CA2009671A1 - Ag-sno electrical contact materials and manufacturing method thereof - Google Patents

Abstract

Abstract of the Disclosure Novel Ag-SnO electrical contact materials are dis-closed, which are made of Ag alloys consisting of 5-20 weight % of Sn and a balance of Ag, the alloys having been prepared by melting and having been internal oxidized. No-vel manufacturing methods are also disclosed, in which inte-rnal-oxidation is conducted in an oxygen atmosphere of 10 atm to 200 atm, and at a temperature of 750°C to 500°C.

Description

Title of the Invention 21~0~7~
Ag-SnO electrical contact materials and manufacturing method thereof Backqround of the Invention This invention relates to electrical contact materials which are used for electrical contacts employed in electri-cal apparatuses such as switches,~breakers, contactors, and ~l -:
the like.
Electrical contact materlals dealt with ln this inven- 10 tion are particularly those ma:de of Ag-Sn alloys which are made by melting Ag and Sn and which are internally oxidized.
Those belong to a different category from those which are prepared by mixing Ag and SnO powders and~powdermetallurgi-cally sintering them.

Heretobefore, Ag-Sn oxides alloys in which Ag is a matrix and Sn, solute metal thereof is internal-oxidized to Sn oxides, are widely used as electrical contact materials for the electrical apparatuses of the kind mentioned above.
As a similar eleatrical contact materlal, Ag-Cd oxides 20 alloys are known, while electrical contact materials made of Ag-Sn oxides alloys are more extensively employed today in view of the prevention of pollution, since Cd is harmeful to health.
However, there is a serious problem in the manufacture . , - of Ag-SnO alloy contact materials. That is, it is lmpossib-~ le to completely internal-oxidize a total amount of Sn by `: :

~ 1 Z(~09671 oxygen which penetrates from the outside of Ag matrix and diffuses into the inside of the matrix, if said Sn is more than about 5 weight ~ of the Ag matrix. This is a phenome-non commonly accepted by those skilled in this art. And, for example, it is described in the Information ~registra-tion No. 1-11 ) published by DODUCO of West Germany in April, 1966 that in Ag-Sn alloys containing more than 5% of Sn, this Sn can not be oxidized by an internal oxidation method.
It is pointed out there that this is because of segregation layers of Sn oxides which are inevitably formed at outer 10 surface areas of such alloys and retard oxygen to penetrete into the alloys for developing the internal oxidation in inner areas. As mentioned above, this has been conceived unanimously by those skilled in industries related to elec-trical contact materials.
In order to solve this problem, it becomes necessary for a successful internal-oxidation to employ auxiliary solute metals which have higher diffusion velocities or which are more capable to carry oxygen and to convey the oxygen more efficiently into deeper inner areas of Ag mat- 20 rices. Such auxiliary solute metals are typically In and Bi.
There is issed U.S. Patent No. 3,933,485 in which Ag-Sn-In system alloys are internal-oxidezed for obtaining modern electrical contact materials, and in which In is used as an auxiliary solute metal for the successful internal-oxidation of the alloys. Said electrical contact materials - .:. ~ . :. ~.. .

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- - ~ ::
.. ..
, ~ . .. ,. -Z~?0967~
which are more specifically consisted of 5-10 weight ~ of Sn, 1.0-6 weiqht % of In, and a balance of Ag, and are internal-oxidized. They are one of the most excellent con-tact materials which are industrially used today.
Nevertheless, even when In which can perform well inte-rnal-oxidation assisting functlons, as explained above, is employed as an auxiliary solute metal, it is not easy to internal-oxidize more than 5% of Sn evenly throughout its Ag matrix. It is sometimes observed that Sn oxides happen to segregate excessively at outer surface areas of the Ag 10 matrix, and such segregation makes subscales which are air-tight, while a depletion layer of Sn oxides is consequently produced in inner areas of the Ag matrix.
It has been noted also that since InO and BiO have a comparatively lower refractoriness, and are comparatively weak metal oxides, it has been desired long since to inter-nal-oxidize Ag-Sn alloys without the employment of In or Bi, if possible.
It will be noted also that compared to secondary Ag-Sn alloys, Ag-Sn-In alloys and Ag-Sn-Bi alloys which are ter- 20 tiary, are provlded with lower electrical conductivities.
In this respect too, it is preferable not to use In or Bi as auxiliary elements for the sake of internal-oxidation.

Brief SummarY of the Invention In view of the above, this invention is to provide entirely novel electrical contact materials which are pre-,, ;, ... .. .

