U.S. patent application number 14/341668 was filed with the patent office on 2014-11-13 for magnesium alloy having high ductility and high toughness, and preparation method thereof.
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 Ha-Sik Kim, Young Min Kim, Sung Hyuk Park, Chang Dong Yim, Bong Sun You.
Application Number | 20140332121 14/341668 |
Document ID | / |
Family ID | 46689424 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140332121 |
Kind Code |
A1 |
Park; Sung Hyuk ; et
al. |
November 13, 2014 |
MAGNESIUM ALLOY HAVING HIGH DUCTILITY AND HIGH TOUGHNESS, AND
PREPARATION METHOD THEREOF
Abstract
A magnesium alloy having high ductility and high toughness, and
a preparation method thereof are provided, in which the magnesium
alloy includes 1.0-3.5 wt % of tin, 0.05-3.0 wt % of zinc, and the
balance of magnesium and inevitable impurities, and a preparation
method thereof. Magnesium alloy with a relatively small tin content
is added with zinc, and optionally, with one or more alloy elements
selected from aluminum, manganese and rare earth metal, at a
predetermined content ratio. As a result, the alloy exhibits
superior ductility and moderate strength due to the suppression of
excessive formation of precipitates and some precipitates hardening
effect, respectively. Accordingly, compared to extruded material
prepared from conventional commercial magnesium alloys, higher
ductility and toughness are provided, so that the alloy can be
widely applied over the entire industries including automotive and
aerospace industries.
Inventors: |
Park; Sung Hyuk;
(Changwon-si, KR) ; Kim; Young Min; (Changwon-si,
KR) ; Kim; Ha-Sik; (Changwon-si, KR) ; You;
Bong Sun; (Changwon-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: |
46689424 |
Appl. No.: |
14/341668 |
Filed: |
July 25, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/KR2012/011831 |
Dec 31, 2012 |
|
|
|
14341668 |
|
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Current U.S.
Class: |
148/557 ;
148/406; 148/420; 164/76.1; 420/405; 420/408; 420/409; 420/411;
420/412 |
Current CPC
Class: |
C22F 1/06 20130101; C22C
23/00 20130101; C22C 23/04 20130101; C22C 1/02 20130101; B21C 23/08
20130101; C22C 23/02 20130101; B21C 23/002 20130101; B22D 21/007
20130101 |
Class at
Publication: |
148/557 ;
164/76.1; 420/411; 420/408; 420/405; 420/412; 148/420; 148/406;
420/409 |
International
Class: |
C22F 1/06 20060101
C22F001/06; B21C 23/00 20060101 B21C023/00; C22C 23/04 20060101
C22C023/04; B21C 23/08 20060101 B21C023/08; C22C 23/00 20060101
C22C023/00; C22C 23/02 20060101 C22C023/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 30, 2012 |
KR |
1020120008995 |
Claims
1. A magnesium alloy having high ductility and high toughness
comprising 1.0 to 3.5 wt % tin (Sn), 0.05 to 3.0 wt % zinc (Zn),
remainder magnesium (Mg) and unavoidable impurities.
2. The magnesium alloy as set forth in claim 1, wherein the
magnesium alloy further comprises one or more alloying elements
selected from the group consisting of aluminum (Al), manganese (Mn)
and rare earth metal.
3. The magnesium alloy as set forth in claim 2, wherein the
aluminum is contained in an amount of 0.05 to 3.0 wt %.
4. The magnesium alloy as set forth in claim 2, wherein the
manganese is contained in an amount of 0.05 to 1.5 wt %.
5. The magnesium alloy as set forth in claim 2, wherein the rare
earth metal is contained in an amount of 0.05 to 1.5 wt %.
6. The magnesium alloy as set forth in claim 2, wherein the rare
earth metal is one or more selected from the group consisting of
cerium (Ce), yttrium (Y) and gadolinium (Gd).
7. A preparation method of a magnesium alloy having high ductility
and high toughness, comprising: melting magnesium alloy raw
material (Step 1); casting the melt of magnesium alloy raw material
of Step 1 (Step 2); homogenizing the cast of magnesium alloy of
Step 2 (Step 3); and working the homogenized magnesium alloy cast
of Step 3 (Step 4).
8. The preparation method as set forth in claim 7, wherein the
magnesium alloy raw material of Step 1 comprises 1.0 to 3.5 wt %
tin (Sn), 0.05 to 3.0 wt % zinc (Zn), remainder magnesium (Mg) and
unavoidable impurities.
9. The preparation method as set forth in claim 7, wherein the
magnesium alloy raw material of Step 1 further comprises: 0.05 to
3.0 wt % aluminum (Al); 0.05 to 1.5 wt % manganese (Mn); and 0.05
to 1.5 wt % rare earth metal.
