Note: Descriptions are shown in the official language in which they were submitted.
10~7235
This invention relates to an electrical contact
composed of a base portion made from non~precious metals such
as copper and clad with Ag-SnO alloy metals as a contact portion.
More particularly, this invention relates to a novel
composite electrical contact of the kind mentioned above, in
which the contact and base portions are fusion bonded to each
other by means of a Ag-Cu interfacial alloy layer between the
said two portions, and also by means of a diffusion layer of Cu
which extends deeply into the matrix of the contact portion,
said two layers having been produced by subjecting the composite
electric contact for a comparatively short period of time to
a temperature about or higher than the eutectic temperature of
Ag and Cu, viz., 779C. This heat treatment, which would be
comparable with liquid phase sintering production of a contact,
not only produces the aforementioned layers which firmly affili-
ate the contact and base portions, but also keeps an even
dispersion of metallic oxides throughout the metrix of the
contact portion of Ag-SnO. It shall be noted also that said
heat treatment, which can be held after or simultaneously with
binding of the base and contact portions by cold or hot press
working, can release from the contact physical stresses produced
in the contact by the press working.
It has been widely known to produce a clad electrical
contact by clothing a base portion, such as for example a
copper rivet-shape stem, with a thin plate of contact material
made from silver-metallic oxides alloys, such as for example
Ag-CdO alloys, by means of cold press. This clothing operation
is firstly for improving physical and electrical properties
of a composit electrical contact, especially its anti-welding
property, by means of a Ag contact portion alloyed with metallic
oxides, and secondly for minimizing the amount of expensive
Ag in a contact and for increasing proportionately the amount
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of Cu in the contact.
The first point mentioned above as an advantage of
the clothing operation is partly affirmative. ~lowever, the
second point is questionable in its real merit. For example,
in the case of a conventional contact of -the type having a
Ag-CdO contact portion and a Cu base portion mechani.cally bonded
to each other by cold press, the contact portion o~ten acci-
dentally separates from the base por-tion when the former is
only partially consumed (e.g. to only half its thickness).
This occurs because the binding force between the contact and
base portions relies primarily upon mecha.nical or physical
stress to cause the metal to become plastic and to flow between
the two portions, and hence the resulting bond, which has been
extrinsically weakened by metallic oxides existing about the
interface between the two portions and pulverized by the cold
press binding process, inherently is not strong enough to stand
up against the different contact conditions which occur with
the consumption of the contact. Assumed that the thickness or
volume of the Ag-CdO contact portion is equal to the base
portion, the life of this type of composite contact is only one
fourth the life of a comparative solid contact, which is made
wholly from Ag-CdO alloys, ~Ience, it is doubtful whether the
saving of a half amount of Ag-CdO or Ag can compensate for the
shortening of its brief life expectancy, when considered in the
light of the expensive and laborious steps and processes that
are involved in manufacturing such a bimetallic composite contact.
In order to eliminate -the drawbacks mentioned above,
it has been tried by the present inventor to fusion bond a most
conventional Ag-CdO alloy contact portion to a Cu base portion.
~his trial failed as no prior literature has disclosed a composite
electrical contact composed of a contact portion of Ag-internal .
oxidized metal-and of a Cu base portion which are fusion or
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diffusion bonded to each o-ther. In case of a composite electri-
cal contact comprising a ~g-CdO contact portion, for example,
such fusion bonding was found to be impossible, because cadmium
oxides dispersed in the Ag matrix of the contact portion
decomposed or sublimed at a temperature lower than the melting
point of said Ag matrix metal, and the cadmium oxides therefore
produced a segregation or barrier layer facing the inner surface
of the Cu base portion, which is a detriment to a contact of
this kind.
The applicant herein previously developed a specific
Ag-SnO electrical contact material as disclosed in his U.S.
Patent N 3,933,~85. This specific electrical contact comprises
an alloy having metal oxides precipitated therein as the result
of internal oxidation, and being composed of about 5 to about
10% by weight of tin, and 1.0 to about 6% by weight of indium,
the balance being silver. This alloy may contain a trace amount
of less than 0.5% by weight of ferrous or alkali earth metals.
Applicant has also invented anoter specific Ag-SnO
electrical contact material comprising an alloy having metal
oxides precipitated therein as the result of internal oxidation
and being composed of 1.5 to 6% by weight of tin, 0.5 to 3%
by weight of indium, the total amount by weight of said tin
and indium being less than 2 to 6%, a trace amount of less than
0.5% by weight ofiron family element, and the balance being
silver.
The inventor has now found that the Ag-SnO electrical
contact materials~ which he has invented as mentioned above,
can advantageously be employed as a contact portion of a composite
electrical contact composed of a contact portion of Ag-metal
oxides, and a Cu basic portion, said two portions being fusion
or diffusion bonded each to the other. This results from the
findings that tin oxides of the aforementioned Ag-SnO alloys
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are stable in an oxygen atmosphere and at a temperature up to
about 2,000C, and sublime at the hoiling point of Ag, that
these metal oxides are hard enough to withstand a butt press
joining without producing undesireable pluverization of said
oxides but instead producing the wedging of the oxides into
the Cu base portion, which results in preventing the abutting
surfaces of the base and contact portions from sliding trans-
versely to the lonyitudinal axes of said two portions during
the butt press joining operation, and also results in mechanical-
ly strengthening the butt joint between the two portions, that
a heat treatment of the portions at a temperature about the
eutectic temperature of Ag and Cu, which produces the Cu diffusion
into the Ag-SnO alloy matrix of the contact portion, does not
adversely affect alloy structures of the base portion but works
to release the two portions from stresses accompanied with the
joining press work, and that the resultant bimetallic composite
contact will have a useful life proportionate to the overall
volume or thickness of the contact portion-i.e., will be useful
until the contact portion has been substantially completely
consumed.
