Investigation into the Influence of Post-Weld Heat Treatment on the Friction Stir Welded AA6061 Al-Alloy Plates with Different Temper Conditions

In this study, the effect of post-weld heat treatment (PWHT) on the microstructure and mechanical properties of friction stir butt-joined AA6061 Al-alloy plates both in O and T6-temper conditions was investigated by detailed microstructural investigations and microhardness measurements, in combination with transverse tensile testing. It was determined that the PWHT might result in abnormal grain growth (AGG) in the weld zone particularly in the joints produced in O-temper condition depending on the weld parameters used during friction stir welding. The PWHT generally led to an improvement in the mechanical properties even if AGG took place. Thus, the post-weld heat-treated joints exhibited mechanical properties much higher than those of respective as-welded plates and comparable to those of the respective base plates.