Z(~09671 pared by melting, are consisted of 5-20 weight % of Sn and balance of Ag, only, and are internal-oxidized.
As to a Sn amount in this inventlon, its minimum is 5 weight % in order to afford the obtained electrical contact materials with efficient refractoriness, and its maximum is 20 weight %, because if Sn is given in an amount more than 20 weight %, the resultant materlals will be too brittle.
In this invention, though it is characteristic that seconda-ry Ag alloys which are added only by Sn and prepared by mel-ting, are internal-oxidized, one or more elements selected 10 .

form iron family elements (Fe, Co, and Ni) may be added to said secondary Ag alloys. Such addition is not for the acceleration or assistance of internal-oxidation, but merely for fining or minuting alloy crystalline;structures of the resultant alloys. In order to achieve this end, iron family elements will be added at an amount of 0.001-1 weight %.
This invention is also to provide a novel method for preparing the above-mentioned novel electrical contact mate-rials. - ~ ~

To wit, it has been discovered by the present inventors 20 through a large number of experiments that those Ag-Sn (5-20 weight %) alloys which had been impossible to be internal-oxidized, can successfully and completely be internal-oxi-dized when an oxygen atmosphere for the internal-oxidation is made more than 10 atm. This is novel knowledge and judgement first acquired by the present lnventors.
It has been known that in the manufacture~of electrical :

2~09671 contact materials by internally oxidizing Ag alloys, their Ag matrices are heated so that they become active to induce outside oxygen thereinto. A heating temperature for this end is commonly in a range of 500-750C. In this connec-tion, it has been also found by the present inventors that while Ag-Sn (5-20 wel~ght %~ alloys can be internal-oxidized in an oxygen atmosphere of more than 10 atm as discovered by them, the above-mentioned heating temperature shall prefera-bly be made comparatively lower within the above-mentioned range of temperature, when the oxygen atmosphere is selected 10 hiqher. This is because that if the oxygen atmosphere and the heating temperature are both high, Ag matrices become excessively active and consequently take thereinto oxygen too much, resulting in making an oxidation velocity of Sn in the Ag matrices too ~ fast and in producing subscales at surface areas of the Ag matrices on account of the segrega-tion of Sn oxides thereabout. In other~words, when the oxygen atmosphere pressure is made comparatively low above 10 atm, the heating temperature will preferably be made high within the above-mentioned range of about 500-750C. And, 20 on the contrary, it ls preferable that when the oxygen atmosphere is comparatively high above 10 atm, the heating temperature will be made low wi~thin the above-mentioned range of internal-oxidation heating temperature.
When Ag alloys of the above-mentioned specific consti-tuents are internal-oxidized in accordance wlth this inven-tion, it is also preferable to conduct the internal-oxida-S

z~)9671 tion at such condition where the Ag alloys are kept at a solid phose not involving any liquid phase, since if the alloys become liquid even partially, metal oxides precipi-tated by then might move about floatingly towards surface areas of the alloys and subsequently make subscales therea-bout.
In view of the above, when the heating temperature is ;
sided low within the above-mentioned range of temperature or near to its minimum temperature of about 500C, it is better to make the oxygen atmosphere as much as higher. But, in 10 order to prevent the alloys from becoming liquid and on account of safe and economic industrial and commercial ope-rations, the maximum oxygen atmosphere preferably employable in this lnvention will be up to about 200 atm.~ In other words, when Ag-Sn (5-20 weight %)~alloys made by meling are internal-oxidized in accordance with this invention, the lower and upper or minimum and maximum oxygen atmosphere shall preferably be 10 atm and 200 atm, and;its heating temperature shall preferably be in a range of about 750C to about 500 C. 20 Preferred Bmbdlments This invention is explained in a further concrete man-ner in the following examples.
(1~ Ag-Sn 6 weight %~
(2) Ag-Sn 6 weight %-Ni 0.2 weight %
The above constituents (1) and (2) were melted and made z~ 96~71 to ingots of 120mm in diameter and 40mm in length. The ingots were hot-extruded into squre bars of 30mm in thic-kness and SOmm in width. ;The bars were then~cut to a length of 500mm each, and their upper and lower surfaces were shaved by a thickness of 3mm each to obtain square bars of 24mm in thickness, 51Omm in width, and SOOmm in length.
To each lower surface of the square bars, there were bounded pure silver of 2.5mm in thickness. They were rolled by pressure so that they had thickness of 1.2mm. By pun-ching them by a punch having a cutting hole of 6mm in diame- 10 ter, disk-shaped contact materials backed by the pure silver and having 6mm diameter and 1.2mm thickness were obtained.
They were internal-oxidized by heating them ~700C for 48 hours in an oxygen atmosphere of 25 atm.

