U.S. patent application number 10/653352 was filed with the patent office on 2004-03-04 for high strength copper alloy and manufacturing method therefor.
Invention is credited to Sasaki, Fumiaki, Tsugane, Yozo.
Application Number | 20040042928 10/653352 |
Document ID | / |
Family ID | 31972927 |
Filed Date | 2004-03-04 |
United States Patent
Application |
20040042928 |
Kind Code |
A1 |
Sasaki, Fumiaki ; et
al. |
March 4, 2004 |
High strength copper alloy and manufacturing method therefor
Abstract
A high strength copper alloy is made of a prescribed material
composed of Cu and inevitable impurities as well as titanium (Ti)
at 0.1 to 4 weight percent, wherein it is possible to further
include at least one of Ag, Ni, Fe, Si, Sn, Mg, Zn, Cr, and P at a
prescribed weight percent ranging from 0.01 to 2 in total. In a
manufacturing method, the material is subjected to cold rolling,
precipitation treatment, and additional cold rolling sequentially,
wherein the reduction rate of the additional cold rolling is set to
3% or more, and the total reduction rate of the cold rolling and
the additional cold rolling ranges from 15% to 50%, so that a ratio
of yield strength versus tensile strength is set to 0.9 or more. In
addition, it is possible to perform stress relaxation annealing
after the additional cold rolling upon heating of the material for
a prescribed time.
Inventors: |
Sasaki, Fumiaki;
(Fukuroi-shi, JP) ; Tsugane, Yozo; (Asaba-cho,
JP) |
Correspondence
Address: |
DICKSTEIN SHAPIRO MORIN & OSHINSKY LLP
1177 AVENUE OF THE AMERICAS (6TH AVENUE)
41 ST FL.
NEW YORK
NY
10036-2714
US
|
Family ID: |
31972927 |
Appl. No.: |
10/653352 |
Filed: |
September 2, 2003 |
Current U.S.
Class: |
420/485 ;
148/432; 148/685; 420/492 |
Current CPC
Class: |
C22F 1/08 20130101; C22C
9/00 20130101 |
Class at
Publication: |
420/485 ;
148/685; 148/432; 420/492 |
International
Class: |
C22F 001/08; C22C
009/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 30, 2002 |
JP |
2002-255937 |
Claims
What is claimed is:
1. A high strength copper alloy composed of Cu and inevitable
impurities as well as titanium (Ti) at 0.1 to 4 weight percent,
which is produced by subjecting a material to cold rolling,
precipitation treatment, and additional cold rolling sequentially,
wherein a reduction rate of the additional cold rolling is set to
3% or more, and a total reduction rate of the cold rolling and the
additional cold rolling ranges from 15% to 50%, so that a ratio of
yield strength versus tensile strength is set to 0.9 or more.
2. A manufacturing method for a high strength copper alloy,
comprising the steps of: performing cold rolling on a copper alloy
material composed of Cu and irreversible impurities as well as
titanium at 0.4 to 4 weight percent; performing precipitation
treatment on the copper alloy material; and performing additional
cold rolling on the copper alloy material, wherein reduction rate
of the additional cold rolling is set to 3% or more, and total
reduction rate of the cold rolling and the additional cold rolling
ranges from 15% to 50%.
3. The manufacturing method of a high strength copper alloy
according to claim 2, further comprising the step of: performing
stress relaxation annealing after the additional cold rolling,
wherein the copper alloy material is heated to a temperature
ranging from 200.degree. C. to 700.degree. C. for a prescribed time
ranging from 0.5 hour to 15 hours.
4. The manufacturing method for a high strength copper alloy
according to claim 2, further comprising the step of: performing
stress relaxation annealing after the additional cold rolling,
wherein the copper alloy material is heated to a temperature
ranging from 300.degree. C. to 950.degree. C. for a prescribed time
ranging from 10 seconds to 1000 seconds.
5. The manufacturing method for a high strength copper alloy
according to any one of claims 2 to 4, wherein the copper alloy
material includes at least one of Ag, Ni, Fe, Si, Sn, Mg, Zn, Cr,
and P at a weight percent ranging from 0.01 to 2 in total, and
wherein Ni at a weight percent ranging from 0.01 to 0.04, and Si at
a weight percent ranging from 0.01 to 0.1.
