U.S. patent application number 12/387608 was filed with the patent office on 2010-01-28 for method of manufacturing composite copper material.
This patent application is currently assigned to HONDA GIKEN KOGYO KABUSHIKI KAISHA. Invention is credited to Hiroki Baba, Mitsuhiro Funaki, Toshiyuki Horimukai, Shinya Ohyama.
Application Number | 20100021334 12/387608 |
Document ID | / |
Family ID | 30773765 |
Filed Date | 2010-01-28 |
United States Patent
Application |
20100021334 |
Kind Code |
A1 |
Funaki; Mitsuhiro ; et
al. |
January 28, 2010 |
Method of manufacturing composite copper material
Abstract
An element such as Cr is caused to dissolve sufficiently in a
base-material metal (Cu) in a solid solution state at a high
temperature and a material in a supersaturated condition is
obtained by performing quenching. After that, a strain is applied
to this material and this material is subjected to aging treatment
at a low temperature simultaneously with or after the application
of this strain. As a result of this, it is possible to obtain a
copper alloy having properties desirable as an electrode material,
for example, a hardness of not less than 30 HRB, an electrical
conductivity of not less than 85 IACS %, and a thermal conductivity
of not less than 350 W/(mK).
Inventors: |
Funaki; Mitsuhiro;
(Sayama-shi, JP) ; Baba; Hiroki; (Sayama-shi,
JP) ; Ohyama; Shinya; (Sayama-shi, JP) ;
Horimukai; Toshiyuki; (Sayama-shi, JP) |
Correspondence
Address: |
RANKIN, HILL & CLARK LLP
38210 Glenn Avenue
WILLOUGHBY
OH
44094-7808
US
|
Assignee: |
HONDA GIKEN KOGYO KABUSHIKI
KAISHA
TOKYO
JP
|
Family ID: |
30773765 |
Appl. No.: |
12/387608 |
Filed: |
May 5, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10521333 |
Mar 15, 2005 |
7544259 |
|
|
PCT/JP03/09102 |
Jul 17, 2003 |
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12387608 |
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Current U.S.
Class: |
419/12 ;
419/10 |
Current CPC
Class: |
C22C 32/0073 20130101;
B22F 2998/00 20130101; B22F 2998/00 20130101; B22F 2998/10
20130101; H01H 1/0206 20130101; B22F 5/12 20130101; B21C 23/001
20130101; B22F 3/18 20130101; B22F 3/20 20130101; B22F 3/17
20130101; B22F 3/23 20130101; B22F 1/0003 20130101; B22F 2003/208
20130101; C22C 32/0036 20130101; C22F 1/08 20130101; B22F 2998/10
20130101; C22C 9/00 20130101 |
Class at
Publication: |
419/12 ;
419/10 |
International
Class: |
B22F 3/20 20060101
B22F003/20; B22F 3/12 20060101 B22F003/12; B22F 1/00 20060101
B22F001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 18, 2002 |
JP |
2002-210152 |
Jul 18, 2002 |
JP |
2002-210153 |
Jan 7, 2003 |
JP |
2003-000919 |
Jul 17, 2003 |
JP |
2003-198393 |
Jul 17, 2003 |
JP |
2003-198394 |
Jul 17, 2003 |
JP |
2003-198397 |
Claims
1. A method of manufacturing a composite copper material,
comprising the steps of: mixing a copper powder and a ceramic
powder together to forming a mixed powder as a primary shaped body,
and applying a strain to said primary shaped body to form a
secondary shaped body in which base material and ceramic particles
are combined together with refined particle sizes, wherein an
average particle size of the ceramic powder is between about 0.3 to
10 .mu.m, the strain applied to the primary shaped body is
equivalent to an elongation of not less than 200%, the strain is
applied by extruding the primary shaped body that is performed at a
material temperature of not less than 400.degree. C. but not more
than 1,000.degree. C. and a die temperature of not less than
400.degree. C. but not more than 500.degree. C., wherein an average
particle size of a base material of the secondary shaped body to be
obtained is not more than 20 .mu.m, and the average particle size
of ceramic particles is not more than 500 nm.
2. The method of manufacturing a composite copper material
according to claim 1, wherein the primary shaped body is obtained
by green compacting or by filling the mixed powder in a tube.
3. A method of manufacturing a composite copper material in which
titanium boride is dispersed in a copper matrix, comprising the
steps [1] to [3] of: [1] mixing a copper powder, a titanium powder
and a boron powder together to form a primary shaped body; [2]
applying thermal energy to the primary shaped body and thereby
causing the titanium powder and the boron powder to react with each
other in order to form titanium boride in the copper matrix; and
[3] applying a strain to the primary shaped body, in which the
titanium boride is formed, by plastically deforming the primary
shaped body and thereby forming a secondary shaped body.
