Title: High-strength, high conductivity copper alloy excellent in fatigue and intermediate temperature properties
Abstract: The present invention provides a Cu--Cr--Zr alloy material excellent in fatigue and intermediate temperature characteristics, which comprises 0.05 to 1.0% by mass of Cr and 0.05 to 0.25% by mass of Zr with a balance of Cu and inevitable impurities. The alloy comprises inclusion particles based on any one of Zr and a Cu--Zr alloy having a diameter of 0.1 .mu.m or more, and the proportion of the inclusion particles containing 10% or more of sulfur as one of the inevitable impurities is one particle/mm.sup.2.
Patent Number: 6,881,281 Issued on 04/19/2005 to Kanmuri, et al.
| Inventors:
|
Kanmuri; Kazuki (Hitachi, JP);
Fukamachi; Kazuhiko (Hitachi, JP)
|
| Assignee:
|
Nikko Metal Manufacturing Co., Ltd. (JP)
|
| Appl. No.:
|
759217 |
| Filed:
|
January 20, 2004 |
Foreign Application Priority Data
| Jan 23, 2003[JP] | 2003-014810 |
| Current U.S. Class: |
148/432; 148/433; 148/434; 148/435; 148/436; 420/484; 420/492 |
| Intern'l Class: |
C22C 009//00 |
| Field of Search: |
148/432-436
420/484,492
|
References Cited [Referenced By]
| Foreign Patent Documents |
| 0492987 | Jan., 1992 | EP.
| |
| 2001244398 | Sep., 2001 | JP.
| |
| 2002003963 | Jan., 2002 | JP.
| |
Primary Examiner: Ip; Sikyin
Attorney, Agent or Firm: Auerbach; Jeffrey I.
Liniak, Berenato & White
Claims
What is claimed is:
1. A high-strength high-conductive copper alloy excellent in fatigue and
intermediate temperature characteristics comprising 0.05 to 1.0% by mass
of Cr and 0.05 to 0.25% by mass of Zr with a balance of Cu and inevitable
impurities,
the alloy comprising inclusion particles based on any one of Zr and a
Cu--Zr alloy having a diameter of 0.1 .mu.m or more,
the proportion of the inclusion particles containing 10% or more of sulfur
as one of the inevitable impurities being one particles/mm.sup.2.
2. A high-strength high-conductive copper alloy excellent in fatigue and
intermediate temperature characteristics comprising 0.05 to 1.0% by mass
of Cr, 0.05 to 0.25% by mass of Zr and 0.05 to 2.0% by mass of Zn with a
balance of Cu and inevitable impurities,
the alloy comprising inclusion particles based on any one of Zr and a
Cu--Zr alloy having a diameter of 0.1 .mu.m or more,
the proportion of the inclusion particles containing 10% or more of sulfur
as one of the inevitable impurities being one particles/mm.sup.2.
3. A high-strength high-conductive copper alloy excellent in fatigue and
intermediate temperature characteristics comprising 0.05 to 1.0% by mass
of Cr and 0.05 to 0.25% by mass of Zr with a balance of Cu and inevitable
impurities,
the alloy comprising inclusion particles based on any one of Zr and a
Cu--Zr alloy having a diameter of 0.1 .mu.m or more,
the proportion of the inclusion particles containing sulfur as one of the
inevitable impurities being 1,000 particles/mm.sup.2.
4. A high-strength high-conductive copper alloy excellent in fatigue and
intermediate temperature characteristics comprising 0.05 to 1.0% by mass
of Cr, 0.05 to 0.25% by mass of Zr and 0.05 to 2.0% by mass of Zn with a
balance of Cu and inevitable impurities,
the alloy comprising inclusion particles based on any one of Zr and a
Cu--Zr alloy having a diameter of 0.1 .mu.m or more,
the proportion of the inclusion particles containing sulfur as one of the
inevitable impurities being 1,000 particles/mm.sup.2.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-strength high-conductivity copper
alloy excellent in fatigue and intermediate temperature characteristics.