6. A high strength copper alloy according to claim 1, wherein the
reduction rate of the additional cold rolling exceeds one third of
the reduction rate of the cold rolling.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to high strength copper alloys that
contain titanium (Ti) to realize high bend formability and high
yield strength. In addition, this invention also relates to
manufacturing methods for manufacturing high strength copper
alloys.
[0003] 2. Description of the Related Art
[0004] Conventionally, high strength titanium-contained copper
alloy is produced as shown in FIG. 4, in which a prescribed
material therefor is subjected to cold rolling and is then
subjected to solution treatment upon heating to a temperature
ranging from 750.degree. C. to 950.degree. C. for 1000 seconds and
is then subjected to final cold rolling processing; thereafter, it
is subjected to precipitation treatment upon heating to a
temperature ranging from 300.degree. C. to 700.degree. C. for a
prescribed time ranging from 0.5 hour to 15 hours, for example.
This conventional high strength copper alloy contains titanium (Ti)
at 2.9-3.5 weight percent, which may be defined by Japanese
Industrial Standards Code JISH3130C1990. This alloy can be used for
various components and connectors of electronic devices and
electric appliances. Due to recent progress of apparatuses and
machines in compactness and bend formability, it is necessary for
alloy materials to have high bend formability and high yield
strength. In order to realize high tensile strength, it may be
generally required to improve total reduction rate. As a result,
however, an alloy is increased in hardness, causing deterioration
of bend formability in manufacture. Bend formability may be
improved by reducing total reduction rate by sacrificing tensile
strength. The relationship between yield strength and total
reduction rate in final cold rolling is shown by a `solid` curve in
FIG. 3, in which a horizontal axis represents total reduction rate,
and a vertical axis represents a ratio between yield strength and
tensile strength. The total reduction rate is expressed as follows:
1 t 1 - t 2 t 1 .times. 100
[0005] where t1 denotes a plate thickness of a material after cold
rolling, and t2 denotes a plate thickness of a material after final
cold rolling.
[0006] As shown in FIG. 3, there is a problem in that when the
total reduction rate decreases, the yield strength correspondingly
decreases under the constant tensile strength.
SUMMARY OF THE INVENTION
[0007] It is an object of the invention to provide a high strength
copper alloy having high tensile strength and high yield strength
as well as superior bend formability.
[0008] It is another object of the invention to provide a
manufacturing method for manufacturing the aforementioned high
strength copper alloy.
[0009] A high strength copper alloy is made of a prescribed
material composed of Cu and inevitable impurities as well as
titanium (Ti) at 0.1 to 4 weight percent, wherein it is possible to
further include at least one of Ag, Ni, Fe, Si, Sn, Mg, Zn, Cr, and
P at a prescribed weight percent ranging from 0.01 to 2 in
total.
[0010] In a manufacturing method, the material is subjected to cold
rolling, precipitation treatment, and additional cold rolling
sequentially, wherein the reduction rate of the additional cold
rolling is set to 3% or more, and the total reduction rate of the
cold rolling and the additional cold rolling ranges from 15% to
50%, so that a ratio of yield strength versus tensile strength is
set to 0.9 or more.
[0011] In addition, it is possible to perform stress relaxation
annealing after the additional cold rolling, wherein the material
is heated to a temperature ranging from 200.degree. C. to
700.degree. C. for a prescribed time ranging from 0.5 hour to 15
hours, or it is heated to a temperature ranging from 300.degree. C.
to 950.degree. C. for a prescribed time ranging from 10 seconds to
1000 seconds.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] These and other objects, aspects, and embodiments of the
present invention will be described in more detail with reference
to the following drawings, in which:
[0013] FIG. 1 is a brief diagram showing a manufacturing process of
a high strength copper alloy in accordance with a first embodiment
of the invention;
[0014] FIG. 2 is a brief diagram showing a manufacturing process of
a high strength copper alloy in accordance with a second embodiment
of the invention;
[0015] FIG. 3 is a graph showing curves representing ratios of
yield strength versus tensile strength in copper alloys produced in
the present invention compared with a conventional art;
[0016] FIG. 4 shows a manufacturing process for a conventional high
strength copper alloy;
[0017] FIG. 5 is a table showing processing conditions of samples
compared with comparative samples; and
[0018] FIG. 6 is a table showing characteristics of samples
compared with comparative samples.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0019] This invention will be described in further detail by way of
examples with reference to the accompanying drawings.
