Effect of Tool Pin Profile on Microstructure and Hardness of Magnesium Alloy Zk60/SiCp Surface Composites Fabricated by Friction Stir Processing

The combination of stiffness, good castability, high specific strength, and low density makes magnesium alloys ideal materials, particularly in lightweight structural applications. The two major drawbacks of magnesium alloys are poor friction and wear resistance, because they restrict the structural applications. Therefore, it is necessary to enhance the tribological properties of magnesium alloys without creating many adverse effects on the properties of the base metal by using surface engineering. In order to achieve a sound fabrication of surface metal matrix composites on the magnesium plate, friction stir processing (FSP) often serves as a good candidate. However, the process parameters should be suitably selected to fabricate a sound FSP zone. Tool pin profile is a major significant process parameter, particularly in FSP, as it plays major part in the formation of a processed region with a uniform distribution of reinforcement particles. In this study, an attempt was made to understand the major effects of tool pin profiles, namely, cylindrical thread, plain cylindrical, plain tapered cylindrical (PTC), and square on the microstructure characteristics and particle distribution of FSP ZK60/Silicon Carbide particle (SiCp) surface composites. Of the four pin profiles, surface composites fabricated by means of PTC pin profile resulted in a defect-free and higher hardness processed zone. This was attributed to the higher shear force offered by the PTC pin profile, which aids proper material flow with evenly distributed particles.