US2025662A - Copper alloys - Google Patents

Description

Patented Dec. 24, 1935 UNITED STATES PATENT OFFICE COPPER ALLOYS No Drawing. Original application March 8, 1934.

Serial No. 714,614. Divided and this application February 8, 1935, Serial No. 5,578

4 Claims.

This invention relates to alloys and particularly to copper base alloys which have improved mechanical, thermal and electrical properties.

Certain metals have been added to copper to produce an alloy having better mechanical properties, but generally such alloys have been quite inferior to copper as conductors of electricity, and it has been difficult to duplicate the resulting characteristics.

An object of this invention is to produce an alloy of copper in which one or more hardening elements are distributed throughout the resulting alloy in a finely divided state improving the mechanical properties of the alloy and maintaining a high electrical and thermal conductivity comparable to that of copper.

This application is a division of Serial No. 714,614, W. E. Case 17,783, filed March 8, 1934, and directed to Copper alloys.

In order to produce a copper base alloy which will have desired mechanical and electrical properties, one or more metals which can be caused to precipitate to form a dispersion of fine particles throughout copper is added to the copper melt. It has been discovered that a copper alloy containing even small proportions of chromium has excellent mechanical and electrical properties when suitably heated treated. Further, improvement in mechanical and electrical properties of the copper base alloy is obtained by the addition of other metals, such as zirconium, boron, uranium and thorium.

Alloys having excellent mechanical and. electrical properties may be produced by adding chromium to a copper melt. The introduction of the chromium into molten copper to form a solution is dificult for chromium dissolves but slowly in copper and the amount finally dissolved is small. The free chromium difiers in density from copper and tends to segregate in the melt and to result in lack of homogeneity in the resulting solid product. Moreover, chromium be ing lighter than copper, it is dimcult to keep the chromium submerged for the time required to dissolve it. The chromium tends to rise to the surface of the melt where oxides are formed that contaminate the product.

In practice, finely divided chromium may be added to the copper melt in the form of a compacted mass or mixture in order that the chromium will be dissolved in and not tend to segregate from the copper melt. One of the preferred forms in which the chromium is added to the copper melt is as a cake, pellet or rod compacted from intermixed copper and chromium powders.

In producing the cake, pellet or rod of intermixed copper and chromium powders, the copper and chromium metals are powdered to ap- 5 proximately mesh size and then thoroughly mixed and compressed to sufficient density to prevent fioating of the chromium on the molten cop'- per. A pressure of about 60,000 pounds per square inch on the intermixed copper and chromium powders produces a mass which has a density of about 8.5. Lower pressures and lower densities, however, may be employed.

Another method of producing the powdered copper and chromium metals into the form desired is to alternately compress the powdered mixture under a'pressure of 4000 pounds per square inch and then heat the compressed mass in a reducing atmosphere to sinter the particles. A modification of this method is to heat the com- 20 pressed mass in a reducing atmosphere to approximately the melting point of copper and then to quickly strike the mass a hard blow, as in the die under a punch press.

The finely divided chromium powder may also 25 be enclosed in copper tubes of suitable size, instead of in the form of the compressed and sintered masses hereinbefore described. The copper tubes containing the chromium powder are swaged to suitable compactness for addition to the molten metal. Such articles may be employed as hardening and scavenging additions to other alloys.

The copper base alloys which have between .08% and 2.54% chromium content and particularly between .5% and 1.5% chromium content have excellent mechanical and electrical properties and may be employed in making sand castings of complicated design. In casting alloys where the chromium content is above 1.5% there is a tendency for the chromium to separate and segregate to the top of the casting and to thus produce unsound castings. This segregational effect of the high chromium content in the alloy may be reduced by the use of rapidly cooled types 45 of molds. Slower cooled types of molds may be employed where the chromium content of the alloy is about 5%. The alloys formed by such an addition have good pouring qualities and when suitably heat treated have excellent mechanical 50 and electrical properties.

In practice the castings made from the copper base alloys are aged by a suitable heat treatment to develop themechanical and electrical properties of the alloy. A method which has been found 55 to be satisfactory for developing the properties of. the alloy is to heat the casting to between 600 and 1,000 (3., quench or quickly cool it, and then reheat it to between 250 and 600 C. Where ieasible, an intermediate cold working step may be interposed between the quenching and ageing steps.

Copper chromium alloy castings, when heat treated by this method, have been consistently made under commercial conditions with an average conductivity of over and under laboratory conditions with a conductivity of A copper chromium alloy in which the chromium content is' less than 5% when suitably heat treated has a hardness of over Brinell, an ultimate strength or 56,000 pounds per square inch, 25% elongation and high resistance to creep.

Qther additions may be made to the copper chromium melt to obtain a ternary or higher alloy that exhibits high conductivity and excellent mechanical properties. The addition of zirconium to the copper chromium melt produces an alloy, which when cast and heat treated develops better physical properties than the copper chromium alloy. A casting of an alloy containing 1.5% chromium and 2.6% zirconium with the balance copper, after a suitable heat treatment, has a Erinell hardness of 152 while the electrical conductivity of the alloy is 65% of that of copper.

'If the zirconium content is decreased to about 1%, the electrical conductivity of the resulting heat treated alloy is raised to about 80% of that of copper.

Zirconium moreover accomplishes cleansing or scavenging of the alloy without reducing its electrical conductivity. The zirconium content may range from traces to approximately 5%. Alloys having a zirconium content of .5% and a chromium content of from a few hundredths of a percent to about 5% with the balance copper are suitable for many purposes depending on the hardness and conductivity required. It is thus evident that by adjusting the relative amounts of alloying metals, alloys having a desired hardness or a desired conductivity may be secured.

Satisfactory alloys which have high mechanh cal and electrical properties are termed where a content of up to 5% oi? boron, urani and aoaacea thorium is maintained in the copper chromium alloys. Boron, although substantially insoluble in copper, may be brought into solution in the copper chromium melt. Boron, boron carbide and calcium boride, when added to the copper chro- 5 mium melt act as a scavenging flux as well as an alloying element.

Alloys prepared from the difierent alloying elements and within the ranges given above are particularly useful in the manufacture of large 10 castings such as commutator segments and collector rings for dynamo electric machines. These alloys having high strength and high conductivity are particularly adapted to be employed as the tips for mechanically operated welding 15 electrodes, or as welding wheels, or as current collecting nozzles on automatic arc welding heads. Further, an important use for these high strength alloys is as cylinder heads for internal combustion motors such as for automobile engines. 20'

These fields require a metal of high electrical or thermal conductivity combined with high strength at somewhat elevated temperatures.

These alloys are further suitable for use at nor-' mal or low temperatures, as required for trans- 25 1111581011 wires.

It is, of course, to be understood that various modifications may be made in the alloying constituents, as above described, without in any way departing from the spirit of the invention as set 3 forth in the. appended claims.

We claim'as our invention:

1. An alloy comprising from .08% to 2.54% of chromium, from a small but efiective amount up to 5% of metal selected from one of the metals in 35 a group consisting of zirconium and thorium and the balance copper.

2. An alloy consisting of from .08% to 5% oi chromium, from a small but effective amount up to 5% of zirconium and the balance copper. '40

3. An alloy comprising about 1.5% of chromium, about 2.5% of zirconium and the balance copper.

4. An alloy comprising from .08% to 2.54% of chromium, from a small but efi'ective amount up G5 to 5% of thorium and the balance copper.

FRANZ R. SEL.

L I. LARSW.