U.S. patent application number 16/471939 was filed with the patent office on 2020-03-19 for high strength magnesium alloy with excellent flame retardancy, and method for producing same.
The applicant listed for this patent is POSCO, RESEARCH INSTITUTE OF INDUSTRIAL SCIENCE & TECHNOLOGY. Invention is credited to Dae-Hwan CHOI, Hyung-Sub EOM, Sang-Jin KIM, Woo-Jin PARK.
Application Number | 20200087757 16/471939 |
Document ID | / |
Family ID | 62485913 |
Filed Date | 2020-03-19 |
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United States Patent
Application |
20200087757 |
Kind Code |
A1 |
PARK; Woo-Jin ; et
al. |
March 19, 2020 |
HIGH STRENGTH MAGNESIUM ALLOY WITH EXCELLENT FLAME RETARDANCY, AND
METHOD FOR PRODUCING SAME
Abstract
An aspect of the present disclosure relates to a high strength
magnesium alloy with excellent flame retardancy, wherein the
magnesium alloy comprises 2.0-13.0 wt % of Al, 0.1-0.5 wt % of Mn,
0.0015-0.025 wt % of B, and 0.1-1.0 wt % of Y with the remainder
comprising Mg and other unavoidable impurities, and comprises 6.5%
or more of an Mg--Al intermetallic compound in terms of volume
fraction, the Mg--Al intermetallic compound having an average grain
size of 20-500 nm.
Inventors: |
PARK; Woo-Jin; (Pohang-si,
Gyeongsangbuk-do, KR) ; EOM; Hyung-Sub; (Pohang-si,
Gyeongsangbuk-do, KR) ; CHOI; Dae-Hwan;
(Gangneung-si, Gangwon-do, KR) ; KIM; Sang-Jin;
(Pohang-si, Gyeongsangbuk-do, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
POSCO
RESEARCH INSTITUTE OF INDUSTRIAL SCIENCE & TECHNOLOGY |
Pohang-si, Gyeongsangbuk-do
Pohang-si, Gyeongsangbuk-do |
|
KR
KR |
|
|
Family ID: |
62485913 |
Appl. No.: |
16/471939 |
Filed: |
December 21, 2017 |
PCT Filed: |
December 21, 2017 |
PCT NO: |
PCT/KR2017/015291 |
371 Date: |
June 20, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22F 1/06 20130101; C22C
1/02 20130101; C22F 1/002 20130101; C22C 23/02 20130101 |
International
Class: |
C22C 23/02 20060101
C22C023/02; C22C 1/02 20060101 C22C001/02; C22F 1/00 20060101
C22F001/00; C22F 1/06 20060101 C22F001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 21, 2016 |
KR |
10-2016-0176119 |
Claims
1. A high strength magnesium alloy having excellent flame
retardancy, comprising: by weight %, 2.0 to 13.0% of aluminum (Al),
0.1 to 0.5% of manganese (Mn), 0.0015 to 0.025% of boron (B), 0.1
to 1.0% of yttrium (Y), a remainder of magnesium (Mg), and
unavoidable impurities, the magnesium alloy comprising a Mg--Al
intermetallic compound in a volume fraction of 6.5% or more,
wherein the Mg--Al intermetallic compound has an average particle
diameter of 20 to 500 nm.
2. The high strength magnesium alloy having excellent flame
retardancy of claim 1, wherein the magnesium alloy further
comprises 0.5 to 1.5 weight % of zinc (Zn).
3. The high strength magnesium alloy having excellent flame
retardancy of claim 1, wherein the magnesium alloy further
comprises one or more of an Al--Mn intermetallic compound and an
Al--Y intermetallic compound, and a total content of the Al--Mn
intermetallic compound and the Al--Y intermetallic compound is 5%
or less in a volume fraction.
4. The high strength magnesium alloy having excellent flame
retardancy of claim 1, wherein the magnesium alloy has an ignition
temperature of 700.degree. C. or higher.
5. The high strength magnesium alloy having excellent flame
retardancy of claim 1, wherein the magnesium alloy is a hardness of
70 Hv or more.
6. The high strength magnesium alloy having excellent flame
retardancy of claim 1, wherein the magnesium alloy has a tensile
strength of 130 MPa or more and an elongation of 3% or more.
