U.S. patent application number 11/416048 was filed with the patent office on 2007-11-08 for method for producing a metal alloy.
This patent application is currently assigned to Taiwan Advanced Materials Technologies Corporation. Invention is credited to I-Lin Cheng, Mei-Wen Kao.
Application Number | 20070256520 11/416048 |
Document ID | / |
Family ID | 38660019 |
Filed Date | 2007-11-08 |
United States Patent
Application |
20070256520 |
Kind Code |
A1 |
Cheng; I-Lin ; et
al. |
November 8, 2007 |
Method for producing a metal alloy
Abstract
A method for producing a metal alloy includes the steps of: (A)
preparing a first melt containing a base metal which has not been
alloyed; (B) preparing a second melt containing a base metal and at
least one alloying element, the base metals in the first and second
melts being the same; and (C) mixing the first and second melts to
dilute the concentration of the alloying element.
Inventors: |
Cheng; I-Lin; (Kaohsiung
City, TW) ; Kao; Mei-Wen; (Taipei Hsien, TW) |
Correspondence
Address: |
OSTROLENK FABER GERB & SOFFEN
1180 AVENUE OF THE AMERICAS
NEW YORK
NY
100368403
US
|
Assignee: |
Taiwan Advanced Materials
Technologies Corporation
|
Family ID: |
38660019 |
Appl. No.: |
11/416048 |
Filed: |
May 2, 2006 |
Current U.S.
Class: |
75/646 |
Current CPC
Class: |
C22B 15/006 20130101;
C22C 9/00 20130101; C22C 1/02 20130101; B22D 11/004 20130101 |
Class at
Publication: |
075/646 |
International
Class: |
C22B 15/00 20060101
C22B015/00 |
Claims
1. A method for producing a metal alloy, comprising: (A) preparing
a first melt containing a base metal which has not been alloyed;
(B) preparing a second melt containing a base metal and at least
one alloying element, the base metals in the first and second melts
being the same; and (C) mixing the first and second melts to dilute
the concentration of the alloying element.
2. The method of claim 1, wherein the steps of (A), (B), and (C)
are carried out in a single enclosed space.
3. The method of claim 2, further comprising using first and second
furnaces in the enclosed space, the second furnace being disposed
on top of the first furnace.
4. The method of claim 3, wherein step (A) is first carried out in
the second furnace, the method further comprising the step of
delivering the base metal of the first melt from the second furnace
to the first furnace before carrying out step (B).
5. The method of claim 4, wherein step (B) is carried out in the
second furnace, and step (C) is carried out in the first furnace,
the method further comprising the step of delivering the second
melt from the second furnace to the first melt in the first furnace
before step (C).
6. The method of claim 1, wherein the base metal has a high degree
of purity.
7. The method of claim 6, wherein the base metal is a nonferrous
metal.
8. The method of claim 7, wherein the nonferrous metal is
copper.
9. The method of claim 8, wherein the alloying element is selected
from the group consisting of platinum, palladium, and silver.
10. The method of claim 8, wherein the alloying element is selected
from the group consisting of magnesium and calcium.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a method for producing a metal
alloy.
[0003] 2. Description of the Related Art
[0004] Super ultra fine wires of gold, copper, aluminum, etc., are
used extensively as bonding wires in electronic packages. Although
gold bonding wires are most typically used, copper bonding wires
are gradually replacing the gold bonding wires to minimize costs.
For many reasons, super ultra fine metal wires must satisfy
relatively stringent requirements. The conductivity, ball shape,
breaking load, and elasticity of the material forming the wires are
considered.
[0005] For a 99.99% pure metal material, it is hard to enhance its
mechanical properties during the forming process. Thus, an
improvement is usually made on the starting material. An alloying
element is added into the starting material, which is a metal
material of a high purity, during smelting so as to enhance the
mechanical properties and weldability of the material.
[0006] Through addition of an alloying element to a starting
material, the conductivity, elasticity, strength, etc., of the
material can be enhanced to a degree sufficient to satisfy the
strict requirements associated with, for example, dentology
equipment and wafer-testing microprobes.
