Wear assessment of Al/Al2O3 nano-composite surface layer produced using friction stir processing

An innovative technique, friction stir processing (FSP) was employed for the fabrication of Al/Al2O3 nano-composite surface layer on an Al alloy substrate. Aluminum work pieces with pre-placed nano-sized Al2O3 powder which was filled in a shallow groove were subjected to various numbers of passes from one to four. Scanning electron microscopy studies showed that increase in the number of FSP passes causes a more uniform dispersion of alumina particles and thus, decreases particles clustering. In addition, an increasing in the number of FSP passes was found to decrease the matrix grain size of the surface nano-composite layers. The mean micro hardness value of the surface nano-composite layer was found to be improved by almost three times as compared to that of the as-received Al alloy substrate. A significant improvement in wear resistance was exhibited by surface nano-composite layer in comparison to the as-received substrate. The surface nano-composite layer produced by four FSP passes showed superior wear resistance; this is attributed to its greater micro hardness value (due to presence of finer matrix grains and uniform dispersion nano-sized Al2O3 particles).