7. A method of producing a high strength magnesium alloy having
excellent flame retardancy, the method comprising: preparing a
molten metal including, by weight %, 2.0 to 13.0% of aluminum (Al),
0.1 to 0.5% of manganese (Mn), 0.0015 to 0.025% of boron (B), 0.1
to 1.0% of yttrium (Y), a remainder of magnesium (Mg), and
unavoidable impurities; casting the molten metal to obtain a
magnesium alloy casting material; subjecting the magnesium alloy
casting material to a solution treatment at a temperature ranging
from 370 to 490.degree. C. for 2 to 20 hours to obtain a magnesium
alloy; cooling the magnesium alloy to 100.degree. C. or lower; and
aging the magnesium alloy cooled in the cooling of the magnesium
alloy at a temperature of 150 to 250.degree. C. for 2 to 48
hours.
8. The method of producing a high strength magnesium alloy having
excellent flame retardancy of claim 7, wherein the molten metal
further comprises, by weight %, 0.5 to 1.5% of Zn.
9. The method of producing a high strength magnesium alloy having
excellent flame retardancy of claim 7, wherein the preparing of the
molten metal is performed by charging a crucible with Mn, B and Y
mixed with Mg or Al in the form of a master alloy.
10. The method of producing a high strength magnesium alloy having
excellent flame retardancy of claim 7, wherein the preparing of the
molten metal is performed by charging the crucible sequentially
from an element having a low melting point.
11. The method of producing a high strength magnesium alloy having
excellent flame retardancy of claim 7, wherein the cooling is
performed at a cooling rate of 1 to 100.degree. C./second.
Description
TECHNICAL FIELD
[0001] The present disclosure relates to a high strength magnesium
alloy having excellent flame retardancy, and a method of producing
the same.
BACKGROUND ART
[0002] Magnesium is one of the lightest metals in practical use,
and thus, may be applied to portable electronic products such as
smart phones, tablet PCs, laptop computers, and structural
materials of transportation means for vehicles, trains, aircraft
and the like. Magnesium alloys, having various elements added to
magnesium, are attracting attention as eco-friendly lightweight
metal materials.
[0003] Magnesium alloys have excellent castability. Therefore,
casting products of magnesium alloy, which are mainly produced by
die casting methods such as high pressure casting, low pressure
casting or gravity casting, have been mainly applied to practical
products. In recent years, development and market expansion of
products for use in telegraph materials using magnesium alloys,
which may be manufactured through processing such as rolling,
extrusion or the like, have been promoted.
[0004] In general, the types of alloying elements used in magnesium
alloys for casting or magnesium alloys for wrought product are
similar. Most commonly used types of magnesium alloys are AZ-based
alloys with Al and Zn added, and AM-based alloys with Al and Mn
added. The two types of alloys commonly contain Al to improve the
castability and tensile strength of magnesium.
[0005] The AZ and AM magnesium alloys, which account for most of
the commercial magnesium alloys, are suitable for producing various
casting products due to improvement in the flowability of molten
metal by Al addition, and are also suitable for billet casting and
plate casting. However, yield strength or tensile strength thereof
is significantly lower than those of competitive aluminum alloys,
and there is a problem in that a thickness of the product should be
increased or the product shape should be modified.
[0006] In addition, the magnesium alloy has a high possibility of
ignition due to high oxygen affinity, which limits the use
conditions.
[0007] Therefore, there is a demand for developing a high strength
magnesium alloy having excellent flame retardancy and a method of
producing the same.
PRIOR ART DOCUMENT
[0008] (Patent Document 1) Korean Patent Laid-Open Publication No.
10-2015-0077494
DISCLOSURE
Technical Problem
[0009] An aspect of the present disclosure is to provide a high
strength magnesium alloy having excellent flame retardancy and a
method of producing the same.
[0010] On the other hand, the object of the present disclosure is
not limited to the above description. It will be understood by
those of ordinary skill in the art that there is no difficulty in
understanding the additional objects of the present disclosure.
Technical Solution
[0011] According to an aspect of the present disclosure, a high
strength magnesium alloy having excellent flame retardancy
includes, by weight %, 2.0 to 13.0% of aluminum (Al), 0.1 to 0.5%
of manganese (Mn), 0.0015 to 0.025% of boron (B), 0.1 to 1.0% of
yttrium (Y), a remainder of magnesium (Mg), and unavoidable
impurities, the high strength magnesium alloy including a Mg--Al
intermetallic compound in a volume fraction of 6.5% or more. The
Mg--Al intermetallic compound has an average particle diameter of
20 to 500 nm.
