Fabrication, microstructures, and tensile properties of magnesium alloy AZ91/SiCp composites produced by powder metallurgy

The tensile properties and microstructural evolution of hot extruded AZ91 magnesium alloy with and without reinforcement of SiC particles have been investigated in terms of extrusion parameters, such as extrusion ratio and extrusion temperature. Also, the effect of SiC particles on the grain size of the matrix in the composites was evaluated using the Hall-Fetch equation. The AZ91 magnesium alloy powders prepared by wet attrition milling from magnesium machined chips were hot pressed with and without SIC particles, hot extruded and then solution treated. Microstructural observation revealed that both the composites and the magnesium alloy have fine equiaxed grains due to the dynamic recrystallisation during hot extrusion. The tensile strength of both materials increased with increasing extrusion ratio, and the strengths of the composites were higher than that of the magnesium alloy without reinforcement. It was found that the tensile strength of both the materials decreased after solution treatment, and the decrease in tensile strength of the composites was considerably smaller than that of the magnesium alloy. From analyses of the microstructures and the mechanical properties, combined with examination of the Hall-Perch relationship the refinement of the matrix was primarily responsible for the improvement in the yield strength of the composites. The grain growth of the matrix was inhibited by the introduction of the SiC particles. (C) 1997 The Institute of Materials.