Particularly, the present invention relates to conductive spring materials
used for various terminals, connectors, relays and switches.
2. Description of the Related Art
The following characteristics are required of conductive spring materials
used for various terminals, connectors, relays and switches:
(a) sufficient strength for generating high contact pressure even when in
the form of thin sheets;
(b) a low stress relaxation ratio with the contact pressure not decreasing
after a long-term use at high temperatures;
(c) a high conductivity with small Joule heating, which is generated by a
flowing electric current, and radiation of the generated heat;
(d) prevention of crack and roughness formation at bent portions even when
applying severe bend processing; and
(e) a high elastic limit so as to enable the alloy to be used under high
stress.
Phosphor bronze has been used as a conductive spring material for various
terminals, connectors, relays and switches. However, since electronic
appliances and components thereof have been required to be small in size
and thin, demands for suitable materials have increased accordingly, and
improvements in strength, conductivity, heat resistance and fatigue
characteristics have been required. Various kinds of Cu--Cr alloys and
Cu--Cr--Zr alloys have been developed to comply with these requirements.
Patent Reference 1: Japanese Unexamined Patent Application Publication No.
9-087814
Patent Reference 2: Japanese Unexamined Patent Application Publication No.
7-258804
Patent Reference 3: Japanese Unexamined Patent Application Publication No.
7-258806
Patent Reference 4: Japanese Unexamined Patent Application Publication No.
7-258807
Patent Reference 5: Japanese Unexamined Patent Application Publication No.
7-268573
Patent Reference 6: Japanese Patent No. 2682577
The drawability of Cu--Cr alloys decreases at intermediate temperatures
around 400.degree. C. While the alloys are not used at temperatures as
high as 400.degree. C. in the field of the present invention, and the heat
resistance required is around 100.degree. C., or about 200.degree. C.
under the most severe conditions required in the present invention, the
drawability at intermediate temperatures of around 400.degree. C. is used
as a standard of heat resistance. Cu--Cr--Zr alloys have been developed to
have improved strength at intermediate temperatures of around 400.degree.
C. While Cu--Cr--Zr alloys have excellent fatigue characteristics compared
with Cu--Cr alloys, the conductivity of the alloy decreases by increasing
the amount of Zr added.
Cu--Cr--Zr alloys are precipitation hardening alloys, and their strength is
improved by allowing Cr, Zr or Cu--Zr compounds to precipitate in the
copper matrix by aging after solution treatment. However, Cr, Zr or Cr--Zr
compounds that are included and which crystallize or precipitate during
the casting process remain in the alloy.
Cu--Cr--Zr alloy are usually manufactured by the steps of blending the
materials, melting, casting, homogenization annealing, hot rolling, cold
rolling if necessary, solution treatment, cold rolling and aging (cold
rolling) sequentially applied in this order.
However, the fatigue characteristics are deteriorated in Cu--Cr--Zr alloys
since Cu--Zr compounds are readily cleaved by dislocation, and sulfur as
one of the inevitable impurities may be concentrated at grain boundaries.
The inventors of the present invention found that the grain boundary
strength is decreased by concentration of sulfur at the grain boundaries.
Accordingly, the object of the present invention is to provide a
Cu--Cr--Zr alloy excellent in fatigue and intermediate temperature
characteristics.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a
Cu--Cr--Zr alloy excellent in fatigue and intermediate temperature
characteristics.
In first and second aspects, the present invention provides a high-strength
high-conductivity copper alloy excellent in fatigue and intermediate
temperature characteristics comprising 0.05 to 1.0% by mass of Cr and 0.05
to 0.25% by mass of Zr with a balance of Cu and inevitable impurities, and
a high strength conductive copper alloy excellent in fatigue and
intermediate temperature characteristics comprising 0.05 to 1.0% by mass
of Cr, 0.05 to 0.25% by mass of Zr and 0.05 to 2.0% by mass of Zn with a
balance of Cu and inevitable impurities, respectively. The alloy comprises
inclusion particles based on Zr or a Cu--Zr compound having a diameter of
0.1 .mu.m or more, and the proportion of the inclusion particles
containing 10% or more of sulfur as one of the inevitable impurities is
one particles/mm.sup.2 or more.