[0012] According to another aspect of the present disclosure, a
method of producing a high strength magnesium alloy having
excellent flame retardancy includes:
[0013] preparing a molten metal including, by weight %, 2.0 to
13.0% of aluminum (Al), 0.1 to 0.5% of manganese (Mn), 0.0015 to
0.025% of boron (B), 0.1 to 1.0% of yttrium (Y), a remainder of
magnesium (Mg), and unavoidable impurities;
[0014] casting the molten metal to obtain a magnesium alloy casting
material;
[0015] subjecting the magnesium alloy casting material to a
solution treatment at a temperature ranging from 370 to 490.degree.
C. for 2 to 20 hours to obtain a magnesium alloy;
[0016] cooling the magnesium alloy to 100.degree. C. or lower;
and
[0017] aging the magnesium alloy cooled in the cooling of the
magnesium alloy at a temperature of 150 to 250.degree. C. for 2 to
48 hours.
[0018] In addition, the solution of the above-mentioned problems
does not list all features of the present disclosure. The various
features of the present disclosure and the advantages and effects
thereof may be understood in more detail with reference to the
following specific embodiments.
Advantageous Effects
[0019] According to an embodiment of the present disclosure, there
is provided an effect of providing a high strength magnesium alloy
having excellent flame retardancy and a method of producing the
same.
DESCRIPTION OF DRAWINGS
[0020] FIGS. 1A and 1B are images of microstructures of magnesium
alloy casting materials of comparative material 1(a) and inventive
material 7(b).
[0021] FIG. 2 is an image of a microstructure after a solution
treatment of comparative material 1 is completed.
[0022] FIG. 3 is an image of a microstructure after a solution
treatment of inventive material 7 is completed.
[0023] FIGS. 4A and 4B are graphs illustrating the results of
measuring hardness values of comparative material 1(a) and
inventive material 7(b) according to the aging time at 200.degree.
C.
[0024] FIGS. 5A to 5C are images illustrating microstructures of a
magnesium alloy after an aging treatment of comparative member
1(a), inventive material 7(b), and comparative material 5 (c).
[0025] FIG. 6 is a graph illustrating a change in hardness value
based on the aging time of Inventive material 7 and a change in
Mg--Al intermetallic compound size within a crystal grain.
[0026] FIG. 7 is a graph illustrating a volume fraction of Mg--Al
intermetallic compound based on the aging time of Inventive
Material 7.
BEST MODE FOR INVENTION
[0027] Hereinafter, embodiments of the present disclosure will be
described. However, the embodiments of the present disclosure may
be modified into various other forms, and the scope of the present
disclosure is not limited to the embodiments described below.
Further, the embodiments of the present disclosure are provided to
more fully explain the present disclosure to those skilled in the
art.
[0028] As a result of deep research to solve the problems of
ignition characteristics and low strength of magnesium alloys, the
present inventors have found that a large amount of intermetallic
compounds may be finely distributed by adding B and Y in
combination and performing an aging treatment thereon, and thus
excellent flame retardancy and high strength thereof may be
secured, and the present disclosure has been obtained.
[0029] High Strength Magnesium Alloy Having Excellent Flame
Retardancy
[0030] Hereinafter, a method of producing a high strength magnesium
alloy having excellent flame retardancy according to an embodiment
in the present disclosure will be described in detail.
[0031] According to an embodiment in the present disclosure, a high
strength magnesium alloy having excellent flame retardancy
includes, by weight %, 2.0 to 13.0% of Al, 0.1 to 0.5% of Mn,
0.0015 to 0.025% of B, 0.1 to 1.0% of Y, a remainder of Mg, and
unavoidable impurities, and includes a Mg--Al intermetallic
compound in a volume fraction of not less than 6.5%. An average
grain size of the Mg--Al intermetallic compound is 20 to 500
nm.
[0032] First, the alloy composition according to an embodiment will
be described in detail. Hereinafter, the unit of each element
content refers to weight % unless otherwise specified.
[0033] Al: 2.0 to 13.0%
[0034] Al increases the tensile strength or yield strength, and
improves the castability by improving the fluidity of alloy molten
metal.
