U.S. patent application number 12/532929 was filed with the patent office on 2010-04-08 for cu-ni-si system alloy for electronic materials.
This patent application is currently assigned to Nippon Mining & Metals Co., Ltd.. Invention is credited to Naohiko Era.
Application Number | 20100086435 12/532929 |
Document ID | / |
Family ID | 39830918 |
Filed Date | 2010-04-08 |
United States Patent
Application |
20100086435 |
Kind Code |
A1 |
Era; Naohiko |
April 8, 2010 |
Cu-Ni-Si SYSTEM ALLOY FOR ELECTRONIC MATERIALS
Abstract
An object of the present invention is to provide a Corson alloy
having significantly improved characteristics, i.e. high strength
and high electrical conductivity, by enhancing the effect of
addition of Cr to a Cu--Ni--Si system alloy. There is provided a
copper alloy for electronic materials comprising 1.0-4.5% by mass
Ni, 0.50-1.2% by mass Si, 0.003-0.3% by mass Cr wherein the weight
ratio of Ni to Si satisfies the expression:
3.ltoreq.Ni/Si.ltoreq.5.5, and the balance being Cu and incidental
impurities, wherein particles of Cr--Si compounds having a size of
0.1 .mu.m to 5 .mu.m are dispersed in the alloy and the dispersed
particles having an atomic concentration ratio of Cr to Si of 1 to
5 and a dispersion density of no more than
1.times.10.sup.6/mm.sup.2.
Inventors: |
Era; Naohiko; (Ibaraki,
JP) |
Correspondence
Address: |
DRINKER BIDDLE & REATH;ATTN: INTELLECTUAL PROPERTY GROUP
ONE LOGAN SQUARE, 18TH AND CHERRY STREETS
PHILADELPHIA
PA
19103-6996
US
|
Assignee: |
Nippon Mining & Metals Co.,
Ltd.
Tokyo
JP
|
Family ID: |
39830918 |
Appl. No.: |
12/532929 |
Filed: |
March 28, 2008 |
PCT Filed: |
March 28, 2008 |
PCT NO: |
PCT/JP08/56138 |
371 Date: |
September 24, 2009 |
Current U.S.
Class: |
420/476 ;
420/485; 420/487 |
Current CPC
Class: |
C22F 1/08 20130101; C22F
1/02 20130101; H01B 1/026 20130101; C22F 1/00 20130101; C22C 9/06
20130101 |
Class at
Publication: |
420/476 ;
420/485; 420/487 |
International
Class: |
C22C 9/06 20060101
C22C009/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2007 |
JP |
2007-094441 |
Claims
1. A copper alloy for electronic materials, comprising 1.0-4.5% by
mass Ni, 0.50-1.2% by mass Si, 0.003-0.3% by mass Cr wherein the
weight ratio of Ni to Si satisfies the expression:
3.ltoreq.Ni/Si.ltoreq.5.5, and the balance being Cu and incidental
impurities, wherein particles of Cr--Si compounds having a size of
0.1 .mu.m to 5 .mu.m are dispersed in the alloy, the dispersed
particles having an atomic concentration ratio of Cr to Si in the
range of 1 to 5 and a dispersion density of no more than
1.times.10.sup.6/mm.sup.2.
2. The copper alloy for electronic materials according to claim 1,
wherein the dispersion density of the particles of the Cr--Si
compounds having a size of 0.1 .mu.m to 5 .mu.m is higher than
1.times.10.sup.4/mm.sup.2.
3. The copper alloy for electronic materials according to claim 1,
further comprising 0.05-2.0% by mass of at least one element
selected from Sn and Zn.
4. The copper alloy for electronic materials according to claim 1,
further comprising 0.001-2.0% by mass of at least one element
selected from Mg, Mn, Ag, P, As, Sb, Be, B, Ti, Zr, Al, Co and
Fe.
5. A wrought copper product comprising the copper alloy according
to any one of claims 1 to 4.
6. A component for electronic devices, comprising the copper alloy
according to any one of claims 1 to 4.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to precipitation hardening
copper alloys, and in particular, to Cu--Ni--Si--Cr system alloys
suitable for use in components for various electronic devices.
