A1 |
PARK; Sung Hyuk ; et
al. |
November 5, 2015 |
METHOD FOR MANUFACTURING EXTRUDED MAGNESIUM ALLOY AND EXTRUDED
MAGNESIUM ALLOY MANUFACTURED THEREBY
Abstract
Provided are a method of preparing a magnesium alloy extrudate
and a magnesium alloy extrudate prepared thereby. Specifically, the
present invention is related to a method of preparing a magnesium
alloy extrudate including melting a magnesium alloy raw material
(step 1), casting the magnesium alloy raw material melted in step 1
to prepare a magnesium alloy billet (step 2), homogenizing the
magnesium alloy billet prepared in step 2 (step 3), applying 3% to
20% of compressive deformation to the homogenized magnesium alloy
billet of step 3 (step 4), and extruding the compressive deformed
magnesium alloy billet of step 4 (step 5), and a magnesium alloy
extrudate prepared thereby.
Inventors: |
PARK; Sung Hyuk;
(Changwon-si, KR) ; YOU; Bong Sun; (Changwon-si,
KR) ; KIM; Ha-Sik; (Masan-si, KR) ; MOON;
Byoung-Gi; (Changwon-si, KR) ; BAE; Jun Ho;
(Pohang-si, KR) ; KIM; Young Min; (Jinhae-si,
KR) ; YIM; Chang Dong; (Changwon-si, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KOREA INSTITUTE OF MACHINERY AND MATERIALS |
Daejeon |
|
KR |
|
|
Assignee: |
KOREA INSTITUTE OF MACHINERY AND
MATERIALS
Daejeon
KR
|
Family ID: |
51062293 |
Appl. No.: |
14/712609 |
Filed: |
May 14, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/KR2013/009795 |
Oct 31, 2013 |
|
|
|
14712609 |
|
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Current U.S.
Class: |
148/557 ;
148/420 |
Current CPC
Class: |
B21C 23/002 20130101;
C22F 1/06 20130101; C22C 23/04 20130101; C22C 23/00 20130101; B22D
21/04 20130101; C22C 23/02 20130101 |
International
Class: |
C22F 1/06 20060101
C22F001/06; C22C 23/00 20060101 C22C023/00; C22C 23/04 20060101
C22C023/04; C22C 23/02 20060101 C22C023/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 4, 2013 |
KR |
10-2013-0001125 |
Jul 16, 2013 |
KR |
10-2013-0083597 |
Claims
1. A method of preparing a magnesium alloy extrudate, the method
comprising: melting a magnesium alloy raw material; casting the
melted magnesium alloy raw material melted in step 1 in a
temperature range of 650.degree. C. to 750.degree. C. to prepare a
magnesium alloy billet; homogenizing the magnesium alloy billet
prepared in by heat treating in a temperature range of 400.degree.
C. to 550.degree. C. for 0.5 hours to 96 hours and cooling;
applying 3% to 20% of compressive deformation to the homogenized
magnesium alloy billet; and extruding the compressive deformed
magnesium alloy billet.
2. (canceled)
3. (canceled)
4. The method as set forth in claim 1, wherein the homogenizing is
performed after preheating in a temperature range of 250.degree. C.
to 350.degree. C.
5. The method as set forth in claim 1, wherein the compressive
deformation is performed in a longitudinal direction of the
magnesium alloy billet.
6. The method as set forth in claim 1, wherein the compressive
deformation is performed in a temperature range of room temperature
to 250.degree. C.
7. The method as set forth in claim 1, wherein the extrusion is
performed after preheating in a temperature range of 200.degree. C.
to 450.degree. C.
8. The method as set forth in claim 1, further comprising
performing an aging treatment after the extrusion.
9. The method as set forth in claim 8, wherein the aging treatment
is performed in a temperature range of 150.degree. C. to
250.degree. C. for 1 hour to 360 hours.
10. A magnesium alloy extrudate prepared by the method of claim
1.
11. A part for transportation equipment manufactured using the
magnesium alloy extrudate of claim 8.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present disclosure relates to a method of preparing a
magnesium alloy extrudate and a magnesium alloy extrudate prepared
thereby, and more particularly, to a method of preparing a
magnesium alloy extrudate having more improved strength and
elongation than those obtained from a typical extrusion method by
applying a predetermined amount of compressive deformation to a
homogenized billet.
