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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.degree. C. for 30-45 min.

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First Claim