BACKGROUND OF THE INVENTION
[0002] Copper alloys for electronic materials used in components
for various electronic devices such as lead frames, connectors,
pins, terminals, relays, and switches must satisfy both high
strength and high electrical conductivity (or high thermal
conductivity) as basic characteristics. Recent rapid advances of
high integration and reductions in size and thickness of electronic
components have accelerated requirements for higher performances of
copper alloys used in components for electronic devices.
[0003] In recent years, in consideration of high strength and high
electrical conductivity of copper alloys for electronic materials,
the use of precipitation hardening copper alloys has increased, in
place of traditional solid solution strengthened copper alloys such
as phosphor bronze and brass. In the precipitation hardening copper
alloys, age hardening of supersaturated solid solution after
solution treatment facilitates uniform dispersion of fine
precipitates and thus an increase in strength of the alloys. It
also leads to a decrease in amount of solute elements in copper
matrix and thus an improvement in electrical conductivity. The
resulting materials have superior mechanical properties such as
strength and spring properties, as well as high electrical and
thermal conductivities.
[0004] Among precipitation hardening copper alloys, Cu--Ni--Si
copper alloys known as Corson alloys are typical copper alloys
having compatibility of relatively high electrical conductivity and
strength, proper stress relaxation, and excellent bendability.
Corson alloys are now being actively developed in the industry. In
such copper alloys, fine particles of a NiSi intermetallic compound
are precipitated in a copper matrix, thereby improving strength and
electrical conductivity.
[0005] The precipitation of a NiSi intermetallic compound generally
has a stoichiometric composition. For example, Japanese Unexamined
Patent Application Publication No. 2001-207229 discloses that
satisfactory electrical conductivity is achieved by bringing the
mass ratio Ni/Si in an alloy close to the mass composition ratio of
the intermetallic compound Ni.sub.2Si [(Ni atomic
weight).times.2/(Si atomic weight).times.1)], i.e. a weight
concentration ratio of Ni/Si in the range of 3 to 7.
[0006] Although characteristics may be improved by bringing the
mass ratio Ni/Si close to the mass composition ratio of the
intermetallic compound Ni.sub.2Si [(Ni atomic weight).times.2/(Si
atomic weight.times.1)] as mentioned in Japanese Unexamined Patent
Application Publication No. 2001-207229, the presence of an excess
amount of Si leads to some reductions in electrical conductivity. A
possible countermeasure to increase the electrical conductivity is
addition of elements that form compounds with excess Si. Cr is one
of these elements, and forms Cr-containing Cu--Ni--Si system
alloys.
[0007] Examples of the Cu--Ni--Si system alloys containing Cr as an
alloy element are disclosed in Japanese Patent Nos. 2862942 and
3049137. Japanese Patent No. 2862942 discloses a method of heat
treatment of a Corson alloy containing 1.5-4.0% by weight of Ni,
0.35-1.0% by weight of Si, optionally 0.05-1.0% by weight of at
least one metal selected from the group consisting of Zr, Cr, and
Sn, and the balance being Cu and incidental impurities, wherein the
Corson alloy is heated (or cooled) in the temperature range of 400
to 800.degree. C., so as to reduce the tensile thermal strain of
the Corson alloy to a level not exceeding 1.times.10.sup.-4. The
patent states that the method can prevent an ingot from cracking
during the heat treatment.
[0008] Japanese Patent No. 3049137 discloses a high strength copper
alloy containing 2-5% by weight of Ni, 0.5-1.5% by weight of Si,
0.1-2% by weight of Zn, 0.01-0.1% by weight of Mn, 0.001-0.1% by
weight of Cr, 0.001-0.15% by weight of Al, 0.05-2% by weight of Co,
not more than 15 ppm of S as an impurity, and the balance being Cu
and incidental impurities. This copper alloy exhibits excellent
bendability. This patent states that Cr is an element which
reinforces grain boundaries in an ingot and leads to an improvement
in hot workability. It also states that a Cr content exceeding 0.1%
by weight causes oxidation of molten metal and poor casting
performance. In addition, it states that the copper alloy is
covered with charcoal in a cryptol furnace to be melted and cast in
the atmosphere.