10. The preparation method as set forth in claim 9, wherein the
rare earth metal is one or more selected from the group consisting
of cerium (Ce), yttrium (Y) and gadolinium (Gd).
11. The preparation method as set forth in claim 7, wherein the
casting of Step 2 is performed at a temperature range of
650.degree. C. to 750.degree. C.
12. The preparation method as set forth in claim 7, wherein the
homogenizing of Step 3 comprises heat treatment at a temperature
range of 400.degree. C. to 550.degree. C. for a duration of 0.5 hr
to 96 hr, and quenching.
13. The preparation method as set forth in claim 12, wherein the
homogenizing of Step 3 is performed after pre-heating at a
temperature range of 250.degree. C. to 350.degree. C.
14. The preparation method as set forth in claim 7, wherein the
working of Step 4 is performed after pre-heating at a temperature
range of 200.degree. C. to 450.degree. C.
15. The preparation method as set forth in claim 7, wherein the
preparation method further comprises a step of performing aging
treatment after Step 4.
16. The preparation method as set forth in claim 15, wherein the
aging treatment is performed at a temperature range of 150.degree.
C. to 250.degree. C. for a duration of 1 hr to 360 hr.
17. A magnesium alloy having high ductility and high toughness
prepared by the method as set forth in claim 7.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a continuation of International Patent Application
No. PCT/KR2012/011831, filed Dec. 31, 2012, which claims the
benefit Korean Patent Application No. 10-2012-0008995, filed on
Jan. 30, 2012. Each of these is incorporated herein by reference in
its entirety.
FIELD
[0002] The present invention relates to a magnesium alloy having
high ductility and high toughness, and preparation method
thereof
BACKGROUND
[0003] Recently, researchers seek ways to further increase energy
efficiency of transportation equipments by way of power source
development and performance improvement, or light-weighting of
parts. Among these efforts, researchers particularly study ways to
improve light-weightness and subsequent fuel efficiency, because
components of lighter weight can increase energy efficiency at
lower cost.
[0004] As a metal material that can be considered for the purpose
of light-weighted parts, magnesium alloys are in increasing demand
in the transportation machines, portable component-related industry
or other area in need of weight reduction, because the magnesium
alloys have minimum density (1.8 g/cm.sup.3) among the alloys for
structural purpose that have been developed so far, and because
these also provide good shielding against electromagnetic waves and
vibration absorption.
[0005] However, since magnesium with hexagonal crystalline
structure has low formability at room temperature, compared to the
other metals with cubic crystalline structure such as copper, iron
or aluminum, magnesium has been less considered for extended
application in the industries.
[0006] That is, because plastic deformation of a metal is
dominantly caused by slip system, the metal with more slip systems
in the crystalline structure is more apt to plastic
deformation.
[0007] The `slip` as used herein refers to an irreversible shear
displacement of one part of a crystal relative to another in a
definite crystallographic direction, which leads into plastic
deformation. The slip occurs on a specific crystal plane to a
specific crystal direction, and the number of slip systems varies
depending on the crystalline structure of a material.
[0008] For example, magnesium with hexagonal close packed (HCP)
structure has three (3) slip systems, while the metals such as
aluminum, copper or iron with cubic structure have twelve (12) slip
systems, thus indicating that magnesium is relatively hardly
plastic deformable compared to aluminum, copper or iron.
[0009] Table 1 below lists tensile characteristics of commercial
extruded magnesium alloys, indicating that the commercial extruded
magnesium alloys developed so far have too low elongation to be
applied in the component manufacturing industry considering that
this industry generally requires working into a variety of
forms.
TABLE-US-00001 TABLE 1 Tensile Yield Tensile strength Alloy
strength strength Elongation elongation name Condition (MPa) (MPa)
(%) (MPa %) AZ31 F 200 260 15 3900 F 250 340 7 2380 AZ80 T5 275 380
7 2660 (In the `condition` column, letter `F` denotes extruded
material, and T5' denotes extruded material which underwent aging
treatment after extrusion.)
[0010] To resolve the problems occurring in the conventional art as
mentioned above, researchers have been seeking ways to improve
specific strength, ductility and toughness of magnesium alloys so
as to extend the application area over the entire industries.
[0011] For example, SHIN et al. attempted to improve mechanical
characteristic of AM60 magnesium alloy with good toughness
characteristic, by adding aluminum (Al), silicon (Si) and calcium
(Ca) thereto (SHIN, Gwang-Sun and others,[Influence of Si and Ca
addition to gravity cast AM60 magnesium alloy on consolidation
behavior], Korea Foundry Society Journal (Casting), Book 18-4,1998,
pp. 364 to 372.) Shin et al. found that as the silicon content
increases in the magnesium alloy, the tensile strength and yield
strength increase, while the elongation is in decreasing pattern
overall. The elongation increases when a certain amount of calcium
is added to the alloy, or when the aluminum content is decreased.
