Development of Thermomechanical Processes as an Alternative to Grain Refiners in 18 Carat Gold Alloys

The use of grain refiners, such as iridium, in 18 kt gold alloys is a common practice in jewelry industrial applications. The use of these elements leads, however, to an increase in the costs of raw materials and greater attention during the solidification phases and during the refining and recycling of alloys is required. This work aims to demonstrate that through the optimization of thermo-mechanical processes, it is possible to obtain a result comparable to that obtained with refiner in terms of workability, mechanical and aesthetic properties and corrosion behavior. The study focused on evaluating the grain growth in annealing processes after plastic deformation, also examining the casting phase and the effect of the different cooling rates. The samples, after the different thermo-mechanical treatments, were characterized in terms of microstructure, grain size and micro-hardness comparing the results with the ones of an iridium-containing alloy. The results showed that with proper optimization of annealing time is possible to obtain, without grain refiners, gold alloys with properties similar to ones obtained with Iridium as a grain refiner.