4. The method of manufacturing a composite copper material
according to claim 3, wherein the secondary shaped body is
subjected to heat treatment while applying the strain by plastic
deformation or following application of the strain.
5. The method of manufacturing a composite copper material
according to claim 3, wherein plastic deformation involves applying
a strain equivalent to an elongation of not less than 200%.
6. The method of manufacturing a composite copper material
according to claim 3, wherein the plastic deformation is extrusion
that is performed at a material temperature of not less than
400.degree. C. but not more than 1000.degree. C.
7. The method of manufacturing a composite copper material
according to claim 3, wherein the plastic deformation is extrusion
that is performed at a die temperature of not less than 400.degree.
C. but not more than 500.degree. C.
8. The method of manufacturing a composite copper material
according to claim 3, wherein the primary shaped body is obtained
by green compacting or by filling a mixed powder in a tube.
9. The method of manufacturing a composite copper material
according to claim 3, wherein an average particle size of the
ceramic powder is 0.3 to 10 .mu.m, an average particle size of a
base material of the secondary shaped body to be obtained is not
more than 20 .mu.m, and an average particle size of titanium boride
particles is not more than 500 nm.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a division of application Ser. No.
10/521,333, filed Mar. 15, 2005, now U.S. Pat. No. ______.
BACKGROUND OF INVENTION
[0002] 1. Technical Field
[0003] The present invention relates to a copper alloy and a
composite copper material that are suitable for wiring connectors
of electric vehicles or the like and electrode materials for
welding, and methods of manufacturing the copper alloy and the
composite copper material.
[0004] 2. Background Art
[0005] With the increasing EV (electric vehicle) design of
automobiles, the consumption of harnesses and connectors that are
connection parts of wires tends to increase. In the adoption of
EVs, ensuring safety and gas mileage by electronic control
techniques is also a purpose.
[0006] Connectors that are incorporated in automobiles are used in
severe environments of high temperature and vibration and,
therefore, the reliability of connection and contact stability are
required. Also, with increasing adoption of EVs, copper-based
materials that have small energy losses, i.e., high conductivity
are desired.
[0007] Also for electrode materials for welding, properties having
values above prescribed ones are required in all respects of
mechanical strength, thermal properties and electrical
properties.
[0008] For mechanical strength, it is known as the Hall-Petch law
that mechanical strength is generally improved by refining the
crystal structures of metal materials.
[0009] For example, when metal or alloy materials are deformed,
material strength increases due to work hardening. This is
understood as follows. That is, various kinds of defects (point
defect, dislocation, stacking fault, etc.) are accumulated in
materials due to working (plastic deformation), and as a result of
the interactions of these defects, the introduction and migration
of new defects become difficult and the materials obtain resistance
to external force.
[0010] To apply plastic deformation (strain) to metal materials,
extrusion, drawing, shearing, rolling, forging, etc. have hitherto
been carried out. Concretely, the HIP (High Pressure Torsion)
process that involves twisting a material while applying high
pressure to the material, the CEC (Cyclic Extrusion Compression)
process that involves repeatedly threading a material through a
constricted pipe, and the ARB (Accumulative Roll Bonding) process
that involves cutting a metal sheet the thickness of which has been
reduced by rolling and repeatedly rolling superimposed metal sheets
have been proposed, and in particular, as a concrete method of
refining the grains of an aluminum alloy, the ECAE
(equal-channel-angular extrusion) process that involves applying
shearing deformation to a material by lateral extrusion without a
reduction of sectional area of the material has been proposed as
disclosed in the Japanese Patent Laid-Open No. 9-1 37244, the
Japanese Patent Laid-Open No. 10-258334, the Japanese Patent
Laid-Open No. 11-114618, the Japanese Patent Laid-Open No.
2000-271621, etc.
[0011] On the other hand, for copper alloys, methods disclosed in
the Japanese Patent Laid-Open No. 11-140568, the Japanese Patent
Laid-Open No. 2000-355746, etc. have been proposed. In these
conventional techniques, to improve the properties (machinability
and dezincification corrosion) of brass (Cu--Zn) that is used as a
material for water faucet fittings and the like among other copper
alloys, dynamic recrystallization is caused to occur by hot
extrusion thereby to obtain the refinement of crystal grains and
specific ratios of crystal structures (ratios of the .alpha.-phase,
.beta.-phase and .gamma.-phase).