[0020] FIG. 1 shows a manufacturing process for a high strength
copper alloy in accordance with a first embodiment of the present
invention. Herein, a copper alloy material containing titanium (Ti)
at 1 to 4 weight percent is subjected to cold rolling and is then
subjected to solution treatment upon heating to a temperature
ranging from 750.degree. C. to 950.degree. C. for a prescribed time
ranging from 10 seconds to 1000 seconds. Prior to precipitation,
cold rolling is performed on the material; thereafter,
precipitation treatment is performed at a temperature ranging from
300.degree. C. to 700.degree. C. for a prescribed time ranging from
0.5 hour to 15 hours. Thereafter, additional cold rolling is
performed on the material. Incidentally, the aforementioned
material is prepared by way of a vacuum melting furnace introducing
pure copper (Cu) and pure titanium (Ti) and is then cast into an
ingot having prescribed dimensions such as 50 mm thickness and 150
mm width, for example.
[0021] In the first embodiment, the reduction rate of the
additional cold rolling is set to 3% or more, so that the total
reduction rate may range from 15% to 50%. Thus, it is possible to
express an additional cold rolling reduction rate in accordance
with an equation 1, in which reference symbol t1 denotes a plate
thickness of a material produced by the cold rolling, t2 denotes a
plate thickness of a material produced by the cold rolling before
precipitation, and t3 denotes a plate thickness of a material
produced by the additional cold rolling, as follows: 2 Additional
cold rolling reduction rate = t 2 - t 3 t 2 .times. 100
[0022] In addition, the total reduction rate may be defined as the
total reduction rate counting the cold rolling before precipitation
and the additional cold rolling; therefore, it can be expressed in
an equation 2 as follows: 3 Total reduction rate = t 1 - t 3 t 1
.times. 100
[0023] The reasons why the additional cold rolling reduction rate
is set to 3% or more will be described below.
[0024] That is, if the additional cold rolling reduction rate is
less than 3%, it is necessary to increase the total reduction rate
in order to realize a high strength for a copper alloy, which,
however, results in deterioration of bend formability. Since the
reduction rate of the conventional art is substantially set to 0%,
the present embodiment becomes close to the conventional art in
property if the reduction rate is less than 3%, wherein in order to
produce yield strength matching 90% or more of the tensile
strength, it is necessary to increase the total reduction rate to
be 50% or more, whereas if the total reduction rate exceeds 50%, a
hardening process may be caused to occur intensely in cold rolling
so that a copper alloy product must be deteriorated in bend
formability. Thus, it is preferable for the present embodiment to
set the additional cold rolling reduction rate to be 3% or
more.
[0025] The reasons why the total reduction rate is set in a range
from 15% to 50% will be described below.
[0026] That is, if the total reduction rate is less than 15%, yield
strength becomes less than 90% of the tensile strength; in other
words, yield strength must be greatly decreased. In contrast, if
the total reduction rate exceeds 50%, a hardening process may be
caused to occur intensely in cold rolling so that a copper alloy
product must be deteriorated in bend formability. Thus, it is
preferable for the present embodiment to set the total reduction
rate in a range from 15% to 50%.
[0027] The present embodiment is characterized in that the
precipitation treatment is followed by the additional cold rolling;
in other words, the precipitation treatment is performed before the
final cold rolling (i.e., additional cold rolling). Thus, it is
possible to actualize a high yield strength in a copper alloy
product upon a reduced value of cold rolling reduction rate (or
total reduction rate).
[0028] A dotted curve shown in FIG. 3 represents the property of a
high strength copper alloy. Compared with the solid curve
representing the property of the conventional copper alloy, a value
of yield strength against the tensile strength is increased to be
higher and is therefore improved in the copper alloy of the present
embodiment at the same total reduction rate. FIG. 3 noticeably
shows that the present embodiment can offer a sufficient high value
of yield strength matching 90% of the tensile strength at a
lower-limit value of 15% of the total reduction rate.
