Eliminating root defect in Al/Ti dissimilar friction stir welded via the double-side process

The root defect is easy to occur in the conventional friction stir welded (C-FSW) Ti/Al dissimilar joints because of the thermophysical properties of titanium alloy. Double-side friction stir welding (DS-FSW) may be a solution to eliminate root defects. This work performed microstructure analyses of the Al/Ti interface for both C-FSW and DS-FSW joints and comprehensively investigated the effects of root defects. The results show that the mechanical properties of the Al/Ti C-FSW joints are severely weakened by root defects. Tensile strength of the DS-FSW joints was 310.8 MPa, which is 73 MPa high than the C-FSW joints. The DS-FSW process can effectively remove the root defects which offers a novel approach to achieve high-quality joining of Al/Ti dissimilar structures.