[0012] Also, to bring out prescribed properties from age-hardening
type copper alloys to which an element that does not dissolve or
scarcely dissolves in a solid solution state at room temperature,
such as chromium (Cr), zirconium (Zr), beryllium (Be), titanium
(Ti) and boron (B), is added, this element is first caused to
dissolve sufficiently in a solid solution sate at a high
temperature and then quenched and brought to a supersaturated
condition, which is followed by aging treatment at a prescribed
temperature, thereby causing the added element in a supersaturated
condition to precipitate.
[0013] Even when the above-described work aging or aging treatment
for aluminum alloys and copper alloys is applied as it is to
age-hardening type copper alloys to which an element, such as
chromium (Cr), zirconium (Zr), beryllium (Be), titanium (Ti) and
boron (B), is added, it is impossible to simultaneously satisfy all
respects of mechanical strength, thermal properties and electrical
properties.
[0014] That is, in order to ensure that the thermal properties and
electrical properties required of connectors used in electric
vehicles or the like, electrode materials, etc. are developed, it
is necessary to ensure that an added element that dissolves in a
solid solution state is caused to precipitate in the largest
possible amount. In order to cause this element to precipitate in a
large amount, it is necessary to raise the aging temperature.
However, when the aging temperature is raised, grain growth
proceeds and mechanical properties decrease. That is, mechanical
strength and thermal and electrical properties are in a tradeoff
relation.
[0015] For thermal properties and electrical properties, copper
alloys in which an oxide such as alumina is dispersed in the copper
matrix are excellent in electrical conductivity and heat resistance
and, therefore, these copper alloys are widely used in materials
for electric parts. Many proposals to improve the properties and
manufacturing methods of these copper alloys have been made.
[0016] For example, a proposal has been made to improve electrical
conductivity and softening properties by adding, as elements that
perform internal oxidation, not only aluminum, but also tin as a
third element. (Japanese Patent Laid-Open No. 59-150043)
[0017] There has been proposed a copper alloy in which the amount
of particles of not more than 50 .mu.m is not less than 70 wt %
owing to the use of a copper alloy powder of not more than 300
.mu.m which is manufactured by the atomizing process and in which a
readily oxidizing metal such as aluminum is caused to dissolve in a
solid solution state. (Japanese Patent Laid-Open No. 60-141
802)
[0018] There has also been proposed a method that involves
internally oxidizing a Cu--Al alloy powder thereby to convert Al to
Al.sub.2O.sub.3, making the surface of this alloy powder smooth,
green compacting the powder to form a green compact, and hot
forging this green compact at 600 to 1,000.degree. C. Japanese
Patent Laid-Open No. 63-241126)
[0019] Also, there has been proposed a method that involves
internally oxidizing a plate-like copper alloy containing Al to
convert Al to Al.sub.2O.sub.3, working this plate-like alloy in
coil form, sealing this coiled alloy in a metal tube, and hot
working this metal tube at 900.degree. C. in a desired shape.
Japanese Patent Laid-Open No. 2-38541)
[0020] Also, there has been proposed a method that involves filling
an alloy powder obtained by internally oxidizing Cu--Al alloy chips
in a carbon die and hot pressing the alloy powder at 900.degree. C.
and at a pressure of 400 kg/cm.sup.2. (Japanese Patent Laid-Open
No. 2-93029)
[0021] Furthermore, there has been proposed a method that involves
improving sinterability by causing an annular hard layer of
Al.sub.2O.sub.3 to be present in the interior of a Cu--Al alloy
powder. (Japanese Patent Laid-Open No. 4-80301)
[0022] In all of the above-described conventional techniques, hot
working at high temperatures is performed and, therefore,
structures tend to become coarse due to grain growth. Thus, in the
conventional methods, it is impossible to obtain materials that
simultaneously satisfy, as the properties required of connectors of
electric vehicles and electrode materials for welding, the
requirements that hardness be not less than 30 HRB, preferably not
less than 40 HRB, that electrical conductivity be not less than 85
IACS %, preferably not less than 90 IACS %, and that thermal
conductivity be not less than 350 W/(mK), preferably not less than
360 W/(mK).
[0023] When hardness is not less than 30 HRB, it is possible to
prevent the tip of an electrode material from becoming deformed and
generating heat. When electrical conductivity is not less than 85
IACS %, it is possible to prevent an electrode material from
reacting with a steel sheet and sticking to the steel sheet. When
thermal conductivity is not less than 350 W/(mK), it is possible to
prevent the deposition of an electrode material during welding
because the cooling efficiency increases.
[0024] Because Al.sub.2O.sub.3 does not dissolve in Cu in a solid
solution state even at a high temperature, a conventional technique
by which Al.sub.2O.sub.3 is caused to precipitate by aging
treatment after dissolution in a solid solution cannot be applied
to a Cu--Al alloy.
