Processing, microstructure and mechanical properties of bimodal size SiCp reinforced AZ31B magnesium matrix composites

The bimodal size SiC particulates (SiCp) reinforced magnesium matrix composites with different ratios of micron SiCp and nano SiCp (M-SiCp:N-SiCp = 14.5:0.5, 14:1, and 13.5:1.5) were prepared by semisolid stirring assisted ultrasonic vibration method. The AZ31B alloy and all as-cast SiCp/AZ31B composites were extruded at 350 °C with the ratio of 12:1. Microstructural characterization of the extruded M14 + N1 (M-SiCp:N-SiCp = 14:1) composite revealed the uniform distribution of bimodal size SiCp and significant grain refinement. Optical Microscopy(OM) observation showed that, compared with the M14.5 + N0.5 (M-SiCp:N-SiCp = 14.5:0.5) composite, there are more recrystallized grains in M14 + N1 (M-SiCp:N-SiCp = 14:1) and M13.5 + N1.5 (M-SiCp:N-SiCp = 13.5:1.5) composites, but in comparison to the M13.5 + N1.5 composite, the average grain size of the M14 + N1 composite is slightly decreased. The evaluation of mechanical properties indicated that the yield strength and ultimate tensile strength of the M14 + N1 composite were obviously increased compared with other composites