U.S. patent application number 14/119080 was filed with the patent office on 2014-04-03 for alloy production method and alloy produced by the same.
This patent application is currently assigned to KOREA INSTITUTE OF INDUSTRIAL TECHNOLOGY. The applicant listed for this patent is Se-Kwang Kim. Invention is credited to Se-Kwang Kim.
Application Number | 20140093420 14/119080 |
Document ID | / |
Family ID | 47217864 |
Filed Date | 2014-04-03 |
United States Patent
Application |
20140093420 |
Kind Code |
A1 |
Kim; Se-Kwang |
April 3, 2014 |
ALLOY PRODUCTION METHOD AND ALLOY PRODUCED BY THE SAME
Abstract
Provided are an alloy production method that may easily
distribute a compound in a matrix of an alloy while maintaining the
quality of a molten metal, and an alloy produced by the same. In
accordance with an exemplary embodiment, the method includes
forming a molten metal in which a mother alloy including at least
one kind of first compound and a casting metal are melted, and
casting the molten metal, wherein the mother alloy is a magnesium
mother alloy or aluminum mother alloy.
Inventors: |
Kim; Se-Kwang; (Seoul,
KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Kim; Se-Kwang |
Seoul |
|
KR |
|
|
Assignee: |
KOREA INSTITUTE OF INDUSTRIAL
TECHNOLOGY
Chungcheongnam-do
KR
|
Family ID: |
47217864 |
Appl. No.: |
14/119080 |
Filed: |
May 16, 2012 |
PCT Filed: |
May 16, 2012 |
PCT NO: |
PCT/KR2012/003849 |
371 Date: |
November 20, 2013 |
Current U.S.
Class: |
420/591 ;
164/55.1; 164/57.1 |
Current CPC
Class: |
B22D 21/04 20130101;
B22D 25/00 20130101; C22C 1/03 20130101; C22C 23/02 20130101; C22C
1/02 20130101; C22C 21/06 20130101; C22C 23/00 20130101 |
Class at
Publication: |
420/591 ;
164/55.1; 164/57.1 |
International
Class: |
B22D 25/00 20060101
B22D025/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 20, 2011 |
KR |
10-2011-0048192 |
Claims
1. A method of producing an alloy, comprising: forming a molten
metal in which a mother alloy including at least one kind of first
compound and a casting metal are melted; and casting the molten
metal wherein the mother alloy is a magnesium mother alloy or
aluminum mother alloy.
2. The method of claim 1, wherein the first compound has a higher
melting point than the casting metal.
3. The method of claim 1, wherein the casting metal is any one
selected from the group consisting of tin, aluminum, zinc,
magnesium, copper, nickel, cobalt, iron, titanium, vanadium,
molybdenum, tungsten, and alloys thereof.
4. The method of claim 1, wherein the first compound is formed by
exhausting at least a portion of a second compound in which at
least two components are bonded in a magnesium molten metal or
aluminum molten metal.
5. The method of claim 4, wherein the first compound is formed by
substantially completely exhausting the second compound in a
magnesium molten metal or aluminum molten metal.
6. The method of claim 4, wherein the first compound is a compound
in which a component supplied from the exhausted second compound
and a metal component in the magnesium molten metal are bonded to
each other.
7. The method of claim 6, wherein the metal component is magnesium
or aluminum.
8. The method of claim 4, wherein the first compound is a compound
produced by a bonding between components respectively supplied from
the exhausted at least two kinds of second compounds.
9. The method of claim 1, wherein the first compound is a compound
formed by melting at least a portion of any one of calcium or
strontium in the magnesium molten metal or aluminum molten
metal.
10. The method of claim 1, wherein the first compound is a compound
added in a molten metal of the mother alloy.
11. The method of claim 10, wherein the first compound is a
compound produced by a mechanical alloying.
12. The method of claim 1, wherein the first compound comprises a
magnesium compound.
13. The method of claim 12, wherein the magnesium compound
comprises at least one selected from the group consisting of a
magnesium-calcium compound, a magnesium-aluminum-calcium compound,
a magnesium-strontium compound, and a magnesium-silicon
compound.
14. The method of claim 12, wherein the magnesium compound
comprises at least one selected from the group consisting of
Mg.sub.2Ca, (Mg,Al).sub.2Ca, Mg.sub.2Sr, Mg.sub.23Sr.sub.6,
Mg.sub.38Sr.sub.9, Mg.sub.17Sr.sub.2, and Mg.sub.2Si.
15. The method of claim 1, wherein the first compound comprises an
aluminum compound.
16. The method of claim 15, wherein the aluminum compound comprises
at least one selected from an aluminum-calcium compound, an
aluminum-strontium compound, and an aluminum-cesium compound.
17. The method of claim 15, wherein the aluminum compound comprises
at least one selected from the group consisting of Al.sub.2Ca,
Al.sub.4Ca, Al.sub.4Sr, Al.sub.2Sc, and Al.sub.2Ce.
18. The method of claim 1, wherein the first compound comprises a
calcium-silicon compound.
19. The method of claim 18, wherein the calcium-silicon compound
comprises CaSi.
20. The method of claim 4, wherein the second compound comprises a
calcium-based compound, a strontium-based compound, a silicon-based
compound, or a rare earth metal compound.
21. The method of claim 20, wherein the calcium-based compound
comprises at least one selected from the group consisting of
calcium oxide (CaO), calcium cyanide (CaCN.sub.2), and calcium
carbide.
22. The method of claim 20, wherein the strontium-based compound
comprises strontium oxide (SrO).
23. The method of claim 20, wherein the silicon-based compound
comprises silicon oxide (SiO.sub.2).
24. The method of claim 20, wherein the rare earth metal compound
comprises at least one of scandium oxide (Sc.sub.2O.sub.3) and
cesium oxide (CeO.sub.2).
25. The method of claim 1, wherein the producing of the magnesium
mother alloy comprises: adding at least one kind of second compound
in which two or more components are bonded to a magnesium molten
metal; exhausting at least a portion of the second compound; and
casting the magnesium molten metal to produce a first magnesium
mother alloy.
26. The method of claim 25, wherein the producing of the magnesium
mother alloy further comprises adding the first magnesium mother
alloy to a magnesium molten metal and diluting the first magnesium
mother alloy to form a second magnesium mother alloy.