[0035] If the Al content is less than 2.0%, the above-mentioned
effect is insufficient. On the other hand, if the Al content
exceeds 13.0%, the brittleness may be increased and the workability
and ductility may be reduced. Therefore, the Al content may be 2.0
to 13.0%.
[0036] Further, in detail, a lower limit of the Al content may be
2.5%, and in further detail, the lower limit thereof may be 6.5% to
secure a tensile strength of 160 MPa or more. In detail, an upper
limit of the Al content may be 12.0%, and in more detail, the upper
limit thereof may be 11.0%.
[0037] Mn: 0.1 to 0.5%
[0038] Mn is an element contributing to an increase in tensile
strength by forming an intermetallic compound with Al to allow for
fine grains. In addition, Mn serves to lower a corrosion rate of
magnesium by lowering Fe, which is a typical impurity element
unnecessary for a magnesium alloy, through intermetallic compound
formation.
[0039] If the Mn content is less than 0.1%, the above-mentioned
effect is insufficient. On the other hand, if the Mn content
exceeds 0.5%, brittleness due to excessive formation of an acicular
intermetallic compound may be caused. Therefore, the Mn content may
be 0.1 to 0.5%.
[0040] Further, in more detail, a lower limit of the Mn content may
be 0.11%, and in further detail, an upper limit thereof may be
0.45%.
[0041] B: 0.0015 to 0.025%
[0042] B (boron) has a significantly high melting point, and
solubility thereof in a magnesium solid phase or liquid phase is
close to zero. Thus, B is known as an element not commonly used in
general magnesium alloys.
[0043] However, in an embodiment of the present disclosure, B is
added to ensure flame retardancy and high strength. In detail, B
contributes to forming a large amount of Mg--Al intermetallic
compound by adding B and Y in combination to a magnesium alloy and
performing an aging treatment thereon, thereby improving tensile
strength. In addition thereto, in this case, flame retardancy and
strength may be further improved as compared with the case in which
B is added alone. In addition, since B may contribute to prevention
of oxidation of molten metal to reduce the amount of expensive
SF.sub.6 gas used for preventing oxidation of molten metal and
SO.sub.2 gas which may cause environmental pollution, B may
contribute to reduction in production costs and environmental
protection.
[0044] If the B content is less than 0.0015%, the above-mentioned
effect is insufficient. On the other hand, if the B content exceeds
0.025%, there is a problem in which an Al--B compound is formed on
grain boundaries, reducing ductility. Therefore, the B content may
be 0.0015 to 0.025%.
[0045] Further, in detail, a lower limit of the B content may be
0.002%, and in more detail, an upper limit thereof may be
0.02%.
[0046] Y: 0.1 to 1.0%
[0047] Y bonds with Al to form a precipitate, to contribute to the
improvement of strength, and is an element that has a high oxygen
affinity to firmly protect a surface protective film of molten
metal to suppress oxidation of the molten metal. In addition, Y is
an element to improve flame retardancy even after
solidification.
[0048] In addition, as described above, Y is added together with
Bin combination to be subjected to an aging treatment, thereby
contributing to formation of a large amount of Mg--Al intermetallic
compound to improve tensile strength. Furthermore, in this case,
flame retardancy may be further improved as compared with the case
in which Y is added alone.
[0049] If the Y content is less than 0.1%, the above-mentioned
effect is insufficient. On the other hand, if the Y content exceeds
1.0%, ductility may be reduced due to formation of a coarse Al--Y
compound. Therefore, the Y content may be 0.1 to 1.0%.
[0050] Further, in detail, a lower limit of the Y content may be
0.11%, and in more detail, an upper limit thereof may be 0.95%.
[0051] In the embodiment of the present disclosure, the remainder
component is magnesium (Mg). Further, in the ordinary producing
process, impurities which are not intended may be mixed from a raw
material or a surrounding environment, which cannot be excluded.
These impurities are known to any person skilled in the art, and
thus, are not specifically mentioned in this specification. For
example, the impurities may be Fe, Cu, Ni, Ca, Na, Ba, F, S, N or
the like.
[0052] In this case, in addition to the above alloy composition,
0.3 to 3.0 wt % of Zn may be further included.