Shin et al. also found that the alloy with the superior
characteristic, e.g., the magnesium alloy that undergoes slag
formation to optimize alloy reinforcing, shows 193 MPa of tensile
strength, 79 MPa of yield strength and 11.2% of elongation.
According to Shin et al., although the magnesium alloy has improved
tensile characteristic compared to the other commercial magnesium
alloys, the magnesium alloy still has limited formability.
Additional reference can be found in Korean Patent Publication No.
10-2001-0019353(Published date: 2002 Oct. 19) which discloses
quasi-crystal phase hardened Mg-based alloy exhibiting superior
warm and hot formability. Specifically, KR Pat. 10-2001-0019353
discloses magnesium alloy with superior formability, by employing
basic alloy composition of magnesium (Mg)-zinc (Zn)-yttrium (Y),
having two-phase region of quasi-crystal phase and metal solid
solution present therein, and by regulating the same to such an
alloy composition in which zinc content is adjusted to a range of 1
at. % to 10 at. %, and yttrium to a range of 0.1 at. % to 3 at. %
(KR 10-2001-0019353 A 2002 Oct. 19). However, the above-mentioned
effect was mainly due to the presence of quasi-crystal phase, and
therefore, it is necessary to increase the amount of zinc to
increase the content of quasi-crystal phase. Therefore, the
increasing zinc content causes deteriorating ductility of the
material, and it can also cause irregular quality of the final form
of magnesium alloy depending on areas.
[0012] The present inventors have been in search for magnesium
alloy with superior tensile characteristic, and found that it is
possible to fabricate magnesium alloy with superior ductility and
toughness by adding zinc and also optionally adding one or more
alloy elements selected from the group consisting of aluminum,
manganese and rare earth metal at appropriate content ratio to
magnesium alloy containing a small tin (Sn) content, and then
casting, homogenizing and working the same in a way of suppressing
excessive formation of precipitate in the magnesium alloy that can
cause deterioration of ductility, and completed the present
invention.
DISCLOSURE
Technical Problem
[0013] An objective of the present invention is to provide a
magnesium alloy with high ductility and high toughness.
[0014] Another objective of the present invention is to provide a
preparation method of magnesium alloy with high ductility and high
toughness.
Technical Solution
[0015] To achieve the above-mentioned and other objectives of the
present invention, an embodiment provides a magnesium alloy having
high ductility and high toughness, containing 1.0 to 3.5 wt % tin
(Sn) and 0.05 to 3.0 wt % zinc (Zn), and remainder magnesium and
unavoidable impurities.
[0016] Further, the present invention provides a preparation method
of magnesium alloy having high ductility and high toughness,
including steps of:
[0017] melting magnesium alloy raw material (Step 1);
[0018] casting the melt of magnesium alloy raw material of Step 1
(Step 2);
[0019] homogenizing the cast of magnesium alloy of Step 2 (Step 3);
and
[0020] working the homogenized magnesium alloy cast of Step 3 (Step
4).
Advantageous Effects
[0021] The magnesium alloy according to the present invention can
be widely applied over the entire industries including
transportation equipments due to relatively higher ductility and
toughness than the extruded materials prepared from conventional
commercial magnesium alloys, because degradation of ductility due
to excessive presence of precipitates is minimized and precipitate
hardening effect is provided, by adding zinc and optionally adding
one or more species selected from the group consisting of aluminum,
manganese and rare earth metal at a predetermined content ratio to
a magnesium alloy which has a small tin content and which can have
precipitate hardening, thus limiting formation of micro precipitate
phase to a small amount.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is inverse pole figure map, as measured by electron
back scattered diffraction (EBSD), of TZ22 alloy according to the
present invention (FIG. 1: Example 3).
[0023] FIG. 2 is (0002) basal pole figure, as measured by EBSD, of
TZ22 alloy according to the present invention (FIG. 2: Example
3).
[0024] FIG. 3 is grain size distribution, as measured by EBSD, of
TZ22 alloy according to the present invention (FIG. 3: Example
3).
[0025] FIG. 4 is TEM image of TZ22 alloy according to the present
invention (FIG. 4: Example 3).
[0026] FIG. 5 is a graph showing tensile strength and elongation of
the magnesium alloy according to the present invention (FIG. 5:
Examples 1 to 11; Comparative Examples 1 to 8; Commercial AZ31
extrusion material; commercial AZ80 extrusion material).
DETAILED DESCRIPTION
[0027] Prior to explaining the present invention in detail, it is
defined that a phrase `A to B` is understood as a range of `A or
above and less than B`.
