EP0508055B1

EP0508055B1 - Silver-base metal oxide material for electrical contacts

Info

Publication number: EP0508055B1
Application number: EP92101915A
Authority: EP
Inventors: Yuzo c/o Kabushiki Kaisha Higashi Fuji Uemura; Shigeo c/o Kabushiki Kaisha Higashi Fuji Shibuya; Manabu c/o Kabushiki Kaisha Higashi Fuji Aoki
Original assignee: Mitsubishi Materials Corp
Current assignee: Mitsubishi Materials Corp
Priority date: 1991-04-12
Filing date: 1992-02-05
Publication date: 1997-05-02
Anticipated expiration: 2012-02-05
Also published as: DE69219397T2; KR930006167A; DE69219397D1; KR0121724B1; EP0508055A1

Description

Background of the invention

(Field of the invention)

This invention relates to silver-base metal oxide materials for electric contacts for use in various electrical or electronic apparatus.

(Prior art)

A great many conventional electrical contact materials have been proposed or used in various electrical or electronic apparatus. Among widely used electric contact materials, there are silver-base composites with dispersed metal oxides as described in "Metals Handbook", 10th edition, vol.2, page 857, published by ASM International Handbook committee, 1990. It is stated, that such silver-based composites can be produced by internal oxidation. in this process, a silver alloy (such as silver-cadmium alloy) is first cast into ingots, which are rolled into strips or fabricated further into the finished product form. This silver alloy material is then heated in air or oxygen, so that the oxygen diffuses into the alloy and forms metal oxide particles (such as CdO in the case of Ag-Cd-alloy), dispersed in the silver matrix.
Specifically, there is known, e.g. from US-A-3 933 485 and DE-24 28 147 C2 which both correspond to JP-B-55-004 825 an electric contact material, which is formed by subjecting an Ag-base alloy consisting essentially of, in weight-% (hereinafter, the percentage is weight-%) 5 - 10 % Sn, 1 - 6 % In and, if required, less than 0,5 % of at least one element selected from the group consisting of Fe, Ni, and Co, and the balance Ag and inevitable impurities, to an internal oxidation treatment in which the Ag-base alloy is soaked in an oxidizing atmosphere at a temperature of 650 - 750 °C for a predetermined time period to achieve the formation of uniform micro-crystals in the structure of internal oxidation.In DE-2428 147 C2 it is said that in the preparation of electrical contacts normally a completely homogeneous internal structure, i.e. a complete internal oxidation throughout is to be achieved.
In recent years, there has been made a remarkable progress in the development of electrical and electronic apparatus having improved performance and prolonged service lives. Accordingly, there is an increasing demand for materials for electric contacts for use in these electrical and electronic apparatus which have improved deposition resistance and consumption resistance. However, in actuality, conventional electric contact materials, inclusive of the above mentioned known Ag-base composite electric contact material do not have sufficient deposition resistance and consumption resistance to satisfy the requirements imposed by recently developed electrical and electronic apparatus.

Summary of the invention

It is therefore the object of the invention to provide silver-base metal oxide materials for electric contacts which have excellent deposition resistance and consumption resistance and hence prolonged service lives.
To attain the above object, the present invention provides a silver-base metal oxide material for electric contacts having excellent deposition resistance and consumption resistance, said material being formed by subjecting to an internal oxidation treatment an Ag-base alloy consisting of (in weight-%)

Sn 4 - 11 %

In 1 - 5 %

Te 0,05 - 4 % and

Ag and impurities: the balance
If required, at least one of the following elements (a) and (b) may be added to the alloy:

a) at least one element selected from the group consisting of Fe, Ni and Co: 0,01- 1 %
b) Cd: 0,05 - 3 %

Preferred embodiments of the invention are defined in the subclaims.
The invention also provides a process for preparing said silver-base metal oxide material, and rivets for electrical contacts made from such material, see claims 10 to 12.
The above and other objects, features, advantages of the invention will become more apparent from the following detailed description.