27. The method of claim 1, wherein the producing of the aluminum
mother alloy comprises: adding at least one kind of second compound
in which two or more components are bonded in an aluminum molten
metal; exhausting at least a portion of the second compound; and
casting the aluminum molten metal to produce a first aluminum
mother alloy.
28. The method of claim 27, wherein the producing of the aluminum
mother alloy further comprises adding the first aluminum mother
alloy to an aluminum molten metal and diluting the first aluminum
mother alloy to form a second aluminum mother alloy.
29. The method of claim 25, wherein the second compound is
dispersively added to a surface of an upper layer portion of the
magnesium molten metal.
30. The method of claim 29, wherein the upper layer portion of the
magnesium molten metal is stirred.
31. The method of claim 30, wherein the stirring is performed in
the upper layer portion from the surface of the magnesium molten
metal to a point which is not more than 20% of a total depth of the
magnesium molten metal.
32. The method of claim 25, wherein any one component of the second
compound is removed upward from a surface of the magnesium molten
metal.
33. The method of claim 1, wherein the producing of the mother
alloy comprises: adding calcium or strontium to a mother alloy
molten metal; and exhausting at least a portion of the calcium or
strontium in the magnesium molten metal.
34. The method of claim 1, wherein the aluminum mother alloy is
produced by adding a magnesium alloy in an aluminum molten metal,
and the magnesium alloy is produced by a process comprising: adding
calcium or strontium to a magnesium molten metal; and melting at
least a portion of the calcium or strontium in the magnesium molten
metal.
35. The method of claim 1, wherein the aluminum mother alloy is
produced by adding an aluminum alloy in an aluminum molten metal,
and the aluminum alloy is produced by a process comprising: adding
calcium or strontium to an aluminum molten metal; and melting at
least a portion of the calcium or strontium in the aluminum molten
metal.
36. The method of claim 1, wherein the magnesium mother alloy is
produced by adding an aluminum alloy in a magnesium molten metal,
and the aluminum alloy is produced by a process comprising: adding
calcium or strontium to an aluminum molten metal; and melting at
least a portion of the calcium or strontium in the aluminum molten
metal.
37. The method of claim 1, wherein the magnesium mother alloy is
produced by adding a magnesium alloy in a magnesium molten metal,
and the magnesium alloy is produced by a process comprising: adding
calcium or strontium to a magnesium molten metal; and melting at
least a portion of the calcium or strontium in the magnesium molten
metal.
38. The method of claim 1, wherein the producing of the aluminum
mother alloy comprises adding a magnesium alloy containing the
first compound to the aluminum molten metal.
39. The method of claim 38, wherein the producing of the magnesium
alloy containing the first compound comprises: adding a second
compound to a magnesium molten metal; and casting the magnesium
molten metal.
40. An alloy comprising: a metal matrix; and a first compound
existing in the metal matrix, wherein the first compound is a
compound which is included in a magnesium mother alloy or aluminum
mother alloy and is added in a molten metal produced so as to cast
the alloy.
41. The alloy of claim 40, wherein the metal matrix comprises any
one selected from the group consisting of tin, aluminum, zinc,
magnesium, copper, nickel, cobalt, iron, titanium, vanadium,
molybdenum, tungsten, and alloys thereof.
42. The alloy of claim 40, wherein the first compound comprises a
magnesium compound.
43. The alloy of claim 42, wherein the magnesium compound comprises
at least one selected from the group consisting of a
magnesium-calcium compound, a magnesium-aluminum-calcium compound,
a magnesium-strontium compound, and a magnesium-silicon
compound.
44. The alloy of claim 42, wherein the magnesium compound comprises
at least one selected from the group consisting of Mg.sub.2Ca,
(Mg,Al).sub.2Ca, Mg.sub.2Sr, Mg.sub.23 Sr.sub.6, Mg.sub.38Sr.sub.9,
Mg.sub.17Sr.sub.2, and Mg.sub.2Si.
45. The alloy of claim 40, wherein the first compound comprises an
aluminum compound.
46. The alloy of claim 45, wherein the aluminum compound comprises
at least one selected from an aluminum-calcium compound, an
aluminum-strontium compound, and an aluminum-cesium compound.
47. The alloy of claim 45, wherein the aluminum compound comprises
at least one selected from the group consisting of Al.sub.2Ca,
Al.sub.4Ca, Al.sub.4Sr, Al.sub.2Sc, and Al.sub.2Ce.
48. The alloy of claim 45, wherein the first compound comprises a
calcium-silicon compound.
49. The alloy of claim 48, wherein the calcium-silicon compound
comprises CaSi.
50. The alloy of claim 40, wherein the alloy comprises an inclusion
at a concentration which is lower than that of an inclusion of an
alloy in which a mother alloy no containing the first compound is
added and which is produced under the same condition.
Description
BACKGROUND
[0001] The present disclosure relates to an alloy production method
and an alloy produced by the same, and more particularly, to an
alloy production method in which a mother alloy is used in casting,
and an alloy produced by the same.
[0002] Alloys may be produced by adding an alloy element to a
liquid molten metal and performing a casting. In producing an alloy
using such a casting technique, the quality of molten metal has a
great influence on characteristics of the alloy. Particularly, in
the case where magnesium, aluminum or the like having a high
oxidation property is added as an alloy element in a molten metal,
a tendency that an impurity such as inclusion is increased in the
molten metal by oxidation of the alloy element is shown. Such an
impurity may cause degradation of alloys in view of mechanical and
chemical properties. Therefore, in order to improve properties of
an alloy produced by casting, it is necessary to maintain cleanness
in the molten metal as high as possible. To obtain a high quality
molten metal, a method of producing the molten metal in vacuum or a
method of protecting a surface of the molten metal by coating the
surface of the molten metal with a protection gas.
[0003] Meanwhile, in order to improve mechanical and chemical
characteristics of an alloy, various compounds may be formed on a
matrix of the alloy. For example, when an intermetallic compound
having a high hardness is distributed on a matrix of an alloy, the
intermetallic compound functions as a structure suppressing the
movement of dislocations to improve the strength of the alloy. Such
a compound may be crystallized as a thermodynamically stable phase
while a liquid phase metal is solidified in casting, or after being
solidified, precipitated through a proper mechanical processing or
heat treatment.