[0028] According to the present invention, a magnesium alloy having
high ductility and high toughness is provided, which contains 1.0
to 3.5 wt % tin (Sn) and 0.05 to 3.0 wt % zinc (Zn), remainder
magnesium (Mg) and unavoidable impurities.
[0029] Further, the present invention provides a preparation method
of magnesium alloy having high ductility and high toughness,
including steps of:
[0030] melting magnesium alloy raw material (Step 1);
[0031] casting the melt magnesium alloy raw material at Step 1
(Step 2);
[0032] homogenizing the cast of magnesium alloy of Step 2 (Step 3);
and
[0033] working the homogenized magnesium alloy cast of Step 3 (Step
4).
[0034] The present invention will be explained in greater detail
below.
[0035] Before explaining the present invention in detail, it is
noted that the enhanced mechanical characteristic of the magnesium
alloy according to the present invention will be explained based on
the following principles which are applicable in the pertinent
field of art.
[0036] Generally, an alloy becomes stronger than pure metal form
when solute atom incorporates into lattice of solvent atom for
solid solution. For example, when different metal such as tin,
zinc, aluminum, manganese and rare earth metal penetrates into
crystal lattice of magnesium metal, or substituted with some of the
magnesium atoms, the original mechanical characteristic of the
magnesium can alter.
[0037] To be specific, because of the presence of second metal of
different size in the atom lattice of the magnesium metal either in
interstitial or substitutional manner, the magnesium lattice
deforms from the original lattice form, thus altering mechanical
characteristic of magnesium itself. This process is called `solid
solution strengthening`.
[0038] The solid solution strengthening can enhance yield strength,
tensile strength and hardness of pure metal, and also can enhance
resistance at high temperature.
[0039] However, because enhancement of mechanical characteristics
such as yield strength, tensile strength and hardness by solid
solution strengthening alone is limited, additional metal hardening
can be employed, which precipitates second phase from super
saturated solid solution with heat treatment, and the resultant
alloy with such effects is referred to as `precipitate hardening
alloy`.
[0040] The solvent atoms and solute atoms (second phase) in the
precipitate hardening alloy have difference in solid solubility
depending on temperatures thereof, and the metal hardens as the
temperature decreases and thus the second phase solid solubility
decreases to precipitate.
[0041] According to the present invention, the magnesium alloy
containing tin has enhanced mechanical characteristic, by
additionally including zinc and selectively, aluminum, manganese,
cerium, yttrium and gadolinium, according to a predetermined
composition ratio.
[0042] The present invention will be explained in detail based on
the principles explained above.
[0043] The present invention provides magnesium alloy having high
ductility and high toughness, containing 1.0 to 3.5 wt % tin (Sn)
and 0.05 to 3.0 wt % zinc (Zn), remainder magnesium (Mg) and
unavoidable impurities.
[0044] In the magnesium alloy according to the present invention,
the tin has maximum solubility limit of 14.5 wt % in the magnesium
matrix at 561.degree. C., and it forms Mg2Sn precipitate phase upon
heat treatment to thus show age hardening behavior. The magnesium
alloy containing less than 1.0 wt % tin has insufficient amount of
Mg2Sn precipitate phase upon extrusion so that the final form of
magnesium alloy has insufficient precipitate hardening effect and
decreasing strength. On the contrary, the magnesium alloy
containing 3.5 wt % or more tin therein has excessive formation of
Mg2Sn precipitate phase so that increasing precipitate size causes
the final form of magnesium alloy to have deteriorated
ductility.
[0045] Further, in the magnesium alloy according to the present
invention, zinc is the element that can increase precipitate
strengthening effect when added to magnesium-tin alloy, and also
enhance strength of the alloy via solid solution strengthening. The
magnesium alloy containing less than 0.05 wt % of zinc can hardly
have enhanced strength of the alloy by precipitate hardening and
solid solution strengthening, while the magnesium alloy containing
3.0 wt % or more zinc can hardly have homogenization at temperature
exceeding 360.degree. C. due to low solidus line temperature of the
magnesium alloy, resulting in increasing Mg2Sn phase fraction in
the structure and subsequently deteriorating elongation of the
magnesium alloy.
[0046] Further, the magnesium alloy according to the present
invention may additionally include one or more elements selected
from the group consisting of aluminum (Al), manganese (Mn) and rare
earth metal.
[0047] The magnesium alloy according to the present invention
contains the aluminum in an amount of 0.05 to 3.0 wt % with respect
to the total weight of the magnesium alloy.
[0048] The aluminum addition to magnesium-tin alloy can enhance
precipitate hardening effect and also increase strength of the
alloy by way of solid solution. Further, the aluminum combines with
manganese to form a variety of dispersion particles, leading to an
enhancement of alloy's strength by way of particle strengthening
and grain refining. The magnesium alloy containing less than 0.05
wt % aluminum can hardly have the effects mentioned above, while
the magnesium alloy containing 3.0 wt % or more aluminum can hardly
homogenize at a temperature exceeding 380.degree. C. due to low
solidus line temperature of the magnesium alloy, and therefore,
subsequently deteriorating elongation of the magnesium alloy.
