Effect of TiO2 nanoparticles addition on microstructure and mechanical properties of dissimilar friction stir welded AA6063-T4 aluminum alloy and AZ31B-O magnesium alloy

In this research, dissimilar AA6063-T4 aluminum alloy and AZ31B-O magnesium alloy sheets were joined using friction stir welding (FSW) by incorporating the TiO2 nanoparticles to the interface of weld joints through creating a novel groove design in the faying surfaces in order to prevent nanoparticles dissipation during welding. A process window was acquired to recognize optimal welding parameters and sound welds with appropriate metallurgical bonding and mechanical interlocking were obtained. The applied rotation and travel speeds were varied within 700-900 rpm and 40-60 mm/min, respectively. The variation of heat input played the most important role in microstructure evolution, nanoparticles distribution and formation of Al3Mg2 and Al12Mg17 intermetallic compounds (IMCs). The weld joint fabricated at 800 rpm and 40 mm/min reached the highest tensile strength of 132 MPa which was almost two times higher than nanoparticles-free weld joint indicating the substantial effect of nanoparticles on strengthening. Fine microstructure, presence of IMCs as well as nanoparticles distributed in the stir zone (SZ) were known as the main reason of a significant increase in the microhardness profile that reached the value of 196 HV. Meanwhile, brittle fracture mode was observed for most of the weld joints, while relative ductile fracture signs also existed.