[0007] A conventional method for smelting a metal alloy includes
the step of refining a base metal in a smelting apparatus, which is
placed in a vacuum state, so as to remove the impurities and obtain
a high degree of purity of the base metal. Afterwards, the smelted
high purity base metal is transferred to a continuous casting
apparatus to conduct addition of an alloying element and to conduct
casting. The continuous casting apparatus is provided with a
protective gas, such as an inert gas, to protect the molten metal.
An elongated metal alloy having the alloying element is obtained
from these operations for use in a subsequent drawing
operation.
[0008] Although the conventional method for producing a metal alloy
can achieve its intended purpose, the concentration of the alloying
element in the resulting precious metal alloy is difficult to
control. Since precious metals are very expensive, the quantity of
such a precious metal used in a smelting batch is usually small,
for example, about ten kilograms. If a metal alloy having less than
100 ppm of an alloying element (including impurities and alloying
elements) is desired, the amount of the alloying element that must
be added to 10 kilograms of a base metal is 0.7 gram after the
amount of impurities inherently present in the base metal,
generally about 30 ppm, is included in the calculation. Since a
quantitative loss is inevitable in feeding an alloying element
through an elongated tubular feeding device as a result of, for
example, adhesion to the feeding device, when a small quantity (0.7
gram) of the alloying element is added into the smelted base metal,
the proportion of the alloying element in the base metal can vary
significantly due to such quantitative loss. The concentration of
the alloying element in the smelted metal alloy is therefore hard
to accurately control.
SUMMARY OF THE INVENTION
[0009] Therefore, the object of the present invention is to provide
a method for producing a metal alloy that permits easy control of
the concentration of an alloying element in the metal alloy.
[0010] According to this invention, a method for producing a metal
alloy comprises the steps of: (A) preparing a first melt containing
a base metal which has not been alloyed; (B) preparing a second
melt containing a base metal and at least one alloying element, the
base metals in the first and second melts being the same; and (C)
mixing the first and second melts to dilute the concentration of
the alloying element.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] Other features and advantages of the present invention will
become apparent in the following detailed description of the
preferred embodiment with reference to the accompanying drawings,
of which:
[0012] FIG. 1 is a flow chart illustrating the preferred embodiment
of a method for producing a metal alloy according to the present
invention; and
[0013] FIG. 2 is a sectional view of an example of a continuous
casting apparatus to which the method of the present invention is
applied.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0014] Referring to FIG. 1, the preferred embodiment of a method
for producing a metal alloy according to the present invention is
shown to comprise the steps of: (A) preparing a first melt
containing a base metal which has not been alloyed; (B) preparing a
second melt containing a base metal and at least one alloying
element, the base metals in the first and second melts being the
same; and (C) mixing the first and second melts to dilute the
concentration of the alloying element. The base metal may be a
nonferrous metal, such as copper, gold, etc. In the preferred
embodiment, a copper alloy having less than a 100 ppm concentration
of an alloying element is produced.
[0015] In step (A), a conventional smelting apparatus, which can be
placed in a near vacuum state, is used for preparing a first melt
that contains a base metal which has not been alloyed. In this
embodiment, an electrolytic copper, which has a high degree of
purity, is used as the base metal and is refined into pure 5N
copper. It should be noted that the obtained pure copper includes
about 10 ppm of hard-to-remove elements, such as high melting point
impurities.
[0016] In step (B), ten kilograms of copper is prepared in another
smelting apparatus which is protected by an inert gas. Seven grams
of pure platinum (alloying element) is added to the smelting
apparatus, and is mixed with the smelted copper to form a second
melt that has a 700 ppm concentration of platinum. The added
platinum has a purity of about 99.99%.
[0017] In the preferred embodiment, while the addition of the pure
platinum is cited, palladium (Pd), or silver (Ag), or any
combination of the aforesaid three elements may be used to form a
solid solution strengthening mechanism. Further, other metals, such
as magnesium (Mg) calcium (Ca), or any combination thereof may be
used to form a precipitation strengthening mechanism. The
aforementioned strengthening mechanisms can limit dislocation
movement or deformation of the alloyed material so that the tensile
strength thereof is enhanced. Moreover, through the addition of
these alloying elements, formation of large grains in the smelted
alloyed material can be prevented to thereby improve corrosion
resistance, breaking strength, and weldability without affecting
the conductivity of the material.
