U.S. patent application number 10/380291 was filed with the patent office on 2003-10-09 for high-strength copper alloy excellent in bendability and method for producing the same and terminal and connector using the same.
Invention is credited to Fukamachi, Kazuhiko, Shigyo, Masato.
Application Number | 20030188814 10/380291 |
Document ID | / |
Family ID | 18865354 |
Filed Date | 2003-10-09 |
United States Patent
Application |
20030188814 |
Kind Code |
A1 |
Fukamachi, Kazuhiko ; et
al. |
October 9, 2003 |
High-strength copper alloy excellent in bendability and method for
producing the same and terminal and connector using the same
Abstract
The invention aims at providing high-strength copper alloy,
especially phosphor bronze, with excellent bending workability. The
excellently bendable high-strength copper alloy is obtained through
grain size control whereby a finally cold rolled copper alloy with
a tensile strength and 0.2% yield strength different by not more
than 80 MPa is allowed to have characteristics such that its mean
grain size (mGS) after annealing at 425.degree. C. for 10,000
seconds is not more than 5 .mu.m and the standard deviation of the
mean grain size (.sigma.GS) is not more than 1/3XmGS. Improvements
in characteristics presumably attributable to the synergistic
effect of grain-boundary strengthening and dislocation
strengthening are stably achieved by the adjustments of cold
rolling and annealing conditions and by the study of the
correlation between pertinent characteristic values after the final
rolling. The method of processing the alloy comprises cold rolling
to a reduction percentage of at least 45%, final annealing to the
extent that the mean grain size (mGS) is not more than 3 .mu.m and
the standard deviation of the mean grain size (.sigma.GS) is not
more than 2 .mu.m, and final cold rolling to a reduction percentage
of 10-45%.
Inventors: |
Fukamachi, Kazuhiko;
(Kanagawa, JP) ; Shigyo, Masato; (Kanagawa,
JP) |
Correspondence
Address: |
DRINKER BIDDLE & REATH
ONE LOGAN SQUARE
18TH AND CHERRY STREETS
PHILADELPHIA
PA
19103-6996
US
|
Family ID: |
18865354 |
Appl. No.: |
10/380291 |
Filed: |
March 10, 2003 |
PCT Filed: |
December 26, 2001 |
PCT NO: |
PCT/JP01/11483 |
Current U.S.
Class: |
148/684 ;
148/433 |
Current CPC
Class: |
C22C 9/02 20130101; C22F
1/08 20130101 |
Class at
Publication: |
148/684 ;
148/433 |
International
Class: |
C22C 009/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2000 |
JP |
2000-400837 |
Claims
What is claimed is:
1. A high-strength copper alloy having excellent bending
workability characterized in that it is a finally cold rolled
copper alloy with a tensile strength and 0.2% yield strength
different by not more than 80 MPa, the alloy having characteristics
such that the mean grain size (mGS) thereof after annealing at
425.degree. C. for 10,000 seconds is not more than 5 .mu.m and the
standard deviation of the mean grain size (.sigma.GS) is not more
than 1/3XmGS.
2. A high-strength copper alloy having excellent bending
workability according to claim 1 characterized by comprising from 1
to 11 mass % Sn, from 0.03 to 0.35 mass % P, and the balance Cu and
unavoidable impurities, with a tensile strength termed TS.sub.sn
(MPa) being TS.sub.sn>500+15XSn (Sn: tin concentration (mass
%)), the alloy having characteristics such that the mean grain size
(mGS) thereof after annealing at 425.degree. C. for 10,000 seconds
is not more than 5 .mu.m and the standard deviation of the mean
grain size (.sigma.GS) is not more than 1/3X mGS.
3. A high-strength copper alloy having excellent bending
workability according to claim 1 or 2 characterized by comprising
from 1 to 11 mass % Sn, from 0.03 to 0.35 mass % P, and the balance
Cu and unavoidable impurities, the alloy having characteristics
such that the mean grain size (mGS (.mu.m)) thereof after annealing
at 425.degree. C. for 10,000 seconds is mGS<2.7X exp (0.0436XSn
(Sn: tin concentration (mass %)).
4. A high-strength copper alloy having excellent bending
workability according to claim 1, 2, or 3 characterized by being a
phosphor bronze which comprises from 1 to 11 mass % Sn, from 0.03
to 0.35 mass % P, from 0.05 to 2.0 mass %, in total, of one, two,
or more selected from among Fe, Ni, Mg, Si, Zn, Cr, Ti, Zr, Nb, Al,
Ag, Be, Ca, Y, Mn, and In, and the balance Cu and unavoidable
impurities.
5. A high-strength copper alloy having excellent bending
workability according to 1, 2, or 3 characterized by being a
phosphor bronze which comprises from 1 to 11 mass % Sn, from 0.03
to 0.35 mass % P, from 0.05 to 2.0 mass %, in total, of one, two,
or more selected from among Fe, Ni, Mg, Si, Zn, Cr, Ti, Zr, Nb, Al,
Ag, Be, Ca, Y, Mn, and In, and the balance Cu and unavoidable
impurities, with particles that mainly consist of precipitation or
crystallization products of the alloying metals, 0.1 .mu.m or more
in diameter, being present in a number of not fewer than 100 per
square millimeter of a cross section cut in parallel to the rolling
direction.
6. A method of manufacturing high-strength copper alloy having
excellent bending workability characterized by the steps of cold
rolling to a reduction percentage of at least 45%, final annealing
tothe extent that the mean grain size (mGS) is not more than 3
.mu.m and the standard deviation of the mean grain size (.sigma.GS)
is not more than 2 .mu.m, and final cold rolling to a reduction
percentage of from 10 to 45%.
7. A method of manufacturing high-strength copper alloy having
excellent bending workability characterized by the steps of cold
rolling to a reduction percentage of at least 45%, final annealing
to the extent that the mean grain size (mGS) is not more than 2
.mu.m and the standard deviation of the mean grain size (.sigma.GS)
is not more than 1 .mu.m, and final cold rolling to a reduction
percentage of from 20 to 70%.
8. A method of manufacturing high-strength copper alloy having
excellent bending workability according to claim 6 or 7
characterized by stress relief annealing of the cold rolled
material that has been finally cold rolled to a reduction ratio X
(%) and has a tensile strength of TS.sub.0 (MPa), until the tensile
strength TS.sub.a (MPa) after the annealing is
TS.sub.a<TS.sub.0-X.
9. A method of manufacturing high-strength copper alloy having
excellent bending workability defined in any of claims 1 to 5
characterized by the steps of cold rolling to a reduction ratio of
at least 45%, final annealing to the extent that the mean grain
size (mGS) is not more than 3 .mu.m and the standard deviation of
the mean grain size (.sigma.GS) is not more than 2 .mu.m, and final
cold rolling to a reduction ratio of from 10 to 45%.
10. A method of manufacturing high-strength copper alloy having
excellent bending workability defined in any of claims 1 to 5
characterized by the steps of cold rolling to a reduction ratio of
at least 45%, final annealing to the extent that the mean grain
size (mGS) is not more than 2 .mu.m and the standard deviation of
the mean grain size ((.sigma.GS) is not more than 1 .mu.m, and
final cold rolling to a reduction ratio of from 20 to 70%.