[0009] A compound of Cr and Si is disclosed in Japanese Unexamined
Patent Application Publication No. 2005-113180. This patent refers
to the hot working temperature and heat treatment temperature for
age hardening of an ingot of a copper alloy having excellent
etching and punching workability for electronic devices. The copper
alloy contains 0.1-0.25% by weight of Cr, 0.005-0.1% by weight of
Si, 0.1-0.5% by weight of Zn, 0.05-0.5% by weight of Sn, and the
balance being Cu and incidental impurities, wherein the weight
ratio Cr/Si is in the range of 3 to 25, particles of Cr--Si
compounds having a size of 0.05 .mu.m to 10 .mu.m are present in a
number density of 1.times.10.sup.3 to 5.times.10.sup.5/mm.sup.2 in
the copper matrix while particles of Cr compounds (other than the
Cr--Si compound) having a size greater than 10 .mu.m are not
present. According to this method, both etching and punching
workability are preferably available.
SUMMARY OF THE INVENTION
[0010] Rapid advances of high integration and reductions in size
and thickness of electronic components in recent years have also
placed a requirement on Cr-containing Cu--Ni--Si system alloys to
have significantly improved performance. In Japanese Unexamined
Patent Application Publication No. 2001-207229, Cr is not added and
the excess Ni and Si actually reduce electrical conductivity in
some degree. This means the significant progress in performance is
unfulfilled yet. Although Cr is added in Cu--Ni--Si system alloys
in Japanese Patent Nos. 2862942 and 3049137, it is added for solid
solution hardening in Japanese Patent No. 2862942 and for an
improvement in hot workability in Japanese Patent No. 3049137. No
description of Cr--Si compounds, which is a key component of the
present invention, is found in these documents. Accordingly, these
patent documents do not suggest the solution achieved by the
present invention.
[0011] Although Japanese Unexamined Patent Application Publication
No. 2005-113180 discloses that etching and punching workabilities
are improved by controlling the number density and size of the
Cr--Si compounds, consideration is focused on the conditions for
the formation of the Cr--Si compounds and no consideration is paid
for the formation of NiSi compounds because no Ni is added.
Accordingly, Japanese Unexamined Patent Application Publication No.
2005-113180 also does not suggest the solution achieved by the
present invention.
[0012] An object of the present invention is to provide a Corson
alloy having significantly improved characteristics, i.e. high
strength and high electrical conductivity, by enhancing the effect
of Cr contained in a Cu--Ni--Si system alloy.
[0013] Through extensive research for solving the problem, the
inventors have accomplished an invention as described below. In a
Cu--Ni--Si system alloy, the Si content is in excess of the Ni
content so that nickel silicide is surely precipitated from the
contained Ni in order to improve the strength, while the excess Si
is combined with the contained Cr to achieve high conductivity of
the alloy. The essence of the present invention is to control the
excess growth of particles of Cr--Si compounds so as to prevent a
shortage of Si, which combines with Ni. In particular, the
inventors have found that the control of the temperature and
cooling rate of the heat treatment can enhance such effects,
through investigation on the preferred composition, size, and
number density of particles of the Cr--Si compounds.
[0014] The present invention includes the following Aspects:
[0015] (1) A copper alloy for electronic materials, comprising
1.0-4.5% by mass Ni, 0.50-1.2% by mass Si, 0.003-0.3% by mass Cr
(wherein the weight ratio of Ni to Si satisfies the expression:
3.ltoreq.Ni/Si.ltoreq.5.5), and the balance being Cu and incidental
impurities, wherein particles of Cr--Si compounds having a size of
0.1 .mu.m to 5 .mu.m are dispersed in the alloy, the dispersed
particles having an atomic concentration ratio of Cr to Si of 1 to
5 and a dispersion density of no more than
1.times.10.sup.6/mm.sup.2.