[0003] 2. Description of the Related Art
[0004] Research into weight reduction of products and developing
new materials has been actively conducted worldwide to increase the
efficiency of transportation equipment and cope with environmental
pollution caused by exhaust gas and various environmental
regulations. Light metals, such as aluminum and magnesium, and
alloys thereof have emerged as main target materials, and the use
thereof as a new material for structural components of
transportation industries requiring high specific strength has been
significantly increased.
[0005] Magnesium alloys have been on the spotlight due to their
excellent properties, such as machinability, electromagnetic
shielding properties, and vibration absorption capacity, as well as
high specific strength, while being a lightweight metallic material
having the lowest density among all structural materials. Also,
since magnesium alloys may be used for special purposes by
controlling an alloy composition according to each application,
research into utilizing the magnesium alloys in various fields,
such as automotive parts, aircraft parts, and portable electronic
devices, has been actively conducted.
[0006] There are generally two types of magnesium alloy product.
One is cast products manufactured by casting and the other one is
wrought products manufactured by processing a cast billet or slab
by rolling, extrusion, or forging. With respect to the casting
method, magnesium alloy parts may be manufactured by various
casting processes such as sand casting, gravity casting, precision
casting, die casting, and a semi-solid forming technique, and most
of the magnesium alloy parts are currently manufactured by die
casting. However, in a case where a magnesium alloy is manufactured
by casting, a post-treatment process is required because the
surface thereof is very rough after the casting, and it is not
suitable for manufacturing a high quality alloy product requiring
high strength due to casting defects such as inclusions,
interdendritic shrinkage voids, porosity, and cavity. Therefore, a
technique of manufacturing a wrought material, such as a rolled
material, an extrudate, and a forged material, having superior
mechanical properties than cast materials, is essential in order to
expand the use and application of magnesium alloys.
[0007] Although wrought magnesium alloys have better strength and
ductility than cast materials, the wrought magnesium alloys have
lower mechanical properties than commercial wrought aluminum
alloys. Thus, many efforts to improve the strength and ductility of
the wrought magnesium alloys through various methods, such as the
addition of alloying elements, the application of powder
metallurgy, and the control of process conditions, are
underway.
[0008] For example, as a method of improving the strength of a
typical magnesium alloy, Korean Patent Application Laid-Open
Publication No. 10-2008-0085662 (publication date: 2008 Sep. 24)
discloses a manufacturing method, in which the composition of a
magnesium alloy is controlled and die casting and plastic
deformation are combined, as a method of improving mechanical
strength of a magnesium alloy. Also, Korean Patent Application
Laid-Open Publication No. 10-2012-0095184 (publication date: 2012
Aug. 28) discloses a method of controlling the composition of a
magnesium alloy as a method of improving mechanical strength and
ductility of a magnesium alloy extrudate. However, as in the
present invention, a method of simultaneously improving the
strength and ductility of a magnesium alloy extrudate by applying a
predetermined amount of compressive deformation to a magnesium
alloy billet homogenized before extrusion has not been disclosed
yet.
[0009] Accordingly, during research into a method of preparing a
magnesium alloy extrudate having excellent strength and ductility,
the present inventors developed a method of preparing a magnesium
alloy extrudate by extrusion after a predetermined amount of
compressive deformation is applied to a homogenized magnesium alloy
billet. The present inventors recognized that a magnesium alloy
extrudate having improved mechanical strength as well as improved
ductility may be prepared by adding a simple compressive
deformation process to a typical extrusion method as in the above
method, thereby leading to the completion of the present
invention.
SUMMARY OF THE INVENTION
[0010] It is an object of the present invention to provide a method
of preparing a magnesium alloy extrudate.
[0011] It is another object of the present invention to provide a
magnesium alloy extrudate prepared according to the above
method.
[0012] To achieve the above objects, the present invention provides
a method of preparing a magnesium alloy extrudate including:
melting a magnesium alloy raw material (step 1); casting the
magnesium alloy raw material melted in step 1 to prepare a
magnesium alloy billet (step 2); homogenizing the magnesium alloy
billet prepared in step 2 (step 3); applying 3% to 20% of
compressive deformation to the homogenized magnesium alloy billet
of step 3 (step 4); and extruding the compressive deformed
magnesium alloy billet of step 4 (step 5).