11. A method of manufacturing high-strength copper alloy having
excellent bending workability defined in any of claims 1 to 5
characterized by the steps of cold rolling to a reduction ratio of
at least 45%, final annealing to the extent that either (a) the
mean grain size (mGS) is not more than 3 .mu.m and the standard
deviation of the mean grain size (.sigma.GS) is not more than 2
.mu.m, and final cold rolling to a reduction ratio of from 10 to
45% or (b) the mean grain size (mGS) is not more than 2 .mu.m and
the standard deviation of the mean grain size (.sigma.GS) is not
more than 1 .mu.m, and final cold rolling to a reduction ratio of
from 20 to 70%, and thereafter stress relief annealing the cold
rolled material that has been finally cold rolled to the reduction
ratio X (%) and having a tensile strength of TS.sub.0 (MPa), until
the tensile strength TS.sub.a (MPa) is TS.sub.a<TS.sub.0-X.
12. Terminal connectors using the high-strength copper alloys
having excellent bending workability according to any of claims 1
to 5.
Description
FIELD OF THE INVENTION
[0001] This invention relates to high-strength copper alloys,
especially high-strength phosphor bronze, having excellent bending
workability for use in electronic parts such as terminal
connectors, a method of manufacturing the same, and terminal
connectors using the same.
PRIOR ART
[0002] Narrow strips of phosphor bronze such as C5210 and C5191 (in
conformity with JIS H 3110 and JIS H 3130, respectively) and copper
alloy materials such as C2600 (JIS H 3100) that have outstanding
workability and mechanical strength are widely employed for such
uses as electronic parts like terminal connectors.
[0003] Recent years have witnessed stronger tendencies toward
slimmer and smaller electronic parts than ever, and accordingly
there have been demand for thinner strips of copper alloy as
materials for those parts. Thinner materials are required to
possess, in themselves, sufficient strength to maintain the contact
pressure and other forces needed of the resulting connectors and
the like. Meanwhile, the manufacture of tinier electronic parts
calls for material of adequately high bendability to permit bending
to smaller bend radii than heretofore so that the parts can fulfill
their functions within narrower spaces. Thus, the materials are
required to have contradictory properties of high strength and good
bending workability.
[0004] In attempts to meet the demand, high-strength copper alloys
such as beryllium copper and titanium copper and, where electric
conductivity is an additional requirement, Corson (Cu--Ni--Si)
alloy and chromium-copper (Cu--Cr, Cu--Cr--Zr, Cu--Cr--Sn, etc.)
alloys have come into use.
[0005] However, those high-strength copper alloys that are
comparatively new varieties of copper alloys for electronic parts
have limitations in the demand and supply and distribution in the
market. For example, difficulties are involved in their extensive
acceptance in the market where more and more weight is being placed
on global standards. Another factor that hinders wide-spread
adoption of those high-strength copper alloys is that they are
costlier than ordinary phosphor bronze and other existing copper
alloys.
[0006] In view of the foregoing, there is demand for further
improvements in strength and workability of the conventional copper
alloys such as brass and phosphor bronze that have been deemed to
have relatively great mechanical strength among ordinary copper
alloys. As for the workability, good bending property is desired in
particular. This is because more and more severe bending is
involved in the fabrication of terminal connectors, lead frames,
and other metallic members of electronic components to keep pace
with the progress of higher density packaging in the fields of PDA
(Personal Digital Assistance), digital cameras, and video
cameras.
[0007] In general, attempts to enhance the strength of metals
depend on combinations of solid-solution, precipitation,
grain-boundary, dislocation and other hardening or strengthening
techniques. Phosphor bronze whose compositional ranges are
standardized is a copper alloy of the solid-solution strengthening
type. Efforts have been made to improve its strength by proper
conditioning such as cold rolling and annealing from the viewpoints
of intergranular strengthening and dislocation hardening. Actual
developments, however, are behind the rapid progress of demand for
lighter, thinner, and smaller electronic parts in recent years.
[0008] (Problem that the Invention is to Solve)
[0009] Under such circumstances, the problem that the invention is
to solve is to develop a technique whereby high strength and
bendability are combinedly imparted to solid-solution strengthened
type copper alloys, especially to general-purpose phosphor
bronze.
[0010] (Means of Solving the Problem)
[0011] Copper alloys of the solid-solution strengthened type,
especially general-purpose phosphor bronze, when further
strengthened by grain-boundary and dislocation techniques, i.e., by
heat treatment and rolling, give final products that are unable to
observe clearly its grain boundaries. In other words, as
deformation of a metal strip due to cold working proceeds,
variations of local transgranular deformation become increasingly
conspicuous, giving birth to many different deformation bands such
as shear bands and micro-bands. These deformation bands make the
grain boundaries that had been formed by recrystallization before
cold working discontinuous, and, when the cross section is etched
and then observed under an optical microscope, the crystal
structure looks indistinct. Inspection of the structure by a
transmission electron microscope shows that the structure, even
after cold working to a reduction ratio of about 20%, retains part
of the pre-working recrystallization grain boundaries. It is
already covered with a cell structure, which hampers precise
determination of the grain size. This has been a major obstacle to
improvements in the properties of cold rolled materials.
[0012] The present inventors have adjusted the conditions for cold
rolling and annealing of phosphor bronze and investigated the
correlations among various property values after final rolling. As
a result, they have succeeded in steady improvements in the
properties presumably owing to the composite effects of
grain-boundary strengthening and dislocation strengthening. The
present invention provides high-strength copper alloys with
excellent bending workability that can be defined as follows:
[0013] (1) A high-strength copper alloy having excellent bending
workability characterized in that it is a finally cold rolled
copper alloy with a tensile strength and 0.2% yield strength
different by not more than 80 MPa, the alloy having characteristics
such that the mean grain size (mGS) thereof after annealing at
425.degree. C. for 10,000 seconds is not more than 5 .mu.m and the
standard deviation of the mean grain size (.sigma.GS) is not more
than 1/3XmGS.
[0014] (2) A high-strength copper alloy having excellent bending
workability according to (1) characterized by comprising from 1 to
11 mass % Sn, from 0.03 to 0.35 mass % P, and the balance Cu and
unavoidable impurities, with a tensile strength termed TS.sub.sn
(MPa) being TS.sub.sn>500+15XSn (Sn: tin concentration (mass
%)), the alloy having characteristics such that the mean grain size
(mGS) thereof after annealing at 425.degree. C. for 10,000 seconds
is not more than 5 .mu.m and the standard deviation of the mean
grain size ((.sigma.GS) is not more than 1/3XmGS.
[0015] (3) A high-strength copper alloy having excellent bending
workability according to (1) or (2) characterized by comprising
from 1 to 11 mass % Sn, from 0.03 to 0.35 mass % P, and the balance
Cu and unavoidable impurities, the alloy having characteristics
such that the mean grain size (mGS (.mu.m)) thereof after annealing
at 425.degree. C. for 10,000 seconds is mGS<2.7Xexp (0.0436XSn
(Sn: tin concentration (mass %)).