BRIEF SUMMARY OF THE INVENTION
[0025] A material that simultaneously satisfies all of the
mechanical strength, thermal properties and electrical properties
required of a material for connectors used in the wiring of
electric vehicles or an electrode material for welding is obtained
by ensuring that a second element that dissolves in a solid
solution state at a high temperature, but does not dissolve or
scarcely dissolves in a solid solution state (cannot maintain a
solid solution state) at room temperature is caused to dissolve in
a base-material metal (Cu) in a solid solution state, that crystal
grain refinement is achieved by applying a strain equivalent to an
elongation of not less than 200% to this material, and that this
material is subjected to aging treatment simultaneously with or
after the application of this strain, thereby to promote
precipitation of the second element among crystal grains.
[0026] Concretely, in a copper alloy containing a second element
that does not dissolve or scarcely dissolves in a solid solution
state at room temperature, it is possible to obtain a copper alloy
the average grain size of which is not more than 20 .mu.m and in
which the second element precipitates among crystal grains. This
copper alloy has a hardness of not less than 30 HRB, an electrical
conductivity of not less than 85 IACS %, and a thermal conductivity
of not less than 350 W/(mK). The second element is any of chromium
(Cr), zirconium (Zr), beryllium (Be), titanium (Ti) and boron
(B).
[0027] Extrusion, drawing, shearing, rolling or forging can be
considered as means for applying a strain to the material and
conditions for the extrusion are such that lateral extrusion is
performed at a die temperature of 400 to 500.degree. C. and an
extrusion speed of 0.5 to 2.0 mm/sec. It is also possible that
before a strain is applied to the material, the material is
subjected to aging treatment beforehand.
[0028] On the other hand, in order to obtain a material that
simultaneously satisfies all of the mechanical strength, thermal
properties and electrical properties from a ceramic powder (alumina
or titanium boride) that does not dissolve in copper in a solid
solution state even at a high temperature, a copper powder and a
ceramic powder are mixed together, thereby to form a mixed powder
as a primary shaped body, and a strain is applied to this primary
shaped body, thereby to form a secondary shaped body in which base
material and ceramic particles are combined together with refined
particle sizes. As a result of this, a composite copper material
having a hardness of not less than 60 HRB, an electrical
conductivity of not less than 85 IACS %, a thermal conductivity of
not less than 350 W/(mK), and a hardness of not less than 30 HRB is
obtained.
[0029] Incidentally, as the means for applying a strain, for
example, lateral extrusion is performed at a material temperature
of not less than 400.degree. C. but not more than 1,000.degree. C.
and a die temperature of not less than 400.degree. C. but not more
than 500.degree. C. Why the specified raw material temperature is
400.degree. C. to 1,000.degree. C. is that if the raw material
temperature is less than 400.degree. C., extrusion becomes
difficult because of large deformation resistance and sufficient
bonding strength cannot be obtained between the parent phase
(matrix) and particles and that if the raw material temperature
exceeds 1,000.degree. C., this temperature exceeds the melting
point of copper and copper melts, making it impossible to apply a
strain. The reason why the specified die temperature is 400.degree.
C. to 500.degree. C. is that if the die temperature is too low,
extrusion becomes difficult and if die temperature is too high, the
die itself becomes annealed.
[0030] The primary shaped body can be obtained by green compacting
or by filling the mixed powder in a tube. Furthermore, the average
particle size of the ceramic powder is 0.3 to 10 .mu.m, a strain
applied to the primary shaped body is equivalent to an elongation
of not less than 200%, the average particle size of a base material
of the secondary shaped body to be obtained is not more than 20
.mu.m, and the average particle size of ceramic particles is not
more than 500 nm.
[0031] As described above, because titanium boride is not mixed
with a copper power and instead, a titanium powder that becomes
titanium boride as a result of a reaction and a boron powder are
formed in the copper matrix, it is possible to increase mechanical
strength as fine particles. Therefore, in another aspect of the
invention, a method of manufacturing a composite copper material in
which titanium boride is dispersed in the copper matrix comprises
the following steps [1] to [3]: [0032] [1] the step of mixing a
copper powder, a titanium powder and a boron powder together,
thereby to form a primary shaped body; [0033] [2] the step of
giving thermal energy to the primary shaped body, thereby causing
the titanium powder and the boron powder to react with each other
in order to form titanium boride in a copper matrix; and [0034] [3]
the step of applying a strain to the primary shaped body in which
the titanium boride is formed by plastically deforming the primary
shaped body, thereby to form a secondary shaped body.