[0013] The present invention also provides a magnesium alloy
extrudate prepared by the above method.
[0014] Furthermore, the present invention provides a part for
transportation equipment manufactured using the above magnesium
alloy extrudate.
Advantageous Effect
[0015] A method of preparing a magnesium alloy extrudate according
to the present invention may provide a magnesium alloy extrudate
having simultaneously improved mechanical strength and ductility
using a simple method by adding a simple compressive deformation
process to a typical extrusion method, wherein a magnesium alloy
extrudate is prepared by applying a predetermined amount of
compressive deformation to a homogenized magnesium alloy billet and
then extruding the magnesium alloy billet.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] FIG. 1 is a schematic view illustrating a method of
preparing a magnesium alloy extrudate according to the present
invention;
[0017] FIG. 2 is a result of analyzing magnesium alloy billets
before and after room temperature compressive deformation using an
optical microscope;
[0018] FIG. 3 is a result of analyzing magnesium alloy billets
before and after room temperature compressive deformation using an
optical microscope;
[0019] FIG. 4 is electron back scattered diffraction (EBSD)
analysis images illustrating an inverse pole figure map and a twin
boundary map of an AZ31 alloy after room temperature compressive
deformation according to the present invention;
[0020] FIG. 5 is EBSD analysis images illustrating inverse pole
figure maps and grain size distribution of magnesium alloy
extrudates of Example 1 according to the present invention and
Comparative Example 1;
[0021] FIG. 6 is a result of analyzing magnesium alloy extrudates
of Examples 1 to 3 according to the present invention and
Comparative Examples 1 to 3 using an optical microscope; and
[0022] FIG. 7 is a result of analyzing magnesium alloy extrudates
of Examples 4 to 6 according to the present invention and
Comparative Examples 4 to 6 using an optical microscope.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Hereinafter, the present invention will be described in
detail.
[0024] As illustrated in FIG. 1, the present invention provides a
method of preparing a magnesium alloy extrudate including:
[0025] melting a magnesium alloy raw material (step 1);
[0026] casting the magnesium alloy raw material melted in step 1 to
prepare a magnesium alloy billet (step 2);
[0027] homogenizing the magnesium alloy billet prepared in step 2
(step 3);
[0028] applying 3% to 20% of compressive deformation to the
homogenized magnesium alloy billet of step 3 (step 4); and
extruding the compressive deformed magnesium alloy billet of step 4
(step 5).
[0029] Hereinafter, the method of preparing a magnesium alloy
extrudate according to the present invention will be described in
detail for each step.
[0030] In the method of preparing a magnesium alloy extrudate
according to the present invention, step 1 is melting a magnesium
alloy raw material.
[0031] Any magnesium alloy raw material may be used without
limitation as long as it is a commercial magnesium alloy. Since the
present invention uses a technique using a concept in which a twin
is easily generated in magnesium or magnesium alloys during room
temperature deformation due to insufficient slip systems, the
present invention may be applied to all magnesium alloys regardless
of their compositions. That is, magnesium pure metal or magnesium
alloys may be used as the magnesium alloy raw material, and any
composition of the magnesium alloy raw material may be used without
limitation.
[0032] Also, in addition to the magnesium alloys, the present
invention may be equally applied to titanium (Ti), zinc (Zn), and
cobalt (Co) alloys having a hexagonal close-packed (HCP) structure
in which a twin is easily generated by deformation.
[0033] Next, in the method of preparing a magnesium alloy extrudate
according to the present invention, step 2 is casting the magnesium
alloy raw material melted in step 1 to prepare a magnesium alloy
billet.
[0034] In step 2, the magnesium alloy raw material melted in step 1
(hereinafter, referred to as "magnesium alloy melt") may be cast in
a temperature range of 650.degree. C. to 750.degree. C. In the case
that the magnesium alloy melt is cast at a temperature less than
650.degree. C., since the fluidity of the magnesium alloy melt may
decrease, casting may be difficult. In the case in which the
magnesium alloy melt is cast at a temperature greater than
750.degree. C., since the magnesium alloy melt may be rapidly
oxidized, an impurity may be mixed during the casting. Thus, the
purity and quality of the magnesium alloy billet thus prepared may
be decreased.
