US2169188A - Copper base alloy - Google Patents

Description

Patented Aug. 8, 1939 UNITED STATES COPPER BASE ALLOY James M. Kelly, Traflord, Pa., assignor to Westinghouse Electric 8:

Manufacturing Company,

East Pittsburgh, Pa., acorporation of Pennsylvania No Drawing. Application October 21, 1938, Serial No. 238,300

8 Claims.

This invention relates to alloys and particularly to copper base alloys which have improved mechanical, thermal and electrical properties, and the utilization of the alloys as articles of manufacture.

The present application comprises a continuation-in-part of my copending application, Serial No. 149,146, filed June 19, 1937 now Patent No. 2,147,844.

Certain metals have been alloyed with copper to produce an alloy having better mechanical properties but generally such alloys have been inferior to copper as conductors of electricity and heat. In the copper base alloys which have been produced and which have the desired conductivity or mechanical strength, the characteristics are difllcult to duplicate.

An object of this invention is to produce a copper base alloy having high physical strength and good electrical and thermal conductivity.

Another object of this invention is to provide a copper base alloy which will have the characteristics of high physical strength and good electrical and thermal conductivity when precipitation hardened.

A further object of this invention is to utilize a copper base alloy formed to shape and precipitation hardened to give high physical strength and good electrical and thermal conductivity.

A more specific object of this invention is to produce a copper base alloy which may be precipitation hardened to give it high physical strength and good conductivity and which will retain its strength and be resistant to creep when subjected to elevated temperatures.

Other objects of this invention will be apparent from the following description taken in conjunction with the appended claims.

In order to produce a copper base alloy which will have desired mechanical and electrical properties, metals which can be precipitated to effeet a dispersion of fine particles throughout a copper base when suitably heat treated, are added to a copper melt. It has been found that a copper base alloy containing even small proportions of cobalt, iron and either zinc or cadmium has excellent mechanical and good electrical properties when heat treated.

In preparing the alloy, the metals, cobalt and iron, may be added directly to the copper melt in any suitable form, such as powders or in lump form, since they are not easily oxidized as compared to copper. The zinc or cadmium is added to the melt just prior to the pouring of the alloy because of their inherent tendency to become oxidized. The alloying content may thus be maintained substantially constant during the heat forming operations.

In practice, the alloy may be prepared by heating a melt of copper such as commercial electrolytic copper under a covering of charcoal in a graphite crucible and adding the alloying elements cobalt and iron in any suitable form to the copper melt. In order to complete deoxidation of the melt, it may be held at a temperature of between 1150" C. and 1200 C. for a period of time suificient for the completion of the reaction of the graphite crucible with the oxygen after which the zinc or cadmium is added to the melt. Where desired, the alloy may also be prepared by heating the melt in a ceramic crucible with a cover of lump charcoal over the melt. Although not always necessary as in the making of other copper base alloys, where desired, small quantities of calcium or phosphorus or other suitable deoxidizers may be added to the melt of copper, cobalt and iron to insure complete deoxidation of the melt prior to the addition of the zinc or cadmium. The alloying elements are readily soluble in copper and enter into solution providing an alloy in which the alloying elements are uniformly distributed throughout the structure.

The alloy may be cast in massive, intricate or fine form in any suitable type of mold, such as a sand casting or chill cast mold. Where desired, the alloy may be cast directly into the predetermined shape of the article which is to be manufactured, after which it may be easily machined as required, or it may be cast to a pattern suitable for forging to the desired shape. In its cast condition, the copper, cobalt, iron and either zinc or cadmium alloy is comparatively ductile, being easily forged or drawn to shape.

Alloys comprising from small but effective amounts up to by weight of each of cobalt and iron and from a small but eilective amount up to 3% of metal selected from the group zinc or cadmium with the balance substantially all copper when heat treated, as hereinafter described, to precipitation harden them have been found to have high physical strength and good electrical and thermal conductivities.

In order to develop the mechanical strength and the electrical properties of the alloy, it may be subjected to a precipitation hardening treatment comprising subjecting the alloy to a high temperature below the melting point of the alloy for obtaining a high solid solution of the alloying metals in the copper, quenching the alloy from the high temperatures to retain the alloying metals in the solid solution, and then reheating the alloy to a lower or ageing temperature and holding it at this temperature for a period of time suflicient to precipitate the alloying elements from the solid solution state. In practice, heating at a temperature of between 750 C. and 1075 C. is found to effect a high solid solution of the alloying metals in the copper while a. re-heat at a temperature of between 450 C. and 600 C. effects an efficient precipitation of the alloying constituents.

Alloys comprising copper, cobalt, iron and either zinc or cadmium within the ranges hereinbefore given, when heat treated as described, have a high hardness, high ultimate strength and good conductivity. The heat treatment is found to be of special benefit to alloys comprising between .5% to 3% of each of the elements cobalt and iron and from a small but effective amount up to 3% of either zinc or cadmium with the balance substantially all copper.