[0029] As shown in FIG. 4, a Cu-Ti alloy is produced through
precipitation treatment that is performed generally at a relatively
high temperature, which results in a high heat resistance. The
present embodiment is characterized in that the additional cold
rolling is performed after the precipitation process, which may
present a possibility that the heat resistance will be reduced.
Actually, however, the copper alloy of the present embodiment can
demonstrate substantially the same heat resistance compared with
the conventional copper alloy. This is because dislocation due to
the additional cold rolling after the precipitation process may be
subjected to pinning by precipitates and be avoided.
[0030] As described above, the present embodiment can increase the
yield strength to match 90% or more of the tensile strength even
when the total reduction rate is 50% or less. When the copper alloy
of the present embodiment is compared with the conventional copper
alloy at the same total reduction rate, it is possible to actualize
the following advantages:
[0031] (i) It is possible to increase both the tensile strength and
yield strength.
[0032] (ii) It is possible to actualize the bend formability to
match that of the conventional copper alloy or higher.
[0033] (iii) It is possible to bend the material at a relatively
small bending radius.
[0034] In the conventional copper alloy (see the solid curve in
FIG. 3), it is necessary to increase the total reduction rate to be
50% or more in order to realize a sufficiently high yield strength
substantially matching 90% or more of the tensile strength. That
is, it is necessary to perform cold rolling with a relatively large
scale or power, which noticeably deteriorates bend formability. In
contrast, the present embodiment can offer a ratio of yield
strength versus tensile strength at 0.9 even when the total
reduction rate is set to 15%.
[0035] Next, a second embodiment of the present invention will be
described with reference to FIG. 2. Similar to the first embodiment
shown in FIG. 1, the second embodiment shown in FIG. 2 performs
cold rolling, solution treatment, cold rolling before
precipitation, precipitation treatment, and additional cold rolling
in turn. The second embodiment is characterized by performing
stress relaxation annealing after the additional cold rolling,
wherein an alloy coil is put into a batch type furnace in which it
is heated to a temperature ranging from 200.degree. C. to
700.degree. C. for a prescribed time ranging from 0.5 hour to 15
hours; preferably, it is heated to a temperature of 350.degree. C.
for three hours, for example. Alternatively, an alloy coil is put
into a continuous furnace in which it is heated to a temperature
ranging from 300.degree. C. to 950.degree. C. for 10 seconds to
1000 seconds; preferably, it is heated to a temperature of
500.degree. C. for 30 seconds, for example.
[0036] Since the second embodiment performs stress relaxation
annealing after the additional cold rolling under the
aforementioned conditions, it is possible to improve spring
characteristics (e.g., spring limit values), which have been
slightly reduced in the additional cold rolling. Therefore, it is
possible to obtain relatively high spring limit values while
securing relatively high bend formability and relatively high yield
strength.
[0037] The aforementioned stress relaxation annealing is performed
for the purpose of improvements of spring characteristics without
deteriorating the material in strength, conductivity, and bend
formability. Specifically, the batch type furnace or continuous
furnace is used to perform the stress relaxation annealing. In the
batch type furnace, heating is performed at a temperature ranging
from 200.degree. C. to 700.degree. C. for 0.5 hour to 15 hours.
This is because it is difficult to improve spring characteristics,
which have been reduced in the additional cold rolling, at a
relatively low temperature less than 200.degree. C., and yield
strength must be reduced due to progress of recrystallization at a
relatively high temperature higher than 700.degree. C. In addition,
it is difficult to expect uniform annealing progressed in the batch
type furnace when annealing is performed only for 0.5 hour.
Furthermore, aging must be progressed too rapidly to realize
improvement of spring characteristics so that bend formability must
be deteriorated when annealing is performed for 15 hours or
more.
[0038] In the continuous furnace, heating is performed at a
temperature ranging from 300.degree. C. to 900.degree. C. for 10
seconds to 1000 seconds. This is because when the heating
temperature is less than 300.degree. C., heating must be performed
for a long time, resulting in a reduction of productivity, wherein
it is difficult to improve spring characteristics, which have been
reduced in the additional cold rolling, when heating temperature is
very low. In addition, when heating temperature is higher than
900.degree. C., solution treatment is progressed so rapidly that
yield strength and conductivity are reduced. Furthermore, when
heating is performed for a short time less than 10 seconds, the
material cannot be sufficiently heated so that spring
characteristics cannot be improved. When heating is performed for a
long time greater than 1000 seconds, productivity must be
reduced.
