US2161575A - Silver alloy - Google Patents

Description

Patented June 6,1939

UNITED ATES PATENT OFFICE-9 SILVER ALLOY Frans B. Hansel, Kenneth L. and James W. Wiggl, Indianapolis, Ind., assign'orl to 1'. IL

characteristics.

Mallory a 00., Inc., Indianapolis poration of Delaware No Drawing. Application March 1s, 19:

Serial No,

This invention relates to a new silver alloy and is concerned more particularly with an alloy which has improved physical and electrical It is one of the objects of the invention to provide a silver base material which can be used for an electrical make and break contact, containing very low contact resistance, having negligible material transfer, having great resistance under. "severe electrical loads, to welding and sticking.

Another object of the invention is, to provide a new silver base alloy, which has greatly increased tensile strength, and which shows a great improvement in resistance to tarnishing and corrosion.

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

While a preferred embodiment of the invention is described herein, it is' contemplated that a considerable variation may be made in the methad of procedure and the combination of elements, without departing from the spirit of the inven- 'tion.

' The present invention comprises basically silver, to which has been added magnesium and cadmium. In the formation of the new alloy, it is preferable to provide a composition of the materials specified in the following proportions:

. Percent Magnesium .05 to 15 ('adminm ,5 to Silver Substantially the balance The preferred range of magnesium is .1 to 8%, because up'to that percentage, the magnesium is taken up in alpha solid solution in silver, and we have found that silver and magnesium up to 8%, can be alloyed very. readily and the cast ingots can be rolled, swaged, or .drawn into desirable shapes, such as sheet; bar stock, wire, strip and.

the like.

Silver and cadmium form a solid solution up to 45%; therefore, alloys of the class described in the present patent, are ternary solid solutions of magnesium, cadmium and silver.

Wehave investigated a series of compositions and have found that the following alloys, which are given by way of example only, have shown very excellent results, such as increased strength and increased tarnish resistance. The alloys have also shown particularly good electrical properties if used in the form of electrical contacts.

Silver The ingredients in the. proportions named above, may be melted together by conventional methods, and poured into suitable molds. m

It was found desirable to add the magnesium in the form of a silver-magnesium master alloy of high magnesium concentration. Alloys of this type have a lower melting point, and therefore will go readily into the silver melt, Since silvermagnesium has a tendency to oxidize and form a dross, it has been found desirable to melt such alloys, either in a reducing or neutral atmosphere,

or use suitable fluxes, which cover the melt.

The addition of magnesium in the form of a master alloy has also reduced the loss of magnesium, and therefore has, made it possible to hold .closer tolerances in chemical composition.

The resultant alloys within therange of ternary solid solutions have electrical conductivlties, ranging from 20 to International annealed copper standard according to the respective compositions.

An alloy, for instance, containing 356% magnesium and 7% cadmium, had an electrical con- 40 ductivity of 22%. The hardness of this material in the as cast condition, was 26 Rockwell 1". After swaging 30%, this hardness increased to 85 Rockwell F. We'have found that a Brinell hardness of 70 to 130, can be easily obtained with 46 these types of alloys with the proper amount of cold working.

The alloys of the class described have shown very excellent qualities, when used for electrical purposes. A comparison test was conducted 50 were tested on a resistive inductive circuit, at 470 cycles per minute, and wherein the current flowing in the circuit was increased periodically, to obtain definite current values of alloys in the nature described above, in comparison with contact materials produced in the prior art. The amount of material transfer of one contact to the other, was used as the prime method of comparison.

A most surprising result was found in this test. It was discovered that contacts of the type described, and more particularly ones formed from an alloy containing 3.5% magnesium and 7% cadmium, showed no material transfer whatsoever. Fine silver under the same conditions would show a material transfer of .010", and coin silver would show a material transfer of .011".

The test data is tabulated as follows:

i A Critical Transfer current height Amperec Fine silver 12 .010 negative. Coin silver 11 .011" negative. $59k g*'-7.0% Cd3.5% Mg 12 None.

The final contact resistance on these new alloys, the compositions of which are given above, did not substantially exceed values obtained for fine silver, under identical test conditions. In fact, under these severe operating conditions, the contact resistance actually measured .28 milliohm for the alloy containing 3 magnesium,-

and 7% cadmium.

The alloys of the present invention have been found useful for a large number of electrical contact applications, such as for instance, sensitive direct current relays, over-load cut outs, voltage wherein contacts of similar physical dimensions regulators, indicating and recording gaugers, thermostatic. controls, and the like.

The other uses on the new alloy are in the form of silverware, such as is being used for jewelry purposes, tableware, industrial and simi-' intended to cover the invention broadly, within the spirit and scope of the appended claims.

What is claimed is:

1. A silver base alloy consisting of magnesium .1 to 15%, cadmium .5 to 25% and silver substantially the entire balance.

2. A silver base alloy consisting of magnesium .1 to 8%, cadmium .5 to 25% and silver substantially the entire balance.

3. A silver base alloy consisting of magnesium 1 to 4%, cadmium .5 to 25% and silver substantially the entire balance.

4. A silver base alloy consisting of magnesium 1 to 4%, cadmium 5 to 20% and silver substantially the entire balance.

5. A silver base alloy consisting of about 3.5% magnesium, about 7% cadmium and about 89.5% silver.

FRANZ R. HENSEL. IQIN'NETH L. EMMERT. JAMES W. WIGGS.