Effect of thermal treatment and recycling on the tribological behaviour of an AlSiMg–SiCp composite

The tribological behaviour of an AlSiMg–SiCp composite, produced by the PRIMEX CAST™ method (patented by LANXIDE) was studied under dry sliding conditions against a surface hardened AISI 1055 carbon steel, using a slider-on-cylinder tribometer. The effect on the wear resistance of both a T6 thermal treatment and of the use of recycled material in the casting process (50 and 100% recycling) was investigated. At the lowest applied load (10 N) a mild wear regime with high coefficients of friction was always found for all the tested composites. At higher loads (20 and 30 N) and low sliding speed (0.3 m s−1) the as-cast composites exhibited a better wear resistance than the T6 aged ones, despite their lower hardness. In fact, their lower matrix hardness and higher ductility prevented conditions for subsurface softening and delamination. On the contrary, the T6 aged composites showed delaminative wear, caused by crack formation and propagation. With increasing sliding speed, even the as-cast materials displayed a transition toward the high wear regime due to a degradation of the matrix properties, probably induced by the high temperature at the contacting surfaces. Regarding the effect of material recycling, the composite with 50% recycled material showed similar wear resistance as the not recycled composite with the same reinforcement percentage. The composites with 100% of recycled material, instead, displayed a slightly higher wear damage both due to the lower reinforcement content (20 vol.%) and to the inhomogeneous particle distribution.