[0049] Furthermore, the magnesium alloy according to the present
invention may preferably include the manganese at an amount of 0.05
to 1.5 wt % with respect to total weight of the magnesium
alloy.
[0050] The manganese is the alloy element that brings about not
only the solid solution strengthening effect, but also enhanced
alloy strength and corrosion resistance by combining with the
aluminum mentioned above to form a variety of dispersion particles.
The magnesium alloy containing less than 0.05 wt % of manganese can
hardly have the effects mentioned above, while the magnesium alloy
containing manganese at an amount exceeding 1.5 wt % can have
deteriorated elongation of the final form of magnesium alloy due to
the presence of coarse manganese particles which are formed in
magnesium alloy melt at temperatures below 750.degree. C.
[0051] Further, the magnesium alloy according to the present
invention may preferably include the rare earth metal at an amount
of 0.05 to 1.5 wt % with respect to total weight of the magnesium
alloy.
[0052] The magnesium alloy according to the present invention may
additionally include one or more rare earth elements from the group
consisting of cerium (Ce), yttrium (Y) and gadolinium (Gd).
[0053] The rare earth element in larger atom size (approximately,
180 pm) than magnesium atom (approximately, 160 pm) coexists with
the other elements with a smaller atom size (approximately, 120 pm
to 140 pm) such as tin, zinc, aluminum and manganese in the
magnesium alloy, and matches well with the magnesium atoms to
provide an effect of generating slip plane within the alloy crystal
to allow easy deformation during plastic working and also to
provide an effect of providing crystal nucleus during
solidification to thus form fine cast microstructure. The magnesium
alloy containing less than 0.05 wt % of rare earth metal has
deteriorating yield strength of the alloy and can have insufficient
work hardening effect and corrosion resistance, while the magnesium
alloy containing rare earth metal at an amount of 1.5 wt % or more
has excessive presence of intermetallic compounds, thus having
deteriorated ductility and formability.
[0054] Accordingly, the magnesium alloy according to the present
invention can have enhanced elongation, without compromising
tensile characteristic thereof, which leads into superior toughness
and ductility than the commercial magnesium alloys, by the addition
of zinc and by selective addition of one or more elements selected
from the group consisting of aluminum, manganese and rare earth
metal, to a magnesium-tin alloy base, according to the composition
ratio mentioned above.
[0055] Further, the present invention provides a preparation method
of magnesium alloy having high ductility and high toughness,
including steps of:
[0056] melting magnesium alloy raw material (Step 1);
[0057] casting the melt of magnesium alloy raw material of Step 1
(Step 2);
[0058] homogenizing the cast of magnesium alloy of Step 2 (Step 3);
and
[0059] working the homogenized magnesium alloy cast of Step 3 (Step
4).
[0060] The preparation method of magnesium alloy having high
ductility and high toughness according to the present invention
will be explained below step by step.
[0061] According to the preparation method of magnesium alloy of
the present invention, Step 1 involves melting magnesium alloy raw
material.
[0062] The magnesium alloy raw material may include 1.0 to 3.5 wt %
tin (Sn) and 0.05 to 3.0 wt % zinc (Zn), remainder magnesium and
unavoidable impurities.
[0063] Further, the magnesium alloy raw material may additionally
include one or more alloying elements selected from the group
consisting of 0.05 to 3.0 wt % aluminum, 0.05 to 1.5 wt %
manganese, and 0.05 to 1.5 wt % rare earth metal.
[0064] For the rare earth metal, one or more selected from the
group consisting of cerium (Ce), yttrium (Y) and gadolinium (Gd)
may be selected and used, but not limited thereto.
[0065] According to the preparation method of magnesium alloy of
the present invention, the magnesium alloy raw material may include
tin, zinc, aluminum, manganese and rare earth metal which may bring
about the effects mentioned above, at specific composition ratios
mentioned above for the reasons mentioned above.
[0066] According to the preparation method of magnesium alloy of
the present invention, the magnesium alloy raw material may use
each of the pure metals or an alloy containing a combination of the
metals, but not limited thereto. Accordingly, any preparation
method may be employed provided that it allows easy regulation of
the composition of the magnesium alloy mentioned above.
[0067] Further, according to the preparation method of magnesium
alloy of the present invention, Step 2 relates to casting the melt
of magnesium alloy raw material of Step 1.
