Wear and mechanical properties of surface hybrid metal matrix composites on Al–Si aluminum alloys fabricated by friction stir processing

Aluminum-base surface hybrid composites have been fabricated by mixtures of SiO2 and Al2O3 particles on an Al–Si cast aluminum alloy using friction stir processing with the aim of achieving higher wear properties in the Al piston alloy via surface hybrid composites fabrication. The distribution of particles in the stir zone was evaluated via scanning electron microscope. Microstructures of the composites revealed that the reinforcing particles were uniformly distributed in the stir zone. Furthermore, the mechanical properties of each composite were determined using hardness tests indicating that increase in the relative content of SiO2 resulting in a decrease in the average hardness of the stir zone. Additionally, the wear resistance of the surface hybrid composites was investigated under normal load, sliding speed, and distances of 20 N, 1 m/s, and 4000 m, respectively. It was found that the wear mass loss of the 20% SiO2–80% Al2O3 hybrid composites (which was about 4.2 mg) was improved when compared with that of the A356 base alloy (nearly 19 mg). Moreover, by increasing the relative content of SiO2 particles from 0% to 100% in the hybrid composites, the friction coefficient of the composites rose from 0.55 to 0.73. It can be concluded by adding Al2O3 and SiO2 particles in the Al matrix, wear mass loss can be decreased by about five times compared with that of the base metal, in which the Al2O3 particle increases the hardness and SiO2 particles acts as lubricating agent, and the combination of these leads to better wear properties. The best combination of the hybrid particles in order to achieve the best wear properties for the hybrid composites is 20% Al2O3 and 80% SiO2.