Influence of welding speed on the root defects formation and mechanical properties of FSWed 6082-T6 Al alloy joint

In this paper, 5-mm thick 6082-T6 aluminum alloy plates were friction stir welded in a position control mode at rotation rate of 1800 rpm and welding speeds ranging from 200 to 600 mm/min. The metallurgical morphology of root defects was elucidated. As indicated by observation on electropolished samples that contains the root defects, it was found that there are three types of bonding states near the faying surface at the joint root, which are fully bonded state without cracks, incomplete bonding state in the form of non-continuous cracks (the kissing bond), and unbonded state in the form of continuous cracks (the lack-of-penetration defect). The vertical position of welding tool during the welding pocess is recorded, and it is found that, as the welding speed increased, the rebound amount of the welding tool increased during actual welding process because of increasing deformation resistance. It consequently leads to the decrease of insertion depth of the welding tool, which significantly increases formation tendency of the root defect.