US2161574A - Silver alloy - Google Patents

Description

Patented June 6, 1939 SILVER ALLOY Franz R. Hensel, Kenneth L. Emmert, and James W. Wins. Indianapolis, Ind., assignors to P. R. Mallory & 00., Inc., Indianapolis, Ind., a corporation of Delaware No Drawing.

Application February 21, 1939, Serial No. 257,666

3 Claims. 01. 75-113) This invention relates to a new silver alloy and is concerned more particularly with an alloy which has improved physical and electrical characteristics. I

,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 retaining very low contact resistance, having negligible material transfer and having great resistance to welding and sticking under severe electrical loads.

Another object of the invention is to provide a new silver base alloy which has greatly increased tensile strength and which also shows considerable improvements so i'ar as corrosion resistance is concerned.

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 products thereof brought out and exemplifiedin the disclosure hereinafter set forth, the scope In the formation of ,the new alloy it is preferable to provide a composition of the materials specified in the following proportions Per cent Magnesium .05 to 15 Gold .05 to 25 Balance substantially all silver.

The preferred range 'of magnesium is .05 to 8% because up to that percentage the magnesium is taken upin alpha 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, strips, or the'like. The range of magnesium from 1 to 4% is especially useful. 1

Silver and gold form a continuous series of solid solutions, therefore alloys of silver and gold may readily be formed in any proportions. Gold-.

magnesium,- however, forms only a very limited alpha solution up to approximately 3% of mag-- nesium in gold. Our experiments were directed to a series of ternary compositions which form ternary solid solutions. It was found, however, that for certain purposes and applications where workability is not of prime importance alloys falling outside this ternary solid solution range can be used. One useful range of alloys is that con- 5 taining upto 3% of gold. Others fall within the range extending to gold.

,We have investigated a series of compositions and have found that the following alloys which .Per cent 1. Magnesium 3 Gold 1.8 Silver Balance 2. Magnesium 4 G l 7.5 Silver. Balance 3. Magnesium 2.5

Gold 20 Silver Balance 4. Magnes 15 Gold I 3 Silver Balance These ingredients in the proportions named above are melted together and poured into a suitable mold. It was found desirable to add the magnesium in the form'of a silver-magnesium master alloy of highymagnesiurn concentration. Alloys of this type have a lower melting point and therefore will go readily into the silver melt. Since silver-magnesium has a tendency to oxidize and form a dross it has been found desirable to melt such master 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 the chemical composition.

The resultant alloys within the range of a ternary solid solution have an electrical conductivity ranging from 15 to 30% International Annealed Copper Standard according to the respective compositions.

The tensile strength is materially increased by the magnesium without any appreciable loss of ductility. Brinell hardness of to can easily be obtained with this type of alloy'with the proper amount of cold working. The alloys of the present invention havea much higher recrystallization temperature than, for instance, 55

er temperatures without annealing. on the other hand-if sufiiciently high temperatures are employed such as approximately 650 to 800 C.,

the materials can be brought in a soft condition in which they can be readily cold worked.

The superior qualities of the present alloy for electrical purposes is outstanding. A comparison test was conducted wherein contacts of similar physical dimensions 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 priorart. The amount of material transfer of one contact to the other was also used as a method of comparison.

Contacts of the following compositions when operated under the above stated conditions gave outstanding performances compared to alloys'of the prior art. Some of the results are here given:

' Height of Limiting Contact material material current transfer A all 37 i 1 87 1d Ampere n oy magnes um go Alhaguancaitlven :.ig ;-.ia Greater than 19 .002 max.

or 11158119! 1111 8 1 balance silver Greater than 20 .001 max. Fine silver I 12 .010 (Join silver (silver-% copper) 11 .011

In the case of 'all these alloys transfer was experienced in a directional manner from the anode to the cathode, that is, from the positive to the negative side. The final contact resistance on these new alloy j, the composition'o'f 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 new composition containing 7.5%

.25 milliohms'for the alloy containing 1.8% gold and 3% magnesium, and .27 milliohms for the gold and 4% magnesium by weight:-

It will be noted from the above test results that the metallic transfer due to the operation of these contacts very markedly reduce the transfer experience on fine silver and that also this reduction in transfer has been attained in spite of the fact that the new alloys were operated at much higher current values and therefore under much more severe transfer producing conditions.

general the above data. show conclusively that the new compositions have reduced the transfer 2,161,574 fine silver and can therefore be subjected to highas compared to fine silver by values in the range 80 to 90% and have at the same time increased the limiting current by values in the range 90 to 100%.

Under the column above headed "Limiting cur rent we have stated the limiting currents to be over 19 amperes and over 20 amperes. It was not possible, with the source of power in use on the test bank at the time, to subject the new alloys to more severe conditions, therefore it is indicatedthat new alloys of the type we are disclosing I have current carrying capacities in excess of 100% over the current carrying capacity of fine silver for carrying current under the given test conditions.

The alloy of the present invention have been found useful for a large number of electrical contact applications such as, for instance, sensitivedirect current relays, overload cutouts, voltage regulators, indicating and recording gauges, thermostat controls and the like.

The other uses of the new alloy are in the form of silverware such as is used for jewelry purposes, tableware, industrial and similar applications. These alloys have color similar to gold, an advantage where the materials are used for jewlery purposes.

The alloy of the present invention has a commercial advantage since the addition of magnesium in the percentage contemplated provides a material of low specific gravity, the actual gravity of an alloy containing 7.5% of gold and 4% magnesium being 9 grins. per cc. as compared with fine silver which has a density of 10.5 grins. per cc. Therefore it is possible with such low density alloys as contemplated in the present invention to produce a larger number of finished products per 'unit weight of material.

While the present invention and its objects and advantages has been described herein, as carried out in the 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. A silver base alloy consisting oi .05 to 15% magnesium, .05 to 25% gold, baiance substantially all silver.

2. An alloy consisting of 1 to 4% magnesium, .05 to 10% gold, balance substantially all silver. 3. An alloy consisting of 1 to 4% magnesium, .5 to 3% gold, balance substantially all silver.