[0035] For example, if the average grain size of a titanium powder
and a boron powder is 0.3 to 10 .mu.m, it can be ensured that the
average particle size of a base material of the secondary shaped
body to be obtained is not more than 20 .mu.m, and that the average
particle size of titanium boride particles is not more than 400 nm,
and hence it is possible to obtain a composite copper material
having small deformation by pressurization during welding as an
electrode material for welding (due to low compressive strength of
the material).
[0036] Part of titanium and boron dissolve in copper in a solid
solution state when thermal energy is applied to the primary shaped
body. However, if the titanium and boron in this solid solution
state remain in an unreacted condition, the composite copper
material is inferior in electrical conductivity and thermal
conductivity. Therefore, it is preferred that the secondary shaped
body be subjected to heat treatment in the same step as the step of
applying a strain by plastic deformation or a step following this
step, whereby the unreacted solute elements (titanium and boron)
are caused to precipitate.
[0037] The means for applying plastic deformation, the material
temperature, the die temperature, the extrusion speed and the
number of times of extrusion are the same as described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0038] FIG. 1 is a drawing to explain the steps for obtaining a
copper alloy related to the invention;
[0039] FIG. 2 is a drawing to explain a die used in the ECAE
treatment;
[0040] FIG. 3(a) is a micrograph of a crystal structure of a copper
alloy related to the invention;
[0041] FIG. 3(b) is a micrograph of a crystal structure before ECAE
treatment;
[0042] FIG. 4 is a graph that shows the relationship between die
temperature and hardness;
[0043] FIG. 5 is a graph that shows the relationship between die
temperature and electrical conductivity;
[0044] FIG. 6 is a graph that shows the relationship between die
temperature and thermal conductivity;
[0045] FIG. 7 is a graph that compares the weldability of a copper
alloy obtained by a manufacturing method related to the invention
with that of conventional copper alloys in terms of the occurrence
of spatters and weld sticking;
[0046] FIG. 8 is a graph that compares the weldability of a copper
alloy obtained by a manufacturing method related to the invention
with that of conventional copper alloys in terms of the number of
welds in continuous spot welding;
[0047] FIG. 9 is a graph that shows the relationship between the
amount of added Ti and electrical conductivity of a copper alloy
subjected to aging treatment and a copper alloy not subjected to
aging treatment;
[0048] FIG. 10 is a graph that shows the relationship between the
amount of added Ti and electrical conductivity of a copper alloy
subjected to aging treatment and a copper alloy subjected to aging
treatment and heavy working (applying a strain equivalent to an
elongation of not less than 200%);
[0049] FIG. 11 is a graph that shows the relationship between the
amount of added Ti and hardness (mHV) of a copper alloy subjected
to aging treatment and a copper alloy subjected to aging treatment
and heavy working (applying a strain equivalent to an elongation of
not less than 200%);
[0050] FIG. 12 is a graph that shows the relationship between
electrical conductivity and hardness (mHV);
[0051] FIG. 13 is a graph that shows the relationship between
methods of adding TiB and electrical conductivity;
[0052] FIG. 14 is a drawing to explain a method of manufacturing a
composite copper material related to the invention;
[0053] FIGS. 15(a) and 15(b) are each a micrograph of a crystal
structure of a copper alloy obtained by a manufacturing method
related to the invention, FIG. 15(a) showing a composite copper
alloy to which alumina is added and FIG. 15(b) showing a composite
copper alloy to which titanium boride is added;
[0054] FIG. 16 is a graph that compares the weldability of
composite copper materials obtained by a manufacturing method
related to the invention with that of a conventional composite
copper material in terms of the number of welds in continuous spot
welding;
[0055] FIG. 17 is a drawing to explain a method of manufacturing a
composite copper material related to the invention;
[0056] FIG. 18 is a micrograph that shows the condition of a
structure after sintering; and
[0057] FIG. 19 is a drawing that shows the relationship between
electrical conductivity and amount of added TiB when heavy working
is performed and when heavy working is not performed.
BEST MODE FOR CARRYING OUT THE INVENTION
[0058] As shown in FIG. 1, first Cr is caused to melt into a base
material (Cu) in an amount of 0.1 to 1.4 wt % and a material in
which Cr dissolves in Cr in a solid solution state in a
supersaturated manner is obtained by quenching the melt.
Subsequently, a strain equivalent to an elongation of not less than
200% is applied to this material. Incidentally, it is desirable to
use a material that is subjected to aging treatment after solution
treatment.
[0059] When an added element is Zr, the Zn content is 0.15 to 0.5
wt %. In the case of Be, the Be content is 0.1 to 3.0 wt %. In the
case of Ti, the Ti content is 0.1 to 6.0 wt %. And in the case of
B, the B content is 0.01 to 0.5 wt %.