[0016] (4) A high-strength copper alloy having excellent bending
workability according to (1), (2) or (3) characterized by being a
phosphor bronze which comprises from 1 to 11 mass % Sn, from 0.03
to 0.35 mass % P, from 0.05 to 2.0 mass %, in total, of one, two,
or more selected from among Fe, Ni, Mg, Si, Zn, Cr, Ti, Zr, Nb, Al,
Ag, Be, Ca, Y, Mn, and In, and the balance Cu and unavoidable
impurities.
[0017] (5) A high-strength copper alloy having excellent bending
workability according to (1), (2) or (3) characterized by being a
phosphor bronze which comprises from 1 to 11 mass % Sn, from 0.03
to 0.35 mass % P, from 0.05 to 2.0 mass %, in total, of one, two,
or more selected from among Fe, Ni, Mg, Si, Zn, Cr, Ti, Zr, Nb, Al,
Ag, Be, Ca, Y, Mn, and In, and the balance Cu and unavoidable
impurities, with particles that mainly consist of precipitation or
crystallization products of the alloying metals, 0.1 .mu.m or more
in diameter, being present in a number of not fewer than 100 per
square millimeter of a cross section cut in parallel to the rolling
direction.
[0018] The invention also provides methods of manufacturing
high-strength copper alloys having excellent bending workability,
under the conditions defined below.
[0019] (6) A method of manufacturing high-strength copper alloy
having excellent bending workability characterized by the steps of
cold rolling to a reduction ratio of at least 45%, final annealing
to the extent that the mean grain size (mGS) is not more than 3
.mu.m and the standard deviation of the mean grain size (.sigma.GS)
is not more than 2 .mu.m, and final cold rolling to a reduction
ratio of from 10 to 45%.
[0020] (7) A method of manufacturing high-strength copper alloy
having excellent bending workability characterized by the steps of
cold rolling to a reduction ratio of at least 45%, final annealing
to the extent that the mean grain size (mGS) is not more than 2
.mu.m and the standard deviation of the mean grain size (.sigma.GS)
is not more than 1 .mu.m, and final cold rolling to a reduction
ratio of from 20 to 70%.
[0021] (8) A method of manufacturing high-strength copper alloy
having excellent bending workability according to (6) or (7)
characterized by stress relief annealing of the cold rolled
material that has been finally cold rolled to a reduction ratio X
(%) and has a tensile strength of TS.sub.0 (MPa), until the tensile
strength TS.sub.a (MPa) after the annealing is
TS.sub.a<TS.sub.0-X.
[0022] The methods (6) to (8) are applicable to the manufacture of
the copper alloys defined in (1) to (5). The invention further
provides methods of manufacturing high-strength copper alloys
having excellent bending workability, under the conditions defined
below.
[0023] (9) A method of manufacturing high-strength copper alloy
having excellent bending workability defined in any of (1) to (5)
characterized by the steps of cold rolling to a reduction ratio of
at least 45%, final annealing to the extent that the mean grain
size (mGS) is not more than 3 .mu.m and the standard deviation of
the mean grain size (.sigma.GS) is not more than 2 .mu.m, and final
cold rolling to a reduction ratio of from 10 to 45%.
[0024] (10) A method of manufacturing high-strength copper alloy
having excellent bending workability defined in any of (1) to (5)
characterized by the steps of cold rolling to a reduction ratio of
at least 45%, final annealing to the extent that the mean grain
size (mGS) is not more than 2 .mu.m and the standard deviation of
the mean grain size (.sigma.GS) is not more than 1 .mu.m, and final
cold rolling to a reduction ratio of from 20 to 70%.
[0025] (11) A method of manufacturing high-strength copper alloy
having excellent bending workability defined in any of (1) to (5)
characterized by the stress relief annealing, in relation to (9) or
(10), of a cold rolled material that has been finally cold rolled
to a reduction ratio X (%) and has a tensile strength of TS.sub.0
(MPa), until the tensile strength TS.sub.a (MPa) is
TS.sub.a<TS.sub.0-X.
[0026] As for the applications, the invention provides:
[0027] (12) Terminal connectors using the high-strength copper
alloys having excellent bending workability according to any of (1)
to (5).
[0028] (Modes of Embodying the Invention)
[0029] The grounds on which the various elements that constitute
the present invention are restricted will now be explained for
individually claimed inventions (called also collectively the
present invention).
[0030] (The Invention of High-strength Copper Alloy having
Excellent Bending Workability According to (1) above)
[0031] The invention according to (1) above defines that a
high-strength copper alloy having excellent bending workability
with a difference between tensile strength and 0.2% yield strength
being not more than 80 MPa, has properties such that the mean grain
size (mGS) thereof after annealing at 425.degree. C. for 10,000
seconds is not more than 5 .mu.m and the standard deviation of the
mean grain size (.sigma.GS) is not more than 1/3 mGS.
[0032] For the purposes of the invention the grain size is
determined by the cutting method in conformity with the procedure
specified in JIS H 0501 (JIS stands for Japanese Industrial
Standards). To be more concrete, the number of the grains
completely sectioned along a predetermined length of segment is
counted, and the mean value of the cut lengths is measured as the
grain size. The standard deviation that characterizes the
dispersion does not represent a standard deviation of the cut
lengths but a standard deviation of the grain sizes.
[0033] The copper alloy according to the present invention is
obtained as an end product, basically, by a method which comprises
cold rolling of the alloy material to a reduction ratio of at least
45%, and thereafter either final annealing to the extent that the
mean grain size (mGS) is not more than 3 .mu.m and the standard
deviation of the mean grain size (.sigma.GS) is not more than 2
.mu.m, and final cold rolling to a reduction ratio of from 10 to
45% or, alternatively, final annealing to the extent that the mean
grain size (mGS) is not more than 2 .mu.m and the standard
deviation of the mean grain size (.sigma.GS) is not more than 1
.mu.m, and final cold rolling to a reduction ratio of from 20 to
70%. As noted already, addition of strength by grain-boundary and
dislocation strengthening techniques, i.e., by heat treatment and
rolling, makes it impossible for the end product to observe clearly
its grain boundaries. Stated differently, as deformation of a metal
strip by cold working proceeds, variations in local transgranular
deformation grains become so conspicuous that many different
deformation bands such as shear bands and micro-bands result. These
deformation bands make the grain boundaries that had been formed by
recrystallization before cold working discontinuous, and, when the
cross section is etched and then observed under an optical
microscope, the crystal structure looks indistinct. Even after cold
working to a ratio of about 20%, the structure inspected under a
transmission electron microscope shows that the structure retains
part of the pre-working recrystallization grain boundaries. It is
already covered with a cell structure, which hampers precise
determination of the grain size. Thus, precise determination of the
grain size has been extremely difficult.
[0034] It has now been found that there is a correlation between
the recrystallization behavior of a copper alloy after cold working
and the properties of the alloy that combines bending workability
and strength. The correlation is helpful in identifying the
material. Thus, the present invention provides a copper alloy which
combines excellent bending workability with high strength, with a
tensile strength and 0.2% yield strength different by not more than
80 MPa, the alloy having characteristics such that the mean grain
size (mGS) thereof after annealing at 425.degree. C. for 10,000
seconds is not more than 5 .mu.m and the standard deviation of the
mean grain size (.sigma.GS) is not more than 1/3 mGS.
[0035] When a metal material is annealed and cold worked, it is
common that as the degree of cold rolling increases the difference
between the tensile strength and the 0.2% yield strength decreases.
