Silver alloy compositions

Abstract

Fire-scale resistant, work-hardenable-jewelry, silver-alloy compositions having desirable properties of reduced fire scale, reduced porosity, oxide formation and reduced grain size relative to traditional sterling silver alloys while providing improved work hardening performance. These compositions contain at least 86% by weight silver, 0-5-7.5% by weight copper, 0.07-6% by weight of a mixture of zinc an silicon with silicon being present in an amount from about 0.02 to about 2.0% by weight, and from about 0.01 to no more than 2.0% by weight germanium.

Description

FIELD OF THE INVENTION [0001] This invention relates to silver alloy compositions. [0002] This invention has particular references to sterling silver alloy compositions of silver content of at least 92.5% for jewelry, flatware coinage and other applications where a work hardening alloy is required and for illustrative purposes reference will be made to this application. However, it is to be understood that this invention could be used to produce other types of silver alloys suitable for use as for example, electrical contacts or the like. BACKGROUND OF THE INVENTION [0003] In general, silver as a material for the production of silverjewellery, certain coinage and the like is specified to be sterling silver comprising at least 925 parts per thousand by weight fine silver and is specified as “0.925 silver”. 0.925 silver accordingly typically comprises an alloy 92.5% by weight silver, generally alloyed with copper for hardness traces of other metals as additives or impurities. [0004] C...

AI Technical Summary

Benefits of technology

[0008] The present invention aims to provide silver alloy compositions which substantially alleviate at least one of the foregoing disadvantages. A further object of the present invention is to provide silver alloys having the desirable properties of reduced fire scale, reduced porosity and oxide formation and reduced grain size relative to traditional sterling silver alloys whilst providing improved work hardening performance over the current firescale resistant alloys. Other objects and advantages of this invention will hereinafter become apparent.

[0017] Preferably, the alloy also includes rheology modifying and other additives to aid in improving the castability and / or wetting performance of the molten alloy. For example, about 0.0 to 3.5% by weight of a modifying additive selected from one or a mixture of indium and boron may be advantageously added to the alloy to provide grain refinement and / or reduce surface tension, thereby providing greater wettability of the molten alloy. Where used, preferably the amount of boron utilized in the composition is from about 0 to 2% by weight boron and / or about 0 to 1.5% by weight indium. Other alloying elements may be added such as gold, tin or platinum. Where tin is included in the composition, this may be advantageously used up to about 6% by weight, and is preferably utilized in an amount of from about 0.25 to 6%.

Problems solved by technology

Principal limitations include a characteristic firescale formation tendency attributable to oxidation of copper and other metals at the surface of cast or hot worked pieces.

Additionally, traditional alloys have exhibited undesirable porosity in the recast metal and less than desirable grain size properties.

A disadvantage of the hereinbefore described firescale resisting alloys is that the alloys exhibit poor work hardening qualities thus not achieving the mechanical strength of traditional worked 0.925 silver goods.