[0004] However, in order to produce a molten metal in vacuum, an
additional apparatus for maintaining vacuum is required, and a
protection gas coated on a surface of the molten metal is expensive
or may cause environmental problems. Also, it is difficult to
control the amount or distribution of a phase crystallized during
casting, and a mechanical processing or heat treatment should be
accompanied in order to form a precipitate phase.
SUMMARY
[0005] The present disclosure provides an aluminum alloy and a
method of producing the same that can improve mechanical
characteristics by distributing an intermetallic compound
(hereinafter, magnesium-silicon compound) including magnesium and
silicon in an aluminum matrix without a heat treatment. The above
subject matter is only exemplary, and the scope of the present
disclosure is not limited by the subject matter.
[0006] The present disclose provides an alloy production method
that may easily distribute a compound in a matrix of an alloy while
maintaining the quality of a molten metal, and an alloy produced by
the same. The above subject matter is only exemplary, and the scope
of the present disclosure is not limited by the subject matter.
[0007] In accordance with an exemplary embodiment, there is
provided a method of producing an alloy. A molten metal in which a
mother alloy including at least one kind of first compound and a
casting metal are melted is formed. The molten metal is cast. The
mother alloy may be a magnesium mother alloy or aluminum mother
alloy.
[0008] The first compound may have a higher melting point than the
casting metal.
[0009] The casting metal may be any one selected from the group
consisting of tin, aluminum, zinc, magnesium, copper, nickel,
cobalt, iron, titanium, vanadium, molybdenum, tungsten, and alloys
thereof.
[0010] The first compound may be a compound formed by exhausting at
least a portion of a second compound in which at least two
components are bonded in a magnesium molten metal or aluminum
molten metal. The first compound may be a compound in which a
component supplied from the exhausted second compound and a metal
component in the magnesium molten metal are bonded to each other,
and the metal component may be magnesium or aluminum.
[0011] The first compound may be a compound produced by a bonding
between components respectively supplied from the at least two
kinds of exhausted second compounds.
[0012] The first compound may be a compound formed by melting at
least a portion of any one of calcium or strontium in the magnesium
molten metal or aluminum molten metal.
[0013] The first compound may be a compound added to a molten metal
of the mother alloy. The first compound may be produced by a
mechanical alloying.
[0014] The first compound may include a magnesium compound. The
magnesium compound may include at least one selected from the group
consisting of a magnesium-calcium compound, a
magnesium-aluminum-calcium compound, a magnesium-strontium
compound, and a magnesium-silicon compound.
[0015] The first compound may include an aluminum compound. The
aluminum compound may include at least one selected from an
aluminum-calcium compound, an aluminum-strontium compound, and an
aluminum-cesium compound.
[0016] The first compound may include a calcium-silicon
compound.
[0017] The second compound may include a calcium-based compound, a
strontium-based compound, a silicon-based compound, or a rare earth
metal-based compound.
[0018] The producing of the magnesium mother alloy may include:
adding at least one kind of second compound in which two or more
components are bonded to a magnesium molten metal; exhausting at
least a portion of the second compound; and casting the magnesium
molten metal to produce a first magnesium mother alloy.
[0019] The producing of the magnesium mother alloy may further
include: adding the first magnesium mother alloy to a magnesium
molten metal and diluting the magnesium molten metal to form a
second magnesium mother alloy.
[0020] The producing of the aluminum mother alloy may include:
adding at least one kind of second compound in which at least two
components are bonded to an aluminum molten metal; exhausting at
least a portion of the second compound; and casting the aluminum
molten metal to produce a first aluminum mother alloy.
[0021] The producing of the aluminum mother alloy may further
include: adding the first aluminum mother alloy to an aluminum
molten metal and diluting the aluminum molten metal to form a
second aluminum mother alloy.
[0022] The second compound may be dispersively added to a surface
of an upper layer portion of the magnesium molten metal, and the
upper layer portion of the magnesium molten metal may be stirred.
The stirring may be performed in the upper layer portion from a
surface of the magnesium molten metal to a point which is not more
than 20% of a total depth of the magnesium molten metal.
[0023] The producing of the mother alloy may include: adding
calcium or strontium to a mother alloy molten metal; and exhausting
at least a portion of the calcium or strontium in the magnesium
molten metal.
[0024] The aluminum mother alloy may be produced by adding a
magnesium alloy in an aluminum molten metal, and the magnesium
alloy is produced by a process including: adding calcium or
strontium to a magnesium molten metal; and melting at least a
portion of the calcium or strontium in the magnesium molten
metal.
[0025] The aluminum mother alloy may be produced by adding an
aluminum alloy in an aluminum molten metal, and the aluminum alloy
is produced by a process including: adding calcium or strontium to
an aluminum molten metal; and melting at least a portion of the
calcium or strontium in the aluminum molten metal.
[0026] The magnesium mother alloy may be produced by adding an
aluminum alloy in a magnesium molten metal, and the aluminum alloy
is produced by a process including: adding calcium or strontium to
an aluminum molten metal; and melting at least a portion of the
calcium or strontium in the aluminum molten metal.
[0027] The magnesium mother alloy may be produced by adding a
magnesium alloy in a magnesium molten metal, and the magnesium
alloy is produced by a process including: adding calcium or
strontium to a magnesium molten metal; and melting at least a
portion of the calcium or strontium in the magnesium molten
metal.
[0028] The producing of the aluminum mother alloy may include
adding a magnesium alloy containing the first compound to the
aluminum molten metal. The producing of the magnesium alloy
containing the first compound may include adding a second compound
in a magnesium molten metal, and casting the magnesium molten
metal.
[0029] In accordance with another exemplary embodiment, an alloy
includes a metal matrix, and a first compound existing in the metal
matrix. The first compound may be a compound which is included in a
magnesium mother alloy or aluminum mother alloy and is added to a
molten metal produced so as to cast the alloy.
[0030] The metal matrix may include any one selected from the group
consisting of tin, aluminum, zinc, magnesium, copper, nickel,
cobalt, iron, titanium, vanadium, molybdenum, tungsten, and alloys
thereof.
[0031] The first compound may include a magnesium compound, an
aluminum compound, or a calcium-silicon compound.
