Friction and abrasion resistance of cast aluminum alloy-fly ash composites

The abrasive wear properties of stir-cast A356 aluminum alloy-5 vol pct fly ash composite were tested against hard SiC _p abrasive paper and compared to those of the A356 base alloy. The results indicate that the abrasive wear resistance of aluminum-fly ash composite is similar to that of aluminum-alumina fiber composite and is superior to that of the matrix alloy for low loads up to 8 N (transition load) on a pin. At loads greater than 8 N, the wear resistance of aluminum-fly ash composite is reduced by debonding and fracture of fly ash particles. Microscopic examination of the worn surfaces, wear debris, and subsurface shows that the base alloy wears primarily by microcutting, but the composite wears by microcutting and delamination caused by crack propagation below the rubbing surface through interfaces between fly ash and silicon particles and the matrix. The decreasing specific wear rates and friction during abrasion wear with increasing load have been attributed to the accumulation of wear debris in the spaces between the abrading particles, resulting in reduced effective depth of penetration and eventually changing the mechanism from two-body to three-body wear, which is further indicated by the magnitude of wear coefficient.