[0016] (2) The copper alloy for electronic materials according to
Aspect (1), wherein the dispersion density of the particles of the
Cr--Si compounds having a size of 0.1 .mu.m to 5 .mu.m is higher
than 1.times.10.sup.4/mm.sup.2.
[0017] (3) The copper alloy for electronic materials according to
Aspect (1) or (2), further comprising 0.05-2.0% by mass of at least
one element selected from Sn and Zn.
[0018] (4) The copper alloy for electronic materials according to
any one of Aspects (1) to (3), further comprising 0.001-2.0% by
mass of at least one element selected from Mg, Mn, Ag, P, As, Sb,
Be, B, Ti, Zr, Al, Co and Fe.
[0019] (5) A wrought copper product comprising the copper alloy
according to any one of Aspects (1) to (4).
[0020] (6) A component for electronic devices, comprising the
copper alloy according to any one of Aspects (1) to (4).
[0021] The present invention can provide the Corson copper alloy
having significantly improved strength and electrical conductivity
suitable for electronic materials due to the positive effect of Cr,
which is an element contained in the alloy.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Amounts of Ni and Si to be Added
[0022] Ni and Si form nickel silicides (e.g. Ni.sub.2Si) as an
intermetallic compound through suitable heat treatment, resulting
in high strength without a decrease in conductivity. The mass ratio
of Ni to Si is preferably close to the stoichiometric ratio as
described above, i.e. 3.ltoreq.Ni/Si.ltoreq.5.5, more preferably
3.5.ltoreq.Ni/Si.ltoreq.5.0.
[0023] However, even if the ratio Ni/Si is within the range,
desired strength is not achieved at a Si content of less than 0.5%
by mass. Furthermore, a Si content of more than 1.2% by mass is not
preferred because of significantly reduced conductivity and poor
hot workability due to formation of a liquid phase in a segregation
region, despite enhanced strength. As a result, the preferred Si
content is in the range of 0.5% to 1.2% by mass, preferably 0.5% to
0.8% by mass. The amount of Ni to be added may be determined so as
to satisfy the preferable ratio described above. In view of balance
with the Si content, the suitable Ni content is in the range of
2.5% to 4.5% by mass, preferably 3.2% to 4.2% by mass, more
preferably 3.5% to 4.0% by mass.
Amount of Cr to be Added
[0024] In general Cu--Ni--Si system alloys, increased
concentrations of Ni and Si raise the total number of precipitated
particles, and thus enhance strength through precipitation
strengthening. Such increased concentrations, however, are
accompanied by an increased amount of solid solution that does not
contribute to precipitation. This causes a reduction in
conductivity at a maximum strength, regardless of an increase in
the maximum strength after age precipitation. In this regard, when
0.003% to 0.3% by mass of, preferably 0.01% to 0.1% by mass of Cr
is added to the Cu--Ni--Si system alloy, higher conductivity can be
achieved without a reduction in strength compared to a Cu--Ni--Si
system alloy having the same Ni--Si concentrations. Furthermore, a
higher yield can be achieved due to improved hot workability.
[0025] Regarding the composition of particles precipitated in the
Cr-containing Cu--Ni--Si system alloy, particles primarily composed
of elemental Cr having a bcc structure are readily precipitated as
well as particles of Cr--Si compounds. Since Cr can easily
precipitate chromium silicides (e.g. Cr.sub.3Si) in the copper
matrix through proper heat treatment, the dissolved Si component,
which has not precipitated in the form such as Ni.sub.2Si during a
combined process of solution treatment, cold rolling and aging, can
be precipitated as Cr--Si compounds. This process can suppress a
reduction in conductivity caused by the dissolved Si and thus
achieve high conductivity without a reduction in strength.
[0026] A low concentration of Si in Cr particles leads to residual
Si in the matrix, resulting in a reduction in conductivity. On the
other hand, a high concentration of Si in Cr particles causes a
decreased concentration of Si contributing to precipitation of
particles of a NiSi compound, resulting in a reduction in strength.