In third and fourth aspects, the present invention provides a high-strength
high-conductivity copper alloy excellent in fatigue and intermediate
temperature characteristics comprising 0.05 to 1.0% by mass of Cr and 0.05
to 0.25% by mass of Zr with a balance of Cu and inevitable impurities, and
a high strength conductive copper alloy excellent in fatigue and
intermediate temperature characteristics comprising 0.05 to 1.0% by mass
of Cr, 0.05 to 0.25% by mass of Zr and 0.05 to 2.0% by mass of Zn with a
balance of Cu and inevitable impurities, respectively. The alloy comprises
inclusion particles based on Zr or a Cu--Zr compound having a diameter of
0.1 .mu.m or more, and the proportion of the inclusion particles
containing sulfur as one of the inevitable impurities is 1,000
particles/mm.sup.2 or more.
The inevitable impurities as used in the present invention refer to
elements having a mean concentration of 100 ppm maximum in the alloy.
The functions of the elements Cr, Zr, Zn, and S are as follows.
Cr and Zr
Cr and Zr serve to improve the strength by being precipitated in the copper
matrix by aging after the solution treatment of the alloy. The effect of
Cr cannot be achieved when the content of Cr is less than 0.05% by mass,
while the strength is not further increased adding Cr in an amount
exceeding 1.0% by mass. The effect of Zr cannot be obtained when the
content of Zr is less than 0.05% by mass, while the strength is not
further increased by adding Zr in an amount exceeding 0.25% by mass.
Zn
Zn is an element added to improve the heat-peeling resistance of tin and
solder plating. The effect of Zn to improve the heat-peeling resistance of
tin and solder plating cannot be obtained when the content of Zn is less
than 0.05% by mass, while conductivity of the alloy decreases when the
content of Zn exceeds 2.0% by mass.
Sulfur
While the Cu--Cr--Zr alloy is manufactured by melting cathode copper or
oxygen-free copper as a principal material with the addition of Cr and Zr,
sulfur is usually contained in a proportion of about 20 ppm as an
inevitable impurity. However, sulfur may be concentrated at grain
boundaries, and concentration of sulfur at the grain boundaries decreases
the grain boundary strength. Although it is possible to decrease sulfur as
the inevitable impurity below the level described above, it is not
preferable considering the productivity and production cost. The inventors
of the present invention found that the sulfur concentration at the grain
boundaries could be reduced by allowing the inclusions based on Zr or a
Cu--Zr compound to contain a larger amount of sulfur. The grain boundary
strength at an intermediate temperature in the range of 250 to 550.degree.
C. as well as drawability at an intermediate temperature of around
400.degree. C. can be improved by the effect described above.
Although the Cu--Cr--Zr alloy is excellent in fatigue characteristics, the
Cu--Zr compound is readily cleaved by dislocation to soften cleaved
sliding faces causing uneven distribution of strain and deterioration of
the fatigue characteristics. However, the strength of the Cu--Zr compound
itself increases by allowing the compound to contain sulfur to prevent
cleavage of the compound by dislocation from occurring while the fatigue
characteristics are further improved.
Incidentally, the inclusion particles based on Zr or a Cu--Zr compound is
able to contain more sulfur even when a material containing a high
concentration of sulfur (for example greased scrap) is used after melting.
Effect of Reducing the Size of the Compound
The size of the compound is preferably fine considering the strength,
etching processibility, bending processibility and fatigue
characteristics. It was found that large Cu--Zr particles with a diameter
of 10 .mu.m or more could be extinguished under the conditions of the
present invention in which Zr or the Cu--Zr compound contains sulfur.