[0068] The melt of magnesium alloy raw material of Step 1, i.e.,
the melt of magnesium alloy may preferably be cast at a temperature
range of 650.degree. C. to 750.degree. C. The magnesium alloy can
hardly be cast at a temperature lower than 650.degree. C. because
of low flow rate of the magnesium alloy melt, while the magnesium
alloy melt exceeding 750.degree. C. is abruptly oxidized, thus
generating oxide (i.e., impurities) which can then ingress in the
melt during casting.
[0069] Further, the casting at Step 2 may use gravity casting,
continuous casting, sand casting or pressure casting, but not
limited thereto. Accordingly, any other generally used method in
the pertinent field may be used.
[0070] Further, the melt of magnesium alloy of Step 2 may
preferably be formed into billets by casting, but not limited
thereto. Accordingly, the melt of magnesium alloy may be cast into
a variety of forms depending on use or convenience of person
skilled in the art.
[0071] Furthermore, according to the preparation method of
magnesium alloy of the present invention, Step 3 homogenizing the
cast of magnesium alloy of Step 2.
[0072] The homogenization can change irregular structure caused by
segregation of alloying elements formed during casting to
homogenized structure, and also improve hot workability and
mechanical characteristics of the magnesium alloy.
[0073] The homogenization of the magnesium alloy cast may be
performed by heat treatment at a temperature range of 400.degree.
C. to 550.degree. C. for a duration of 0.5 hr to 96 hr, followed by
quenching. The magnesium alloy cast homogenized at a temperature
lower than 400.degree. C. can have insufficient tin content
dissolved in the magnesium matrix, which can lead into a decrease
of strengthening effect of alloy acquired by the dynamic
precipitation occurring during hot plastic working. Further, since
the coarse Mg2Sn phase generated at the segregation portion of the
cast is not sufficiently eliminated in the heat treatment,
ductility of the resultant magnesium alloy can deteriorate.
Further, when the homogenization of the magnesium alloy cast is
done at a temperature exceeding 550.degree. C., homogenizing at
higher heat treatment temperatures than the solidus line
temperature of magnesium alloy causes partial melting of the
magnesium alloy cast and thus causes irregular structure of the
processed material.
[0074] Further, when the homogenization of the magnesium alloy cast
is performed at the above-mentioned temperature range for the
duration shorter than 0.5 hr, the effect acquired from the heat
treatment can be insufficient. When the homogenization of the
magnesium alloy cast is performed at the above-mentioned
temperature range for the duration exceeding 96 hr, the enhancement
effect is not so great compared to the time taken, so that the
working is not economical.
[0075] In the homogenization of the magnesium alloy, the magnesium
alloy cast may preferably be heat treated and then cooled by water
quenching according to the method explained above, but not limited
thereto. Accordingly, any quenching may be applied, provided that
the quenching does not require a long quenching time which will
cause precipitation of coarse Mg2Sn phase during quenching and
subsequent deterioration of strengthening effect due to reduced
dynamic precipitation during working.
[0076] Further, the operation at Step 3 may additionally include,
before the homogenization, a step of pre-heating at a temperature
range of 250.degree. C. to 350.degree. C. for the purpose of
suppressing local melting phenomenon of second phase due to abrupt
temperature rise.
[0077] Further, according to the preparation method of magnesium
alloy of the present invention, Step 4 involves working the
homogenized magnesium alloy cast of Step 4.
[0078] According to the present invention, to facilitate the
working of the magnesium alloy, Step 4 may additionally include a
step of pre-heating at a temperature range of 200.degree. C. to
450.degree. C. When the pre-heating temperature is lower than
200.degree. C., the working of the homogenized magnesium alloy cast
cannot be performed efficiently, while when the pre-heating
temperature exceeds 450.degree. C., such high temperature can
deteriorate the strength of the final form of the magnesium alloy
due to the grain growth of the magnesium alloy during the working
process of the homogenized magnesium alloy cast.
[0079] Further, the working may generally employ extrusion,
although not limited thereto. Accordingly, a variety of methods may
be employed properly, depending on use or purpose of a worker.
[0080] When extrusion is adopted for the working of the magnesium
alloy cast, direct or indirect or continuous extrusion may be
employed, although not limited thereto. Accordingly, any method may
be properly used to suit use or purpose of a worker.
[0081] Furthermore, the preparation method of the magnesium alloy
according to the present invention may additionally include a step
of aging treatment after Step 4.
[0082] By the aging treatment, the solute atoms contained in the
solvent atoms, e.g., alloy atoms other than magnesium contained in
the magnesium matrix, precipitate on the grain boundary or
dislocation, thus restraining motion of dislocations to further
increase the strength of the magnesium alloy.
[0083] According to the preparation method of magnesium alloy of
the present invention, the aging treatment may preferably be
performed at a temperature range of 150.degree. C. to 250.degree.
