Effect of extrusion ratio on the microstructure, texture and mechanical properties of (Mg/AZ91)m-SiCp composite

Cast Mg/SiCp and AZ91/SiCp composites were successfully hot extruded vis-à-vis cast and unreinforced Mg and AZ91 alloy up to low (R=15:1) and high (R=54:1) extrusion ratios at 350 °C. Significant matrix grain refinement was noticed after extrusion due to dynamic recrystallization; the degree of refinement being relatively higher for the two composites. The AZ91 based materials (AZ91 and AZ91/SiCp) exhibited comparatively finer grain size both in cast condition and after extrusion due to strong pinning effect from alloying elements as well as Mg17Al12 intermetallic phase. Compositional analyses eliminated the possibility of any interfacial reaction between matrix (Mg/AZ91) and second phase reinforcement (SiCp) in case of the composites. Texture evolution shows the formation of 〈101¯0〉∥ED texture fibre for all the materials after extrusion irrespective of SiCp addition or alloying which is primarily due to the deformation of the matrix phase. Micro-hardness did not significantly increased on extrusion in comparison to the respective cast materials for both composites and unreinforced alloys. Dynamic mechanical analysis, however, confirmed that the damping properties were affected by the extrusion ratio and to a lesser extent, due to the presence of second phase at room temperature as well as at higher temperature (300 °C).