It has been found also that among the aforementioned
Ag-SnO electrical contact materials, those containing ferrous
or alkali earth metals such as nickel and cobalt are most
preferable as materials for the contact portion of the present
invention, because such elements urge metal oxides to produce
about spherical nuclei, causing the resultant Ag-SnO alloy
to have a good elongation percentage, which is a prerequisite
for the cold butt joîning of said alloy to a Cu base portion,
utilizing plastic metallic flows therebetween.
For example, the following alloys, which were made
by wires of 2mm in diameter and subjected to internal oxidation
under oxidizing atmosphere at 750C. for 24 hours, have
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respective elollgatioll percentages as follows:
Sn 1.5% - In 0.5~ - Ni 0.1% - balance Ag
(elongation ~ 11%)
Sn 3% - In 1.3% - Ni 0.1~ - balance Ag
(elongation 8%)
Sn 4.2~ - In 1.8~ - Ni 0.1~ - Ag
(elongation ~ 4%)
I-lence, the present invention provides a heat-treated
composite electrical contact composed of a base portion made from
copper or copper-matrix alloys, and a contact portion clad to
the base portion and made from an alloy having metal oxides pre-
cipitated therein as the result of internal oxidation and being
composed of 1.5 to 10% by weight of tin, 0.5 to 6% by weight of
indium, and a trace amount of less than 0.5~ by weight of iron
family element metals, the balance being silver; the contact and
base portions are joined by an interfacial alloy layer composed
of Ag and the matrix metal of the base portion, and the contact
portion adjacent the alloy layer is diffused by the matrix
metal of the base portion to a depth greater than the thickness
of the alloy layer as the result of heat treatment of the contact
for a brief period of time, and at a temperature about or higher
than the eutectic temperature of Ag and the matrix metal of the
base portion.
The heat treatment of the contact is preferably effected
at a temperature higher than 779C for a period of less than 10
seconds.
The invention also provides a method of manufacturing
a composite electrical contact, which comprises clading an in-
ternally oxidized contact member, made from an alloy of 1.5-10%
by weight tin, 0.5-6.0% by weight indium, a trace amount of an
iron family element metal and the balance silver, to a base member
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1~87235
made from copper or copper-matrix alloys, and subjecting the
composite contact to a temperature approximately equal to or
higher than the eutectic temperature of Ag and the matrix metal
of the base member, and for an interval sufEicient to cause the
metal of the kase member to difEuse into the matrix of the contact
member.
The following non-restrictive examples illustrate
the invention.
EXAMPLE 1
A composite electrical contact of the rivet type
(Sample A) was prepared from a contact portion of 5mm diameter
and 0.5 mm. thickness made from a Ag-SnO alloy of Sn 5% - In
1.8% - Ni 0.3~-Ag, and a copper base portion having a base part
of 5mm diameter and 1.0 mm thickness and an integral shank part
of 2.5 mm diameter and 2.5 mm length by cladding the base with
the contact portion by cold press butt joining. This Sample _
was heated at 800C for 10 seconds at atmospheric conditions. The
Sample A thus heat-treated was cut and etched, and observed by
an electron microscope at a magnification of x 2~00. There were
observed an interfacial alloy layer of Ag-Cu of about 7/u around
the boundary of the base and contact~
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1087Z3~
portions (and immediately adjacent the copper base), and a
diffusion layer of Cu into the contact portion at a depth of
about 51/u adjacent to the aforementioned Ag-Cu alloy layer,
and at the side thereof remote from the Cu base or matrix.
It was also observed that the alloy structure of the contact
portion, especially its metal oxides and the even distribution
thereof, were not adversely affected by said Cu diffusion.
Sample B, having a construction similar tO the
Sample _ but utilizing Ag-CdO 13%, was prepared without the
above-noted heat-treatment.
Both samples A and B were subjected to switching tests
of 50,000 cycles (AC 200V, 75A, for 0.6 second with a switching
cycle of 3 seconds). Average loss of weight in Sample _ was
20.66 mg., while in Sample B 29.52 mg. Noticeable part of the
contact portion of Sample B was broken off.
EXAMPLE 2
Sample A of Example 1, Sample C of dimensional
structures same to the Sample A, but made wholly from Ag-CdO
13%, and a sample D of dimensions same as Sample _ but made
wholly (i.e. both contact and base portions) from Ag-SnO alloy
of Sn 5% - In 1.8% - Ni 0.3% - Ag, were tested for 2000 cycles
under AC 200 V, 32A, 60 cycles per minute, contact force of
100 g. and opening force of 80g. Average hardness (HRF) of
these three Samples when measured vertically from contact
surfaces were 80 (Sample A), 107 (Sample C), and 110 (Sample D).
Times of welding and average force (g) are as follows.
Sample A 19 times 117g
Sample C 21 times 138g
Sample D 4 times 228g
Contact resistances (m~ )of the samples are as
follows:
At 1000 cycles -
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Sample A 2.7 m
Sample C 3.0 m,~
Sample D 3.2 m ,~
At 1500 cycles -
Sample _ 1.9 mlZ
Sample C 3.8 m ~Z
Sample D 5.3 m
At 2000 cycles
Sample A 3.7 m
Sample C 4.3 m ~z
Sample D 4.5 m ~
Thus low contact resistance and good thermal dissipa-
tion were observed in Sample _.
In the present invention instead of Cu and its alloy,
A1 and Ni and their alloys can be employed also as a base
portion. The heat-treatment of the contact for producing a
fusion binding therein can, of course, be made simultaneously
with a cold forging operation of the contact, for example by
providing heat to cold forging dies.
