Fabrication and Properties of Cast and Extruded SiCw/AZ91Mg Composites

Summary

Cast composites of SiC whisker reinforced AZ91 magnesium alloy were fabricated by high pressure infiltration of the alloy melt, and extruded composites by subsequent hot-extrusion of the cast composites. Structures of both composites were compared including the aspect ratio distribution of the SiC whiskers, and mechanical properties were examined at room and elevated temperatures. Unidirectional alignment of SiC whiskers was attained by hot extrusion accompanied with a significant decrease in the average aspect ratio due to their breakage. Both elastic modulus and tensile strength at room temperature of the extruded composites were higher than those of the cast counterparts. Thus, the extruded composites showed remarkably high specific modulus and specific strength. At elevated temperatures, decreases in tensile strength are more pronounced for the extruded composites, and the cast composites showed higher tensile strength at above 473 K. Higher elongation was observed for the extruded composites at these temperatures. Differences in mechanical properties between the cast and extruded composites at elevated temperatures were explained by the differences in grain size of the matrix. The extruded composites showed much finer grain structures developed by hot-extrusion.