[0060] FIG. 2 shows a die that applies a strain by use of a Cu
tube. The above-described mixture is filled in the Cu tube and
extruded at a die temperature of 400 to 500.degree. C. and an
extruding speed of about 1 mm/sec by repeating the extrusion four
times (ECAE treatment). Thus, a strain is applied to a copper alloy
in which Cr dissolves in a solid solution state in a supersaturated
manner. By this operation, the crystal grain size decreases to not
more than 20 .mu.m from 200 .mu.m.
[0061] If .DELTA.e: amount of strain, .psi.: 1/2 of inner angle of
joint, ERR: area ratio before and after working, A0: sectional area
before working, A: sectional area after working, EAR: reduction
ratio of equivalent sectional area before and after working, EE:
equivalent strain (elongation), then the following relationships
hold:
.DELTA.e=2/ 3 cotan .psi.
ERR=A0/A=exp(.DELTA.e)
EAR=(1-1/ERR).times.100
EE=(ERR-1).times.100
[0062] The crystal structure becomes grain-refined by the
above-described lateral extrusion (ECAE treatment). Because
extrusion conditions overlap aging treatment, the precipitation of
a second element is promoted at the same time with grain
refinement.
[0063] The crystal structure of a copper alloy obtained by this
ECAE treatment is shown in a micrograph of FIG. 3(a). The crystal
structure before ECAE treatment is shown in a micrograph of FIG.
3(b). From these micrographs, it is apparent that an added element
has precipitated (black points in the photograph) among crystal
grains due to the ECAE treatment.
[0064] FIG. 4 is a graph that shows the relationship between die
temperature and hardness, FIG. 5 is a graph that shows the
relationship between die temperature and electrical conductivity,
and FIG. 6 is a graph that shows the relationship between die
temperature and thermal conductivity. From these graphs it is
apparent that a copper alloy related to the invention has
properties required of an electrode material such as a welding tip,
i.e., a hardness of not less than 30 HRB, an electrical
conductivity of not less than 85 IACS %, and a thermal conductivity
of not less than 350 W/(mK).
[0065] That is, from FIGS. 4 to 6, it is apparent that a material
not subjected to ECAE treatment (solution treatment+aging
treatment) is inferior in electrical conductivity and thermal
conductivity although it has high hardness, that a material
obtained by subjecting a material which has been subjected to only
the solution treatment to ECAE treatment is excellent in electrical
conductivity and thermal conductivity although it has low hardness,
and that a material obtained by subjecting a material which has
been subjected to aging treatment after solution treatment to ECAE
treatment is excellent in all respects of hardness, electrical
conductivity and thermal conductivity.
[0066] FIG. 7 is a graph that compares the weldability of a copper
alloy obtained by a manufacturing method related to the invention
with that of conventional copper alloys in terms of the occurrence
of spatters and weld sticking. The copper alloy related to the
invention is equivalent to the alumina-dispersed copper and the
copper alloy before aging treatment in terms of appropriate current
conditions, and weld sticking does not occur.
[0067] FIG. 8 is a graph that compares the weldability of a copper
alloy obtained by a manufacturing method related to the invention
with that of conventional copper alloys in terms of the number of
welds in continuous spot welding. When the copper alloy related to
the invention was used as a welding tip, it was possible to produce
1475 welds in continuous spot welding.
[0068] As described above, a copper alloy related to the invention
has a fine crystal structure and a large amount of added element
precipitates among crystal grains and, therefore, it is possible to
ensure that a copper alloy related to the invention simultaneously
provides mechanical strength and thermal and electrical properties
that have hitherto been in a tradeoff relation.
[0069] In particular, it is possible to obtain a copper alloy that
has the properties required of an electrode material such as a
welding tip, concretely, a hardness of not less than 30 HRB, an
electrical conductivity of not less than 85 IACS %, and a thermal
conductivity of not less than 350 W/(mK).
[0070] Next, titanium (Ti) was selected as an element to be added
and copper alloys were obtained in the same method as described
above. Results are shown in FIGS. 9 to 12.
[0071] FIG. 9 is a graph that shows the relationship between the
amount of added Ti and electrical conductivity. The maximum degree
of dissolution of Ti in a solid solution state is essentially about
8 wt % and is not very large. As shown in FIG. 9, even after aging
treatment, about 0.5 wt % of Ti remains in a solid solution state.
It might be thought that this Ti in a solid solution state lowers
the electrical conductivity of copper alloys.
[0072] FIG. 10 is a graph that shows the electrical conductivity of
a copper alloy that is heavily worked (by application of a strain
equivalent to an elongation of 200%) after being subjected to aging
treatment at 470.degree. C. for two hours and the electrical
conductivity of a copper alloy subjected to only aging treatment.