DETAILED DESCRIPTION

Under the above stated circumstances, the present inventors have made many studies in order to obtain silver-base metal oxide material for electric contacts having improved deposition resistance and consumption resistance, and reached the following finding:
A silver-base metal oxide material for electric contacts, which is formed by subjecting an Ag-base alloy consisting a part from impurities of:

Sn 4 - 11%;

In 1 - 5%;

Te 0.05 - 4%;

and, if required, at least one of the following elements (a) and (b):

(a) at least one element selected from the group consisting of Fe, Ni, and Co: 0.01 - 1%;
and
(b) Cd: 0.05 - 3%; and

Ag and impurities: the balance, to an internal oxidation treatment under the above-mentioned conditions, i.e.:

Atmosphere:: Oxidizing atmosphere;
Oxidizing Temperature:: 650 - 750°C; and
Soaking Time:: 8 - 26hr,

The present invention is based upon the above finding, and the silver-base metal oxideelectric contact material according to the invention has the aforementioned chemical compositions.
The reasons for specifying as above the contents of the component elements of the Ag-base alloy before being subjected to the internal oxidation treatment will now be described:

(a) Sn:
The Sn forms oxides in the alloy, which act to enhance the deposition resistance. However, if the Sn content is less than 4%, the deposition resistance cannot be enhanced to a desired extent, whereas if the Sn content exceeds 11%, the resulting electric contacts will have excessive contact resistance, and further the silver-base metal oxide material will have degraded workability in manufacturing electric contacts therefrom. Therefore, the Sn content should be limited to a range of 4 to 11%. A preferable Sn content range is 5 to 8%.
(b) In:
The In acts to promote oxidation of the Sn component, and also the In itself forms oxides which act to enchance the deposition resistance and consumption resistance. However, if the In content is less than 1%, the above actions cannot be performed to a satisfactory extent, whereas if the In content exceeds 5%, the resulting electric contact material will even have degraded deposition resistance. Therefore, the In content should be limited to a range of 1 to 5%, and preferably 1.5 to 3%.
(c) Te:
The Te forms oxides which can easily sublime upon generation of an arc due to closure or opening of the electric contacts to thereby further enchance the deposition resistance and consumption resistance. However, if the Te content is less than 0.05%, the above action cannot be performed to a desired extent, while if the Te content is in excess of 4%, it will result in degraded workability. Therefore, the Te content should be limited to a range of 0.05 to 4%, and preferably 0.1 to 1%.
(d) Fe, Ni, and Co:
One or more of these elements may be added according to necessity. If added, they dissolve in the matrix to finely divide the oxides and the Ag grains to thereby improve the deposition resistance. However, if the total content of these elements is below 0.01%, the above action cannot be performed to a satisfactory degree, whereas if the total content exceeds 1%, degraded workability will result.
Therefore the total content of Fe, Ni, and Co should be limited a range of 0.01 to 1%, and preferably 0.05 to 0.2%.
(e) Cd:
Cd may be added if required, since the Cd cooperates with the Te to further enhance the deposition resistance. If the Cd content is less than 0.05%, desired improvement in the deposition resistance cannot be obtained, whereas in excess of 3%, the consumption resistance will even degrade. Thus, the Cd content should be limited to a range of 0.05 to 3%, and preferably 0.1 to 2%.
Next, examples of silver-base metal oxide electric contact materials according to the invention will be described.

Example 1

Ag-base alloys having chemical compositions shown in Tables 1 and 2 were smelted in an ordinary type high-frequency smelting furnance ce and cast under conventional ordinary casting conditions into ingots. The ingots were each hot extruded into a plate having a thickness of 5mm. The plate was then hot rolled, followed by being cold rolled into a sheet having a thickness of 0.6mm. The sheet was cut or sliced in its longitudinal direction into a strip having a width of 2mm. The strip was subjected to an internal oxidation treatment under an oxygen atmosphere at a temperature of 700°C and for a soaking time of 24 hours. The internally oxidized strips were put together and compacted into a billet having a diameter of 70mm. The billet was extruded into a diameter of 7mm, followed by being subjected to wire drawing into a wire having a diameter of 2mm. Finally, the wire was formed, by a header machine, into rivets having a head diameter of 4mm, a head height of lmm, a leg diameter of 2mm, and a leg length of 2mm. The obtained rivets were adapted as specimens of the silver-base metal oxide electric contact material according to the present invention (hereinafter referred to as "the present invention contact materials Nos. 1 - 13") and specimens of conventional silver-base metal oxide electric contact materials (hereinafter referred to as "the conventional contact materials Nos. 1 - 11").
Then, electrical tests were conducted on the present invention contact materials Nos. 1 - 13 and the conventional contact materials Nos. 1 - 11 by the use of an electric contact testing machine according to ASTM under the following conditions to examine the number of times of deposition and the amount of consumption in order to evaluate the deposition resistance and the consumption resistance:

DC Voltage 14V;

Making Current 150A;

Breaking Current 30A;

Switching Time ON for 1 sec. - OFF for 9 sec.;

Contact Force 80g;

Opening Force 80g;

Number of Times of Switchings 10,000
The results of the tests are shown in Tables 1 and 2.

