Multi-pass Friction Stir Welding of Al-TiC-Zn-Mg Composite: Microstructure and Mechanical Characteristics

In this study, friction stir welding joints between dissimilar magnesium and aluminum alloy sheets were made with the addition of TiC reinforcing particles and Zn foil metal interlayer. The impact of process passes on the microstructural behaviors, intermetallic compounds (IMCs), and mechanical characteristics of weld specimens were studied, and the strengthening and toughening mechanism was displayed. It was shown that the TiC particles play a significant role in the microstructure modification and enhanced mechanical properties of weld samples, while the Zn foil interlayer plays a vital role in avoiding the formation of Al-Mg IMC phases. MgZn and MgZn2 IMCs, Mg and Al solid solution were the main detected common phases in the stirred zone instead of the generation of the hard and brittle Al-Mg intermetallic. The results indicated that the welding passes significantly influenced the microstructure of the stir zone due to the opposite moving direction of the welding tool between the consecutive passes. The increasing process passes from 1 to 3, noticeably improved homogenized the microstructure and mechanical characteristics of weld specimens due to fine uniform distribution of TiC nanoparticles, improved wettability and plastic flow of materials, and reduction in IMCs formation. This resulted in an improvement in maximum hardness and ultimate strength of weld specimens from 139 to 211 Hv and 118 to 203 MPa as the pass number increased from 1 to 3.