In the alloy of this invention, it is desired to maintain the ratio of the cobalt to iron content between .5 and 1.25% since it is found that such ratios produce the best combination of properties in the alloy. Since the conductivity and hardness values of the alloy may be taken as a criterion of the alloy, it is evident that the best alloying proportions which will give the highest value as a product of the hardness and conductivity is to be preferred. In all cases, the highest product of the conductivity and hardness values for different combined cobalt and iron contents within the limits given is found to be obtained when the ratio of the cobalt to iron content approximates 1.

Either the zinc or cadmium additions to the alloy within the range given are effective in giving it a high ultimate strength and good conductivity. Further, it has been found that zinc or cadmium imparts a deionization effect to the alloys so that the alloy of this invention finds special use as a contact member of electrical switching apparatus. In this application, the zinc or cadmium which possesses a high vapor pressure aids in breaking up the arc encountered when contactors open under load. The presence of zinc in the alloy also imparts free machining characteristics to the alloy, while zinc or cadmium in amounts up to 3% functions to render the alloys more resistant to softening when exposed to high temperatures of about 500 C. for long periods of time. Such properties permit the alloy of this invention to be utilized in many different applications.

As representative of the benefits afforded the alloy by the addition of either zinc or cadmium, the following table gives the results obtained with different zinc and cadmium additions to an alloy in which the cobalt and iron contents are maintained constant at a preferred ratio of 1. In the table the copper content is omitted, it being understood that the balance of the alloying content comprises copper with possible incidental impurities occurring during the alloying process:

The alloys given in the foregoing table were subjected to a heat treatment consisting of quenching them from a temperature of 1000 C. and reheating or ageing them at a temperature of 500 C. for a period of time of 16 hours. With approximately 25% of cold working before ageing them the ultimate strength of these alloys can be increased to 90,000 pounds per square inch with a corresponding hardness of 90 Rockwell B. By ageing the alloys for 100 hours at 500 C., it is found that the conductivity values increase without decreasing the hardness values. This property of the alloys of retaining their hardness at high temperatures is of importance in many applications.

Although the heat treated alloys produced in accordance with this invention have an extremely high hardness, as cast, they are quite ductile and may be readily worked into the shape or form desired. These alloys have an extremely high hardness in the as quenched state and can be employed in place of bronze and brass in intricate designs and where there is danger of overheating such metals. The alloys prepared from the different alloying elements and within the ranges given hereinbefore are particularly useful in the manufacture of large castings such as commutator segments. Other uses of the alloys are as welding electrode tips or welding wheels or other articles where a good conductivity is required, together with high physical strength. These alloys may also be efficiently employed in applications such as cylinder heads for internal combustion engines where high thermal conductivity is required combined with high physical strength. The alloys may be cast directly into the predetermined shape of the article of manufacture or into a pattern suitable for forging or drawing.

It is, of course, to be understood that this invention is described with reference to specific embodiments thereof and that other and various modifications may be made without in any way departing from the spirit of the invention as set forth in the appended claims.

I claim as my invention:

1. An alloy comprising from a small but effective amount up to 5% of cobalt, from a small but effective amount up to 5% of iron, from a small but effective amount up to 3% of metal selected from the group consisting of zinc and cadmium, and the balance substantially all copper.

2. An alloy comprising from about .5% to 3% of cobalt, from about .5% to 3% of iron, from a small but effective amount up to 3% of metal selected from the group consisting of zinc and cadmium, and the balance substantially all copper.

3. An alloy comprising from about .5% to 3% of cobalt, from about .5% to 3% of iron, from a small but effective amount up to 3% of metal selected from the group consisting of zinc and cadmium, and the balance substantially all copper, the ratio of the cobalt to the iron being between .5 and 1.25 to 1.

4. An alloy comprising from .5% to 3% of cobalt, from about .5% to 3% of iron, from .2% to 1.5% of zinc and the balance substantially all copper.

5. An alloy comprising from .5% to 3% of cobalt, from about .5% to 3% of iron, from .2% to 1.5% of cadmium, and the balance substantially all copper.

6. An age hardened alloy comprising from about .5% to 3% of cobalt, from about .5% to 3% of iron, from a small but effective amount up to 3% of metal selected from the group consisting of zinc and cadmium and the balance substantially all copper, which has been quenched from a temperature of between 750 C. and 1075 C. and aged at a temperature of between 450 C. and 600 C.

7. As an article of manufacture, an alloy comprising from about .5% to 3% of cobalt, from about .5% to 3% of iron, from a. small but eflective amount up to 3% of metal selected from the group consisting of zinc and cadmium, and the balance substantially all copper, formed to a predetermined shape and precipitation hardened to give high physical strength and good conductlvlty.

8. An alloy comprising about 2% of cobalt, about 2% or iron and about 1.0% of cadmium with the balance substantially all copper.

JAIWES M. KELLY.