Reducing the number of larger particles is particularly effective when
large quantities of Cr and Zr are added.
Comparing the results of strength measurement at the intermediate
temperature and the sulfur concentration in the inclusions based on Zr or
Cu--Zr compound, the inventors of the present invention found (1) a
quantitative relationship showing that the strength at the intermediate
temperature is excellent when the concentration of the inclusion is 1
particle/mm.sup.2 or more while the strength at the intermediate
temperature is insufficient when the concentration of the inclusion is 1
particle/mm.sup.2 or less, by counting the number of the inclusion
particles containing 10% or more of sulfur obtained from the measurement
of the sulfur concentration only in the inclusions based on Zr or the
Cu--Zr compound having a particle diameter of 0.1 .mu.m or more, and (2) a
quantitative relationship showing that drawability at the intermediate
temperature is excellent when the concentration of inclusions is 1000
particles/mm.sup.2 or more while drawability at the intermediate
temperature is insufficient when the concentration of inclusions is 1000
particles/mm.sup.2 or less, by measuring the sulfur concentration in all
the inclusions based on the Zr or Cu--Zr compound, and by counting the
number of compound particles in which sulfur is detected by field
emission-scanning electron microscopy/energy diverse spectroscopy
(FE-SEM/EDS), field emission-Auger electron microscope (FE-AES) or
transparent electron microscope (TEM).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the high-strength high-conductivity copper alloy excellent
in fatigue and intermediate temperature characteristics according to the
present invention will be described in detail hereinafter.
Components were blended in a prescribed proportion using cathode copper or
oxygen-free copper as a major material, and the material was cast into an
ingot after melting the material in an inert atmosphere or in a vacuum.
Then, the ingot was annealed for homogenization at 800 to 1000.degree. C.
for 1 hour or more followed by hot rolling and solution treatment.
Subsequently, the ingot was annealed after cold rolling followed by cold
rolling again and aging to allow strain relaxation.
The order of the manufacturing steps in this embodiment is approximately
the same as the order of steps in the conventional manufacturing process.
However, the solution treatment condition is determined depending on the
result of the sulfur concentration analysis in this embodiment after
analyzing the sulfur concentration in the inclusions to adjust the
concentration profile. The high-strength high-conductivity copper alloy is
obtained by increasing the sulfur concentration of the inclusions by the
manufacturing method in this embodiment, in which concentration profiles
are adjusted by controlling the solution treatment. Samples in the
examples are obtained in this embodiment by applying the solution
treatment using a combination of air cooling and water cooling after
maintaining the sample at a high temperature of 800.degree. C. or more.
The solution treatment in this embodiment may be applied by controlling the
water cooling method during winding of a coil immediately after hot
rolling, or the wound coil after hot rolling may be air-cooled or
water-cooled after transferring the coil to a heating furnace and leaving
there for a given period of time. Hot rolling and solution treatment are
applied approximately at the same time in the former case.
EXAMPLES
The sample in Example 1 was prepared by the manufacturing method of this
embodiment using an alloy with a composition of
Cu--Cr(0.2%)-Zr(0.08%)-Zn(0.15%), and the sample in Comparative Example 1
was prepared according to the conventional method.
The sample in Example 2 was prepared by the manufacturing method of this
embodiment using an alloy with a composition of Cu--Cr(0.2%)-Zr(0.04%),
and the sample in Comparative Example 2 was prepared according to the
conventional method.
The sample in Example 3 was prepared by the manufacturing method of this
embodiment using an alloy with a composition of Cu--Cr(0.6%)-Zr(0.15%),
and the sample in Comparative Example 3 was prepared according to the
conventional method.
