Ti 6Al-4V FSW weldability: mechanical characterization and fatigue life analysis

Friction stir welding (FSW) is an innovative solid-state process, patented in 1991 by The Welding Institute, which avoids solidification problems associated with conventional fusion welding, providing joints having excellent mechanical and metallurgical properties. Due to its many advantages, FSW is successfully applied to weld various aluminium, magnesium and copper alloys. In recent years, FSW of high melting temperature materials such as steels and titanium alloys has become a key research topic. However, the high softening temperature of high melting temperature materials result in extreme stress of the pin tool during FSW, which adds to the difficulty in creating defect-free joints, especially for titanium alloys. This work is a preliminary investigation of FSW application on titanium alloy Ti–6Al–4V. The research focused on optimization of tool material and geometry, as well as process parameters. Complete microstructural and microhardness evaluations were conducted in addition to surface examinations. In order to evaluate the service behaviour of the joints realized with the optimized parameters, an in-depth investigation was also conducted on the fatigue properties of FSW joints.