[0032] The alloy may include an inclusion at a concentration which
is lower than that of an inclusion of an alloy in which a mother
alloy no containing the first compound is added and which is
produced under the same condition.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] Exemplary embodiments can be understood in more detail from
the following description taken in conjunction with the
accompanying drawings, in which:
[0034] FIG. 1 is a flow diagram showing an embodiment of a method
of producing an alloy according to the present disclosure;
[0035] FIG. 2 is a flow diagram showing an embodiment of a method
of producing a magnesium mother alloy according to the present
disclosure;
[0036] FIG. 3 is a schematic view showing a decomposition process
of calcium oxide in an upper layer portion of a magnesium molten
metal when calcium oxide is added in the magnesium molten
metal;
[0037] FIG. 4 is a flow diagram showing an embodiment of a method
of producing an aluminum mother alloy according to the present
disclosure;
[0038] FIGS. 5A through 5D show composition analysis results of
magnesium mother alloys produced by adding calcium oxide according
to an embodiment of the present disclosure;
[0039] FIGS. 6A through 6E show results analyzing components of an
aluminum alloy in which a magnesium mother alloy is added and an
aluminum alloy in which pure magnesium is added;
[0040] FIGS. 7A and 7B show results observing states of an aluminum
molten metal in which a magnesium mother alloy produced by an
embodiment of the present disclosure is added, and an aluminum
molten metal in which pure magnesium is added;
[0041] FIG. 8 is a graph showing oxidation resistance test results
of an aluminum alloy according to an embodiment of the present
disclosure; and
[0042] FIG. 9 is a graph showing comparison results of oxidation
resistance of a related art aluminum-magnesium alloy having the
same composition as an aluminum-magnesium alloy according to an
embodiment of the present disclosure.
DETAILED DESCRIPTION OF EMBODIMENTS
[0043] Hereinafter, the present invention will be described in
detail by explaining preferred embodiments of the invention with
reference to the attached drawings. The present disclosure may,
however, be embodied in many different forms and should not be
construed as being limited to the embodiments set forth herein;
rather, these embodiments are provided so that this disclosure will
be thorough and complete, and will fully convey the concept of the
invention to those skilled in the art. Further, the present
invention is only defined by scopes of claims.
[0044] According to an exemplary embodiment, a mother alloy
including at least one kind of compound is produced, and then is
added in a molten metal to produce an alloy. At this time, the
compound included in the mother alloy is called a `first
compound`.
[0045] FIG. 1 is a flow diagram of a method of producing an alloy
according to an exemplary embodiment. Referring to FIG. 1, a molten
metal in which a casting metal is melted is formed (S11). The
casting metal is a metal that may be added to a mother alloy, and
may be any selected from the group consisting of tin (Sn), zinc
(Zn), magnesium (Mg), aluminum (Al), copper (Cu), nickel (Ni),
cobalt (Co), iron (Fe), titanium (Ti), vanadium (V), molybdenum
(Mo), and tungsten (W), or an alloy thereof.
[0046] Next, a mother alloy including a first compound is added to
the molten metal of the casting metal (S12). Next, a molten metal
in which the mother alloy and the casting metal are melted is cast
to produce an alloy (S13).
[0047] In addition to the method of producing the alloy in which
the mother alloy is added in the molten metal of the casting metal
as shown in FIG. 1, the alloy may be produced by a method in which
the mother alloy and the casting metal are installed together in a
melting furnace and then melted at the same time. This is equally
applied to the adding of a method of producing a mother alloy to be
described later.
[0048] Here, the mold may be any selected from the group consisting
of a metal mold, a ceramic mold, a graphite mold, and equivalents.
Also, examples of the casting may include a sand casting, a die
casting, a gravity casting, a continuous casting, a low pressure
casting, a squeeze casting, a lost wax casting, a thixo casting,
and the like.
[0049] In an exemplary embodiment, the mother alloy may use pure
magnesium or a magnesium alloy as a mother material, and the pure
magnesium and the magnesium alloy are all called a magnesium mother
alloy. Alternatively, the mother alloy may use pure aluminum or an
aluminum alloy as a mother material, and the pure aluminum and the
aluminum alloy are called an aluminum mother alloy. Also, the
magnesium molten metal is defined for convenience as indicating
pure magnesium molten metal or a magnesium alloy molten metal in
which a different alloy element is added in the pure magnesium
molten metal, and this definition is equally applied to the
aluminum molten metal. Also, the magnesium mother alloy molten
metal and the aluminum mother alloy molten metal may be commonly
called a mother alloy molten metal.
[0050] At this time, at least one kind of first compound included
in the mother alloy may be one which is formed by adding a second
compound in which at least two components are bonded in the
magnesium molten metal and then exhausting at least a portion of
the second compound. Hereinafter, a method of producing a magnesium
mother alloy including a first compound will be described in
detail.
[0051] FIG. 2 is a flow diagram showing an exemplary embodiment of
a method of producing a magnesium mother alloy. Referring to FIG.
2, the method of producing a magnesium mother alloy includes
forming a magnesium molten metal (S21), adding a second compound
(S22), stirring (S23), and casting (S24).
[0052] In the forming (S21) of the magnesium molten metal, pure
magnesium or a magnesium alloy is put in a crucible and heated to
form a magnesium molten metal. Here, the heating temperature may be
in a range of 400.degree. C. to 800.degree. C.
[0053] Although in the case of pure magnesium, a molten metal is
formed at 600.degree. C. or higher, in the case of the magnesium
alloy, a molten metal may be formed at a temperature not higher
than 600.degree. C. and not lower than 400.degree. C. due to a
melting point drop that may appear by alloying.
[0054] Here, when the heating temperature is less than 400.degree.
C., it is difficult to form a magnesium molten metal, and when the
heating temperature exceeds 800.degree. C., sublimation in the
magnesium molten metal occurs or there is a danger of ignition.
[0055] The magnesium alloy used in the forming (S21) of the
magnesium molten metal may be any one selected from the group
consisting of AZ91D, AM20, AM30, AM50, AM60, AZ31, AS141, AS131,
AS121X, AE42, AE44, AX51, AX52, AJ50X, AJ52X, AJ62X, MRI153,
MRI230, AM-HP2, Mg--Al, Mg--Al--Re, Mg--Al--Sn, Mg--Zn--Sn, Mg--Si,
Mg--Zn--Y, and equivalents thereof, but the present disclosure is
not limited thereto. Any magnesium alloy may be used if it is
generally used in industry fields.
[0056] Meanwhile, in order to prevent the magnesium molten metal
from igniting, a small amount of protection gas may be provided to
the magnesium molten metal. The protection gas includes SF.sub.6,
SO.sub.2, CO.sub.2, HFC-134a, Novec.TM.612, inert gases and
equivalents thereof, and mixture gases thereof, and may suppress
ignition of the molten metal.
