Metallurgical processes for hardening of 22Karat Gold for light weight and high strength jewelry manufacturing

摘要

The present work reports about the process developed for hardening 22Karat gold (Au-5.8wt.%Cu-2.5wt.%Ag). The present hardness of 22Karat gold is 85–90HV (Vickers scale). The target hardness aimed is 150HV in the final jewelry product, similar to the hardness of 18Karat gold, however without compromising luster and purity (91.7wt.%). Titanium is added as the quaternary element in micro concentrations that grain refines the as-cast structure of 22Karat gold and improves the strength of the cast jewelry products. On other hand the narrow solid solubility of Ti in Au is used to convert the 22Karat gold into age hardenable gold alloy suitable for making hand-made jewelry products. This paper reports the optimization of various process parameters in industrial scale, required for producing hard 22Karat gold containing Ti through age hardening process. In lab scale the titanium concentration required was optimized to 0.5wt.%, to obtain effective age hardenability in 22Karat gold was studied. In industry the melting and casting trials of 22Karat gold with the addition of 0.5wt.% of Ti to obtain maximum yield was performed. The annealing and cold-working operations were conducted to the Ti-22Karat gold that lead to production of hand-made bangles were studied. The age hardening treatments (Solutionizing and Artificial Aging (AA)) were conducted to the Ti-22Karat gold bangles to obtain hardness >150HV.