Strengthening of Calcium Microalloying in Pure Gold

The mechanical properties of calcium(Ca) microalloyed 24 carat gold(Au 99.9 Ca 0.1) were measured and the corresponding microstructure was observed by TEM in order to investigate the strengthening mechanism.It was observed that the microalloying of 0.1wt% Ca improved the tensile strength(by 79% and 57% for the rolling and annealing states,respectively),hardness and E-Modulus as well as reduced the ductility of the 24 carat Au.Dispersed nano-sized precipitates and high density deformation twins were found in the rolled Au 99.9 Ca 0.1,which are attributed to be the major strengthening factors.The twins subsided after annealing and the strengthening of the annealed Au 99.9 Ca 0.1 is mainly contributed by the coarsened semi-coherent precipitates.