[0053] Zn: 0.3 to 3.0%
[0054] Zn is a solid solution strengthening element and is an
element which promotes formation of Mg.sub.17Al.sub.12 phase or
improves tensile strength by forming a separate intermetallic
compound containing Zn such as in Mg.sub.2Zn or the like.
[0055] If the Zn content is less than 0.3%, the above-mentioned
effect is insufficient. On the other hand, if the Zn content
exceeds 3.0%, a large amount of a separate intermetallic compound
including Zn, such as Mg.sub.2Zn or the like, is formed to increase
brittleness, which may lead to a decrease in ductility and
toughness.
[0056] Therefore, the Zn content may be 0.3 to 3.0%. In more
detail, the Zn content may be within a range of from 0.5 to 1.5 wt
%, considering the improvement of the strength and the reduction in
brittleness.
[0057] A high-strength magnesium alloy having excellent flame
retardancy according to an embodiment in the present disclosure not
only satisfies the alloy composition described above, but also
contains a Mg--Al intermetallic compound in a volume fraction of
6.5% or more. An average grain size of the Mg--Al intermetallic
compound is 20 to 500 nm.
[0058] When the main alloy element added to magnesium is Al, an
Mg--Al intermetallic compound may be formed, and a typical Mg--Al
intermetallic compound is Mg.sub.17Al.sub.12 phase. The Mg--Al
intermetallic compound serves to secure high strength.
[0059] Since a maximum addition amount of Al or other alloying
elements to be added to a magnesium alloy is smaller than a maximum
high capacity of each alloying element to Mg, most Al is solidified
in the Mg matrix, rather than inducing intermetallic compound
formation in the grain, and thus, formation of an Mg--Al
intermetallic compound is not a general phenomenon. Thus, it is
difficult to form a large amount of an Mg--Al intermetallic
compound. In the case of an embodiment in the present disclosure, a
large amount of Mg--Al intermetallic compound may be secured by
adding B and Y in combination and performing an aging treatment
thereon.
[0060] If the volume fraction of the Mg--Al intermetallic compound
is less than 6.5%, it is difficult to ensure high strength.
Accordingly, the volume fraction of the Mg--Al intermetallic
compound may be 6.5% or more, in detail, 7.0% or more, in further
detail, 7.5% or more.
[0061] An upper limit of the volume fraction of the Mg--Al
intermetallic compound is not particularly limited, but if the
content thereof exceeds 30%, the grain size of the Mg--Al
intermetallic compound may be coarsened, and brittleness may be
increased. Thus, the volume fraction of the Mg--Al intermetallic
compound may be 30% or less, and in detail, may be 25% or less.
[0062] If the average grain size of the Mg--Al intermetallic
compound is less than 20 nm, the fraction of the Mg--Al
intermetallic compound is low and it is difficult to secure high
strength. If the average grain size thereof is more than 500 nm,
brittleness increases.
[0063] In this case, one or more of an Al--Mn intermetallic
compound and an Al--Y intermetallic compound is further included,
and the total amount thereof may be 5% or less in a volume
fraction. If the total amount thereof exceeds 5%, the Mn and Y
contents are excessive and thus, brittleness may increase.
[0064] In this case, the magnesium alloy according to an embodiment
in the present disclosure may have an ignition temperature of
700.degree. C. or higher.
[0065] In addition, the magnesium alloy according to an embodiment
in the present disclosure may have a hardness of 70 Hv or more.
[0066] The magnesia alloy according to an embodiment in the present
disclosure may have a tensile strength of 130 MPa or more and an
elongation of 3% or more. Further, a tensile strength of 160 MPa or
more may be secured by controlling the Al content and the like.
[0067] Method of Producing High-Strength Magnesium Alloy Having
Excellent Flame Retardancy
[0068] Hereinafter, a method for producing a high strength
magnesium alloy having excellent flame retardancy according to
another embodiment in the present disclosure will be described in
detail.
[0069] According to another aspect of the present disclosure, there
is provided a method of producing a high strength magnesium alloy
having excellent flame retardancy, including: preparing a molten
metal satisfying the above-described alloy composition; casting the
molten metal to obtain a magnesium alloy casting material;
subjecting the magnesium alloy casting material to a solution
treatment at a temperature ranging from 370 to 490.degree. C. for 2
to 20 hours to obtain a magnesium alloy; cooling the magnesium
alloy to 100.degree. C. or lower; and aging the cooled magnesium
alloy at a temperature of 150 to 250.degree. C. for 2 to 48
hours.
