Elimination of lazy S defect in friction stir welded joint of 20mm-6063 alumimum alloy

20 mm thick 6063 aluminum alloy plate were joined by friction stir welding with gas protection.The result showed that the sound joint without lazy S can be achieved.The average tensile strength of welds is 148.9 MPa,which is 81.9% of that of the base metal.Optical microscopy revealed the stir zone presents particularly fined equiaxed gains formed by dynamic recrystallization.The microstructure in TMAZ,in which some degree of dynamic recrystallization occurs,consists of deformed gains.The result shows that lazy S of 6063 aluminum alloy can be eliminated by FSW with gas protection.