Assessment of Mechanical and Tribological Properties of SiC- and Multi-walled Carbon Nanotube-Reinforced Surface Composites of AA7075-T6 Fabricated via Friction Stir Processing

Friction stir processing (FSP) is an energy-efficient technique that modifies surfaces and has been used to generate surface metal matrix composites (SMMCs). The AA7075-T6-based two different composites were fabricated in this study by reinforcing multi-walled carbon nanotubes, i.e., SMMC1 and silicon carbide, i.e., SMMC2, through FSP. The matrix material, i.e., AA7075 alloy, is widely used in aerospace and automotive industries due to its good strength/weight ratio. Three-pass FSP with tool speeds of 730 rpm and 65 mm/min was used to develop SMMCs with 7% volume of the reinforcement particles (RPs). Uniform dispersion of the RPs was confirmed through electron probe microanalysis. To investigate the microstructure of the composites and base material, electron backscatter diffraction was employed. To compare the effect of RPs, the SMMCs were examined for mechanical properties, i.e., microhardness, Charpy impact, and tensile strength, and tribological properties. Further, the wear tracks were analyzed for wear mechanism using scanning electron microscopy, and energy-dispersive x-ray analysis revealed the main particles on the tracks. Fractography of the Charpy and tensile specimens provided fracture mechanism. Both the composites outperformed the base metal in terms of mechanical properties and resistance to wear. Regarding the measured attributes, SMMC1 was better than SMMC2 with tensile strength of 629 MPa, impact energy of 25 J, hardness of 160 HV and wear weight loss of 10.2 mg.