[0039] The copper alloy has a prescribed composition including
titanium (Ti) at 0.1 to 4 weight percent. If the titanium content
is appropriately set, it may be possible to produce a copper alloy
having a high strength because the titanium content is increased so
that an amount of precipitation hardening must be increased during
manufacturing processes. However, conductivity and bend formability
must be reduced, so that productivity must be correspondingly
reduced. That is, when the titanium content is less than 0.1 weight
percent, a copper alloy must be decreased in strength because of a
relatively small amount of precipitation hardening. When it exceeds
4 weight percent, a copper alloy must be deteriorated in
characteristics so that productivity must be decreased. Because of
the aforementioned reasons, the titanium content is set in a range
from 0.1 to 4 weight percent.
[0040] In the second embodiment, it is possible to selectively use
at least one of Ag, Ni, Fe, Si, Sn, Mg, Zn, Cr, and P, which can be
contained in the material at a ratio ranging from 0.01 to 2 weight
percent in total. These elements may present an improvement of the
strength of Cu-Ti alloy due to precipitation hardening and solid
solution hardening. When the total of these elements is less than
0.01 weight percent, it is very difficult to obtain the
aforementioned effect. When it exceeds 2 weight percent, these
elements must deteriorate reduction rate in production of Cu--Ti
alloy, which may result in reduction of conductivity and bend
formability.
[0041] Next, characteristics of the embodiments will be described
in detail upon comparison between samples (corresponding to the
embodiments) and comparative samples that do not match the
embodiments in compositions and processing conditions.
[0042] As a material, pure Cu and pure Ti are adequately blended
together and are then introduced into a vacuum melting furnace,
thus producing an ingot having prescribed dimensions such as 50 mm
thickness and 150 mm width. The material is heated up to
900.degree. C. and subjected to homogenization; then, the material
is subjected to solution treatment upon heating to a temperature of
900.degree. C. for 70 to 200 seconds. Then, cold rolling before
precipitation is performed under prescribed conditions, which are
shown in FIG. 5. Then, the material is subjected to precipitation
treatment upon heating at a temperature of 450.degree. C. for 6
hours; thereafter, the additional cold rolling after precipitation
is performed under prescribed conditions shown in FIG. 5. Thus, it
is possible to produce samples 1-11 (corresponding to the
embodiments), each of them is subjected to additional cold rolling
to realize a plate thickness of 0.30 mm after final cold rolling.
In addition, comparative samples 12-22 are also produced without
performing additional cold rolling, wherein each of them is
subjected to cold rolling before precipitation to realize a plate
thickness of 0.30 mm after final cold rolling. In the above,
samples 8-11 (corresponding to the embodiments) and comparative
samples 19-20 are subjected to stress relaxation annealing after
additional cold rolling.
[0043] Characteristics of copper alloys that are produced as
samples 1-11 and comparative samples 12-22 are shown in FIG. 6,
wherein assessments using Japanese Industrial Standards (JIS) are
performed with respect to tensile strength according to JIS-Z2241,
yield strength according to JIS-Z2241 (allowing 0.2% offset in
yield strength), elongation according to JIS-Z2241 (breaking
elongation), conductivity according to JIS-H0505, spring
characteristics according to JIS-H3130 (spring limit values), bend
formability according to JIS-H3130 (W bending), and heat resistance
according to stress relaxation characteristics, for example.
Incidentally, the bend formability is assessed through the
observation of the exterior of a bent portion upon estimation of a
minimum bent radius causing no crack at a prescribed total
reduction rate, as follows:
[0044] (i) If no crack occurs even when a sample is bent at a
certain radius, identical to that of the conventional alloy or
less, the assessment result is "fine" (denoted by `.largecircle.`
in FIG. 6) in bend formability.
[0045] (ii) If cracks occur when a sample is bent at a greater
radius, the assessment result is "not good" (denoted by `X` in FIG.
6) in bend formability.