The samples in Examples 1 to 3 and Comparative Examples 1 to 3 were
electropolished after mechanical polishing, and the texture of the metal
was observed by SEM, EDS, FE-SEM, AES, FE-AES and TEM depending on the
size of the inclusions contained in each sample to determine the size of
the inclusion and the concentration of sulfur in the inclusion. Two
hundred or more inclusions having a particle diameter of 0.1 .mu.m or more
were randomly selected from an area of 1 mm.times.1 mm or more, and the
sulfur concentration in the selected inclusions was measured. The results
of measurements of the sulfur concentration in the inclusions are shown in
Table 1.
TABLE 1
The The
maximum number of
concentration inclusions The
of S with a number of
contained in diameter second
the second The number of of 0.1 .mu.m phase
phase second phase or more particles
Cross-
particles with particles and S with a
section
a diameter of (particles/mm.sup.2) content of
diameter of reduction
Alloy 0.1 .mu.m or in which S is 10% or 10 .mu.m or
ratio
Composition more detected more more
(400.degree. C.)
Example 1 Cu-Cr(0.2%)- 20.1% 1550 320 0
67%
Zr(0.08%)-
Zn(0.15%)
Comparative Cu-Cr(0.2%)- 7.5% 480 0 2
53%
Example 1 Zr(0.08%)-
Zn(0.15%)
Example 2 Cu-Cr(0.2%)- 25.3% 1010 137 0
60%
Zr(0.04%)
Comparative Cu-Cr(0.2%)- 7.3% 410 0 3
49%
Example 2 Zr(0.04%)
Example 3 Cu-Cr(0.6%)- 25.6% 2160 530 0
70%
Zr(0.15%)
Comparative Cu-Cr(0.6%)- 6.7% 590 0 15
55%
Example 3 Zr(0.15%)
Cross-
section
reduction Fragility at 0.2%
ratio intermediate proof Electric
Fatigue
(500.degree. C.) temperature stress
conductivity characteristics
Example 1 60% Excellent 580 80% IACS
Excellent
MPa
Comparative 35% Poor 570 81% IACS
Poor
Example 1 MPa
Example 2 54% Excellent 520 86% IACS
Excellent
MPa
Comparative 32% Poor 505 85% IACS
Poor
Example 2 MPa
Example 3 57% Excellent 670 68% IACS
Excellent
MPa
Comparative 33% Poor 650 70% IACS
Good
Example 3 MPa
The maximum concentrations of sulfur contained in the inclusions with a
diameter of 0.1 .mu.m or more were as high as 20.1%, 25.3% and 25.6%,
respectively, in Examples 1, 2 and 3. These results show that the alloy
contains at least one inclusion with a diameter of 0.1 .mu.m or more
containing at least 10% of sulfur. On the contrary, the maximum
concentrations of sulfur contained in all the inclusions with a diameter
of 0.1 .mu.m or more were less than 10%, or 7.5%, 7.3% and 6.7%,
respectively, in Comparative Examples 1, 2 and 3. This means that the
alloy contains no inclusions with a diameter of 0.1 .mu.m or more
containing 10% or more of sulfur.
The numbers of inclusions having a diameter of 0.1 .mu.m or more and a
sulfur content of 10% or more per 1 mm.sup.2 were as high as 320, 137 and
530, respectively, in Examples 1, 2 and 3. On the contrary, the numbers
were zero in all the alloys in Comparative Examples 1, 2 and 3, showing
that no inclusions with a diameter of 0.1 .mu.m or more were contained in
the alloys at all.
The numbers of inclusions per 1 mm.sup.2 in which sulfur was detected were
as high as 1550, 1010 and 2160, respectively, in Examples 1, 2 and 3. On
the contrary, the numbers were about a half or less of the numbers above,
or 480, 410 and 590, respectively, in Comparative Examples 1, 2 and 3,
showing that the alloys contained a few inclusions.
It can be statistically concluded that the alloys in the examples of the
present invention contain a considerable number of inclusions containing
sulfur, and the content exceeds 10% in all the alloys. On the other hand,
the contents in all the alloys are less than 10% and the number of
inclusions containing sulfur is small in the comparative examples.