Furthermore, a high concentration of Si in Cr particles accelerates
formation of coarse Cr--Si particles, resulting in decreases in
bendability and fatigue strength. Moreover, a lower cooling rate
after solution treatment and excess heating treatment for aging
cause coarsening of particles of the Cr--Si compounds. This causes
a decrease in Si concentration necessary for formation of a NiSi
compound and thus precludes the formation of a NiSi compound
contributing to strength. This is because diffusion rates in Cu of
Si and Cr are higher than that of Ni, which accelerates coarsening
of particles of the Cr--Si compounds. The precipitation rate of
Cr--Si compounds is thus higher than that of NiSi compounds.
[0027] The composition, size and density of particles of the Cr--Si
compounds can, therefore, be controlled by regulating the cooling
rate after solution treatment and avoiding severer aging conditions
such as higher temperature and longer time than the optimum
conditions for maximum strength. Consequently, the Cr concentration
should be 0.003% by mass to 0.3% by mass, and the atomic ratio of
Cr to Si in Cr--Si compounds should be in the range of 1 to 5.
[0028] Since Cr is preferentially precipitated at crystal grain
boundaries in the cooling process after melting and casting, it can
strengthen the grain boundaries. As a result, cracking during hot
working can be reduced, and thus a high yield can be achieved.
Although Cr precipitated at grain boundaries after melting and
casting is redissolved during the solution treatment, it forms
silicides during the subsequent age precipitation process. In
general Cu--Ni--Si system alloys, part of the added Si does not
contribute to age precipitation and remains dissolved in the
matrix, obstructing an increase in conductivity. Since the addition
of Cr, which is an element to form silicides, leads to further
precipitation of silicides and a reduction in dissolved Si, the
conductivity can be increased without a reduction in strength,
compared to conventional Cu--Ni--Si system alloys.
Size and Dispersion Density of Particles of Cr--Si Compounds
[0029] The size of particles of the Cr--Si compounds has an effect
on bendability and fatigue strength. When the particles of the
Cr--Si compounds have a size of greater than 5 .mu.m or when the
dispersion density of particles of the Cr--Si compounds having a
size in the range of 0.1 to 5 .mu.m exceeds
1.times.10.sup.6/mm.sup.2, the bendability and the fatigue strength
are significantly reduced. Furthermore, since the number density
has an effect on the excess and deficiency of the concentration of
Si in the matrix, the presence of large particles dispersed in
large quantities will become an obstacle to the desired strength.
Consequently, the upper limit of the dispersion density is
1.times.10.sup.6/mm.sup.2, preferably 5.times.10.sup.5/mm.sup.2,
more preferably 1.times.10.sup.5/mm.sup.2. In addition, it is
preferred that the density be more than 1.times.10.sup.4/mm.sup.2,
in order to achieve the significant effect of the addition of
Cr.
Sn and Zn
[0030] Addition of at least one element selected from Sn and Zn in
a total amount of 0.05-2.0% by mass to the Cu--Ni--Si system alloy
of the present invention can improve stress relaxation and other
characteristics without significant reductions in strength and
conductivity. An amount of less than 0.05% by mass leads to
insufficient effect of addition. On the other hand, an amount of
more than 2.0% by mass causes poor production characteristics such
as castability and hot workability and low conductivity of the
products. It is therefore preferred that the amount of these
elements should be added from 0.05% by mass to 2.0% by mass.
Other Elements to be Added
[0031] Addition of appropriate amounts of Mg, Mn, Ag, P, As, Sb,
Be, B, Ti, Zr, Al, Co and Fe brings about various effects that are
complementary to each other, for example, enhanced strength and
conductivity, and improved production characteristics such as
bendability, plating property, and hot workability of an ingot due
to the formation of a fine microstructure. Accordingly, at least
one element selected from these elements may be added as necessary
in a total amount of 2.0% by mass or less to the Cu--Ni--Si system
alloy of the present invention, to meet required properties. An
amount of less than 0.001% by mass cannot achieve the desired
effects. On the other hand, an amount of more than 2.0% by mass
causes a significant decrease in conductivity and poor production
characteristics. Accordingly, the total amount of the elements to
be added is preferably 0.001 to 2.0% by mass, more preferably 0.01
to 1.0% by mass. Incidentally, elements not specified in this
specification may be added in a range causing no negative effect on
the characteristics of the Cu--Ni--Si system alloy of the present
invention.