C. for a duration of 1 hr to 360 hr. When the aging treatment is
performed at a temperature lower than 150.degree. C., time for the
magnesium alloy to reach maximum strength is lengthy, which is
uneconomical. When the aging treatment is performed at a
temperature exceeding 250.degree. C., time for the magnesium alloy
to reach the maximum strength can be reduced, but the size of the
precipitates increases due to high temperature, so that the
strength of the magnesium alloy is eventually deteriorated.
[0084] Further, when the aging treatment is performed at the
above-mentioned temperature range for less than 1 hr, the effect
acquired from the aging treatment can be insufficient, while when
the aging treatment is performed for longer than 360 hr, it is not
economical compared to the effect as obtained.
[0085] Accordingly, the magnesium alloy according to the present
invention, which includes tin-containing magnesium alloy added with
zinc and optionally with one or more elements selected from the
group consisting of aluminum, manganese and rare earth metal, at
the composition ratio mentioned above, can provide higher ductility
and toughness than the conventional tin-containing magnesium alloys
or commercial magnesium alloys.
MODE FOR INVENTION
[0086] The present invention will be explained below in detail with
reference to Examples. However, the Examples are provided only for
the purpose of illustration, and should not be construed as
limiting the invention.
EXAMPLES 1 TO 11
Preparation of Extruded Magnesium Alloy Material 1 to 11
Step 1. Melting Magnesium Alloy Raw Material
[0087] Using pure Mg(99.9 wt %), pure Sn(99.9 wt %), pure Zn(99.995
wt %), pure Al(99.9 wt %), Mg--Mn master alloy(Mn:3.17 wt %), pure
Ce(99.9 wt %), pure Y(99.9 wt %) and pure Gd(99.9 wt %), the
magnesium alloy with the composition as listed in Table 2 below was
melt in graphite crucible using high frequency induction melting
furnace. A mixed gas of SF6 and CO2 was applied to the top of the
melt, to prevent oxidization by isolating the melt from possible
exposure to air.
TABLE-US-00002 TABLE 2 Alloying composition(wt %) Alloy Sn Zn Al Mn
Ce Y Gd Mg Example 1 TZ20 2 0.5 -- -- -- -- -- Bal. Example 2 TZ21
2 1 -- -- -- -- -- Bal. Example 3 TZ22 2 2 -- -- -- -- -- Bal.
Example 4 TZA211 2 1 1 -- -- -- -- Bal. Example 5 TZA212 2 1 2 --
-- -- -- Bal. Example 6 TZM210 2 1 -- 0.5 -- -- -- Bal. Example 7
TZAM2110 2 1 1 0.5 -- -- -- Bal. Example 8 TZ21-Ce 2 1 -- -- 0.5 --
-- Bal. Example 9 TZ21-Y 2 1 -- -- -- 0.5 -- Bal. Example 10 TZ-Gd
2 1 -- -- -- -- 0.5 Bal. Example 11 TZA211-Gd 2 1 1 -- -- -- 0.5
Bal.
Step 2. Casting Magnesium Alloy
[0088] The melt of magnesium alloy of Step 1 was maintained at
700.degree. C. for 10 min, and then formed into billet which has 80
mm in diameter and 200 mm in length by pouring into a steel mold
pre-heated at 200.degree. C.
Step 3. Homogenization
[0089] The billet of Step 2 was pre-heated under inert atmosphere
at 330.degree. C. for 2 hr, and then underwent elevation of
temperature at a rate of 1.degree. C./min to 500.degree. C. and
heat treatment at 500.degree. C. for 4 hr. To restrain formation of
coarse precipitate in the quenching process of billet, water
quenching was conducted with room temperature water after the heat
treatment.
Step 4. Working
[0090] To work the magnesium alloy, indirect extruder (max
extrusion force: 500 tonf) was used to extrude 16 mm rod of the
magnesium alloy material (Extrusion condition: billet and die
temperature 250.degree. C., extrusion ratio 25, ram speed 1.3
mm/s).
Example 12
Preparation of Extruded Magnesium Alloy Material 12
[0091] The extruded magnesium alloy material was prepared in the
same manner as Example 2, except for difference that the extruded
magnesium alloy material prepared at Example 2 additionally
underwent aging treatment at 200.degree. C. for 144 hr.
Comparative Examples 1 to 8
Preparation of Extruded Magnesium Alloy Material 13 to
[0092] The extruded magnesium alloy material was prepared in the
same manner as Example 1, except for the difference of using the
magnesium alloy composition as listed in Table 3 below in Step
1.
TABLE-US-00003 TABLE 3 Alloying composition(wt %) Alloy Sn Zn Al Mn
Mg Comparative Example 1 TZ51 5 1 -- -- Bal. Comparative Example 2
TZ52 5 2 -- -- Bal. Comparative Example 3 TZA511 5 1 1 -- Bal.