[0057] Next, in the adding (S22) of the second compound, a second
compound is added to the magnesium molten metal. At this time, the
second compound may be a compound in which two or more components
are bonded, and is partly or completely exhausted in the magnesium
molten metal. As a result of exhausting, a first compound in which
a portion of components constituting the second compound, and a
metal component in the magnesium molten metal are bonded may be
formed.
[0058] Alternatively, in the case where at least two kinds of
different second compounds are added, while the second compounds
are exhausted, a first compound in which components supplied from
each of the second compounds are bonded may be formed.
[0059] That is, after being added to the magnesium molten metal,
the second compound performs a role as a supply source supplying a
component constituting the first compound.
[0060] At this time, the second compound may be a calcium-based
compound, and may include any one of, for example, calcium oxide
(CaO), calcium cyanide (CaCN.sub.2), and calcium carbide
(CaC.sub.2).
[0061] While such a calcium-based compound or strontium-based
compound is exhausted in the magnesium molten metal, a metal
component of the alkali earth metal group and a non-metal component
bonded thereto may be decomposed from each other. Thus, a metal
component supplied from the alkali earth metal-based compound may
be bonded to magnesium that is a metal component in the magnesium
molten metal to form a magnesium compound.
[0062] Such a magnesium compound may be any one of a
magnesium-calcium compound, a magnesium-strontium compound, and a
magnesium-aluminum-calcium compound. For example, calcium (Ca)
decomposed from calcium oxide may be bonded to magnesium to form a
magnesium-calcium compound such as Mg.sub.2Ca and the like, and
strontium (Sr) decomposed from strontium oxide may form a
magnesium-strontium compound, such as Mg.sub.2Sr,
Mg.sub.23Sr.sub.6, Mg.sub.38Sr.sub.9, Mg.sub.17Sr.sub.2, etc.
[0063] In another example, aluminum may be melted as metal
component other than magnesium in the magnesium molten metal, and
the aluminum may be bonded to an alkali earth metal element to form
an aluminum compound. The aluminum compound may include at least
one of an aluminum-calcium compound and an aluminum-strontium
compound. For example, calcium decomposed from calcium oxide may be
boned to aluminum to form an aluminum-calcium compound, such as
Al.sub.2Ca, Al.sub.4Ca, or the like, and strontium (Sr) decomposed
from strontium oxide may be bonded to aluminum to form an
aluminum-strontium compound such as Al.sub.4Sr, or the like.
[0064] According to circumstances, the magnesium component and the
aluminum component in the magnesium molten metal may be bonded
together to form a composite oxide such as (Mg,Al).sub.2Ca, or the
like.
[0065] Another example of the second compound may be a
silicon-based compound. The silicon-based compound may include, for
example, silicon oxide (SiO.sub.2), and the like. Like the above
description, silicon (Si) decomposed from silicon oxide may be
boned to a magnesium component to form a magnesium-silicon
compound, such as Mg.sub.2Si, or the like.
[0066] In another example, the second compound may be a rare earth
compound, and may include, for example, scandium oxide
(Sc.sub.2O.sub.3), cesium oxide (CeO.sub.2), and the like. Like the
above description, a rare earth metal supplied from the rare earth
compound may bond to magnesium or aluminum. For example, cesium
(Cs) may be boned to aluminum to form an aluminum-cesium compound,
such as Al.sub.2Ce or the like, and scandium (Sc) may be boned to
aluminum to form an aluminum-scandium compound, such as
Al.sub.2Sc.
[0067] The second compound may be added in at least two portions
that are different in kind from each other. For example, calcium
oxide and silicon oxide may be added in the magnesium molten metal
at the same time. At this time, calcium supplied from calcium oxide
and silicon supplied from silicon oxide may be bonded to each other
in the magnesium molten metal to form a calcium-silicon compound,
such as CaSi, or the like.
[0068] Meanwhile, oxidation resistance of the magnesium molten
metal can be improved by the second compound added to the magnesium
molten metal. For example, when a calcium-based compound is added
to the magnesium molten metal, oxidation resistance of the
magnesium molten metal is improved and thus ignition resistance is
increased, so that introduction of oxide or other inclusions into
the magnesium molten metal is suppressed. Therefore, the amount of
the protection gas necessary for melting magnesium can be
remarkably reduced or may not be used at all.
[0069] The first compound included in the magnesium mother alloy
may have a higher melting point than a casting metal. For example,
Mg.sub.2Si, Al.sub.2Ca, Al.sub.4Sr, Al.sub.2Sc, and Al.sub.2Se have
melting points of 1085.degree. C., 1078.degree. C., 1040.degree.
C., 1420.degree. C., and 1480.degree. C., respectively, and casting
metals, for example, tin, zinc, magnesium, and aluminum have
melting points of 231.9.degree. C., 419.5.degree. C., 649.degree.
C., and 660.1.degree. C., respectively.
[0070] Therefore, in the case where a magnesium mother alloy
including the first compound having a higher melting point than
such casting metals is added as an alloy element to the molten
metal of the casting metal, the first compound may be distributed
in the matrix of the casting metal after cast. That is, since the
molten metal of the casting metal is maintained in liquid phase at
a lower temperature than the melting point of the first compound,
the first compound added together with the magnesium mother alloy
is not melted in the molten metal of the casting metal but exists
in solid phase, and after cast and solidified, is distributed on
the matrix of the casting metal.
[0071] Therefore, by adding a mother alloy containing the first
compound having a higher melting point than the casting metal, a
compound can be formed on the matrix of the metal without a
separate treatment, such as a heat treatment or a mechanical
processing.
[0072] For example, aluminum alloy 6063 that is a commercial alloy
allows a large amount of Mg.sub.2Si to be distributed on an
aluminum matrix, thus greatly improving the mechanical strength. To
form Mg.sub.2Si, magnesium and silicon are added to aluminum and a
heat treatment is performed to precipitate Mg.sub.2Si on the
aluminum matrix.
[0073] Compared to this, according to an exemplary embodiment, an
aluminum mother alloy containing Mg.sub.2Si as the first compound
may be added to an aluminum molten metal and then cast to easily
produce an aluminum alloy in which Mg.sub.2Si is formed in the
aluminum matrix.
