US2178992A - Copper alloy - Google Patents

Description

Patented Nov. 7, 1939 UNITED STATES PATENT orFlcE COPPER ALLOY Franz R. Hensel Ind., assignors and Earl I. Larsen,

to P. It. dianapolis, Ind., a co Indianapolis, Mallory & Co.,' Inc., Inrporation of Delaware No Drawing. Application August 15, 1939,

Serial No.

2 Claims.

This invention relates to copper alloys, suitable for general uses, but particularly suited for electric conducting or contacting members.

. An object of the invention is to improve copper tacts, sliding contacts, trolley wheels, trolley shoes I and the like.

Another object of the pressure welding ing dies in general.

Other obiects of the invention will be apparent from the following description taken in connection with the appended claims.

The present invention comprises the combination of elements, methods of manufacture and the product thereof, brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims. While a preferred embodiment of the invention isdescribed herein, it is contemplated that considerable variation may be made in the method of procedure and the combination of elements, without departing from the spirit of the invention.

A feature of the present invention is the improvement of copper alloys to producev an alloy which has a high current carrying capacity, has

invention is to improve a high strength at elevated temperatures, a high' annealing point and great wear resistance.

Other advantages are a low contact resistance which remains uniform throughout the life of the 40 contact.

In one of its aspects, the invention makes possible the manufacture of contacts having the desirable properties mentioned, by casting, such as die or .sand casting. The invention also contemplates a material which can be readily worked by casting same into a billet, rolling or extruda billet and working same down into round rods, squares, rectangles, strip, sheet, slab and the like.

The copper alloy of the present invention also can be hardened by heat treatment.

According to the present invention, the alloy is composed of copper, silicon, cobalt and silver. I

55 The'alloy is of thefollowing composition:

Per cent Silicon .1 to .8 Cobalt .5 to 3 Silver .05 to 2.5 0 Copper Balance of the types includ-j electrodes and resistance weld-' A preferred range of the composition is the following:

Percent Silicon .25 to .50

Cobalt 1.50 to 2.40 Silver n- .05 to 1.00 Copper; Balance The alloy for making the electrical conducting members maybe formed by melting together the proper proportions 'of the ingredients. It has been found of advantage to add the cobalt to a copper melt in theform of a pressed powder briquette.

It has been found that in our new'and improved conducting member, the combination of cobalt and silicon, provides a copper base material with a high hardness, a high electrical conductivity and a high annealing point. The addition of silver is necessary in order to retain a low contact resistance and at the same time, silver, being an age hardening ingredient for copper base alloys, further improves the physical properties, such as tensile strength, hardness and impact strength, without lowering the electrical conductivity. As a matter of fact, the addition of silver actually improves the electrical conductivity and raises the values considerably, which are obtained in straight copper-cobalt-silicon alloys.

When the materials of the present invention are used for electrical contacting members, and more particularly for resistance welding electrodes, such as spot welding electrodes or projection welding electrodes, it was found that the presence of silver in the alloys retained a much lower contact resistance than was obtainable withbut the addition of silver. This is due to the fact that silver oxide has entirely different current carrying characteristics than copper oxide, or cobalt oxide. At the same time, silver oxide dissociates very readily at elevated temperatures, forming metallic bridges of silver. These silver, bridges'provide a metal to metal contact and therefore reduce very materially the contact resistance. It has' been found that materials without silver will over-heat very-severely due to the high contact resistance, which overheating will result in softening of the materials or in certain cases, a mushrooming.

As can be seen from the range of compositions given above it is necessary to hold the constituents within very close limits in order to obtain the desired properties, such as a combination of high tensile strength, high electrical and thermal conductivities, low contact resistance and high annealing temperature. It was furthermore found that the elements forming the new alloy must be present in definite ratios. For instance, the silicon should amount to approximately 20% of the cobalt content. In other words, if the preferred range is as given above, the silicon content of an alloy containing 2% cobalt should amount to 40%.

5 A large number of tests were made in which 1 cases to as much as 50% of the value obtained with the correct silicon content.

Another disadvantage of high silicon contents in this particular alloy was found in the fact that alloys tend to embrittle when heated to elevated temperatures. This is apparently due to the fact that the excess silicon is precipitated within the grain boundaries and if the material is heated in oxidizing furnaces part of the silicon is transferred to silica, weakening the entire structure of the alloy. This was particu-- larly noticeable in materials having small crosssections. A large number of tests were conducted with alloys of the kind covered by the 5 present invention and it was found that in a meeting in air or even in certain reducing gases a primary oxide layer would form which would break ofi during forming or similar operations; At the same time, however, a secondary oxide film was formed which could be absorbed microscopically and in which the excess silicon was oxidized. Material of this type showed a tendency to embrittlement and would not stand heavy forming operations. Furthermore, it was found that material with a secondary oxide film was jvery weak when tested in fatigue or in impact.

By readjustingthe silicon content a large number of these disadvantages were overcome. The addition of silver furthermore improved 4 the heat resisting characteristics of the alloy.

It was found that the material could be worked into a very fine spring stock by using annealing cycles and also heat treating cycles in which the heating .medium was a wall of the specific composition which would not attack the alloy and insure a neutral atmosphere.

After casting, bers have a hardness of -85 Rockwell B. The alloys may be subjected to a heat treatment, which may comprise heating to a high temperature, preferably in the order of 900 deg. C., quenching and then aging at a lower temperature,.such as about 450-500 deg. C. The materials of the present invention were also tested in the form of trolley wheels and trolley shoes and gave a superior life to the materials of the prior art. Tests with the present material were made by operation in a 60 cycle 220 volt A. C. circuit, carrying amperes. The load used consisted of air core reactors and resistance grids in series. The contactors were operated 30 times per minute in this circuit. When the materials of the present invention were tested, theygave a superior performance, both as far as contact resistance and wear are concerned.

The material of the present invention, when used in the form of heat treated rod, can be produced with a Rockwell B hardness of 95, a tensile strength of approximately 90,000 to 95,000 p. s. i. and a yield point exceeding 60,000 p. s. i. The materials retain a high ductility, which is in the neighborhood of 12-15%. The electrical conductivity will be a function of the actual composition, but can be maintained very readily in the neighborhood of 50% LA. C. S.

While the present invention as to its objects and advantages has been described herein as carried out in specific embodiments thereof, it

is not desired to be limited thereby, but it is intendedto cover the invention broadly, within the spirit and scope of the appended claims.

What is claimed is:

1. An alloy composed of .1 to .8% silicon, .5 to 3% cobalt, .05 to 2.5 silver, and the balance copper.

2. An alloy composed of .25 to .50% silicon, 1.50 to 2.40% cobalt, .05 to 1.00% silver and the balance copper. 3

FRANZ R. HENSEL.

EARL I. LARSEN.

the electrical contacting mem- 3