Influence of machine variables on the microstructure and mechanical properties of AA6061/TiO2 friction stir welds

The present work explicates the joining of TiO2 (rutile) particles reinforced aluminium matrix composites (AMCs) through the friction stir welding (FSW) technique. Joining of AMCs using conventional fusion welding techniques faces a lot of challenges, which can be overcome by the FSW process. The effect of the two most critical process variables, welding speed, and tool rotational speed on the grain structure of the joint and on the mechanical behaviours was evaluated. The study revealed that machine variables regulate the quantity of heat input, heat exposure duration, and rate of cooling, thereby, significantly altering the grain size in the weld region and mechanical behaviour of the joint. The tool rotational speed had a substantial impact on the joint strength, whereas tool traverse speed facilitates homogeneous dispersion of reinforced particles in the matrix. The 'W'-shaped hardness variation profile was observed across the weld zone, showing the highest hardness in the weld stir zone. The UTS of the welded specimen, measured across the joint was almost equal to the parent material with fracture occurring at the interface of the heat-affected and the thermo-mechanically affected zone which was the weakest point in the weld region.