[0074] Among components of the second compound added to the
magnesium molten metal, a remaining component that is not bonded to
a metal component within the molten metal is discharged in the
state of gas to the atmosphere through a portion over the surface
of the magnesium molten metal or may be floated on the molten metal
in the form of dross or sludge.
[0075] The second compound is advantageous for enhancement of
reactivity when the surface area thereof is as wide as possible,
and thus is added in the form of powder. However, the present
disclosure is not limited thereto, and the silicon-based additive
may be added in the form of pellet or bulk in which powder
particles are agglomerated so as to prevent powder from
scattering.
[0076] The size of the second compound may be in a range of 0.1
.mu.m to 500 .mu.m, and more strictly in a range of 0.1 .mu.m to
200 .mu.m.
[0077] When the size of the second compound is less than 0.1 .mu.m,
the size is so fine that the second compound is scattered by
sublimated magnesium or hot wind and thus have a difficulty in
introducing the same in the crucible. Also, since the second
compounds are agglomerated to form an agglomerate, they are not
easily mixed with the liquid phase molten metal. Such an
agglomerate is not preferred in that it decreases the surface area
for reaction.
[0078] When the size of the second compound exceeds 500 .mu.m, the
surface area for a reaction decreases, and further the second
compound may not react with the magnesium molten metal.
[0079] The second compound may be added in a range of 0.001 wt % to
30 wt %, and more strictly, in a range of 0.01 wt % to 15 wt %.
When the total added amount of the second compound is less than
0.001 wt %, an effect by addition of the second compound is slight
or is almost not generated. Also, when the total added amount of
the second compound exceeds 30 wt %, the fluidity of the molten
metal may be degraded.
[0080] The second compounds may be added to the molten metal at the
same time, or with a time difference. The second compound may be
added at one time by a necessary amount, or may be added in
multi-stage with a constant time difference by dividing the
necessary amount into proper amounts. When the added second
compound is a powder having fine particles, the agglomeration
possibility of the powder may be lowered and the reaction of the
second compound may be promoted by adding the second compound in
multi-stage with a constant time difference.
[0081] To promote decomposition and reaction of the second
compound, the second compound may be dispersively added to a
surface of an upper layer portion of the molten metal. FIG. 3 is a
schematic view exemplarily illustrating a decomposition process of
calcium oxide 20 in an upper layer portion of a magnesium molten
metal 10 when calcium oxide 20 is added to the magnesium molten
metal 10 in a melting furnace 1. Referring to FIG. 3, calcium oxide
20 is decomposed into oxygen (O.sub.2) and calcium (Ca) in the
upper layer portion of the magnesium molten metal 10. The
decomposed oxygen is a gas (O.sub.2), is discharged to the outside
from the melting furnace or is floated on the magnesium molten
metal in the form of dross or sludge. Meanwhile, the decomposed
calcium may react with another element, for example, magnesium (Mg)
or aluminum (Al) in the molten metal to form various compounds.
[0082] Therefore, it is important in this embodiment to create a
reaction environment such that the second compound is not
introduced into the magnesium molten metal but reacts with an
element in the surface of the molten metal. For this, the added
second compound may be maintained such that it stays on the surface
of the molten metal for a long time and is exposed to the
atmosphere.
[0083] In order to more promote the decomposition and reaction of
the added second compound, stirring (S3) of the magnesium molten
metal may be performed. The stirring may start at the same time
with the adding of the second compound or after the added second
compound is heated to a predetermined temperature in the molten
metal.
[0084] In the case of a typical metal alloying, the molten metal
and an alloy element are positively stirred such that a reaction
occurs in the molten metal through convection or stirring. However,
when a positive reaction of the second compound is induced in this
embodiment, the reaction of the second compound is not effective
and thus the frequency that the second compound remains in the
final molten metal in a non-decomposed state increases. In the case
where the second compound remains in the final molten metal, the
remaining second compound may be incorporated into the cast
magnesium alloy to degrade the mechanical characteristics of the
magnesium alloy.
[0085] Table 1 shows a measurement result of the amount of calcium
oxide remaining according to a stirring method when calcium oxide
(CaO) is added to AM60B molten metal. The size of the added calcium
oxide is 70 .mu.m, and the calcium oxide is added by 5 wt %, 10 wt
%, and 15 wt %. Stirring of an upper layer portion of the magnesium
molten metal, inner stirring, and no stirring are selected as a way
for confirming a stirring effect. It can be known from Table 1 that
when the stirring of the upper layer portion of the magnesium
molten metal is performed, most of the added calcium oxide is
reduced into calcium, unlike other cases.
TABLE-US-00001 TABLE 1 Adding of 5 Adding of 10 Adding 15 wt % of
CaO wt % of CaO wt % of CaO Remaining No stirring 4.5 wt % 8.7 wt %
13.5 wt % amount of of CaO of CaO of CaO CaO in Stirring in 1.2 wt
% 3.1 wt % 5.8 wt % alloy molten metal of CaO of CaO of CaO
Stirring in 0.001 wt % 0.002 wt % 0.005 wt % upper layer of CaO of
CaO of CaO portion of molten metal
[0086] The stirring may be performed in an upper layer portion from
the surface of the magnesium molten metal to a point which is not
more than 20% of a total depth of the magnesium molten metal, and
more strictly, in an upper layer portion to a point which is not
more than 10% of the total depth of the magnesium molten metal. At
the depth exceeding 20%, decomposition of the second compound in
the surface does not easily occur.
[0087] The stirring time may be different depending on the
temperature of the molten metal and the state of added powder, and
the stirring may be sufficiently performed until the added second
compound is completely exhausted in the molten metal. The term
"exhausting" indicates that the decomposition of the second
compound is substantially completed.
[0088] Such stirring can more promote the decomposition of the
second compound in the magnesium molten metal and a process in
which a component supplied by such decomposition reacts with a
metal component in the magnesium molten metal to form various first
compounds.
[0089] When the stirring (S23) of the magnesium molten metal is
completed, casting (S24) in which the magnesium molten metal is
injected into a mold to solidify the injected molten metal is
performed to produce a magnesium mother alloy.
[0090] In the adding (S22) of the second compound to the magnesium
molten metal, calcium (Ca) or strontium (Sr) element instead of a
calcium-based compound or strontium-based compound may be added as
the second compound to produce a magnesium mother alloy. In this
case, similarly to the second compound, the added calcium or
strontium may be melted in the magnesium molten metal to form a
first compound.