From this graph it is apparent that the electrical conductivity of
the heavily worked copper alloy increases greatly. It might be
thought that this is because the Ti in a solid solution state
precipitates due to heavy working.
[0073] FIG. 11 is a graph that compares the hardness of a heavily
worked copper alloy with that of a copper alloy subjected to only
aging treatment. As shown in this graph, the hardness of the
heavily worked copper alloy is lower than that of the copper alloy
subjected to only aging treatment. It might be thought that the Ti
that has contributed to solid solution strengthening precipitates
due to heavy working.
[0074] FIG. 12 is a graph that shows the relationship among
hardness, electrical conductivity and heavy working temperature.
From this graph it is apparent that a Cu--Ti alloy is inferior in
electrical conductivity and that electrical conductivity increases
although hardness decreases with increasing heavy working
temperature. Also in this case, it might be thought that the Ti
that has contributed to solid solution strengthening precipitates
due to heavy working.
[0075] Thus, by combining heavy working with aging treatment, it
becomes possible to cause the Ti that dissolves in a solid solution
state to precipitate from the copper matrix although it has
hitherto been impossible to cause this Ti to precipitate by aging
treatment. In addition, the amount of Ti that precipitates can be
controlled by controlling the degree of heavy working. Therefore,
it is possible to make a copper alloy having properties that suit
the purpose.
[0076] Next, boron (B) was selected as an element to be added, and
copper alloys were made by various methods. The relationship
between the boron (TiB) of the obtained copper alloys and
electrical conductivity is shown in FIG. 13. As methods of
obtaining the copper alloys, [1] preparation of a refined material
subjected to solution treatment, [2] addition of a TiB.sub.2 powder
as a compound (ceramic) to copper, and [3] a method of adding a Ti
powder and a B powder independently to copper were adopted.
[0077] From FIG. 13, it became apparent that in all cases
electrical conductivity decreases with increasing addition ratio of
TiB and that in terms of manufacturing methods, the highest
electrical conductivity is obtained in the case of a refined
material although electrical conductivity increases by performing
heavy working.
[0078] FIGS. 14 to 16 explain another embodiment (a composite
copper material). First, as shown in FIG. 14, an alumina
(Al.sub.2O.sub.3) powder or a titanium boride (TiB.sub.2) is mixed
with a base material (a Cu powder). The mixing proportion is 0.1 wt
% to 5.0 wt %. If the mixing proportion is less than 0.1 wt %, wear
resistance is not improved. If the mixing proportion exceeds 5.0 wt
%, electrical conductivity decreases and die life also shortens.
Therefore, the above-described range is specified.
[0079] Subsequently, the above-described mixed powder is formed
into a primary shaped body in order to perform lateral extrusion. A
primary shaped body is formed, for example, by green compacting or
by filling the mixed powder in a Cu (copper) tube. Subsequently, a
strain equivalent to not less than 200%, preferably, about 220% is
applied to the primary shaped body by lateral extrusion.
[0080] Incidentally, in FIG. 14, for the sake of easy
understanding, the diameter of the Cu tube is larger than the
diameter of an insertion hole formed in the die. In actuality,
however, the diameter of the Cu tube is almost the same as the
diameter of the insertion hole formed in the die. The Cu tube is
supported with a jig or the like so that the Cu tube does not fall
while the Cu tube is being pushed in by use of a punch.
[0081] Concrete conditions for the lateral extrusion are such that
the die temperature is 400 to 1000.degree. C. and the extrusion
speed is about 1 mm/sec, and ECAE treatment is performed by
repeating extrusion 12 times under the conditions. By repeating the
extrusion, the parent phase becomes grain-refined and the crushing
and dispersion of the ceramic occur.
[0082] The micrographs of crystal structures of the copper alloys
obtained by this ECAE treatment are shown in FIGS. 15(a) and 15(b).
FIG. 15(a) shows a composite material to which an alumina powder is
added, and FIG. 15(b) shows a composite material to which a
titanium boride powder is added. From these photographs, it is
ascertained that alumina or titanium boride having a particle size
of several nanometers is uniformly dispersed in the copper
matrix.
[0083] FIG. 16 is a graph that compares the weldability of
composite copper materials obtained by a manufacturing method
related to the invention with that of a conventional composite
copper material in terms of the number of welds in continuous spot
welding. The number of welds in continuous spot welding is about
1200 when a commercially available composite copper material in
which alumina is dispersed in copper is used as a welding tip,
whereas the number of welds in continuous spot welding is about
1600 in the case of an alumina-dispersed composite copper material
subjected to ECAE (equal-channel-angular-extrusion) treatment and
1900 welds in continuous spot welding were possible when a
composite copper material related to the invention in which
titanium boride is dispersed was used as a welding tip.