[0035] In this case, a method of casting the magnesium alloy melt
is not particularly limited as long as it is typically used in the
art, and for example, gravity casting, continuous casting, sand
casting, and pressure casting may be used.
[0036] Next, in the method of preparing a magnesium alloy extrudate
according to the present invention, step 3 is homogenizing the
magnesium alloy billet prepared in step 2.
[0037] The homogenization may make more uniform structure by
dissolving the segregation of alloying elements and/or second
phases which occurs in a process of casting the magnesium alloy
melt and may improve high-temperature processability and mechanical
properties of a magnesium alloy billet. The homogenization of the
magnesium alloy billet may be performed by performing a heat
treatment process in a temperature range of 300.degree. C. to
550.degree. C. for 0.5 hours to 96 hours, and then performing a
cooling process. However, the temperature range of the
homogenization treatment may be appropriately selected by the
person skilled in the art according to the type of elements
constituting the magnesium alloy billet.
[0038] For example, with respect to a magnesium (Mg)-tin (Sn)-based
alloy, the homogenization treatment may be performed in a
temperature range of 400.degree. C. to 550.degree. C. In the case
that the homogenization treatment is performed at a temperature
less than 400.degree. C., since an amount of tin dissolved in a
magnesium matrix is decreased, the strengthening effect of the
alloy caused by dynamic precipitation which occurs during plastic
deformation, such as extrusion, rolling, and forging, at warm or
high temperatures may be not significant. Also, since a coarse
Mg.sub.2Sn phase formed during the casting process may not be
sufficiently removed, ductility of the magnesium alloy may be
reduced.
[0039] In the case in which the magnesium alloy billet is
homogenized at a temperature greater than 550.degree. C., since the
homogenization treatment temperature is higher than a solidus
temperature of the magnesium alloy, local melting of the magnesium
alloy billet may occur. Thus, physical properties may be
reduced.
[0040] Furthermore, in the case that the homogenization treatment
of the magnesium alloy billet is performed in the above temperature
range for less than 0.5 hours, the diffusion of the alloying
elements insufficiently occurs so that the effect of the
homogenization treatment may not be obtained. In the case in which
the homogenization treatment of the magnesium alloy billet is
performed for greater than 96 hours, an increase in the effect of
the homogenization treatment over time may not be large, and thus,
it may not be economical.
[0041] Next, in the method of preparing a magnesium alloy extrudate
according to the present invention, step 4 is applying 3% to 20% of
compressive deformation to the homogenized magnesium alloy billet
of step 3.
[0042] The compressive deformation may form twins in the
homogenized magnesium alloy. Twinning in the magnesium alloy having
a hexagonal close-packed structure may act as an important
deformation mechanism at room temperature. In this case, since
twins formed by the compressive deformation may act as nucleation
sites for recrystallization during the subsequent extrusion, a more
uniform and finer structure of the extrudate may be obtained due to
an increase in a fraction of recrystallized region. Thus, the
strength of the magnesium alloy extrudate may be improved. Also,
since a fraction of large unrecrystallized grains, in which cracks
are easily formed during tensile deformation to reduce ductility,
is significantly decreased when the extrusion is performed after
the compressive deformation is applied, elongation as well as
strength may be simultaneously improved.
[0043] 20% to 30% of compressive deformation may be applied to the
magnesium alloy billet homogenized in step 3. In the case that less
than 3% of compressive deformation is applied to the homogenized
magnesium alloy billet, a very small number of twins may be formed
in the magnesium alloy billet, and thus, the strength and
elongation of the magnesium alloy extrudate thus prepared may not
be improved. In the case in which greater than 20% of compressive
deformation is applied to the homogenized magnesium alloy billet,
defects, such as cracks and fracture, may occur in the magnesium
alloy billet. The amount of the compressive deformation may be
appropriately selected by the person skilled in the art according
to the composition of the magnesium alloy. The compressive
deformation may be applied in any direction to the magnesium alloy
billet, and the direction of the compressive deformation may be
appropriately selected by the person skilled in the art according
to the shape of the billet and the conditions of the extrusion.