Simultaneously the ductility decreases, making the metal
susceptible to cracking upon bending. It is now found under the
invention that the decrease in ductility can be minimized by
adjusting the conditions of final annealing before the final
rolling as well as the conditions of the preceding cold working.
This characteristic promises remarkably beneficial effect upon a
high-strength copper alloy having a property such that the
difference between the tensile strength and 0.2% yield strength is
not more than 80 MPa.
[0036] The copper alloy according to the invention is defined also
by its unique property that its mean grain size is maintained below
5 .mu.m when annealed under the condition of 425.degree. C. for
10,000 seconds, which condition allows considerable growth of
grains in ordinary copper alloys. The copper alloy of the
invention, obtained as an end product by either final annealing to
the extent that the mean grain size (mGS) is not more than 3 .mu.m
and the standard deviation of the mean grain size (.sigma.GS) is
not more than 2 .mu.m, and final cold rolling to a reduction ratio
of from 10 to 45% or, alternatively, final annealing to the extent
that the mean grain size (mGS) is not more than 2 .mu.m and the
standard deviation of the mean grain size (.sigma.GS) is not more
than 1 .mu.m, and final cold rolling to a reduction ratio of from
20 to 70%, possesses an ultrafine grains that cannot exhibit the
crystal boundaries in the end product. The ultrafine grains have
the unique character of maintaining a mean grain size of not more
than 5 .mu.m, without grain growth, upon annealing under the
conditions of 425.degree. C. for 10,000 seconds. By utilizing this
character, the copper alloy of the invention can be distinguished
from other copper alloys and defined as such.
[0037] Products of copper alloys according to the present invention
undergo little decreases in ductility upon final cold working in
the process of the products, and they combine high strength with
excellent bending workability.
[0038] The mean grain size (mGS) of the metal after annealing at
425.degree. C. for 10,000 seconds is preferably not more than 3
.mu.m, since it improves the relation between the tensile strength
and bending workability.
[0039] Even if the mean grain size (mGS) is not more than 5 .mu.m,
its beneficial effect is limited if there is a scatter of the size.
As will be described later, the process of products must be
strictly controlled to obtain a homogeneous fine grains. The
over-all tolerance of the scatter, in terms of the standard
deviation of the grain size, should be not more than 1/3 mGS,
because a standard deviation (.sigma.GS) in excess of 1/3 mGS
reduces the improvement upon the bending workability.
[0040] (The Invention of High-strength Copper Alloy having
Excellent Bending Workability According to (2) above)
[0041] This invention restricts the inventive copper alloys to
phosphor bronze having a high tensile strength.
[0042] Unlike other copper alloys, phosphor bronze that contains
tin as a solid-solution strengthening element, varies in the
work-hardening property with its tin concentration. With this in
view, the invention specifically defines the effective range for a
high-strength material, in terms of an empirically obtained
relation between the tin concentration and tensile strength,
as:
[0043] Tensile strength TS.sub.sn (MPa)>500+15XSn (tin conc.,
mass %)
[0044] The better the actual values satisfy the above relation the
elements referred to in (1) above will be the more effective. In
other words, where the reduction ratio of cold working is low, the
decrease of ductility is limited, favorable bending workability is
retained without the need of controlling the grain size, and the
influences of the process conditions prior to the final annealing
are reduced.
[0045] (The Invention of High-strength Copper Alloy having
Excellent Bending Workability According to (3) above)
[0046] This invention again restricts the inventive copper alloys
to phosphor bronze and defines the relation between the mean grain
size (mGS: .mu.m) after annealing at 425.degree. C. for 10,000
seconds and the tin concentration (Sn: mass %) to be:
mGS<2.7X exp (0.0436XSn).
[0047] Phosphor bronze exhibits a grain growth behavior peculiar to
itself. Thus, it is desirable that the grains should be adjusted so
that the mean grain size after the above annealing may be
mGS<2.7X exp(0.0436XSn). This is a formula empirically found
from the correlation among the working conditions, properties
(strength and bending workability), and the grain size after heat
treatment at 425.degree. C. for 10,000 seconds, of a phosphor
bronze containing from 1 to 11%, preferably from 2 to 10%, tin. If
the mGS is more than the level specified above, the effect of
grain-refining is negligible, no appreciable increase in strength
is possible without an increase in the rolling reduction ratio,
ductility of highly strengthened material decrease, and the bending
workability remains unimproved.
[0048] With regard to the relation between the grain size and
strength (yield strength), the major effect of basic importance is
that of grain refinement commonly represented by the Hall-Petch
equation. On this basis it has been found that the grain size after
recrystallization can subsequently increase the work-hardening
ability itself.
[0049] For the purpose of the practical use of phosphor bronze, the
above feature permits high strengthening by rolling at a low
reduction ratio. While the lower limit is not definitely specified,
it should be noted that if the mean grain size (mGS) after the
final annealing is as small as below 0.4 .mu.m, the ductility once
lowered by the cold rolling before the final annealing is not fully
recovered; rather, the ductility further drops as a result of the
final cold rolling. For this reason it is desirable that the mGS
should be not less than 0.4 .mu.m.
[0050] (The Invention of High-strength Copper Alloy having
Excellent Bending Workability According to (4) above)
[0051] This invention adds from 0.05 to 2.0 mass %, in total, of
one, two, or more selected from among Fe, Ni, Mg, Si, Zn, Cr, Ti,
Zr, Nb, Al, Ag, Be, Ca, Y, Mn, and In to the copper alloy,
especially phosphor bronze, specified above.
[0052] The grounds for the addition of Fe, Ni, Mg, Si, or/and Zn
will first be explained.
[0053] Trace addition of Fe, Ni, Mg, or/and Si to phosphor bronze
as a copper alloy results in the formation of intermetallic
compounds between those elements and P. The compounds so formed are
dispersed in the matrix to improve the properties of the phosphor
bronze made primarily by grain-boundary strengthening and
solid-solution strengthening in accordance with any of (1) to (3)
above. Of these combinations, Fe-P or the like, for example, may be
chosen to form an intermetallic compound by precipitation. Its
dispersion not only adds strength by precipitation strengthening of
the resulting alloy itself but also effectively helps pinning of
the grain boundaries by means of the residual particulates of the
precipitation and crystallization products. In addition, it slows
down the growth of grains and facilitates the grain refinement. For
these purposes a total amount of 0.05 mass % is necessary but an
addition of more than 2.0 mass % is rather detrimental to electric
conductivity and other properties.
[0054] Zn is an element which, when added to a copper alloy,
improves the thermal peeling resistance of tin and solder plates
from the alloy surface. It improves effectively when added in an
amount of about 0.1 mass % or more, but the addition of more than
0.5 mass % saturates the beneficial effect and lowers the electric
conductivity.
[0055] As described above, Fe, Ni, Mg, Si, and Zn are the elements
that add strength of phosphor bronze or improve the thermal peeling
resistance of tin and solder plates on the alloy, and their
addition is recommended. The amount to be added is decided in
consideration of the bending workability and electric conductivity
of the resulting alloy and ranges, in all, from 0.05 to 2.0 mass %.
