process for producing a copper germanium boron vorlegierung and its use for the manufacture of silver copper alloys

摘要

A master metal composition adapted for alloying with silver to give an alloy containing at least 77 wt % Ag and at least 0.5 wt % Ge comprises Cu, Ge and boron together with any further ingredients for said alloy and any impurities. It further provides a process for making silver alloy containing silver in an amount of at least 77 wt % Ag, 1-7.2 wt % Cu copper, at least 0.5 wt % Ge and B together with any further ingredients for said alloy and any impurities, comprising the step of melting together fine silver and a master metal composition which is at least a ternary alloy of copper, germanium and boron, e.g. 92.5-92.8 wt % Ag, 6.0-6.3 wt % Cu, about 1.2 wt % Ge and 1-15 ppm boron as grain refiner. The resulting silver alloy exhibits good tarnish and firestain resistance and can exhibit significant precipitation hardening on gradual air cooling. In a further aspect the invention relates to method for manufacturing a copper-based master alloy for use in the manufacture of silver alloy products, wherein the molten master alloy prior to solidification is treated with a decomposable boron compound e.g. a boron hydride or metal borohydride.