~ Vertical sections of the resulted contact materials ::
were observed through a microscope to the effect that there was produced no subscales at and about surface areas of the materials, and that Sn constituents were completely oxi-dized. It was observed also that particles of Sn oxides were extremely fine and were preclpitated evenly in their Ag 20 matrices, irrespectively of Ag grain boundaries of the Ag , ~
matrices. Precipitation distribution and structures of Sn oxides were thus extremely fine, as if they were prepared by powder-metallurgical methods.
In order to make a comparison, the following alloy (3) w~s made. Contact materials which are made by the internal oxldat-on of sald alloy (3) are known as one of the~today's :

, ' '` i . ' ~ ~. ,` ' ''., ' ' ' ., .,' ' ` , ':`' .

2(~09671 best electrical contacts having extremely excellent contact characteristics and performance.

(3) Ag-Sn 6 weight ~-In 1 weight %-Ni 0.2 weight %
This alloy which had been prepared by melting, was processed into disk-shaped contact materials same to those specified in the above (1~ and (2) alloys.
The disk-shaped contacts were internal-oxidized by heating them to 620C for 24 hours at a normal oxygen atmosphere of 1 atm.
The resultant contacts (3) were observed by a micros- 10co?e, similarly to the contacts (1) and (2). It was found that Sn was completely lnternal-oxidized in this contacts too, while they were precipitated squamously along Ag grain boundaries, and were noticeably coarse than those of the contacts (1) and (2).
Hardness (H~P) and electrical conductivity (IACS%) of the above internal-oxidized contact materials ~1), (2), and (3) were as follows.
Hardness Electrical conductivity (1) 78 72 20 (2) 80 70 (3) 95 55 Welding times by anti-welding tests (conducted under ~-electric voltage of DC 240V, initial electric current (dis-charge current from a condensor electric current) of 700A, contact pressure of 200g, and test cycles of 20) were as follows.

.

.. , . , ~ .. .

-2~)09671 (1 ) O
~2) 0 (3) 0 Amounts of consumptlon ~mg) by~ASTM test method (by electric voltage of AC 200V electric:current of 50A con-tact pressure of 400g, and releasing force of 600g) were as .
:follows. ~ `
( 1 )1 0 ,.
(2) 8 ::~
~ (3) 15 ~ 10 - As described and explained above in detail, this inven-tion can provide absolutely novel electrical contact mate-` rials made of Ag-Sn ~5-20 weight %) alloys whlch has been prspared by melting and internal-oxidized. ~As readily known form the above test data, the electrical contact materlals ,~ ~
made in accordance with this invention are substantially secondary Ag-Sn alloy provlded w1th Sn oxldes preclpitated extremely finely and evenly in its Ag matrix and, consequen-~; : tly having exce~llent contact properties includlng their : improved electrical conductivities. 20 : ;

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Claims (8)

1. Ag-SnO electrical contact materials made of Ag-Sn (5-20 weight %) alloys which have been prepared by melting and which have been internal-oxidized.

2. Ag-SnO electrical contact materials as claimed in claim 1, alloys of which are added by one or more elements selec-ted from iron family elements (Fe, Co, and Ni) at an amount of 0.001-1 weight %.

3. Ag-SnO electrical contact materials as claimed in claims 1 or 2, alloys of which have been internal-oxidized in an oxygen atmospher of more than 10 atm and at a condition where the alloys were kept at a solid phase not involving any liquid phase.

4. Ag-SnO electrical contact materials as claimed in claims 1, 2, or 3, alloys of which have been internal-oxidized by heating them in an oxygen atmosphere of 10 atm-200 atm to a temperature of 750-500°C.

5. Manufacturing method of Ag-SnO electrical contact mate-rials, which comprises internal-oxidizing Ag-Sn (5-20 weight %) alloys which have been prepared by melting, by heating them in an oxygen atmosphere of more than 10 atm and at a condition where said alloys are kept solid so that they do not contain any liquid phase.

6. Manufacturing method of Ag-SnO electrical contact mate-rials as claimed in claim 5, in which the alloys are added by one or more elements selected from iron family elements (Fe, Co, and Ni) at an amount of 0.001-1 weight %.

7. Manufacturing method of Ag-SnO electrical contact mate-rials as claimed in claims 5 or 6, in which the oxygen atmosphere is 10 atm to 200 atm.

8. Manufacturing method of Ag-SnO electrical contact mate-rials as claimed in claims 5, 6, or 7, in which a tempera-ture of heating is 750 to 500°C.

Abstract of the Disclosure Novel Ag-SnO electrical contact materials are dis-closed, which are made of Ag alloys consisting of 5-20 weight % of Sn and a balance of Ag, the alloys having been prepared by melting and having been internal oxidized. No-vel manufacturing methods are also disclosed, in which inte-rnal-oxidation is conducted in an oxygen atmosphere of 10 atm to 200 atm, and at a temperature of 750°C to 500°C.