[0084] Because solution treatment is not a starting point in this
embodiment, there is no restriction by the limit of dissolution in
a solid solution state and it is possible to arbitrarily set the
proportion of the particles of a second element (Al.sub.2O.sub.3 or
TiB.sub.2) in a copper alloy. Therefore, it is possible to obtain
properties that could not be obtained in conventional composite
copper materials.
[0085] That is, the purity of the matrix of a copper alloy is high,
a copper alloy is excellent in electrical properties, and the
particle size of particles of Al.sub.2O.sub.3 or TiB.sub.2 that
precipitate at the interfaces of matrix particles is on the order
of nanometers (not more than 500 nm) because of the suppression of
grain growth. Also, the amount to be added can be arbitrarily
set.
[0086] Next, a description will be given of an embodiment in which
as a starting material, a titanium (Ti) powder and a boron (B)
powder are mixed with the base material (Cu powder).
[0087] FIG. 17 is a drawing to explain the processes for obtaining
a composite copper material related to the embodiment, in both of
which the mixing proportion of both the titanium powder and the
boron powder in the starting material is 0.1 wt % to 5.0 wt %. If
the mixing proportion is less than 0.1 wt %, wear resistance is not
improved. If the mixing proportion exceeds 5.0 wt %, electrical
conductivity decreases and die life also shortens. Therefore, the
above-described range is specified.
[0088] Subsequently, the above-described mixed powder is formed
into a primary shaped body in order to perform lateral extrusion.
There are available two processes for obtaining a primary shaped
body. When a product to be produced is a small one like a connector
and an electrode rod, the above-described mixture is filled in the
Cu tube to form a primary shaped body. On the other hand, when a
product to be produced is a long one or a large-sized one, a
primary shaped body is formed by green compacting.
[0089] Subsequently, the above-described primary shaped body is
sintered. The added titanium (Ti) and boron (B) react due to the
thermal energy resulting from this sintering to form titanium
boride. FIG. 18 shows the condition of a structure after sintering.
From this figure it is apparent that the titanium boride not formed
before sintering is formed in the copper matrix after
sintering.
[0090] Incidentally, although sintering was performed as means for
applying thermal energy in the embodiment, thermal energy may be
applied by means other than this.
[0091] A strain equivalent to not less than 200%, preferably not
less than about 220% is applied to the primary shaped body after
sintering thus obtained by lateral extrusion. The lateral extrusion
is performed by the same method as described above.
[0092] Concrete conditions for the lateral extrusion are such that
the material temperature is 400 to 1000.degree. C., the die
temperature is 400 to 500.degree. C. and the extrusion speed is
about 1 mm/sec, and ECAE (equal-channel-angular-extrusion)
treatment is performed by repeating extrusion 12 times under the
conditions. By repeating the operation, the parent phase becomes
grain-refined and the crushing and dispersion of the titanium
boride formed in the copper matrix occur.
[0093] FIG. 19 is a drawing that shows the relationship between
electrical conductivity and amount of added TiB when heavy working
(applying a strain equivalent to an elongation of 220%) is
performed and when heavy working is not performed. From this figure
it became apparent that electrical conductivity is increased by
heavy working. Although titanium boride having electrical
conductivity is formed by the above-described heat treatment,
electrical conductivity cannot be increased. It is not that the
added titanium and boron react stoichiometrically, but that the
added titanium and boron in a solid solution state remain within
the copper matrix while they are still unreacted. Therefore, it
might be thought that the unreacted solute elements (titanium and
boron) precipitate when heavy working is performed, with the result
that electrical conductivity increases.
[0094] Also for complex copper materials related to the invention,
weldability was verified by the number of welds in continuous spot
welding and the same results as shown in FIG. 16 were obtained.
[0095] Because solution treatment is not a starting point in a
method of manufacturing a composite copper material related to this
embodiment, there is no restriction by the limit of dissolution in
a solid solution state, and it is possible to arbitrarily set
titanium and boron to be added to copper, and it is possible to
obtain properties that could not be obtained in conventional
composite copper materials.
[0096] In particular, because titanium boride is not directly added
to copper and because titanium and boron before the reaction are
added to cause titanium boride to be formed in the copper matrix by
the reaction by applying thermal energy to the titanium and boron
before the reaction, the grain refinement of a structure (in the
order of nanometers: not more than hundreds of nanometers) is
promoted and mechanical strength increases.
[0097] A copper alloy and a composite copper material related to
the invention can be used as a material for a connector that
constitutes part of wiring of electric vehicles and the like or a
material for welding electrodes.
* * * * *