[0032] The method of producing alloys of the present invention is
described below. The Cu--Ni--Si system alloy of the present
invention can be produced by any conventional method, except for
conditions of solution treatment and aging treatment for control of
Ni--Si compounds and Cr--Si compounds. Although no specific
explanation would be necessary for those skilled in the art who can
select an optimal method depending on the composition and required
properties, a typical method is described below for illustrative
purposes.
[0033] First, raw materials such as electrolytic copper, Ni, Si,
and Cr are melted in a melting furnace in atmosphere to obtain
molten metal having a desired composition. Next, this molten metal
is cast into an ingot. Through subsequent hot-rolling and repeated
processes of cold-rolling and heat treatment, strips and foils
having a desired thickness and properties are formed. The heat
treatment includes solution treatment and aging treatment. In the
solution treatment, the Ni--Si compounds and the Cr--Si compounds
are dissolved into the copper matrix while the copper matrix is
recrystallized at the same time, during heating at a high
temperature of 700 to 1000.degree. C. The hot rolling may combine
with the solution treatment.
[0034] The important factors in the solution treatment are a
heating temperature and a cooling rate. In conventional methods,
the cooling rate after heating was not controlled, and
water-cooling using a water tank provided at a furnace outlet or
air-cooling in the atmosphere was employed. In that case, the
cooling rate easily varied depending on the set heating
temperature. The conventional cooling rate varied in a wide range
of 1.degree. C./s or less to 10.degree. C./s or more. Consequently,
in the conventional cooling, it was difficult to control properties
of alloys, such as an alloy of the present invention.
[0035] Preferably the cooling rate is in the range of 1.degree.
C./s to 10.degree. C./s. In aging treatment, the Ni--Si compounds
and the Cr--Si compounds dissolved during the solution treatment
are precipitated as fine particles by heating at a temperature in
the range of 350 to 550.degree. C. for at least 1 hour, typically
for 3 to 24 hours. The strength and conductivity increases through
the aging treatment. Before and/or after the aging, cold-rolling
may be employed for higher strength. When the cold-rolling is
performed after the aging treatment, stress relief annealing
(annealing at low temperature) may be performed after the
cold-rolling.
[0036] In one embodiment, the Cu--Ni--Si copper alloy of the
present invention may have a 0.2% yield strength of not less than
780 MPa and a conductivity of not less than 45% IACS; may further
have a 0.2% yield strength of not less than 860 MPa and a
conductivity of not less than 43% IACS; or may still further have a
0.2% yield strength of not less than 890 MPa and a conductivity of
not less than 40% IACS.
[0037] The Cu--Ni--Si system alloy of the present invention can be
shaped into various wrought copper products such as strips,
ribbons, pipes, rods and bars. Furthermore, the Cu--Ni--Si system
alloy of the present invention can be used in components for
electronic devices such as lead frames, connectors, pins,
terminals, relays, switches and foils for secondary batteries,
which require both high strength and high electrical conductivity
(or thermal conductivity).
EXAMPLES
[0038] The following examples are merely illustrative for further
understanding of the present invention and its advantages, and not
limiting to the disclosure in any way.
[0039] The copper alloys used in Examples of the present invention
are copper alloys containing various amounts of Ni, Si and Cr and
further containing optional Sn, Zn, Mg, Mn, Co and Ag, as shown in
Table 1. The copper alloys used in Comparative Examples are
Cu--Ni--Si copper alloys having parameters out of the range of the
present invention.