Test pieces for tensile strength tests were sampled from the plate samples
in Examples 1 to 3 and Comparative Examples 1 to 3, and the tensile
strength test at high temperatures was performed at 400.degree. C. and
500.degree. C. The results are also shown in Table 1.
The cross-section reduction ratio Ra is defined by equation 1.
Ra(%)=[(So-Sf)/So].times.100 (1)
So: cross-sectional area of the test piece before the tensile strength test
Sf: cross-sectional area of the test piece after the tensile strength test
The cross-section reduction ratios by the tensile strength test at
400.degree. C. were 67%, 60% and 70%, respectively, in Examples 1, 2 and
3, while the ratios were 53%, 49% and 55%, respectively, in Comparative
Examples 1, 2 and 3. These results show that the samples in the examples
have larger cross-section reduction ratios than those in the samples in
the comparative examples, and the former samples are superior to the
latter samples in drawability.
The cross-section reduction ratios in the tensile strength test at
500.degree. C. were 60%, 54% and 57%, respectively, in Examples 1, 2 and
3, while the ratios were 35%, 32% and 33%, respectively, in Comparative
Examples 1, 2 and 3. Therefore, the tendency described above becomes more
evident at higher temperatures.
Fatigue test pieces were sampled from the plate samples in Examples 1 to 3
and Comparative Examples 1 to 3, and were evaluated by an in-plane bend
fatigue test. The fatigue characteristics were tested by controlling the
bend stress, and both ends of the plate were displaced relative to a
neutral point by applying a stress in both directions relative to the
plane of the plate. The samples that broke after 10.sup.7 repeated
deformations, 10.sup.6 repeated deformations and 10.sup.7 times or less,
and 10.sup.6 repeated deformations at a stress amplitude of 200 MPa (the
maximum stress) were evaluated as excellent. The results of the fatigue
characteristics tests are shown in Table 1.
While the samples in Examples 1 to 3 did not break with 10.sup.7 repeated
deformations, the samples in Comparative Examples 1 and 2 broke before
10.sup.5 repeated deformations, and the sample in Comparative Example 3
broke between 10.sup.6 to 10.sup.7 repeated deformations. These results
show that the samples in the examples are superior to the samples in the
comparative examples in fatigue characteristics.
Tensile strength test pieces were sampled from the plate samples in
Examples 1 to 3 and Comparative Examples 1 to 3 for the tensile strength
test at room temperature to measure the 0.2% proof stress. The 0.2% proof
stress at room temperature is shown in Table 1.
The 0.2% proof stresses at room temperature were 580 MPa, 520 MPa and 670
MPA, respectively, in Examples 1, 2 and 3, while the values were 570 MPa,
505 MPa and 650 MPa, respectively, in Comparative Examples 1, 2 and 3. The
0.2% proof stresses at room temperature in the examples are slightly
higher than those in the comparative examples.
Test pieces were sampled from the plate samples in Examples 1 to 3 and
Comparative Examples 1 to 3, and their electric conductivity was measured
at room temperature by a four-point method. The results of the
measurements are shown in Table 1.
The values of the electrical conductivity at room temperature were 80%
IACS, 86% IACS and 68% IACS, respectively, in Examples 1, 2 and 3, while
the values were 81% IACS, 85% IACS and 70% IACS, respectively, in
Comparative Examples 1, 2 and 3. These values are almost the same as each
other.
The high-strength high-conductivity copper alloy according to the present
invention is excellent in fatigue characteristics as well as in
drawability at an intermediate temperature of around 400.degree. C. while
the alloy maintains good conductivity. Assembling of electronic components
at a relatively high temperature can be facilitated by using the
high-strength high-conductivity copper alloy according to the present
invention as a material for the electronic components to enable the
characteristics of the electronic components at a relatively high
temperature to be improved while also facilitating the compactness of
electronic appliances.
*