[0044] The compressive deformation in step 4 may be applied in a
temperature range of room temperature to 250.degree. C. In the case
that the compressive deformation is applied at a temperature lower
than room temperature, since the material may be hardened, defects,
such as cracks and fracture, may occur in the magnesium alloy
billet during the application of the compressive deformation. In
the case in which the compressive deformation is applied at a
temperature greater than 250.degree. C., twins are difficult to be
formed due to the activation of non-basal plane slip, and
accordingly, the improvement of the strength and elongation of the
magnesium alloy extrudate thus prepared may not be expected.
[0045] In this case, "room temperature" described as a temperature,
at which the compressive deformation may be applied, denotes a
normal temperature at which heating is not particularly performed,
wherein the room temperature may be defined as a temperature range
of about 0.degree. C. to about 50.degree. C., and for example, may
be a temperature of about 20.+-.5.degree. C.
[0046] The method of preparing a magnesium alloy extrudate
according to the present invention does not require new device and
equipment except a device for applying compressive deformation.
Therefore, the method may be immediately applied to a process of
preparing a magnesium alloy extrudate using a typical extrusion
method.
[0047] Next, in the method of preparing a magnesium alloy extrudate
according to the present invention, step 5 is extruding the
compressive deformed magnesium alloy billet of step 4.
[0048] In the present invention, the extrusion may be performed
after preheating in a temperature range of 150.degree. C. to
450.degree. C. in order to smoothly perform the extrusion of the
compressive deformed magnesium alloy billet of step 4. In the case
that the preheating temperature of the compressive deformed
magnesium alloy billet is less than 150.degree. C., excessive
extrusion pressure may be required during the extrusion of the
compressive deformed magnesium alloy billet. In the case in which
the preheating temperature of the compressive deformed magnesium
alloy billet is greater than 450.degree. C., grains in the
magnesium alloy may grow and become coarse, which reduces the
strength of the magnesium alloy extrudate thus prepared. And,
surface defects may occur because localized melting due to high
extrusion temperature may occur in some alloys according to the
composition of the alloy.
[0049] In this case, the extrusion may be conducted by direct
extrusion, indirect extrusion, and continuous extrusion. However,
the extrusion is not limited thereto, and may be appropriately
selected according to the use or the aim of the person skilled in
the art.
[0050] Also, the method of preparing a magnesium alloy extrudate
according to the present invention may further include processing
the magnesium alloy billet into an appropriate shape suitable for
compressive deformation and extrusion before and after step 4.
[0051] Furthermore, the method of preparing a magnesium alloy
extrudate according to the present invention may further include
performing an aging treatment after step 5. However the aging
treatment in the present invention is only optional, and a
magnesium alloy extrudate having improved strength and ductility
may be prepared even in the case in which the aging treatment is
not performed.
[0052] Since alloying elements other than magnesium that are
included in the magnesium alloy may precipitate at grain boundaries
or in grains by the aging treatment, the strength of the magnesium
alloy extrudate may be further improved by the resulting
precipitation hardening effect.
[0053] For example, the aging treatment may be performed in a
temperature range of 150.degree. C. to 250.degree. C. for 1 hour to
360 hours. In the case that the aging treatment is performed at a
temperature less than 150.degree. C., a time for the magnesium
alloy to reach the maximum strength may be increased, and thus, it
may not be economical. In the case in which the aging treatment is
performed at a temperature greater than 250.degree. C., the time
for the magnesium alloy to reach the maximum strength may be
reduced, but the size of a precipitation phase may be increased due
to high temperature. Thus, the strength of the magnesium alloy may
be decreased.
[0054] Also, the present invention may provide a magnesium alloy
extrudate that is prepared by the above preparation method.
[0055] In general, physical properties of a magnesium alloy are
estimated by the product of tensile strength and total elongation
(TS.times.EL). In general, a metallic material has a tendency that
elongation decreases when tensile strength increases, and the
tensile strength decreases when the elongation increases. Thus, a
magnesium alloy may be estimated in two views of strength and
ductility using a TS.times.EL value of the magnesium alloy. In this
case, it may be estimated that a magnesium alloy having a large
TS.times.EL value has excellent tensile properties. Since the above
TS.times.EL value is proportional to the amount of energy which may
be absorbed by the metallic material during fracture, it may be
estimated that toughness is also excellent.
