Grain growth phenomena in friction stir welded 1100 Al during post-weld heat treatment

Grain growth phenomena during post-weld heat treatment (PWHT) were examined in friction stir (FS) welded 1100 Al. The FS welds were produced at rotational speeds between 550 and 3600 rev min⁻¹. The FS weld produced at the lower rotational speed had the finer equiaxed grain structure containing feature of the more deformed microstructure in the as welded state. It was found that the regions having more deformed microstructure in the as welded state experienced abnormal grain growth more preferentially in the stir zone during PWHT. The stir zone exposed to higher temperature during FSW was more stable at higher PWHT temperatures. When the weld was heated for a long time at a temperature that was high enough for the abnormal grain growth, the stir zone produced at the lower rotational speed had the smaller grown grains. The present study suggested that the abnormal grain growth of the stir zone during PWHT had similar features of primary recrystallisation.