The reasons are that a total amount of less than 0.05 mass % is not
large enough to improve the strength or enhance the thermal peeling
resistance whereas an amount of more than 2.0 mass % deteriorates
the bending workability and reduces the electric conductivity. The
reduction of electric conductivity is particularly profound, with
the low-tin, high-conductivity phosphor bronze having a tin
concentration of about 1 to 4 mass %. Of those addition elements,
Zn desirably ranges in amount from 0.1 to 0.5 mass % for the reason
stated above.
[0056] The addition of the elements other than those mentioned
above, i.e., Cr, Ti, Zr, Nb, Al, Ag, Be, Ca, Y, Mn, and In will now
be explained.
[0057] These elements enhance the strength of copper alloy by
solid-solution strengthening and precipitation strengthening. As
with Fe, Ni, Mg, Si, and Zn described above, such an element or
elements are added in an amount, in all, of not more than 1.0 mass
% for a further increase in the strength of the resulting
alloy.
[0058] Thus the strength of an alloy is improved by the addition of
from 0.05 to 2.0 mass %, in total, of one, two, or more selected
from among Fe, Ni, Mg, Si, Zn, Cr, Ti, Zr, Nb, Al, Ag, Be, Ca, Y,
Mn, and In.
[0059] The addition elements mentioned immediately above are
typical elements useful from the economic viewpoint too. Copper
alloys that contain as auxiliary constituents any other element or
elements primarily capable of solid-solution strengthening without
the deterioration of the conductivity and other properties of the
alloy also come within the scope of the present invention.
[0060] (The Invention of High-strength Copper Alloy having
Excellent Bending Workability According to (5) above)
[0061] This invention defines the distribution of the precipitation
or crystallization product of the alloying elements in the
invention as defined in (4) above.
[0062] With the aim of grain refinement, the optimum state peculiar
to phosphor bronze has now been found out. Presumably closely
related to the intergranular energy and the like of phosphor
bronze, particles ranging in diameter from 0.1 .mu.m to 10 .mu.m
present at the rate of at least 100 particles per square millimeter
as counted by observation of a cross section, prove remarkably
effective in grain refinement. The particles are coarse particles
of precipitation or crystallization product, and regardless of the
composition of the precipitation or crystallization product, the
particles are found to have a grain-refining effect.
[0063] In the process of grain refinement it is presumed that the
particles that actually contribute to the nucleation of glains and
grain boundary pinning include finer particles. So far as the
inspection under a scanning electron microscope is concerned, an
outstanding grain-refining effect is observed in the cross
sectional structure with the above-mentioned particle distribution.
Thus, as a substitutional characteristic of grain refinement, the
distribution of the precipitation or crystallization product is set
forth.
[0064] (The Invention of Method of Manufacturing High-strength
Copper Alloy having Excellent Bending Workability According to (6)
above)
[0065] This invention relates to a method of manufacturing
high-strength copper alloy having excellent bending workability. In
particular, it relates to a method of manufacturing high-strength
copper alloy having excellent bending workability by the repetition
of cold rolling and annealing in specified steps of final cold
rolling, final annealing prior to the cold rolling, and the cold
rolling even before the final annealing.
[0066] Subsequently this invention too is basically aimed at
achieving the effect of grain refinement before the final rolling
that follows the final annealing. Assuming that the thickness of
the material before the cold rolling is to and the thickness after
the cold rolling is t, the reduction ratio X of the cold rolling
before the final annealing is defined as
X=(t.sub.0-t)/t.sub.0X100(%).
[0067] The reduction ratio is then specified to be not less than
45%. This is because a ratio below 45% will scarcely refine the
grain size after the final annealing, despite adjustments of the
heat treatment conditions for the final annealing.
[0068] The mean grain size after the annealing is specified to be
not more than 3 .mu.m and the standard deviation of the mean grain
size is specified to be not more than 2 .mu.m. The ground for these
limits is that a homogeneous fine-grain structure must be obtained
through precise control of the heating temperature profile during
annealing.
[0069] The term fine recrystallized grain as used herein means
that, when the mean grain size (mGS) is 3 .mu.m and the standard
deviation (.sigma.GS) is 2 .mu.m, not less than 99% of the
diameters of the individual crystal grains is mGS+3.sigma.GS, or
not more than 9 .mu.m, although the distribution of grain size is
not normal distribution.
[0070] Existance of grains 8 .mu.im or more in size in a
recrystallized structure is often undesirable, and therefore it is
desired that the standard deviation of grain size is not more than
1.5 .mu.m.
[0071] The influences of the reduction ratio of cold rolling before
the final annealing upon the recrystallized grains after the final
annealing are such that the higher the reduction ratio the finer
the grain size of the recrystallized grain after the annealing. At
the same time, nucleation of grains and the subsequent secondary
recrystallization behavior tend to large dispersion, and a duplex
grain structure is likely to develop.
[0072] Above all, the copper alloy having a pure copper type
recrystallization structure with a high copper concentration shows
a strong tendency.
[0073] On the other hand, brass containing more than 30 mass % Zn
and phosphor bronze containing more than 4 mass % Sn are relatively
easy to regularize the size of the recrystallized grains after high
reduction working.
[0074] It is necessary, in view of the foregoing, to optimize the
annealing conditions, i.e., temperature, time, and temperature
profile, for each alloy to obtain a recrystallized structure.
[0075] If either the mean grain size or the standard deviation is
outside the range specified, i.e., not more than 3 .mu.m or not
more than 2 .mu.m, respectively, the ability of high work hardening
upon the final cold rolling is not obtained.
[0076] Final cold rolling of an alloy having a mean grain size of
not more than 3 .mu.m and a standard deviation of not more than 2
.mu.m to a reduction ratio of 10 to 45%, gives a copper alloy with
high strength and excellent bending workability.
[0077] A reduction ratio of less than 10% is limited in
grain-refining effect and imparting good bending workability for
ordinary copper alloys having a mean grain size of about 10 .mu.m
after the final annealing. On the other hand, a reduction ratio of
more than 45% decreases the bending workability and narrows the
application range of the alloy as a material for contacts and other
metal components worked by bending.
[0078] (The Invention of Method of Manufacturing High-strength
Copper Alloy having Excellent Bending Workability According to (7)
above)
[0079] This invention sets forth that the mean grain size is not
more than 2 .mu.m and the standard deviation of the mean grain size
is not more than 1 .mu.m, thus narrowing the scatter of the grain
size, i.e., a standard deviation of not more than 2 .mu.m,
specified in the invention as defined in (6) above. The consequent
effect of uniform grain refinement permits a further increase in
the reduction ratio of the final cold rolling to 20 to 70%, which
makes it possible to obtain a high-strength copper alloy without a
deteriorating of the bending workability.
[0080] (The Invention of Method of Manufacturing High-strength
Copper Alloy having Excellent Bending Workability According to (8)
above)
[0081] This invention defines the amount of decrease in the tensile
strength of the above-specified copper alloy upon stress relief
annealing after the final rolling. According to the definition, the
tensile strength before the stress relief annealing is TS.sub.0
(MPa), the tensile strength after the stress relief annealing is
TS.sub.a (MPa), and TS.sub.a<TS.sub.0-X (the ratio of reduction
(%) by the final cold rolling).