Comparative Example 4 TZA513 5 1 3 -- Bal. Comparative Example 5
TZ81 8 1 -- -- Bal. Comparative Example 6 TZ82 8 2 -- -- Bal.
Comparative Example 7 TZA813 8 1 3 -- Bal. Comparative Example 8
TZAM8111 8 1 1 1 Bal.
Experimental Example 1
Microstructure Analysis
[0093] In order to analyze the microstructure of the magnesium
alloy fabricated according to the present invention, electron back
scattered diffraction (EBSD) and transmission electron microscope
(TEM) were used, and the following results were obtained (see FIGS.
1 to 4).
[0094] Referring to FIGS. 1 to 3, the magnesium alloy fabricated
according to the present invention shows isotropic microstructure,
with its basal plane being in parallel arrangement along the
direction of extrusion, and average grain size being 23.7
.mu.m.
[0095] Further, referring to FIG. 4, the extruded magnesium alloy
material fabricated according to the present invention has a small
amount of fine second-phase (approximately, 50 to 500 nm in size)
along the grain boundary and within the grain.
[0096] From the result shown in FIG. 4, it is concluded that the
fine second-phases dispersed along the grain boundary and within
the grain of the extruded magnesium alloy material are the Mg2Sn
phase formed by dynamic precipitation during the extrusion process
of the magnesium alloy, which will induce precipitate hardening
effect of the magnesium alloy.
Experimental Example 2
Mechanical Characteristic Evaluation
[0097] In order to evaluate tensile characteristics of the extruded
magnesium alloy material fabricated according to the present
invention, cylindrical tensile samples were prepared (gauge length:
25 mm, gauge diameter: 6 mm), and tensile properties were tested at
room temperature with a strain rate of 1.times.10-3 s-1 using
tensile testing equipment (INSTRON 4206), and the results are shown
in Table 4 below and FIG. 5 (FIG. 5: Examples 1 to 11; Comparative
Examples 1 to 8; extruded commercial AZ31 alloy material; extruded
commercial AZ80 alloy material).
[0098] Generally, a metallic material has decreasing tensile
strength when the elongation increases, and has decreasing
elongation when the tensile strength increases. That is, when the
tensile strength and elongation, which are in inverse relationship
with each other, are multiplied by each other, the resultant value,
i.e., `tensile strength.times.elongation (MPa%)` can be used as a
reference to compare the tensile properties of metallic materials
in view of two aspects (i.e., strength and ductility), so that a
greater `tensile strength.times.elongation` is considered to be
indicative of better tensile properties. Additionally, since the
above value is in proportional relationship with the energy that
can be absorbed by the metallic material during fracture, the
higher value also indicates higher toughness.
TABLE-US-00004 TABLE 4 Tensile Yield Tensile strength .times.
strength strength Elongation elongation (MPa) (MPa) (%) (MPa %)
Example 1 149 227 26.7 6061 Example 2 144 226 27.1 6125 Example 3
136 233 26.4 6151 Example 4 146 236 27.4 6466 Example 5 154 249
27.2 6773 Example 6 170 249 25.2 6275 Example 7 177 260 25.1 6526
Example 8 155 236 26.3 6207 Example 9 155 235 27.3 6416 Example 10
158 236 25.9 6112 Example 11 149 241 28.1 6772 Comparative 188 262
18.4 4821 Example 1 Comparative 191 277 18.6 5152 Example 2
Comparative 190 277 19.0 5263 Example 3 Comparative 195 308 17.1
5267 Example 4 Comparative 241 294 18.1 5321 Example 5 Comparative
238 302 15.7 4741 Example 6 Comparative 221 323 16.1 5200 Example 7
Comparative 264 320 16.7 5344 Example 8
[0099] Referring to Table 4 above, the magnesium alloys fabricated
according to the present invention shows 24% enhancement of
elongation compared to the conventional high-strength magnesium
alloys, without considerably compromising the strength thereof.
[0100] Accordingly, the magnesium alloys fabricated according to
the present invention have superior combination of strength and
ductility (with tensile strength.times.elongation value exceeding
6000 MPa%) and thus exhibit improved tensile properties than
commercial magnesium alloys in Table 1 (tensile
strength.times.elongation value lower than 4000 MPa%) or magnesium
alloys of Comparative Examples 1 to 8 (tensile
strength.times.elongation value lower than 5500 MPa%).
[0101] From the above findings, it is confirmed that the magnesium
alloy fabricated according to the present invention can provide
superior ductility and toughness without considerably compromising
strength when compared with conventional magnesium alloys, and thus
the magnesium alloy can be applied to the weight lightening of the
components across the entire industries including automotive,
aerospace, or the like.
* * * * *