A Comparative Study of Effect of Tool-Offset Position on Defect Dynamics and Formation of Intermetallic Compounds in Friction Stir Welding of Al-Ti Dissimilar Joints

The hybrid structures composed of Al and Ti materials have numerous applications in the aviation and automobile industries. In this work, studies involving friction stir welding of dissimilar AA2519-T87 and high purity titanium sheets are reported. A 2-mm thick sheets were welded by linearly varying the tool-offset position from the faying interface. The effect of tool-offset position on defect dynamics, formation of intermetallic compounds (IMCs), and fracture mechanism were investigated using optical microscope (OM), field emission scanning electron microscope (FESEM) fitted with energy-dispersive X-ray spectroscopy (EDS) facility, X-ray diffraction (XRD), tensile property and microhardness measurements. The maximum tensile strength of 297 MPa was attained in a defect free specimen. At extreme tool-offset distances, defects such as kissing bond, tunnels and joint line remnants were observed. The number density of IMCs increased with decreasing tool-offset positions, and Al 3 Ti and Al 5 Ti 2 were observed at interfaces of all the samples. The variation in fracture mechanisms with defect analysis was studied and could be useful in fabrication of aircraft structures.