TARNISH RESISTANT SILVER ALLOY AND PRODUCING METHOD THEREOF

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Disclosed is a tarnish resistant silver alloy with the composition of (by wt%) : silver 82.5-92.5%, cobalt 1.5-7.5%, nickel 0.5-2.5%, and copper 0.5-15%, wherein the weight ratio of cobalt and nickel is controlled within 2.5~3.5 : 1. The method for producing the silver alloy comprises the following steps : mixing raw materials according to the ratio, melting in a vacuum induction melting furnace, and then cooling to room-temperature to form cast ingot. The silver alloy comprises no noble metal and rare metal; has simple composition and low cost. The alloy can form a thin and dense intercalation oxide CoNiO on surface in atmosphere, has high tarnish resistance and can maintain the gloss of silver. The alloy has a hardness similar to that of sterling silver usually used at present and good machinability, and adapts to jewellry industry. The process of electric plating to the alloy is unnecessary.