[0070] Molten Metal Preparation
[0071] A molten metal satisfying the above alloy composition is
prepared. The molten metal is prepared through general molten metal
preparation for magnesium alloy, without particular limitation.
[0072] For example, the above-described alloying elements are
prepared in accordance with the proposed composition range, and
then charged into a crucible for melting, to then be subjected to a
melting operation. Since the melting point of the magnesium alloy
is relatively low, any method using a gas furnace, an electric
furnace, an induction melting furnace, or the like may be used.
[0073] In preparing the alloying elements, each alloy element may
be prepared in a pure form, but the alloying elements may also be
charged into the crucible in the form of a master alloy in which
Mn, B and Y are mixed with Mg or Al. B, Y and Mn have high melting
points and may thus be charged into the crucible in the form of
master alloy mixed with Mg or Al, which is advantageous in terms of
dissolving.
[0074] In addition, when the prepared dissolving material is
charged into the crucible, the material may be charged into the
crucible in order from the element having a low melting point,
which may be advantageous in terms of dissolving work.
[0075] Casting
[0076] The molten metal is cast to obtain a magnesium alloy casting
material. The casting is not particularly limited as in the case of
the molten metal preparation.
[0077] For example, a method using a movable mold and a method
using a fixed mold may be used. Representative examples of the
method using the movable mold include twin roll casting and belt
casting using a movable mold such as a twin roll or a twin belt.
Also, representative examples of the method using the fixed mold
include semi-continuous casting or continuous casting such as
billet casting, and may also include mold casting such as
high-pressure casting, low-pressure casting and gravity
casting.
[0078] As the casting process, although various methods as
described above may be used, since boron or yttrium having a low
solubility with respect to magnesium is added together with
aluminum, it may be advantageous to apply a casting method capable
of increasing a cooling rate. To this end, the mold should be
cooled with cooling water. When cooling water is used, the mold
surface should be maintained at room temperature or more before
casting so that the condensed water on the surface of the mold may
be removed, and then should be maintained at room temperature or
lower after the condensed water is removed.
[0079] Solution Treatment
[0080] The magnesium alloy casting material is subjected to a
solution treatment at a temperature ranging from 370 to 490.degree.
C. for 2 to 20 hours to obtain a magnesium alloy. Since a Mg--Al
intermetallic compound is formed in the magnesium alloy casting
material, but is formed in the form of coarse Mg--Al or mixed with
a Mg matrix (Lamellar Mg--Al), the solution treatment is performed
to enable such an adverse Mg--Al intermetallic compound to a solid
solution treatment.
[0081] If the solution treatment temperature is less than
370.degree. C. or the holding time is less than 2 hours, the entire
Mg--Al intermetallic compound is difficult to be solidified. If the
solution treatment temperature exceeds 490.degree. C. or the
retention time is more than 20 hours, production costs may be
increased and productivity may be lowered, and an ignition
phenomenon by oxidation may occur before B and Y are added.
Therefore, in more detail, the solution treatment may be carried
out within a temperature range of 400 to 460.degree. C. for 2 to 20
hours.
[0082] Cooling
[0083] The magnesium alloy is cooled to 100.degree. C. or lower, to
significantly reduce a natural aging phenomenon that may appear
before aging treatment.
[0084] In this case, the cooling rate may be 1 to 100.degree.
C./second, and the natural aging phenomenon that may occur during
cooling is significantly reduced and the solidified Al element may
be prevented from being precipitated at random. For example, rapid
cooling may be preferably performed by forced blowing, water
cooling, oil cooling, or the like.
[0085] Aging Treatment
[0086] The cooled magnesium alloy is aged at 150 to 250.degree. C.
for 2 to 48 hours. In the microstructure of the cooled magnesium
alloy after the solution treatment, most of the Al element added as
the alloying element does not form a separate intermetallic
compound in a state of solid solution solidified in the Mg matrix,
so that the strength of the material may not be efficiently
increased. Therefore, in the case of an embodiment of the present
disclosure, a large amount of Mg--Al intermetallic compound is
precipitated through aging to increase the strength and to secure
excellent flame retardancy. For example, when B and Y are combined
in the range suggested according to an embodiment in the present
disclosure, a large amount of Mg--Al intermetallic compound may be
precipitated through the aging treatment described above.