[0082] Phosphor bronze, nickel silver and the like are sometimes
annealed for stress relief. Unlike the recrystallization annealing
that is conducted prior to the final rolling, stress relief
annealing is aimed at recovering the ductility (workability) after
cold rolling and also improving the springiness and other
properties. For these purposes it is commonly performed with copper
alloys such as phosphor bronze for spring use (C5210: JIS H
3130).
[0083] Stress relief annealing may be done, as needed, by a tension
annealing line or the like after the final rolling.
[0084] The copper alloys according to the present invention, even
after the stress relief annealing, is superior in strength and
bending workability than the alloys made by prior art methods.
[0085] When an annealed material of a particularly fine grain size
is to be cold rolled, it is effective to conduct the stress relief
annealing corresponding to the final reduction ratio so as to
minimize the loss of the ductility. Where bending workability is to
be enhanced in particular, the stress relief annealing is done
under conditions such that, assuming that the reduction ratio of
the final cold rolling is X % and the cold rolled material has a
tensile strength (TS.sub.0:MPa), the tensile strength of the cold
rolled material after the stress relief annealing, TS.sub.a (MPa),
will be TS.sub.a<TS.sub.0-X. For example, a cold rolled
material, work hardened to 700 MPa at a final reduction ratio of
30%, is annealed for stress relief to less than 670 MPa to obtain a
material with good bending workability.
[0086] (The Invention of Method of Manufacturing High-strength
Copper Alloy of any of (1) to (5) above having Excellent Bending
Workability, According to any of (9) to (11) above)
[0087] The methods according to (6) to (8) above [sic] are
applicable to the manufacture of the high-strength copper alloy,
especially phosphor bronze, of any of (1) to (5) above. The
explanations already made of the preceding inventions generally
apply to these methods as well.
[0088] (The Invention of Terminal Connectors According to (12)
above)
[0089] The inventions claimed above, in connection with
solid-solution strengthened copper alloys, especially phosphor
bronze type copper alloys, provide high-strength copper alloys
having excellent bending workability and methods of manufacturing
the same. The inventions apply to terminal connectors that require
compactness in size, excellent bending workability, and high
strength.
[0090] The contact portions of the terminal connectors undergo
little deterioration in strength and bending workability upon
plating before or after working, exhibiting the beneficial effects
of the inventions.
WORKING EXAMPLES
[0091] The effects of embodiment of the present invention will now
be explained in connection with various phosphor bronze
products.
(1) Example Series 1
[0092] (Examples of the Inventions Defined in (1) to (3) above)
[0093] Phosphor bronze stocks of the compositions given in Table 1
were charcoal-coated in air, melted, and cast into ingots each
measuring 100 mm wide, 40 mm thick, and 150 mm long.
[0094] The cast ingots were homogenized in an atmosphere of 75%
N.sub.2+25% H.sub.2 at 700.degree. C. for one hour, and the tin
segregation layer formed on the surface was removed by means of a
grinder.
[0095] Cold rolling and recrystallization annealing were then
repeated a plurality of times each. In particular, the cold rolling
reduction ratio before the final annealing, the final
recrystallization annealing, and the final cold rolling reduction
ratio were adjusted so that 0.2 mm thick sheets could be
obtained.
[0096] The properties of the sheets thus obtained are shown in
Table 1.
[0097] (Testing Procedures)
[0098] Tensile strength (TS: MPa) and 0.2% yield strength (YS: MPa)
of a test specimen No. 13B (conforming to JIS Z 2201) sampled in
the direction parallel to the rolling direction of each stock were
found by a tensile test (JIS Z 2241).
[0099] Grain size is determined by the intercept method (JIS H
0501) which consists in counting the number of the grains
completely sectioned along a predetermined length of segment, and
finding the mean value of the cut lengths as the grain size. The
standard deviation (.sigma.GS) is that of the grain size thus
obtained. The sectional structure normal to the rolling direction
as a scanning electron microscope (SEM) image is magnified 4,000
times, and each 50 .mu.m-long line segment is divided by the number
of points of intersections between the line and grain boundary to
find the grain size. For the purposes of the present invention, the
mean of the individual grain sizes so determined with 10 segments
is deemed as the mean grain size (mGS) and the standard deviation
of those grain sizes is deemed as the standard deviation
(.sigma.GS)
[0100] Bending workability (r/t) is determined in the following
way. Each test specimen, 10 mm wide and 100 mm long, is sampled in
the transverse direction to the rolling direction and subjected to
a W bend test (JIS H 3110) to various bend radii. The minimum bend
radius ratio (r (bend radius)/t (thickness of the specimen)) is
found at which a good outward appearance without fracture or orange
peel is obtained at or above Rank C of the evaluation standards
according to Japan Rolled Copper and Brass Association Technical
Standards JBMA T307: 1999. (According to the evaluation standards,
Rank A represents a product with no wrinkle; Rank B, slight
wrinkle; Rank C, much wrinkle; Rank D, slight fracture; and Rank E,
much fracture, Ranks A, B, C being evaluated as passable.) The axis
of bending in the W bend test is parallel to the rolling
direction.
1 TABLE 1 After anneal at 425.degree. C. for 2.7 .times. exp 10,000
sec (0.0436 .times. Sn) TS Composition mGS .phi.QS TS-YS 500 + 15
.times. Sn (82 m) (MPa) r/t (mass %) (.mu.m) (.mu.m) (MPa) (MPa)
Example 1 Cu-4. 2Sn-0.13P 4.9 0.8 7 563 3.2 556 0.5 of 2 Cu-6.
2Sn-0.13P 4.0 0.7 15 593 3.6 830 0.5 Invention 3 Cu-8. 0Sn-0.13P
3.9 0.6 4 620 3.0 733 2.0 4 Cu-10. 0Sn-0.13P 3.5 0.6 22 650 4.2 783
2.0 5 Cu-4. 2Sn-0.13P 2.3 0.6 5 563 3.2 600 0.5 6 Cu-6. 2Sn-0.13P
2.5 0.7 11 593 3.6 652 0.5 7 Cu-8. 0Sn-0.13P 1.5 0.4 4 620 3.8 753
2.0 8 Cu-10. 0Sn-0.13P 1.0 0.3 17 650 4.2 848 3.5 Comparative 1
Cu-4. 2Sn-0.13P 10 1.3 15 563 3.2 550 1.5 Example 2 Cu-6. 2Sn-0.13P
13 2.0 20 593 3.6 625 1.5 3 Cu-8. 0Sn-0.13P 14 1.5 8 620 3.8 728
3.0 4 Cu-10. 0Sn-0.13P 12 2.5 30 650 4.2 790 4.0 Comparative A
Cu-6. 2Sn-0.13P 3.9 1.6 15 593 3.6 627 1.5 Example B Cu-8.
0Sn-0.13P 4.2 0.7 104 620 3.0 715 3.0 C Cu-8. 0Sn-0.13P 15 2.0 117
620 3.8 118 3.5 Com. D Cu-8. 0Sn-0.13P 1.7 0.4 60 620 3.8 684 1.0
Inv. E Cu-8. 0Sn-0.13P 14 2.5 64 620 3.8 681 2.0
[0101] Table 1 shows Examples 1 to 8 of the present invention and
Comparative Examples 1-4 of the prior art materials. Also, in order
to explain the effects of the present invention, additional
examples A to E are shown as classified by way of convenience
according to varied parameters (Com. stands for Comparative Example
and Inv. stands for inventive examples).