Example 2

Rivets were formed from Ag-base alloys having chemical compositions shown in Tables 3 and 4 under the same conditions as in Example 1 described above, to obtain present invention materials Nos. 14 - 29 and conventional materials Nos. 12 - 17.
Then, electrical tests were conducted on the present invention contact materials Nos. 14 - 29 and the conventional contact materials Nos. 12 - 17 by the use of an electric contact testing machine according to ASTM under the following conditions to examine the number of times of deposition and the amount of consumption in order to evaluate the deposition resistance and the consumption resistance:

DC Voltage 24V;

Making Current 100A;

Breaking Current 20A;

Switching Time ON for 1 sec. - OFF for 9 sec.;

Contact Force 100g;

Opening Force 100g;

Number of Times of Switchings 5,000
The results of the tests are shown in Tables 3 and 4.
It will be learned from Tables 1 to 4 that the present invention contact materials Nos. 1 - 29 all show by far more excellent deposition resistance and consumption resistance than the conventional contact materials Nos. 1 - 17.
Since silver-base metal oxide electric contact materials according to the present invention thus possess excellent deposition resistance and consumption resistance, if they are actually used in various electrical or electronic apparatus, they will greatly contribute to improving the performance of the electrical or electronic apparatus as well as to prolongation of the service lives thereof.

Claims

A silver-base metal oxide material for electric contacts, having excellent deposition resistance and consumption resistance, said material being formed by subjecting to an internal oxidation treatment an Ag-base alloy consisting, by weight-%, of: Sn 4 - 11 %; In 1 - 5 %; Te 0.05 - 4 %; and Ag and impurities: the balance.
A silver-base metal oxide material for electric contacts, having excellent deposition resistance and consumption resistance, said material being formed by subjecting to an internal oxidation treatment an Ag-base alloy consisting, by weight-%, of: Sn 4 - 11 %; In 1 - 5 %; Te 0.05 - 4 %; and at least one element selected from the group consisting of Fe, Ni and Co 0.01 - 1 %; and Ag and impurities the balance.
A silver-base metal oxide material for electric contacts, having excellent deposition resistance and consumption resistance, said material being formed by subjecting to an internal oxidation treatment an Ag-base alloy consisting, by weight-%, of: Sn 4 - 11 %; In 1 - 5 %; Te 0.05 - 4 %; Cd 0.05 - 3 % and Ag and impurities the balance.
A silver-base metal oxide material for electric contacts, having excellent deposition resistance and consumption resistance, said material being formed by subjecting to an internal oxidation treatment an Ag-base alloy consisting essentially , by weight-%, of:
A silver-base metal oxide material for electric contacts, as claimed in any of claims 1 - 4, wherein said internal oxidation treatment is carried out under the following conditions: Atmosphere Oxidizing atmosphere Oxidizing Temperature 650 - 750 °C; and Soaking time 8 - 26 hr
A silver-base metal oxide material for electric contacts, as claimed in any of claims 1 - 4, wherein Sn is contained in said Ag-base alloy in an amount of 5 - 8 %.
A silver-base metal oxide material for electric contacts, as claimed in any of claims 1 - 4, wherein In is contained in said Ag-base alloy in an amount of 1.5 to 3 %.
A silver-base metal oxide material for electric contacts, as claimed in any of claims 3 or 4, wherein Cd is contained in said Ag-base alloy in an amount of 0.1 - 2 %.
A silver-base metal oxide material for electric contacts, as claimed in any of claims 2 or 4, wherein at least one element selected from the group consisting of Fe, Ni and Co is contained in said Ag-based alloy in an amount of 0.05 - 0.2 %.
A process for preparing a silver-base metal oxide material for electrical contacts by internal oxidation of any of the alloys of claims 1 to 9, characterized by the following steps:
1) ingots of the silver-base alloy prepared by smelting and casting, are hot extruded into a plate having a thickness of 5 mm;

2) said plate is then hot-rolled, followed by being cold-rolled into a sheet of 0.6 mm thickness;

3) said sheet is cut or sliced in its longitudinal direction into strips having a width of 2 mm;

4) said strips are subjected to an internal oxidation treatment under an oxygen atmosphere at a temperature of 700 °C during 24 hours;

5) said internally oxidized strips are put together and compacted into a billet having a diameter of 70 mm, the billet being extruded into a diameter of 7 mm, followed, if desired, by a wire-drawing into a wire having a diameter of 2 mm.
A rivet prepared from a silver-base metal oxide material which has been subjected to an internal oxidation treatment, according to any of claims 1 to 9.
A rivet prepared according to claim 10.