Microstructure study of particle reinforced AZ91D and AM50 magnesium alloy semisolid casting

摘要

Semisolid metal (SSM) casting offers a number of advantages compared to other casting processes such as reducing cast defects, eliminating dendritic morphology and improving microstructural uniformity. The high shear rate and turbulence involved in the SSM process can contribute to achieving a uniform distribution of the reinforcing phase when producing metal matrix composites (MMCs). Microstructure investigation of SiC particles reinforced AZ91D and AM50 produced by SSM was conducted by means of optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy chemical analysis. Correlation between the process parameters and the microstructure was found. Microstructure stability was studied by performing aging experiments at 180°C, and the microstructure was found to be unstable, namely precipitation of secondary β(Mg₁₇Al₁₂) phase was detected. The instability of the microstructure can be explained on the basis of the solidification process.