[0046] In addition, the stress relaxation characteristics are
assessed under prescribed conditions in which each sample is formed
in 10 mm width and L mm length, and is wound about an instrument
having a radius r, to which a certain stress is applied and which
is heated to 230.degree. C. for 1000 hours; thus, a degree of
stress relaxation is expressed in percent.
[0047] FIG. 6 shows that each of samples 1-4 and 7-11 is superior
in both tensile strength and yield strength in comparison with
comparative samples at the same total reduction rate, wherein a
ratio of yield strength versus tensile strength is 0.9 or more. In
addition, each of them is also superior in bend formability, which
is equal or high than that of the comparative sample. Furthermore,
each of them is superior in heat resistance as well. Each of
samples 5-6 may be somewhat weak in tensile strength and yield
strength because of a reduction of titanium content, wherein
similar to the aforementioned samples, each of them has a
relatively high ratio of yield strength versus tensile strength,
which is 0.9 or more. As shown in FIG. 5, each of samples 8-11 is
subjected to stress relaxation annealing; therefore, each of them
is superior in spring limit value in comparison with the foregoing
samples 1-7 while securing high yield strength and high bend
formability.
[0048] Comparative sample 12 has a relatively low ratio of yield
strength versus tensile strength, which is 0.88, because of a
relatively low additional cold rolling reduction rate that is 2%
(see FIG. 5). Comparative example 13 offers relatively low
elongation and relatively low conductivity because of a relatively
high total reduction rate that is 70%.
[0049] Each of comparative samples 14-18 substantially corresponds
to the conventional alloy that is produced without performing
additional cold rolling, wherein each of them is reduced in a ratio
of yield strength versus tensile strength, and it offers very small
elongation.
[0050] Comparative sample 19 cannot demonstrate improvement in
spring characteristics because of a relatively low temperature in
stress relaxation annealing. In contrast, comparative sample 20 not
only has improved spring characteristics but also degraded bend
formability due to progress of aging because of the relatively long
time in stress relaxation annealing.
[0051] Comparative sample 21 is reduced in strength because of a
relatively small titanium content and is also reduced in heat
resistance. Comparative sample 22 is reduced in both tensile
strength and yield strength because of a relatively high titanium
content and is remarkably reduced in bend formability.
[0052] As described heretofore, this invention have a variety of
effects and technical features, which will be described below.
[0053] (1) It is possible to produce a copper alloy that is
increased in tensile strength and yield strength, wherein it is
possible to increase a ratio of yield strength versus tensile
strength. That is, it is possible to produce a high strength copper
alloy having superior bend formability, which is also improved in
spring characteristics due to stress relaxation annealing.
[0054] (2) Specifically, a high strength copper alloy of this
invention contains titanium (Ti) at 0.4 to 4 weight percent,
wherein it is basically composed of copper (Cu) and inevitable
impurities. That is, a prescribed material is subjected to cold
rolling and precipitation treatment, and is then subjected to
additional cold rolling. Herein, the reduction rate of the
additional cold rolling is set to 3% or more, and the total
reduction rate for the cold rolling and additional cold rolling is
set in a range from 15% to 50%, for example. Thus, it is possible
to realize a relatively high ratio of yield strength versus tensile
strength, which is 0.9 or more.
[0055] (3) In addition, at least one of Ag, Ni, Fe, Si, Sn, Mg, Zn,
Cr, and P can be selectively introduced into a high strength copper
alloy at a prescribed weight percent ranging from 0.01% to 2%, for
example.
[0056] (4) After the additional cold rolling, the material can be
subjected to stress relaxation annealing in which it is heated to a
temperature ranging from 200.degree. C. to 700.degree. C. for 0.5
hour to 15 hours, or it is heated to a temperature ranging from
300.degree. C. to 950.degree. C. for a prescribed time ranging from
10 seconds to 1000 seconds, for example.
[0057] As this invention may be embodied in several forms without
departing from the spirit or essential characteristics thereof, the
present embodiments are therefore illustrative and not restrictive,
since the scope of the invention is defined by the appended claims
rather than by the description preceding them, and all changes that
fall within metes and bounds of the claims, or equivalents of such
metes and bounds are therefore intended to be embraced by the
claims.
* * * * *