Combined effect of high-intensity ultrasonic treatment and Ca addition on modification of primary Mg2Si and wear resistance in hypereutectic Mg-Si alloys

The combined effect of high-intensity ultrasonic treatment (HIUST) and 0.3 wt.%Ca addition on modification of primary Mg2Si and wear resistance in the hypereutectic Mg-5 wt.%Si alloy has been investigated. The results show that without treatment, the dendrites of primary Mg2Si are coarse and non-uniform in size. With HIUST or 0.3 wt.%Ca addition, nearly fine uniform and polyhedral shape of primary Mg2Si are achieved. Interestingly, modification and refinement of primary Mg2Si arise from the combined effect of HIUST and 0.3 wt.%Ca addition. The sample due to combined effect of HIUST and 0.3 wt.%Ca addition has the best wear resistance due to the lowest weight loss among all the other samples for various loads (10, 30 and 50 N) at constant sliding speed (0.3 m/s). Modification mechanisms resulting in the development of microstructures are also investigated.