[0087] Since the precipitation by the aging treatment is a
solid-phase reaction proceeding in the solid phase, an Mg--Al
intermetallic compound having a particle form, an average particle
diameter, a volume fraction, and the like favorable for the
improvement of strength and flame retardancy may be formed.
[0088] If the aging treatment temperature is less than 150.degree.
C. or the holding time thereof is less than 2 hours, it is
difficult to sufficiently secure the Mg--Al intermetallic compound.
On the other hand, if the aging treatment temperature is more than
250.degree. C. or the retention time is more than 48 hours, the
Mg--Al intermetallic compound may be solidified, resulting in
increased production costs and decreased productivity. Therefore,
the aging treatment may be performed at 150 to 250.degree. C. for 2
to 48 hours. In more detail, the temperature and the holding time
may be increased within the above temperature and holding time
depending on the amount of Al added.
MODE FOR INVENTION
[0089] Hereinafter, an embodiment in the present disclosure will be
described in more detail by way of example. It should be noted,
however, that the following examples are intended to illustrate the
present disclosure in more detail and not to limit the scope of the
present disclosure. The scope of the present disclosure is
determined by the matters set forth in the claims and the matters
reasonably inferred therefrom.
Embodiment 1
[0090] A magnesium alloy casting material having a thickness of 10
mm was cast by casting a molten metal having the composition shown
in Table 1 below. The magnesium alloy casting material was
solution-treated at 420.degree. C. for 4 hours, cooled to
20.degree. C., and aged at 200.degree. C. for 12 hours to produce a
magnesium alloy.
[0091] Mechanical properties of a Mg--Al intermetallic compound of
the magnesium alloy were measured and are shown in Table 1 below.
The size of the Mg--Al intermetallic compound was measured by an
average size obtained by measuring a circle-equivalent
diameter.
[0092] Except for the alloying element shown in Table 1, it was
magnesium, and Mg--Al means a Mg--Al intermetallic compound.
[0093] The ignition temperature was measured at a temperature at
which the ignition occurred while raising the temperature inside
the furnace body while leaving a sample of 10 g in the form of a
chip in the furnace under the atmosphere.
TABLE-US-00001 TABLE 1 Mg--Al Mechanical Properties Ignition Alloy
Composition (wt %) Size Fraction TS El Hardness Temperature
Classification Al Mn B Y (nm) (vol %) (MPa) (%) (Hv) (.degree. C.)
Comparative 9 0.34 -- -- 193 2.6 113 5.2 59 530 Material 1
Comparative 3 0.05 0.013 1.23 178 1.7 113 5.2 48 624 Material 2
Comparative 6 0.21 0.001 0.41 205 2.1 121 4.2 53 590 Material 3
Comparative 9 0.45 0.412 0.05 232 3.8 124 3.1 63 647 Material 4
Comparative 3 0.74 -- 0.72 184 1.4 114 4.3 50 634 Material 5
Comparative 6 0.12 0.003 1.21 212 2.4 123 3.4 56 660 Material 6
Comparative 9 0.33 -- 0.21 228 3.1 125 3.2 61 612 Material 7
Inventive 2.8 0.12 0.018 0.92 134 7.5 135 5.8 71 721 Material 1
Inventive 2.7 0.32 0.012 0.63 128 8.1 138 6.2 72 712 Material 2
Inventive 3.1 0.44 0.006 0.31 133 8.7 142 6.1 74 718 Material 3
Inventive 3.4 0.42 0.003 0.13 129 9.8 144 5.7 78 715 Material 4
Inventive 5.6 0.12 0.017 0.12 153 13.3 151 4.6 84 747 Material 5
Inventive 6.2 0.3 0.012 0.54 161 14.4 155 5.8 87 733 Material 6
Inventive 6.2 0.4 0.006 0.81 154 14.7 158 4.7 88 742 Material 7
Inventive 5.8 0.42 0.002 0.88 139 13.8 152 4.4 85 739 Material 8
Inventive 8.5 0.12 0.013 0.14 176 19.1 164 3.5 103 783 Material 9
Inventive 10.6 0.3 0.003 0.51 184 21.6 167 4.6 107 776 Material 10
Inventive 9.8 0.4 0.009 0.94 179 20.3 172 4.2 106 782 Material 11
Inventive 8.7 0.42 0.019 0.45 172 19.4 168 3.7 104 785 Material
12
[0094] It can be confirmed that the inventive materials satisfying
the alloy composition and the producing conditions proposed
according to an embodiment in the present disclosure include a
Mg--Al intermetallic compound in a volume fraction of 6.5% or more
and the average particle diameter of the Mg--Al intermetallic
compound satisfies 20 to 500 nm. Also, it can be confirmed that the
flame retardancy is excellent as an ignition temperature is
700.degree. C. or more, and the mechanical properties are also
superior to the comparative materials.