[0040] The copper alloys having various compositions described in
Table 1 were melted in a high-frequency melting furnace at
1300.degree. C. and each alloy was cast into an ingot having a
thickness of 30 mm. Next, this ingot was heated to 1000.degree. C.,
then was hot-rolled into a plate having a thickness of 10 mm, and
was cooled immediately. After the plate was planed for removal of
scales to a thickness of 8 mm, it was cold-rolled into a thickness
of 0.2 mm. Subsequently, solution treatment was conducted in argon
gas atmosphere at a temperature of 800 to 900.degree. C. for 120
seconds, depending on the addition amount of Ni and Cr, followed by
cooling down to room temperature at various cooling rates. The
cooling rate was controlled by varying the flow rate of gas blowing
against the sample. The cooling rate was determined by the
measurement of the time required for the sample to be cooled from
its attained maximum temperature to 400.degree. C. The cooling rate
of the furnace without gas blow was 5.degree. C./s, and the lower
cooling rate was set at 1.degree. C./s in the case of cooling along
with controlled heating output. After this, the plate was
cold-rolled into a thickness of 0.1 mm, and was finally aged in
inert atmosphere at 400 to 550.degree. C. for 1 to 12 hours
depending on the amount of added elements, thereby samples were
produced.
[0041] The strength and conductivity of each alloy produced as
described above were evaluated. The strength was evaluated by 0.2%
yield strength (YS; MPa) measured by a tensile test in the
direction of rolling. The electric conductivity (EC; % IACS) was
determined from the volume electrical resistivity measured by
double bridges. The bendability was evaluated by W bend test using
a W-shaped mold at a ratio of the bending radius to the thickness
of the sample plate of 1. The evaluation was performed through
observation of the bent surface with an optical microscope. For
samples where no crack was observed, Rank A was given indicating a
satisfactory level in practical use. For samples any crack was
observed, Rank F was given. In a fatigue test, symmetrically
reversed stress load according to JIS Z 2273 was loaded to
determine the fatigue strength (MPa) where the alloy was broken at
10.sup.7 cycles.
[0042] For observation of particles of the Cr--Si compounds by
FE-AES, a plate surface of the samples was electropolished.
Particles having a size of not smaller than 0.1 .mu.m were observed
at many places. Adsorbed elements (C and O) on the surface layer
were removed by Ar.sup.+ sputtering. Auger spectra of individual
particles were measured and the weight concentrations of detected
elements were determined by semiquantitative analysis using
sensitivity coefficients. Particles containing the detected Cr and
Si were extracted as objects. The composition (Cr/Si), size, and
dispersion density of particles of the Cr--Si compounds were
respectively defined as the average Cr/Si ratio, the minimum inside
diameter, and the average number in each observation view for the
particles of the Cr--Si compounds having a size of 0.1 to 5 .mu.m
analyzed at many places by FE-AES observation. The results are
shown in Tables 1 and 2.
TABLE-US-00001 TABLE 1 Solution Mg, Mn, Ag, P, treatment Cooling
Aging As, Sb, Be, B, temperature rate temperature Ni Si Cr Sn Zn
Ti, Zr, Al, Co, Fe (.degree. C. .times. 120 s) (.degree. C./s)
(.degree. C.) Examples 1 2.7 0.6 0.005 800 1 450 2 2.7 0.6 0.05 800
