US2127117A - Copper alloys - Google Patents

Description

Patented Aug. 16, 1938 COPPER ALLOYS Franz R. Hensel, Indianapolis, Ind., assignor to P. It. Mallory 8; 00., Inc., Indianapolis, Ind., a corporation of Delaware No Drawing. Application February 5, 1937, Serial No. 124,230

3 Claims.

This invention relates to alloys and more particularly to copper base alloys of improved characteristics.

An object of the invention is to improve the hardness and tensile properties of copper base alloys of the type disclosed.

Another object is to improve the temperatureresistant characteristics of such an alloy.

Further objects are to improve the electrical characteristics of the alloy such as electrical conductivify.

Still further objects are to improve the pouring qualities and handling characteristics of the alloy during foundry treatment and later operations.

Other objects 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 is described 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.

The present invention contemplates an alloy formed by the combination, in suitable proportions, of copper, chromium and lithium.

It has already been proposed to use chromium as an alloying element with copper, in order to obtain a combination of high tensile'and electrical properties. The disadvantage of a straight copper-chromium alloy has been that durin melting and pouring of such an alloy, an excessive amount of chromium oxide has been formed. Chromium itself, has a greater afiinity for oxygen than copper, and it will therefore reduce copper oxide and form'chromium oxide. prevent the formation of chromium oxide, deoxidizers such as silicon have been added. However, by the addition of silicon, the electrical conductivity is being considerably decreased, because part of the silicon is dissolved in the copper, and it is a generally known fact that a solid solution of copper with another element will have a lower electrical conductivity than pure copper.

' The present invention contemplates the improvement of the electrical conductivity of copper-chromium alloys, which comprises adding from .005 to .1% of lithium to .the copper-chro- In order to mium alloy in the molten state, so that suflicient residual lithium remains to insure that the final product isternary alloy containing copper,- chromium and lithium, preferably in the following proportions:

Percent Lithium .002 to .01 Chromium .1 to 1.5 Copper Remainder While copper-chromium alloys containing an excess of silicon will show an electrical conductivity of approximately 75%, the copper-chromium-lithium alloy of the present invention will show electrical conductivity values as high as to Every increase in electrical conductivity is of enormous importance in the construction of electrical machinery. Not only the electrical conincreased. A decrease of 10% in electrical conductivity, for instance, in such parts as field windings of an electrical machine will cause electrical losses which will raise the operating temperature considerably, and might endanger the life of such a machine, because higher operating tem- 'peratures will mean more creep of the copper parts, and possible damage of the insulation.

' Higher electrical conductivity with the same degree of strength will also be of enormous importance for such parts as spot welding tips and spot welding wheels. The points will not heat up so fast, and-furthermore, they will conduct the heat away much more rapidly from the zones of heat concentration.

A suitable alloy for many purposes has been made having the ingredients in the final alloy, preferably in the following specific proportionsz' Percent Lithium g .003 Chromium .5 Copper Remainder 'From the above compositions, it is evident that the present invention does not contemplate the addition of lithium as a deoxidizer only. Sufficient lithium is added to the copper base to insure that the residue thereof retained in the copper-chromium alloy does not amount to less than a certain desired percentage. For deoxidizing purposes only, it add other elements of the alkali group, such as sodium, potassium, or elements of the alkaline earth group or alloys thereof.

ductivity, but also the heat conductivity is being H is possible to 'incorporated'in the mixture.

In carrying out the present invention, the alloy may be made according to the following proce form of a copper-chromium hardener,.which can be prepared either by melting together copper and chromium, or by compressing copper and chromium powders which are commercially available. If compressed copper-chromium briquettes are beingused, a deoxidizing agent may be also In order to obtain complete freedom of oxide inclusions of either copper oxide, or chromium oxide, it is advisable to add a definite percentage of lithium just before pouring. That is, after the chromium has been alloyed with copper. Such a procedure will give an extremely clean melt and improve the characteristics of the final alloy. If chromium oxide is present in the final alloy, it tends to segregate in the grain boundaries and therefore weaken the grain boundaries, particularly at elevated temperatures.

The inventor has made experiments and found that liquid tin will penetrate into the grain boundaries of a copper-chromium alloy which contains chromium oxide, while it will not penetrate into a copper-chromium-lithium alloy which is completely free of copper and chromium oxide. The property of withstanding intercrystalline attack is very important for such applications as the welding of terne plate. Intercrystalline corrosion in this case will cause cracking, along the grain boundaries and shorten the life of the spot welding tips or spot welding wheels. very considerably.

The completed alloy may be cast in any form suitable for working, suchas billets or plates. The billets can be extruded at a temperature of approximately 1600 C. and can be cold or, hot drawn to the desired dimensions. The material can also be hot or cold rolled.

In the further treatment of the alloy, it may be first heated to a temperature of about 700 C. for such a time as to allow the material to'become homogenous, such as from 10 to 30 minutes. After the metal has reached the desired temperature, it'may be cooled quickly from the high temperature by quenching in water. In this condition the material is extremely soft and has a low electrical conductivity.

The next step is preferably to heat treat or bake the quenched alloy at a temperature below 700 C. for a period from a few minutes to 30 hours or more, depending upon the temperature, and percentage of hardener used, and the results desired. An alloy containing .003% lithium, .5% chromium and the remainder copper, after heat treatment, has a hardness of 65 Rockwell B, and an electrical conductivity better than 85% that of copper. I I

The alloy may then. be cold worked to obtain a cold reduction of approximately 25%, and further cold reduction up to 50% or more may be applied to further increase the hardness. It has been found that the conductivity will not be appreciably decreased by these reductions, while a hardness of 85 on the Rockwell B scale may be obtained.

For maximum hardness and conductivity, a

series of cold reductions alternated with relatively low heat treatment may be applied.

The present alloy ofiers considerable improvements in foundry handling. The chromium recovery during alloying is considerably better than with other deoxidizers previously used. The lithium also appears to protect the chromium in the alloy from burning out when the alloy is heated to high temperatures.

This alloy is exceptionally well adapted, because of the above properties to the production of resistance welding electrodes, commutator segments, collector rings, trolleys, trolley wheels, trolleyshoes, contacts, contactors, field windings and the like. For each application the hardener may be used in such proportions as to obtain the desired hardness and conductivity.

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 intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. An alloy consisting of lithium .002 to 01%,

chromium .10 to 1.5% and the remainder copper. 2. A resistance welding electrode formed from an alloy consisting of lithium substantially .002 to .01%, chromium substantially .1 to 1.5% and the remainder substantially all copper. 3. A heat treated alloy consisting of .10 to 1.5%

chromium, .002 to .01% lithium, and the re-' mainder substantially all copper, which alloy has the high hardness and electrical conductivity imparted by quenching from a temperature above 700 C. and subsequently baking at a temperature below 700 C.

v FRANZ R. HENSEL.