[0056] Also, the present invention may provide a part for
transportation equipment that is manufactured using the magnesium
alloy extrudate.
[0057] A TS.times.EL value of the magnesium alloy extrudate, which
is prepared by applying a predetermined amount of compressive
deformation to the homogenized magnesium alloy billet according to
the present invention and then extruding the magnesium alloy
billet, is increased by about 3% to about 32%. This indicates that
only the strength is not simply improved but overall tensile
properties are improved. Thus, it is expected that the magnesium
alloy extrudate of the present invention may be widely used in
various industrial sectors including transportation equipment
industry, such as aircraft industry, and electronic component
industry.
[0058] In particular, since the magnesium alloy extrudate may
exhibit excellent properties, such as machinability,
electromagnetic shielding properties, and vibration absorption
capacity, as well as high specific strength, the magnesium alloy
extrudate may be manufactured as parts for aircraft requiring high
specific strength and precision processing.
[0059] Hereinafter, the present invention will be described in more
detail according to examples. However, the following examples are
provided for illustrative purposes only, and the scope of the
present invention should not be limited thereto in any manner.
Examples 1 to 6
Preparation of Magnesium Alloy Extrudate
[0060] Step 1: Melting Magnesium Alloy Raw Material
[0061] Pure magnesium (Mg, 99.9 wt %), pure tin (Sn, 99.9 wt %),
pure aluminum (Al, 99.9 wt %), pure zinc (Zn, 99.995 wt %), pure
zirconia (Zr, 99.99 wt %), and pure copper (Cu, 99.997 wt %) were
used, and magnesium alloys having compositions of the following
Table 1 were melted in a graphite crucible using a high frequency
induction melting furnace. An upper portion of the melted magnesium
alloy (magnesium alloy melt) was covered with a mixed gas of
SF.sub.6 and CO.sub.2 to block the contact with air and thus,
oxidation was prevented.
TABLE-US-00001 TABLE 1 Alloy Composition (wt %) name Sn Al Zn Zr Cu
Mg Example 1 AZ31 -- 3 1 -- -- Bal. Example 2 AZ80 -- 8 0.5 -- --
Bal. Example 3 TAZ541 5 4 1 -- -- Bal. Example 4 TAZ811 8 1 1 -- --
Bal. Example 5 ZK60 -- -- 6 0.5 -- Bal. Example 6 ZK60- -- -- 6 0.5
1 Bal. 1Cu
[0062] Step 2: Preparing Magnesium Alloy Billet
[0063] The magnesium alloy melt of step 1 was maintained at
700.degree. C. for 10 minutes, and a magnesium alloy billet having
a diameter of 80 mm and a length of 200 mm was then prepared by
pouring the melt to a steel mold preheated at 200.degree. C.
[0064] Step 3: Homogenizing Magnesium Alloy Billet
[0065] The magnesium alloy billet prepared in step 2 was
homogenized by heating at a rate of 1.degree. C./min in an inert
atmosphere and heat treating in a temperature range of 400.degree.
C. to 490.degree. C. for 12 hours to 15 hours. Also, in order to
suppress the formation of a coarse precipitation phase which may
occur during a cooling process of the billet, the billet was cooled
with water at room temperature. Homogenization treatment conditions
for each example are presented in Table 2 below.
TABLE-US-00002 TABLE 2 Homogenization treatment condition
Temperature Time Alloy name (.degree. C.) (hours) Example 1 AZ31
400 15 Example 2 AZ80 400 15 Example 3 TAZ541 460 12 Example 4
TAZ811 490 12 Example 5 ZK60 400 15 Example 6 ZK60-1Cu 420 15
[0066] Step 4: Applying Compressive Deformation
[0067] 10% of compressive deformation was applied to the magnesium
alloy billet homogenized in step 3 at a strain rate of about 0.1/s
in a longitudinal direction at room temperature using a 150 ton
hydraulic press.