[0091] As another example of the mother alloy, an aluminum mother
alloy may be used. FIG. 4 is a flow diagram showing an exemplary
embodiment of a method of producing an aluminum mother alloy.
Referring to FIG. 4, the method of producing the aluminum alloy
includes forming (S31) of an aluminum molten metal, adding (S32) of
a magnesium mother alloy, stirring (S33), and casting (S34).
[0092] In the forming (S31) of the aluminum molten metal, aluminum
is put in a crucible and then is heated in a temperature range of
600.degree. C. to 900.degree. C. to form an aluminum molten
metal.
[0093] The aluminum in the forming (S31) of the aluminum molten
metal may be any one selected from the group consisting of pure
aluminum, an aluminum alloy, and equivalents thereof. The aluminum
alloy may be any one selected from the group consisting of 1000
series, 2000 series, 3000 series, 4000 series, 5000 series, 6000
series, 7000 series and 8000 series plastic working aluminum
alloys, or 100 series, 200 series, 300 series, 400 series, 500
series, and 700 series casting aluminum alloys.
[0094] Next, in the adding (S32) of the magnesium alloy, a
magnesium alloy which is produced by the above-described method and
includes a first compound is added to the aluminum molten
metal.
[0095] In the adding (S32) of the magnesium alloy, the magnesium
alloy may be added in a range of 0.0001 parts by weight to 30 parts
by weight based on 100 parts by weight of aluminum. When the added
amount of the magnesium mother alloy is less than 0.0001 parts by
weight, an effect according to the adding of the magnesium alloy
may be small. Also, when the added amount of the magnesium mother
alloy exceeds 30 parts by weight, the original characteristics of
the aluminum alloy do not appear.
[0096] The magnesium alloy may be added in the form of an ingot,
but the present disclosure is not limited thereto, and the
magnesium alloy may have other forms such as powder form, granule
form, and the like. Also, the size of the magnesium mother alloy is
not limited.
[0097] In the adding (S32) of the magnesium alloy, the first
compound included in the magnesium alloy is also provided to the
aluminum molten metal. As described above, the magnesium alloy may
have therein the first compound having a higher melting point than
aluminum, and when the magnesium mother alloy including the first
compound is added to the aluminum molten metal, the first compound
may be included in an aluminum alloy.
[0098] Next, the aluminum molten metal is stirred for a
predetermined time (S33), and then the casting (S34) in which the
aluminum molten metal is injected into a mold and is solidified is
performed to produce an aluminum alloy.
[0099] The produced aluminum alloy may be any one selected from the
group consisting of 1000 series, 2000 series, 3000 series, 4000
series, 5000 series, 6000 series, 7000 series and 8000 series
plastic working aluminum alloys, or 100 series, 200 series, 300
series, 400 series, 500 series, and 700 series casting aluminum
alloys.
[0100] Thus, when the magnesium mother alloy or aluminum mother
alloy including the first compound is added as an alloy element to
the molten metal of the casting metal, oxidation resistance of the
molten metal of the casting metal can be improved.
[0101] As describe above, the magnesium mother alloy to which a
calcium-based compound is added may contain a magnesium-calcium
compound, an aluminum-calcium compound, a
magnesium-aluminum-calcium compound, and the like as the first
compound, and the aluminum mother alloy produced by adding such a
mother alloy also contains the first compound described above.
[0102] As the oxidation resistance of the magnesium mother alloy or
aluminum mother alloy including the first compound greatly
increases, the inclusion of impurities such as oxide in the molten
metal of the casting metal remarkably decreases, compared to a case
in which magnesium or aluminum no containing the first compound is
added. Therefore, in the case where the mother alloy according to
an exemplary embodiment is added as an alloy element, although a
protection gas is not used, cleanness of the molten metal of the
casting metal can be greatly enhanced to remarkably improve the
quality of the molten metal. Due to the improvement of the quality
of the molten metal, the physical properties, such as the
mechanical and chemical characteristics of the cast alloy are
greatly improved.
[0103] In the adding (S32) of the magnesium alloy to the aluminum
molten metal, the magnesium mother alloy may be produced by adding
calcium (Ca) or strontium (Sr) in the form of element, instead of
adding the magnesium alloy including the first compound. While
being melted in the aluminum molten metal, such calcium or
strontium may react with aluminum to form a first compound, such as
Al.sub.2Ca, Al.sub.4Ca, Al.sub.4Sr, or the like.
[0104] While all of the above-described methods of producing the
mother alloy includes adding a second compound or pure element to a
mother alloy molten metal and allowing a reaction to occur in the
mother alloy molten metal to form a first compound, the present
disclosure is not limited thereto, and in another exemplary
embodiment, it will be also possible to directly add the first
compound to the mother alloy molten metal. At this time, the first
compound may be one produced by various methods in the outside.
[0105] For example, aluminum powder and calcium powder are put in
an apparatus such as a ball-mill to produce Al.sub.2Ca powder
through a mechanical alloying, and the produced Al.sub.2Ca powder
may be added as a first compound to the aluminum molten metal. In
this case, Al.sub.2Ca is included as the first compound in the cast
magnesium alloy or aluminum alloy.
[0106] As another example, the Al.sub.2Ca powder produced as above
is added to a magnesium molten metal to produce a magnesium alloy
containing Al.sub.2Ca, and then the produced magnesium alloy may be
again added to an aluminum molten metal to produce an aluminum
mother alloy containing Al.sub.2Ca.
[0107] While the mechanical alloying has been suggested as a method
for forming the first compound, the present disclosure is not
limited thereto, and any method will be allowable if it is a method
of capable of forming the first compound.
[0108] Meanwhile, the mother alloy including the first compound may
be further subject to diluting thereof. For example, the magnesium
mother alloy (for convenience, referred to as a first magnesium
mother alloy) produced by the above-described method may be added
to a magnesium molten metal and diluted to form a second magnesium
mother alloy including a first compound having a decreased
concentration. Likewise, it is of course that a second aluminum
mother alloy may be formed by diluting the first aluminum mother
alloy.
[0109] Hereinafter, in order to help understanding of the present
disclosure, experimental examples are provided. It will be
understood that the following experimental examples are not
provided to limit the present disclosure but are only provided to
help the understanding of the present disclosure.
