Fabrication and Characterization of Cast Magnesium Matrix Composites by Vacuum Stir Casting Process

A vacuum stir casting process is developed to produce SiCp reinforced cast magnesium matrix composites. This process can eliminate the entrapment of external gas onto melt and oxidation of magnesium during stirring synthesis. Two composites with Mg-Al9Zn and Mg-Zn5Zr alloys as matrices and 15 vol.% SiC particles as reinforcement are obtained. The microstructure and mechanical properties of the composites and the unreinforced alloys in as-cast and heat treatment conditions are analyzed and evaluated. In 15 vol.% SiCp reinforced Mg-Al9Zn alloy-based composite (Mg-Al9Zn/15SiCp), SiC particles distribute homogenously in the matrix and are well bonded with magnesium. In 15 vol.% SiCp reinforced Mg-Zn5Zr alloy-based composite (Mg-Zn5Zr/15SiCp), some agglomerations of SiC particles can be seen in the microstructure. In the same stirring process conditions, SiC reinforcement is more easily wetted by magnesium in the Mg-Al9Zn melt than in the Mg-Zn5Zr melt. The significant improvement in yield strength and elastic modulus for two composites has been achieved, especially for the Mg-Al9Zn/15SiCp composite in which yield strength and elastic modulus increase 112 and 33%, respectively, over the unreinforced alloy, and increase 24 and 21%, respectively, for the Mg-Zn5Zr/15SiCp composite. The strain-hardening behaviors of the two composites and their matrix alloys were analyzed based on the microstructure characteristics of the materials.