Characterisation of Friction Stir Weld Discontinuities by Non-destructive Evaluation

Friction stir weld (FSW) is an advanced metal joining process recently practised in aerospace industries with application spanning across other engineering fields as well. Friction stir welding being solid-state joining process, the weld is characterised by superior weld properties with proper parameter setting. The morphology of FSWs varies from other welds due to the plastic state formation of the material as against the liquid state of fusion encountered in conventional welding process. The nature of the discontinuities in these joints is significantly different. The presence of discontinuities in the welds due to its unique weld formation process has made the failure pattern in these products also unique. Hence, a comprehensive non-destructive evaluation (NDE) assessment of FSWs is attempted with different techniques and their detecting capability has been discussed. Conventional NDE methods, namely radiography, ultrasonics and eddy current techniques used in FSW discontinuity detection are discussed and compared for each type of discontinuity.