[0018] In step (C), the first melt prepared in step (A) is mixed
with the second melt prepared in step (B) so as to dilute the
concentration of the alloying element from 700 ppm to below 70 ppm.
In the preferred embodiment, one kilogram of the second melt, which
contains platinum, and 9 kilograms of the first melt are mixed and
smelted together so as to obtain a copper alloy containing about 70
ppm of platinum. The total concentration of impurities in the
copper alloy does not exceed 30 ppm, and the concentration of total
alloying elements in the copper alloy including platinum and
impurities does not exceed 100 ppm.
[0019] From the aforementioned description, it is apparent that
during the preparation of the second melt in step (B), adding seven
grams of platinum to the base metal is easier and more accurate
than adding 0.7 gram of an alloying element to the base metal as
carried out in the aforementioned conventional method. This is
because, for a certain quantitative loss of an added alloying
element occurring in a feeding device, errors in the proportion of
the added alloying element can be reduced by increasing the amount
of the alloying element added. Hence, according to the present
invention, accuracy of the concentration of the added alloying
element in the alloyed base metal can be controlled easily.
[0020] The method of the present invention can also be carried out
using a single smelting apparatus, such as a continuous casting
apparatus shown in FIG. 2. The continuous casting apparatus
includes a housing 22, a vacuum pump 24 connected to the housing
22, a removable divider 26 to divide the housing 22 into upper and
lower chambers 221, 222, a turnable second furnace 28 provided in
the upper chamber 221 to heat a copper base metal into molten
copper, a first furnace 30 provided in the lower chamber 222 and
disposed below the second furnace 28 so as to receive the molten
copper poured out from the second furnace 28, an agitating gas
supply unit 32 for supplying an inert gas into the first furnace 30
through a bottom end thereof, a first protective gas supply unit 34
in fluid communication with the lower chamber 222 of the housing
22, a feed input device 36 extending into the housing 22 and
permitting addition of a material into the second furnace 28, a
casting mold 38 connected to the bottom end of the first furnace 30
and extending outwardly from a bottom portion of the housing 22, a
cooling unit 40 surrounding the casting mold 38, a partition plate
42 disposed between the first furnace 30 and the cooling unit 40, a
second protective gas supply unit 44 supplying an inert gas into an
outlet end of the casting mold 38, a drawing unit 46 disposed below
the casting mold 38, and a heat radiation blocking plate 48
disposed above the second furnace 28.
[0021] Preferably, the housing 22 includes first and second windows
223, 224 at a top portion thereof, and a temperature-measuring
device 225 provided in the first window 223 to measure the
temperature inside the housing 22. The second window 224 permits an
operator to view the melting condition of the copper in the housing
22. Each of the second and first furnaces 28, 30 has a graphite
crucible 281, 301, and a high frequency heater 282, 302 surrounding
the corresponding graphite crucible 281, 301. Each of the high
frequency heaters 282, 302 uses a high frequency current signal to
quickly heat and maintain the temperature of the copper in the
corresponding graphite crucible 281, 301, and to agitate the molten
copper in the corresponding graphite crucible 281, 301
simultaneously.
[0022] The partition plate 42 prevents transfer of heat between the
cooling unit 40 and the first furnace 30.
[0023] The second protective gas supply unit 44 protects an
initially solidified copper alloy through supply of the inert gas
into the casting mold 38.
[0024] The drawing unit 46 includes two rollers 461 that rotate in
opposite directions and that draw continuously the solidified
copper alloy out of the casting mold 38.
[0025] The heat radiation blocking plate 48 is provided to reduce
heat loss, and to prevent the second window 224 of the housing 22
from being coated with a thin metal film.
[0026] The manner in which the aforementioned continuous casting
apparatus can produce the metal alloy containing below 100 ppm of
the alloying element is described hereinafter.