[0068] Step 5: Extruding
[0069] The magnesium alloy billet compressive deformed in step 4
was machined into a rod shape with a diameter of 51 mm, and a
magnesium alloy extrudate was then prepared by extruding the
rod-shaped billet into a rod shape with a diameter of 16 mm using
an indirect extruder (maximum extrusion pressure: 500 tonf)
(extrusion temperature: 200.degree. C., extrusion ratio: 20:1, ram
speed: 0.1 mm/s).
Example 7
Preparation of Magnesium Alloy Extrudate
[0070] A magnesium alloy extrudate was prepared in the same manner
as in Example 4 except that 5% of compressive deformation was
applied in step 4 of Example 4.
Example 8
Preparation of Magnesium Alloy Extrudate
[0071] A magnesium alloy extrudate was prepared in the same manner
as in Example 4 except that 15% of compressive deformation was
applied in step 4 of Example 4.
Comparative Examples 1 to 6
Preparation of Magnesium Alloy Extrudate
[0072] Magnesium alloy extrudates were prepared in the same manner
as in Examples 1 to 6 except that compressive deformation of step 4
in Examples 1 to 6 was not applied.
Comparative Example 7
Preparation of Magnesium Alloy Extrudate
[0073] A magnesium alloy extrudate was prepared in the same manner
as in Example 4 except that 2% of compressive deformation was
applied in step 4 of Example 4.
[0074] Analysis
[0075] 1. Microstructure Analysis of Magnesium Alloy Billet
According to Compressive Deformation
[0076] In order to analyze microstructures of the magnesium alloy
billets according to compressive deformation in the present
invention, microstructure analysis was performed using an optical
microscope before and after the compressive deformation, and the
results thereof are presented in FIGS. 2 and 3.
[0077] FIGS. 2 and 3 are results of analyzing the homogenized
magnesium alloy billets before and after the compressive
deformation using an optical microscope. From the above results, it
may be understood that twins were formed in the magnesium alloys
due to the compressive deformation.
[0078] FIG. 4 is a result of analyzing the homogenized AZ31
magnesium alloy billet after the compressive deformation using
electron back scattered diffraction, wherein it may be understood
that many twins were formed and most of the twins were {10-12}
tensile twins.
[0079] Referring to FIGS. 2 to 4, it may be understood that many
twins may be formed in the magnesium alloys by applying compressive
deformation to the homogenized magnesium alloy billets.
Experimental Example 1
Microstructure Analysis of Magnesium Alloy Extrudate
[0080] In order to investigate the effect of the compressive
deformation in the magnesium alloy extrudate according to the
present invention, the magnesium alloy extrudates of Examples 1 to
6 and Comparative Examples 1 to 6 were analyzed using an optical
microscope and electron back scattered diffraction. The results
thereof are presented in FIGS. 5 to 7.
[0081] FIG. 5 is a result of analyzing the magnesium alloy
extrudates of Comparative Example 1 and Example 1 using electron
back scattered diffraction, wherein a significant amount of large
unrecrystallized grains existed in the extrudate of Comparative
Example 1, but since recrystallization occurred throughout the
extrudate of Example 1 subjected to the compressive deformation,
large unrecrystallized grains were almost not included and uniform
fine grains were obtained. As a result, an average gain diameter of
the extrudate was significantly decreased from 10.3 .mu.m to 3.1
.mu.m.
[0082] Referring to FIGS. 6 and 7, the magnesium alloy extrudates
of Examples 1 to 6 subjected to the compressive deformation had
more recrystallized regions and more uniform structure than the
magnesium alloy extrudates of Comparative Examples 1 to 6 which
were not subjected to the compressive deformation. It may be
estimated that the above result of the magnesium alloy extrudates
of Examples 1 to 6 was due to the fact that twins formed by the
compressive deformation acted as recrystallization sites during the
extrusion process to increase a recrystallization fraction.
[0083] Thus, it may be considered that the method of preparing a
magnesium alloy extrudate by applying a predetermined amount of
compressive deformation to the homogenized magnesium alloy billet
and extruding the magnesium alloy billet according to the present
invention may form twins in the magnesium alloy to simultaneously
improve the strength and ductility of the magnesium alloy
extrudate.
