Gold diffusion process and shaped metal articles thereby

Abstract

An improved gold diffusion coated shaped copper alloy article is provided by forming a copper alloy with chemical composition in the range 1 to 10% of aluminum and/or 0 to 10% of tin and optionally from 0 to 5% of free machining additives such as lead, selenium, tellurium, silicon, or others, remainder copper, into a desired shape and heating the shaped article to a temperature of from 700.degree.C to 900.degree.C and thereafter quenching the article at a controlled rate either in a gas or liquid quenchant. The shaped and hardened article is then galvanically coated with a layer of gold or gold alloy from 1 to 5 microns thick, and the gold coating diffused into the hardened copper alloy body by heating at a temperature from 400.degree.C to 900.degree.C for from less than one minute to 30 minutes, thereby diffusing the gold into the hardened base copper alloy. The process is particularly useful in forming watch bezels. The heating and quenching of the shaped copper alloy article forms a fine-grained eutectoid duplex two phase structure which is believed to enhance the rate and depth of diffusion and evenness of penetration of the gold layer. Gold coated hardened copper alloy articles of enhanced durability, resistant to corrosion, and having an aesthetically pleasing finish are obtained. In a preferred embodiment, a watch bezel is shaped from copper alloy with chemical composition of 7% aluminum, 7% tin and optionally up to 5% free machining additive such as lead, selenium, tellurium or others, remainder copper which is shaped and machined to the configuration of the watch bezel, heated to 900.degree.C and quenched at a desired cooling rate by means of gas or liquid quench. The shaped article is then galvanically plated with a 5 micron layer of 24 karat gold and the plated article heated at 600.degree.C for 15 minutes.