[0102] A comparison between Comparative Examples 1 to 4 of the
prior art materials and Examples 1 to 4 and D of the present
invention shows that, while the composition and strength are the
same, Examples 1 to 4 and D of the present invention are improved
in bending workability with lower r/t values.
[0103] Example D of the invention is an example of a high TS-YS
value in (1) above (or an example aimed at clarifying the
definition of TS-YS.ltoreq.80, indicating that its bending
workability is improved over Comparative Example E of about the
same strength).
[0104] Examples 5 to 8 of the invention are examples in which the
grain sizes of Examples 1 to 4, respectively, were made finer. They
show that the strength is improved, the r/t is the same or smaller,
and the bending workability is enhanced through the adjustment of
the grain size according to the tin concentration in conformity
with mGS<2.7X exp (0.0436XSn).
[0105] Comparative Example A is inferior in bending workability to
Example 2 of the invention because its mGS satisfies the
requirement of (1) above but its .sigma.GS does not.
[0106] Comparative Example B is an example that satisfies the
requirement of (1) above as to both mGS and .sigma.GS but fails to
satisfy the TS-YS requirement. Although the grains after the
annealing are fine, the high TS-YS reduces strength and makes the
material about equal to the conventional material C in both
strength and bending workability, with no indication of
improvement.
[0107] Comparative Example C is mentioned by way of comparison with
Comparative Example B.
[0108] Comparative Example E is by way of comparison with
Comparative Example D.
(2) Example Series 2
[0109] (Examples Verifying the Inventions Defined in (4) and (5)
above)
[0110] Test specimens of compositions based on phosphor bronze
constituents with the addition of iron, nickel or the like were
made following the procedure of Example series 1.
[0111] The state of dispersion of precipitation and crystallization
products of the compounds formed by the particular kinds of
elements added was adjusted by appropriate choice of homogeneous
annealing conditions for the cast ingots.
[0112] Recrystallization annealing was adjusted under the
observation of the residual state of coarse precipitation and
crystallization products and the growth of the precipitation
products, along with the adjustment of the grains.
[0113] The numbers of particles of the precipitation and
recrystallization products 0.1 .mu.m or larger across were analyzed
and observed using an energy-distribution analyzer of a
field-emission scanning electron microscope.
[0114] Table 2 summarizes the results.
2 TABLE 2 After anneal at 425.degree. C. for No. of 10,000 sec.
sectnl 2.7 .times. exp Composition mGS .sigma.GS particl TS-YS 500
+ 15 .times. Sn (0.0436 .times. Sn) TS (mass %) (.mu.m) (.mu.m) *
(MPa) (MPa) (.mu.m) (MPa) r/t Inventive 9 Cu-4. 1Sn-0. 13P-0.
2Fe-0.5Zn 3.0 0.4 30 4 562 3.2 506 0.5 for 10 Cu-6. 1Sn-0. 13P-0.
5Ni-0.5Fe 4.3 0.6 55 13 592 3.5 644 0.5 Example 11 Cu-8. 2Sn-0.
13P-0. 5Mg 4.4 0.6 48 4 623 3.9 156 1.5 12 Cu-10. 2Sn-0. 13P-0.
8Ni-0.4Sl 4.7 0.7 67 20 653 4.2 783 2.0 13 Cu-4. 1Sn-0. 13P-0.
2Fe-0.5Zn 2.2 0.4 455 4 562 3.2 608 0.5 14 Cu-6. 1Sn-0. 13P-0.
5Ni-0.5Fe 2.5 0.4 150 10 592 3.5 687 0.5 15 Cu-8. 2Sn-0. 13P-0. 5Mg
1.2 0.3 220 4 623 3.9 789 2.0 16 Cu-10. 2Sn-0. 13P-0. 8Ni-0.8Si 0.9
0.2 240 16 653 4.2 855 3.5 Comparative 1 Cu-4. 2Sn-0. 13P 10 1.3 --
15 563 3.2 550 1.5 Example 2 Cu-6. 2Sn-0. 13P 13 2.0 -- 20 593 3.6
625 1.5 3 Cu-8. 0Sn-0. 13P 14 1.5 -- 8 620 3.8 728 3.0 4 Cu-10.
0Sn-0. 13P 12 2.5 -- 30 650 4.2 780 4.0 Inventive A Cu-6. 1Sn-0.
13P-0. 1Cr-0. 1Ti 1.6 0.3 420 14 592 3.5 701 1.0 Example B Cu-6.
1Sn-0. 13P-0. 2Cr-0. 1Zr 1.3 0.2 530 20 592 3.5 711 1.0 C Cu-6.
1Sn-0. 13P-0. 03Al-0. 2.5 0.7 160 12 592 3.5 669 0.5 3Mn D Cu-6.
1Sn-0. 13P-0. 03Ag-0. 2.4 0.6 150 8 592 3.5 664 0.5 2In E Cu-6.
1Sn-0. 13P-0. 1Be-0. 2.3 0.4 200 11 592 3.5 672 0.5 03Ca F Cu-6.
1Sn-0. 13P-0. 1Be-0. 2Ti 2.0 0.3 260 14 592 3.5 690 0.5 G Cu-6.
1Sn-0. 13P-0. 03Y-0. 1Nb 2.0 0.4 240 14 592 3.5 685 0.5 Comp H
Cu-6. 1Sn-0. 13P-2. 3Fe-0. 4Zn 1.4 0.4 540 15 592 3.5 762 4.5
[0115] Number of particles 0.1 .mu.m or larger per millimeter
square of a section cut in parallel with the rolling direction.
[0116] It is obvious from a comparison with the Cu-Sn-P alloys of
the present invention listed in Table 1 that the addition of minor
amounts of other elements makes the (.sigma.GS smaller and permits
further grain refinement in a stable manner and that the consequent
dispersion of the particles consisting of those elements adds
strength and enhances the bending workability.
[0117] Similar beneficial effects were confirmed with the alloys
that contained Cr, Ti, Zr, Nb, Al, Ag, Be, Ca, Y, Mn, or/and In.
Examples of those alloys are shown too as A to H in Table 2
(wherein Com. stands for Comparative Example and Inv. stands for
inventive example).
[0118] Comparative Example H is an example in which the total
amount of the auxiliary constituents exceeded 2.0 mass % and the
resulting alloy was inferior in bending workability.
(3) Example series 3
[0119] (Examples Verifying the Inventions Defined in (6), (7), (9),
and (10) above)
[0120] The compositions of Examples 17 to 20 of the present
invention correspond, respectively, to those of Examples 1 to 4 in
Table 1. Comparative Examples 5 to 8 are examples of conventional
materials. In order to demonstrate the effects of the present
invention, additional Examples A to F of altered parameters are
shown as classified separately by way of convenience (Com. stands
for Comparative Example and Inv. for inventive example). The
testing procedure was generally in conformity with that used in
Example series 1. Table 3 summarizes the results.
