Development of thermo-mechanical processes as an alternative to grain refiners in 14 carats gold alloys

The use of grain refiners such as iridium in 14 Kt gold alloys is now a common practice in industrial applications also in goldsmith industry. However, the use of these elements leads to an increase in the costs of raw materials and greater attention is required during the solidification phases and when refining and recycling of the material it's necessary. This work aims to demonstrate that through the optimization of thermomechanical processes it is possible to obtain a result comparable in terms of workability, mechanical and aesthetic properties to that obtained with the refiner. The study focused on evaluating grain growth in recrystallization processes during annealing after cold rolling, also examining the melting phase and the effect of different cooling rates during casting. The samples after the different thermo-mechanical treatments were characterized in terms of microstructure, crystals size, micro-hardness and colour properties by comparing the results with those of an alloy containing iridium.