[0027] Step (A) is carried out in the second furnace 28. Nine
kilograms of the electrolytic copper (2N.about.3N purity) is put
into the graphite crucible 281, and then the vacuum pump 24 is
activated so that a vacuum is formed in the upper and lower
chambers 221, 222 of the housing 22 ranging from
2.2.times.10.sup.-1 to 1.0.times.10.sup.-4 torr (or lower).
Afterwards, the high frequency heater 282 is activated to melt the
electrolytic copper into molten copper. The molten copper is then
poured into the first furnace 30, and the high frequency heater 302
is activated so as to maintain the temperature of the molten copper
at 1200.degree. C..about.1500.degree. C. The agitating gas supply
unit 32 is simultaneously activated so as to supply the inert gas
into the graphite crucible 301. The inert gas, formed into bubbles,
agitates the molten copper in the first furnace 30 so that traces
of impurities can float to a liquid surface of the molten copper.
Since the housing 22 is maintained in the aforementioned vacuum
state at this time, the low melting point metal and the impurities
are vaporized and are drawn out of the housing 22 by operation of
the vacuum pump 24, thereby achieving the purpose of refining
smelted molten copper so that a high degree of purity of the same
is obtained.
[0028] Step (B) is carried out in the first furnace 30. The first
protective gas supply unit 34 is activated so as to fill the upper
and lower chambers 221, 222 of the housing 22 with the inert gas to
protect the smelted molten copper in the first furnace 30. The
divider 26 is, at this time, moved between the upper and lower
chambers 221, 222 so as to cut off fluid communication between the
same. Afterwards, ten kilograms of the electrolytic copper and
seven grams of pure platinum are put into the graphite crucible 281
of the second furnace 28 through the material input device 36, and
the vacuum pump 24 and the high frequency heater 282 are activated
so as to melt and refine the electrolytic copper. Since the melting
point of the platinum is higher than that of the copper metal, the
platinum will not vaporize, and thus will not be drawn out from the
housing 22. During refining, the high frequency heater 282, through
its high frequency current signal, agitates the molten copper so
that the platinum can be thoroughly melted and mixed with the
molten copper. An alloyed copper base metal containing 700 ppm of
the pure platinum is obtained from this process.
[0029] It should be noted that if an alloying element, such as
calcium, or magnesium, etc., is added, because the melting point
thereof is lower than that of the copper metal, such an alloying
element should be added into the copper base metal after refining
the base metal.
[0030] To execute step (C), the divider 26 is moved away so that
the upper and lower chambers 221, 222 are in fluid communication
with each other again. One-tenth of the alloyed copper base metal
from the second furnace 28 is then poured into the first furnace
30. Through operation of the agitating gas supply unit 32 and the
high frequency heater 302 of the first furnace 30, the alloyed
copper base metal and the molten copper are agitated and are
thoroughly mix so as to dilute the concentration of the alloying
element. Thus, a copper alloy having a 70 ppm concentration of
platinum and 30 ppm of high melting point impurities (i.e.,
impurities from the pure copper and the added platinum), a combined
total of which does not exceed 100 ppm, is produced.
[0031] Finally, the cooling unit 40 and the second protective gas
supply unit 44 are activated so that the copper alloy is cast by
the casting mold 38. Through operation of the drawing unit 46, the
solid copper alloy is drawn continuously out of the casting mold 38
to form an elongated rod.
[0032] From the aforementioned description, the method of the
present invention has the following advantages:
[0033] 1. The concentration of the alloying element in the metal
alloy can be easily controlled.
[0034] 2. When the method of the present invention is applied to
the continuous casting apparatus of FIG. 2, contamination of the
material is minimized since the refining of the metal and the
addition of the alloying element are accomplished in the same
enclosed space of the continuous casting apparatus.
[0035] While the present invention has been described in connection
with what is considered the most practical and preferred
embodiment, it is understood that this invention is not limited to
the disclosed embodiment but is intended to cover various
arrangements included within the spirit and scope of the broadest
interpretation so as to encompass all such modifications and
equivalent arrangements.
* * * * *