| 摘要 |
<p>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% Si5 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 form the whole or a precursor part of said alloy a compound selecting from 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 3000C for 30-45 min.</p> |
