EFFECT OF SIC PARTICULATE REINFORCEMENT ON THE DRY SLIDING WEAR OF ALUMINUM SILICON ALLOYS (A356)

The dry sliding wear behaviour of cast aluminium 7% silicon alloys (A356) reinforced with SiC particles was investigated by means of a block-on-ring (52100 bearing steel) type wear rig. Wear rates of the composites with 10-20 vol.% SiC were measured over a load range of 1-150 N at sliding velocities of 0.16 and 0.8 m s-1. Detailed electron metallography and X-ray diffraction analyses were undertaken to clarify the effect of SiC particles on the wear mechanisms. Observations indicated the following. (1) At low loads, corresponding to stresses lower than the particle fracture strength, SiC particles acted as load-bearing elements and their abrasive action on the steel counterface caused transfer of iron-rich layers onto the contact surfaces. In this regime, SiC reinforced composites exhibited wear rates about an order of magnitude lower than those of the unreinforced alloys in which wear occurred by subsurface crack nucleation, around the silicon particles, and growth. (2) Above a critical load determined by the size and volume fraction of SiC particles, carbide particles at the contact surfaces were fractured. A subsurface delamination process by the decohesion of SiC-matrix interfaces tended to control the wear, resulting in wear rates similar to those in the unreinforced matrix alloy. (3) An abrupt increase in the wear rates (by a factor of 10(2)) occurred in the unreinforced aluminium-silicon alloy at 95 N. SiC reinforcement was proved to be effective in suppressing the transition to severe wear rate regime.