Effect of submicron size SiC particulates on microstructure and mechanical properties of AZ91 magnesium matrix composites

In the present study, AZ91 magnesium matrix composites reinforced with six volume fractions (0.5, 1, 1.5, 2, 3 and 5 vol.%) of submicron-SiC particulates (0.2 μm) were fabricated by stir casting. The as-cast ingots were forged at 420 °C with 50% reduction, and then extruded at 370 °C with the ratio of 16 at a constant ram speed of 15 mm/s. The microstructure of the composites was investigated by optical microscopy, scanning electron microscope and X-ray diffractometer. Microstructure characterization of the composites showed relative uniform reinforcement distribution, significant grain refinement and presence of minimal porosity. The X-ray diffractometer analysis showed that a strong basal plane texture was formed in both AZ91 alloy and SiCp/AZ91 composites during extrusion and the addition of submicron-SiC particulates could weaken the basal plane texture. The presence of submicron-SiC particulates assisted in improving the thermal stability, micro-hardness, elastic modulus and 0.2% yield strength. Both of the 0.2% yield strength and ultimate tensile strength increased with the increasing of submicron-SiC particulate content, however, decreased as the SiC particulate content overrun 2 vol.%.