Composite fabrication and surface reinforcement of aluminum 7075 by pumice micro and nanoparticles using the friction stir process (FSP)

In this research, the surface of aluminum 7075-T6 was reinforced by pumice micro and nanoparticles using the friction stir process (FSP). First, optimum parameters of pass number (1 & 4 pass), travel speed (40 & 80 mm/min) and tool rotation rate (800 & 1200 rpm) considering the microstructure, hardness and resistance to wear were selected. Results showed that with increasing the pass number, decreasing the travel speed and increasing the tool rotation rate, the grain size in stirred zone (according to the microscopy images) decreased, while the hardness (according to the Vickers micro-hardness test results) and resistance to wear (according to the pin on disk test results) increased. Under conditions of single pass, travel speed of 80 mm/min and tool rotation rate of 800 rpm, average grain size in stirred zone was 10 micron; while under conditions of four passes, travel speed of 40 mm/min and tool rotation rate of 1200 rpm it was reduced to 5 micron that led to an increase in average micro-hardness from 80.2 to 94.6 Vickers and a decrease in wear amount from 33 to 27 mg after a sliding distance of 1000 m. By addition of pumice micro and nanoparticles, average micro-hardness was increased to 99.6 and 107.8 Vickers and wear amount was decreased to 24 and 20 mg, respectively.