The frictional stirring welding （FSW） for 2219-O aluminum alloy with 14mm in thickness was performed with varied welding parameters. The origination of typical flaw in FSW and effects of welding parameters and welding joint on the flaw were approached. The results indicate that compared with those of joint without defects

the yield strength

tensile strength and elongation of joint with void or tunnel defects are decreased by 11%

32% and 153%

respectively. SEM observation reveals that the ductility-brittleness fracture morphology of the joint with defects can be observed

in which the rupture morphology of joint with tunnel defects exhibits dimple morphology with high oxygen content

while the ductility rupture in the joint without defects can be observed. In addition

the microhardness of joint with defects is lower than that of ones without defects. The mechanical properties of the joint with defects were deteriorated.