Experimental Example 2
Mechanical Property Evaluation Test of Magnesium Alloy
Extrudate
[0084] In order to evaluate mechanical properties of the magnesium
alloys according to the present invention, rod-shaped specimens
having a gauge length of 25 mm and a gauge diameter of 6 mm were
prepared using the magnesium alloy extrudates of Examples 1 to 8
and Comparative Examples 1 to 7, and tensile tests were performed
on the rod-shaped specimens at a strain rate of 1.times.10.sup.-3
S.sup.-1 using a room-temperature tensile tester (INSTRON 4206).
The results thereof are presented in Table 3 below. The results of
Example 4, Example 7, Example 8, Comparative Example 4, and
Comparative Example 7, which were prepared from the same TAZ811
alloy, were extracted from the following Table 3 to be presented in
Table 4 below.
TABLE-US-00003 TABLE 3 Yield Tensile Alloy strength strength
Elongation TS .times. EL name (MPa) (MPa) (%) (MPa %) Example 1
AZ31 285 321 19.5 6260 Example 2 AZ80 384 415 15.4 6391 Example 3
TAZ541 377 404 13.6 5494 Example 4 TAZ811 376 392 11.9 4665 Example
5 ZK60 356 371 18.6 6901 Example 6 ZK60-1Cu 383 395 19.0 7505
Example 7 TAZ811 357 374 10.7 4002 Example 8 TAZ811 383 405 12.1
4901 Comparative AZ31 257 289 17.6 5086 Example 1 Comparative AZ80
353 385 13.3 5121 Example 2 Comparative TAZ541 363 388 12.9 5005
Example 3 Comparative TAZ811 337 360 9.8 3528 Example 4 Comparative
ZK60 345 361 18.5 6679 Example 5 Comparative ZK60-1Cu 365 381 15.6
5944 Example 6 Comparative TAZ811 338 363 9.7 3521 Example 7
TABLE-US-00004 TABLE 4 Compressive Yield Tensile deformation
strength strength Elongation TS .times. EL amount (%) (MPa) (MPa)
(%) (MPa %) Comparative -- 337 360 9.8 3528 Example 4 Comparative 2
338 363 9.7 3521 Example 7 Example 7 5 357 374 10.7 4002 Example 4
10 376 392 11.9 4665 Example 8 15 383 405 12.1 4901
[0085] Referring to Table 3, it may be understood that yield
strengths, tensile strengths, elongations, and TS.times.EL values
of the magnesium alloy extrudates of Examples 1 to 8 according to
the present invention were improved in comparison to those of the
magnesium alloy extrudates of Comparative Examples 1 to 7 which
were not subjected to the compressive deformation after the
homogenization treatment.
[0086] In particular, it may be understood that, with respect to
Example 8 using a TAZ811 alloy, the yield strength and tensile
strength were respectively increased by 46 MPa and 45 MPa in
comparison to Comparative Example 4, and with respect to Example 6
using a ZK60-1Cu alloy, the elongation was improved by 22% in
comparison to Comparative Example 6. It may also be understood
that, with respect to Example 8 using a TAZ811 alloy, the
TS.times.EL value was improved by 39% in comparison to Comparative
Example 7.
[0087] Referring to Table 4, it may be confirmed that the yield
strength, tensile strength, and elongation were improved as the
compressive deformation amount increased, and it may be confirmed
that, with respect to Example 4, Example 7, and Example 8 having a
compressive deformation amount of 5% to 15%, the yield strength,
tensile strength, and elongation were significantly improved in
comparison to those of Comparative Example 4 which was not
subjected to the compressive deformation. In particular, with
respect to Example 8, it may be confirmed that 15% of compressive
deformation results in a considerable improvement of the yield
strength, tensile strength, and elongation by 46 MPa, 45 MPa, and
2.2%, respectively.
[0088] Therefore, it may be understood that the method of preparing
a magnesium alloy extrudate according to the present invention may
improve the strength and ductility of the magnesium alloy extrudate
by applying a predetermined amount of compressive deformation to
the homogenized magnesium alloy billet and extruding the magnesium
alloy billet, and it may also be understood that an extrudate
having excellent physical properties may be prepared by increasing
the amount of compressive deformation.
* * * * *