3 TABLE 3 After Reduction rate recrystallization of cold rolling
before anneal Reduction rate Composition recrystallization mGS
.sigma.GS of final cold TS (mass %) anneal (%) (.mu.m) (.mu.m)
rolling (%) (MPa) r/t Inventive 17 Cu-4. 2Sn-0. 13P 48 2.0 1.0 30
623 1.5 Example 18 Cu-6. 2Sn-0. 13P 50 1.8 1.2 25 110 1.0 19 Cu-8.
0Sn-0. 13P 50 1.6 1.0 25 746 1.5 20 Cu-10. 0Sn-0. 13P 60 1.1 0.1 30
901 4.0 Comparative 5 Cu-4. 2Sn-0. 13P 40 6.0 2.1 35 602 2.0
Example 6 Cu-6. 2Sn-0. 13P 40 8.2 2.3 30 652 1.0 7 Cu-8. 0Sn-0. 13P
44 5.0 2.2 25 680 2.0 8 Cu-10. 0Sn-0. 13P 40 4.2 2.1 30 805 3.5
Invention A Cu-8. 0Sn-0 .13P 50 2.6 1.2 25 718 1.5 B Cu-8. 0Sn-0.
13P 50 2.6 1.3 15 626 0 Comparative C Cu-8. 0Sn-0. 13P 40 2.8 2.2
25 710 2.0 Example D Cu-8. 0Sn-0. 13P 50 2.8 2.1 25 715 2.0 E Cu-8.
0Sn-0. 13P 50 2.7 1.3 5 550 0 F Cu-8. 0Sn-0. 13P 50 5.0 2.3 10 560
0
[0121] Comparative Examples 5 to 8 are examples of conventional
materials, with the reduction ratio of the cold rolling before the
final annealing and the mean grain size at the final annealing
being both outside the ranges specified under the invention.
Specimens of Examples 17 to 20 according to the present invention
showed greater strength, lower r/t, and better bending workability
than the coventional ones of Comparative Examples 5 to 8.
[0122] Example A of the invention meets the grain size requirement
of (6) above but not the requirement of (7) above in that the size
after the recrystallization annealing in Example 19 of the
invention was increased to 2.6. Example 19 in which the grain size
was smaller showed somewhat greater strength.
[0123] Example B of the invention is an example in which the
reduction ratio of the final cold rolling satisfied the requirement
of (6) above but was too low to meet the requirement of (7) above.
The bending workability was good in inverse proportion to the
strength.
[0124] Comparative Example C was inferior in bending workability to
Example A of the invention since the reduction ratio of the cold
rolling prior to recrystallization was low and, although the mGS
was made smaller by the recrystallization annealing, the grains
obtained was not fine or homogeneous, with wide scatter of grain
size (.sigma.GS).
[0125] Comparative Example D is an example that met both the
rolling reduction ratio and mGS requirements of (6) and (7) above
but failed to meet the .sigma.GS requirement because of a
unsuitable thermal condition during the recrystallization
annealing. The bending workability was unsatisfactory as in
Comparative Example C.
[0126] Comparative Example E is an example of a low reduction ratio
of final cold rolling. The strength was low, about the level of the
conventional material of Comparative Example F, and indicated no
ameliorating effect.
[0127] Comparative Example F is, as noted above, a conventional
example (with about the same TS and the same r/t as E).
(4) Example Series 4
[0128] (Investigations about the Effect of Stress Relief Annealing
According to (8) and (11) above)
[0129] Referring to Table 4, Examples 21 to 28 of the present
invention, as noted also in the table, correspond, respectively, to
Examples 2, 3, 4, 7, 8, 15, 16, and 20 of the invention mentioned
already, and Comparative Examples 9 to 12 (of conventional
materials) correspond to the above-mentioned Comparative Examples
3, 4, 7, and 8. Comparative Examples A and B, which are cited as
examples of low TS values decreased by the stress relief annealing,
correspond to Examples 16 and 20 of the invention.
[0130] Test specimens of these materials were annealed for stress
relief after varied conditions of different reduction ratio of
final cold rolling and then were evaluated for their properties.
The amounts of decrease in the tensile strength (TS) due to the
stress relief annealing are also given.
4 TABLE 4 Reduction percentage of final cold TS reduced by rolling
of stress-relief annealed stress relief TS specimen (%) annealing
(MPa) (MPa) r/t Example 21 Inventive Example 2 (25) 60 510 0 of the
22 Inventive Example 3 (25) 81 652 0 Invention 23 Inventive Example
4 (25) 35 748 1.5 24 Inventive Example 7 (25) 30 723 1.5 25
Inventive Example 8 (30) 44 804 2.5 26 Inventive Example 15 (25) 29
760 2.0 27 Inventive Example 16 (30) 57 798 2.5 28 Inventive
Example 20 (35) 52 849 3.0 Comparative A Inventive Example 16 (30)
14 841 3.0 Example B Inventive Example 20 (25) 15 886 3.5 9
Comparative Ex. 3 (30) 30 698 2.5 10 Comparative Ex. 4 (30) 84 706
3.0 11 Comparative Ex. 7 (25) 30 650 1.5 12 Comparative Ex. 8 (30)
82 762 3.0
[0131] Example 21 of the invention is a material with a tin
concentration of 6.2 mass %. Its tensile strength (TS) was 570 MPa
and bendng workability (r/t) was 0.
[0132] Examples 22, 24, and 26 of the present invention and
Comparative Examples 9 and 11 of conventional materials all ranged
in tin concentration from 8.0 to 8.2 mass %. However, the examples
of the invention exhibited tensile strength (TS) values from 652 to
760 MPa and bending workability (r/t) from 0 to 2.0, whereas the
comparative examples had tensile strength from 650 to 698 MPa and
r/t from 1.5 to 2.5, indicating that the materials according to the
invention had greater strength and better bending workability.
[0133] Examples 23, 25, 27, and 28 of the invention and Comparative
Examples 10 and 12 had about the same tin concentrations from 10.0
to 10.2 mass %. However, the examples of the invention showed
tensile strength (TS) values from 748 to 849 MPa and bending
workability (r/t) from 1.5 to 3.0, whereas the comparative examples
had tensile strength from 706 to 762 MPa and r/t of 3.0, indicating
again the superiority of the materials according to the invention
in both strength and bending workability.
[0134] Comparative Examples A and B had tensile strength (TS) from
841 to 886 MPa, but the amounts of the TS reduced by stress relief
annealing were small and the bending workability (r/t) values were
not much improved, in the range from 3.0 to 3.5.
[0135] As can be seen from the foregoing, the materials that have
been stress relief annealed in accordance with the present
invention are undoubtedly improved in strength and bending
workability over the conventional materials of the comparative
examples. The strength being about the same, the inventive
materials are remarkably improved in bending workability over the
comparative materials and, the bending workability being the same,
the strength is likewise greatly improved.
[0136] (Effects of the Invention)
[0137] Examples of the present invention thus demonstrate that the
invention makes it possible to impart great strength to copper
alloys, especially phosphor bronze type alloys, without adversely
affecting their bending workability. They also show that the
invention brings improvements in the properties required of copper
alloys for use in terminal connectors of electronic parts.
[0138] The invention further permits the advance of the high-tin
phosphor bronze (Cu-10 mass % Sn-P: CDA52400) in the market of
high-strength copper alloys that has hitherto denied its access on
the ground of poor bending workability and has been dominated by
beryllium coppers and the like.
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