[0110] FIGS. 5A through 5D show analysis results of a magnesium
mother alloy according to an exemplary embodiment by electron probe
micro analyzer (EPMA), in which the magnesium mother alloy is one
produced by adding calcium oxide (CaO) as a second compound to a
magnesium alloy containing aluminum as an alloy element.
[0111] FIG. 5A shows a microstructure of the magnesium mother alloy
observed using a back scattering electron. As shown in FIG. 5A, the
magnesium mother alloy shows a microstructure having a plurality of
crystal grains surrounded by compounds (white portions). The
compounds (white portions) are formed along grain boundaries.
[0112] FIGS. 5B through 5D show distribution regions of aluminum,
calcium, and oxygen that are mapping results of components in the
compound regions (white portions) by EPMA. As shown in FIGS. 5B and
5C, aluminum and calcium were detected from the compounds (white
portion of FIG. 5A) but oxygen was not detected (FIG. 5D).
[0113] From this result, it can be known that an aluminum-calcium
compound that is produced as calcium separated from calcium oxide
reacts with aluminum included in the mother material is
distributed. Such an aluminum-calcium compound may be Al.sub.2Ca or
Al.sub.4Ca that is an intermetallic compound.
[0114] FIGS. 6A through 6E show EPMA analysis results of an
aluminum mother alloy produced according to an exemplary
embodiment. Here, the magnesium mother alloy added to the aluminum
molten metal was one which is produced by adding calcium oxide to a
magnesium molten metal including aluminum.
[0115] FIG. 6A shows a microstructure of an aluminum mother alloy
observed by EPMA, and FIG. 6B through 6E show mapping results of
aluminum, calcium, magnesium, and oxygen that are mapping results
of components by EPMA. As seen from FIGS. 6B through 6D, calcium
and magnesium were detected at the same locations of the aluminum
matrix, but oxygen was not detected as shown in FIG. 6E. From this
result, it can be known that the magnesium-aluminum-calcium
compound which is included as the first compound in the magnesium
mother alloy also exists as the first compound in the aluminum
mother alloy.
[0116] Meanwhile, FIG. 7A shows a state of an aluminum molten metal
which is produced by adding a magnesium mother alloy, and FIG. 7B
shows a state of an aluminum molten metal which is produced by
adding pure magnesium. Referring to FIGS. 7A and 7B, it can be
known that in the case the magnesium mother alloy is added,
although a protection gas is not used, the state of the molten
metal is good, whereas in the case pure aluminum is added, the
surface of the molten metal is changed to black color due to
oxidation of magnesium. From this result, it can be confirmed that
when the magnesium mother alloy produced according to an exemplary
embodiment is added, the oxidation resistance of the molten metal
is remarkably increased.
[0117] Table 2 shows results obtained by observing and comparing
states of a magnesium molten metal according to the added amount of
protection gas, SF.sub.6 in a case where beryllium (Be) is added in
a magnesium molten metal and in a case where calcium oxide is
added. Here, the magnesium molten metal was produced from a
magnesium-aluminum alloy (Mg-0.45Al) in which 0.45 wt % of aluminum
is added.
TABLE-US-00002 TABLE 2 Added amount of Be (wt %) Added amount of
CaO (wt %) SF.sub.6(%) 0 5 10 20 0.01 0.05 0.1 0.3 0 (CO.sub.2 XX X
X X X X .largecircle. .quadrature. 100%) 0.05 X X X .quadrature.
.quadrature. .largecircle. .quadrature. .quadrature. 0.1 X
.quadrature. .quadrature. .largecircle. .largecircle. .largecircle.
.quadrature. .quadrature. 0.2 .quadrature. .largecircle.
.largecircle. .largecircle. .largecircle. .quadrature. .quadrature.
.quadrature. 0.5 .largecircle. .largecircle. .largecircle.
.largecircle. .quadrature. .quadrature. .quadrature. .quadrature.
.quadrature.: Very good, .largecircle.: Good, .quadrature.: Normal,
X: Bad, XX: Very bad
[0118] In the case Be was added by 20 wt % but SF.sub.6 gas was not
added, a bad state such as ignition of the magnesium molten metal
was observed, whereas in the case where calcium oxide was added by
0.1 wt % or more, a good state of the magnesium molten metal was
observed. When the added amounts of SF.sub.6 gas were equal, the
case where calcium oxide was added in an amount which is smaller
than that of beryllium shows more superior state of the molten
metal. From this result, it can be known that the case calcium
oxide is added is more superior than the case beryllium is
added.
[0119] FIG. 8 shows an oxidation resistance measurement result
according to the amount of calcium oxide in the magnesium mother
alloy. The oxidation of the magnesium mother alloy was performed in
an oxygen atmosphere at 550.degree. C. for 40 hours. Referring to
FIG. 8, it can be seen that as the amount of calcium oxide
increases, oxidation resistance is remarkably improved.
[0120] FIG. 9 is a graph for comparison of oxidation resistance in
an aluminum alloy produced according to an exemplary embodiment and
an aluminum alloy produced by a method different from an exemplary
embodiment, both having the same magnesium composition. In the
graph of FIG. 9, x-axis represents isothermal oxidation time
(minute), and y-axis represents weight gain (%), respectively.
Also, red line, green line, and blue line represent 2.5 wt %, 5 wt
%, and 10 wt % of aluminum alloys, respectively, and dotted line
having the same color indicates an aluminum alloy which has the
same magnesium composition, and is produced from a magnesium mother
alloy produced by adding calcium oxide as a second compound.
Referring to FIG. 9, it can be known that the aluminum alloys
according to an exemplary embodiment have superior oxidation
resistance.
[0121] By the production methods according to embodiments of the
present disclosure, although an alloy element having a high
oxidation property, such as magnesium or aluminum is added in a
molten metal, cleanness of the molten metal can be maintained at a
high level, and thus characteristics of the cast alloy can be
remarkably improved. Also, by adding a mother alloy including a
compound as an alloy element, the compound can be formed in the
matrix of the alloy without a separate treatment. The effects of
the present disclosure are not limited to the above descriptions,
and other effects that are not mentioned will be apparently
understood to those skilled in the art from the following
descriptions.
[0122] The descriptions for the specific embodiments of the present
disclosure are provided for the purpose of illustration and
explanation. Therefore, it will be understood by those of ordinary
skill in the art that various modifications and changes, such as
combinations of the embodiments may be made therein without
departing from the technical spirits and scope of the present
invention.
* * * * *