2 450 3 2.7 0.6 0.05 800 4 450 4 2.7 0.6 0.05 800 8 450 5 2.7 0.6
0.05 800 2 400 6 2.7 0.6 0.05 800 2 500 7 2.7 0.6 0.1 800 4 450 8-1
2.7 0.6 0.05 0.1Mg 800 4 450 8-2 2.7 0.6 0.05 1.0Co 800 4 450 8-3
2.7 0.6 0.05 1.0Co, 0.1Mg 800 4 450 9 2.7 0.6 0.05 0.1Mn 800 4 450
10 2.7 0.6 0.05 0.3 800 4 450 11 2.7 0.6 0.05 0.3 0.1Ag 800 4 450
12 2.7 0.6 0.05 0.3 0.5 800 4 450 13 2.7 0.6 0.05 0.3 0.5 0.1Mg 800
4 450 14 4.0 0.9 0.005 900 2 450 15 4.0 0.9 0.05 900 3 450 16 4.0
0.9 0.05 900 6 450 17 4.0 0.9 0.05 900 9 450 18 4.0 0.9 0.05 900 3
400 19 4.0 0.9 0.05 900 3 500 20 4.0 0.9 0.1 900 6 450 21 4.0 0.9
0.17 900 7 450 22 4.0 0.9 0.05 0.2Mg 900 3 450 23 4.0 0.9 0.05
0.1Mn 900 3 450 24 4.0 0.9 0.05 0.3 900 3 450 25 4.0 0.9 0.05 0.3
0.1Ag 900 3 450 Dispersion Composition Aging density of CrSi of
CrSi time particles particles Yield Electrical Bend- Fatigue (h)
(.times.10.sup.5/mm.sup.2) (Cr/Si) Strength Conductivity ability
Strength Examples 1 6 0.3 4 760 48 A 275 2 6 0.5 3 765 48 A 280 3 6
0.4 3 765 48 A 280 4 6 0.2 3 765 47 A 280 5 12 0.5 3 770 47 A 280 6
2 0.5 3 770 47 A 280 7 6 1 2 770 46 A 285 8-1 6 0.5 3 785 46 A 285
8-2 6 0.5 3 790 48 A 285 8-3 6 0.5 3 800 47 A 285 9 6 0.5 3 785 46
A 285 10 6 0.5 3 785 46 A 285 11 6 0.5 3 785 46 A 285 12 6 0.5 3
785 45 A 285 13 6 0.5 3 800 45 A 285 14 4 0.7 4 860 44 A 300 15 4
1.1 3 870 43 A 300 16 4 0.8 3 870 43 A 300 17 4 0.4 3 870 43 A 300
18 10 1.1 3 870 43 A 300 19 2 1.1 3 870 43 A 300 20 4 2.2 2 870 44
A 300 21 4 5.6 2 875 43 A 300 22 4 1.1 3 890 41 A 325 23 4 1.1 3
890 41 A 325 24 4 1.1 3 890 41 A 325 25 4 1.1 3 890 41 A 325
Composition: % by mass
TABLE-US-00002 TABLE 2 Solution Mg, Mn, Ag, P, treatment Cooling
Aging As, Sb, Be, B, temperature rate temperature Ni Si Cr Sn Zn
Ti, Zr, Al, Co, Fe (.degree. C. .times. 120 s) (.degree. C./s)
(.degree. C.) Comparative 1 2.7 0.6 0.05 800 0.5 450 examples 2 2.7
0.6 0.1 800 0.5 450 3 4.0 0.9 0.05 900 0.5 450 4 2.7 0.6 0.05 800
15 450 5 2.7 0.6 0.1 800 15 450 6 2.7 0.6 0.05 800 4 600 7 4.0 0.9
0.05 900 5 600 8 2.7 0.6 0.5 800 4 450 9 4.0 0.9 0.5 900 6 450
Dispersion Composition Aging density of CrSi of CrSi time particles
particles Yield Electrical Bend- Fatigue (h)
(.times.10.sup.5/mm.sup.2) (Cr/Si) Strength Conductivity ability
Strength Comparative 1 6 15 3 700 51 F 225 examples 2 6 20 3 720 49
F 230 3 6 25 3 820 43 F 270 4 6 0.05 20 740 43 A 240 5 6 0.1 25 750
43 A 240 6 6 20 7 680 53 F 200 7 6 25 8 780 44 F 250 8 6 14 3 710
51 F 230 9 4 18 3 810 44 F 270 Composition: % by mass
[0043] Examples 1 to 25 of the present invention show satisfactory
properties, since particles of Cr--Si compounds have a dispersion
density of no more than 1.times.10.sup.6 and a Cr/Si ratio in the
range of 1 to 5 due to a proper cooling rate. In contrast,
Comparative Examples 1 to 3 show insufficient strength and poor
bendability due to excess grow of particles of Cr--Si compounds
caused by a slow cooling rate. Comparative Examples 4 and 5 show
poor strength and conductivity due to insufficient grow of the
particles and excess Si dissolved in the alloy caused by a rapid
cooling rate. Comparative Examples 6 and 7 show insufficient
strength and poor bendability due to excess grow of particles of
Cr--Si compounds caused by a high aging temperature. Comparative
Examples 8 and 9 show poor strength and poor bendability due to
excess grow of particles of Cr--Si compounds caused by an excess
concentration of Cr.
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