Microstructure, Strength, and Wear Behavior Relationship in Al-Fe3O4 Nanocomposite Produced by Multi-pass Friction Stir Processing

Aluminum matrix in situ nanocomposite was produced by one to six passes friction stir processing (FSP) with pre-placed Fe3O4 nanoparticles (15-20 nm). Microstructure studies showed that solid-state reactions between the aluminum matrix and Fe3O4 particles during the process led to in situ formation of Al3Fe and Al5Fe2 in the stir zone. Initial Fe3O4 as well as Al-Fe intermetallic compounds (IMCs) particles were homogeneously dispersed in a fine grain matrix after six passes of FSP. Hardness and ultimate tensile strength of the composites were increased 64 and 27%, respectively, compared to the base metal. The reasons were studied in the light of reinforcing particles distribution, formation of Al-Fe IMCs, and grain size of the aluminum matrix. Pin-on-disk wear test indicated that in comparison with the base metal, the weight loss and friction coefficient of the composite processed by six passes decreased about 70 and 37%, respectively. Impact energy of the composite produced by six passes was considerably higher than that of the composite produced by one pass and reached to ~65% of the impact energy of the annealed aluminum base metal. Moreover, corrosion potential in the composites changed to more noble potentials compared to the base metal.