Effect of friction stir welding parameters on microstructural characteristics and mechanical properties of 2219-T6 aluminum alloy joints

A 2219-T6 aluminum alloy was friction stir welded in the present study. The results indicate that the recrystallized grains in the weld nugget zone (WNZ) of the joints exhibit the largest size in the middle part and the smallest size in the lower part. Furthermore, the void defect is formed in the joint when the rotation speed or welding speed is quite high. As the rotation speed or welding speed increases, the tensile strength of the joint firstly increases to a maximum value and then sharply decreases due to the occurrence of void defect. During tensile test, the defect-free joints welded at lower rotation speed are fractured in the WNZ, while those welded at relatively high rotation speed tend to be fractured in the heat affected zone (HAZ) adjacent to the thermal mechanically affected zone (TMAZ) on the retreating side.