Microstructural and tribological properties of A356 based surface hybrid composite produced by friction stir processing

Fabrication of surface hybrid composite with reinforced particles has been developed in order to enhance tribological properties of aluminum alloys. Among the aluminum alloys, increasing of tribological properties of A356 casting aluminum alloys using different reinforced particles into the surface by FSP, as a surfacing technique, is of great interest, which should be considered. Friction stir processing was attempted in order to produce a surface hybrid composite for improvement of tribological properties with alumina (Al2O3) particles and graphite (Gr) as a lubricant particles. The FSP was carried out with tool rotational speed of 1000 rpm, tool travel speed of 100 mm min(-1) and tilt angle of 2 degrees through two passes. In the present work, the structural and tribological properties of surface hybrid composite of A356 Al alloy are investigated. Structural characterization is evaluated by optical and scanning electron microscopies. Hardness and wear tests are performed in order to investigate tribological behaviors of the FSPed composite samples. The obtained results showed that the composite reinforced by Al2O3 particles exhibits higher hardness value compared to hybrid composite of Al2O3/Gr-particles because of the good bonding between Al2O3 and aluminum matrix as well as higher hardness value of Al2O3 particle itself than the Gr-particle reinforcement. In addition, wear test results depicted that the wear resistance of A356/Al2O3/Gr sample is significantly decreased compared to that of A356 Al alloy. The wear mechanism of all composites were identified adhesive wear mechanism. The reduction friction coefficient of A356/Gr composite presented higher value as opposed to the other composites.