Mechanisms of material removal and subsurface work hardening during low-stress abrasion of a squeeze-cast aluminium alloy-Al2O3 fibre composite

Low-stress abrasive wear behaviour of squeeze-cast aluminium alloy (British Standard LM5) and its composite containing 10 vol.% of Al2O3 fibres has been examined in this study using an ASTM standard rubber wheel abrasion test apparatus. Silica sand particles (size, 212–300 μm) were used as the abrasive. A progressive decrease in wear rate with increasing number of test intervals, until a steady state value was reached, was noticed for the base alloy as well as the composite. Abrasion-induced subsurface work hardening was found to be responsible for the progressive reduction in the wear rate of the base alloy. Factors causing identical behaviour of the composite were noted to be the protusion of the reinforcement, i.e. Al2O3 fibres on the abraded surface offering protection to the softer matrix, as well as the abrasion-induced subsurface matrix hardening. Scanning electron microscope examination of the abraded and transverse sections suggested the material removal mechanism of the composite to consist of preferential removal of the matrix in the beginning, leading to the protrusion of the dispersoid phase (the latter offered protection to the matrix) and finally the subsequent fracture and partial removal of the dispersoid from the surface.