Wear Properties of A356/Al2O3 Metal Matrix Composites Produced by Semisolid Processing

In this study, A356/Al2O3 metal matrix composites were fabricated by conventional stirring and semisolid processing (combination of mechanical stirring in the mushy zone and cooling slope casting) and these composites were subjected to wear tests. The composites containing various weight fractions of Al2O3 particles (1%, 2.5% and 5%) were used in both conventional and rheocasting processes. In conventional stirring, the primary phase remained dendritic while in rheocasting the dendritic primary phase transformed into a globular microstructure. The influences of these processes on the hardness and wear behaviour of the composites were investigated. A pin-on-disc tribometer was used to carry out tribological tests under dry sliding conditions in air. Wear tests were carried out at 1.0 m/s sliding speed under a 20N load and four different sliding distances. A scanning electron microscope was used to examine the wear mechanism on the worn surfaces of the composites. The results showed that the volume loss of the composites produced by semisolid processing was lower than that of those produced by conventional casting. Based on wear rate ranges, all metal matrix composites exhibited moderate wear regimes. The dominant wear mechanism for all materials was ploughing, with some delimitation.