Manufacture of silver-copper-germanium alloy

Abstract

Silver alloys containing copper and germanium e.g. about 1 wt % Ge and of very low copper content e.g. about 0.8 wt % Cu can be precipitation hardened to 65 HV or above, whereas alloys of similar copper content and not containing germanium remain soft. In an embodiment, a silver alloy comprises 92.5-97 wt % Ag, 1-4.5 wt % Cu, 0.4-4 wt % Zn, 0.8-1.5 wt % Ge, 0 to 0.2 wt % Si, In or Sn and 0-0.2 wt % Mn, the balance being boron as grain refiner, incidental ingredients and impurities. The said alloy preferably comprises boron as grain refiner added as a boron hydride, e.g. sodium borohydride. A further group of alloys comprises a ternary alloy of silver, copper and germanium containing from more than 93.5 wt % to 95.5 wt % Ag, from 0.5 to 3 wt % Ge and the remainder, apart from incidental ingredients (if any), impurities and grain refiner, copper, the grain refiner being sodium borohydride or another boron hydride. Silicon-containing casting grain that gives rise to bright as-cast products is also disclosed. In a further embodiment, a zinc-containing silver alloy resistant to tarnish under severe conditions e.g. exposure to human sweat or French dressing comprises 1-5 wt % Zn, 0.7-3 wt % Cu, 0.1-3 wt % Ge, 0-0.3 wt % Mn, 0-0.25 wt % Si, B in an amount effective for grain refinement, up to 0.5 wt % incidental ingredients, the balance being Ag in an amount of 92.5-96 wt %, and impurities. A preferred manufacturing method giving an alloy with favourable physical properties involves melting together the ingredients, and incorporating boron by dispersing into molten silver alloy to foirn the whole or a precursor pait of said alloy a compound selecting fiom alkyl boron compounds, boron hydrides, boron halides, boron-containing metal hydrides, boron-containing metal halides and mixtures thereof The alloy is particularly suitable for castings which may be hardened in an oven e.g. at about 300 DEG C. for 30-45 min.

Description

field of invention [0001] The present invention relates to methods of making precious metal alloys and to precious metal products made from such alloys. Background of the invention [0002] Many attempts have been made to produce silver alloys that resist tarnish and / or firestain. [0003] In nearly all of the largest manufacturing companies, most of the annealing and soldering required to assemble finished or semi-finished products is performed with the flame of an air-fuel gas torch. The oxidizing or reducing nature of the flame and the temperature of the article are controlled only by the skill of the silversmith. Pure silver allows oxygen to pass through easily, especially when the silver is heated above its red hot state. Silver does not oxidize in air, but copper in silver / copper alloys is oxidized to cuprous oxide or cupric oxide. Pickling the oxidized surface of the article in hot dilute sulfuric acid removes the copper oxide at the surface rather than at deeper l...

AI Technical Summary

Problems solved by technology

Above 4:1, the alloy is more prone to exhibit fire spotting, while below 3:1, the high germanium content causes formability issues

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