[0095] Meanwhile, it can be confirmed that the comparative
materials satisfied the producing conditions proposed according to
an embodiment in the present disclosure, but did not satisfy the
alloy composition, so that Mg--Al intermetallic compounds were not
sufficiently secured. In addition, it can be confirmed that the
flame retardancy is poor and the mechanical properties are also
inferior to those of the inventive materials.
Embodiment 2
[0096] The changes in the producing process of the comparative
material 1 and the inventive material 7 shown in Table 1 were
observed more closely.
[0097] FIGS. 1A and 1B are images of the microstructures of the
magnesium alloy casting materials of comparative material 1(a) and
inventive material 7(b). The casting structure of the comparative
member 1 is composed of a Mg matrix and coarse Mg--Al intermetallic
compound, a Mg matrix+Mg--Al intermetallic compound mixed structure
(Lamellar Mg--Al), and an Al--Mn intermetallic compound. In the
case of the casting structure of the inventive material 7 to which
yttrium and boron were added, an Al--Y intermetallic compound
(Al--Y) was observed in addition to the above-mentioned structure,
and no boron-containing intermetallic compound was observed
separately.
[0098] When the comparative material and the inventive material
having the above casting structure are subjected to the solution
treatment, most of the Mg--Al intermetallic compounds except for
Al--Mn or Al--Y intermetallic compounds are solidified as the base
structure as illustrated in FIGS. 2 and 3, and thus, is not
observed. The optical structures of the casting structure and the
solution treatment material are almost similar except for the
presence or absence of the Al--Y intermetallic compound, but show a
large difference in the aging treatment material.
[0099] These differences may be confirmed first in the hardness
measurement results according to aging time. As illustrated in
FIGS. 4A and 4B, the hardness values of the comparative material
1(a) and the inventive material 7(b) were measured at 200.degree.
C. according to the aging time. As a result, it can be confirmed
that the hardness of the inventive material is significantly high.
Also, the hardness value of the comparative material 1 barely
changes according to the aging time, but it can be confirmed that
the hardness value of the inventive material greatly increases when
the aging time exceeds 1 hour. In detail, after the lapse of 3
hours, a maximum hardness value corresponding to peak aging is
shown, and the hardness value at this time is a value of 97 to 107
Hv which is a value increased 60% or more, as compared with the
average hardness value of the casting material aged for 1 hour or
less. In addition, a maximum hardness value of the inventive
material 7 is about two times the maximum hardness value of the
comparative material.
[0100] FIGS. 5A to 5C are images showing the microstructures of the
magnesium alloys after the aging treatment of the comparative
material 1(a), the inventive material 7(b) and the comparative
material 5(c). It can be confirmed that a large amount of Mg--Al
intermetallic compound having a size of several tens of nanometers
is precipitated in the inventive material 7, which shows that the
hardness value of the inventive material is significantly
increased.
[0101] FIG. 6 illustrates changes in the hardness value (rhombus)
and the size (square) of the Mg--Al intermetallic compound in the
crystal grains with respect to the aging time of the inventive
material 7, and FIG. 7 illustrates a volume fraction of Mg--Al
intermetallic compounds with aging time. As illustrated in FIGS. 6
and 7, when the inventive material 7 is aged for 3 hours or more,
it can be seen that the Mg--Al intermetallic compounds are grown to
20 nm or more and 10 vol % or more, respectively, in the average
size and the volume fraction.
[0102] While embodiments have been illustrated and described above,
it will be apparent to those skilled in the art that modifications
and variations could be made without departing from the scope of
the present disclosure as defined by the appended claims.
* * * * *