Abstract: By adding a groove inside nugget zone, titaniumaluminum mix powder can be introduced into friction stir welding (FSW). Intermetallic particles can be produced in situ due to high heat input and severe plastic deformation during FSW. The relationship between the thermal stability of grain structure and the second phase particles in the welds was studied and discussed. The results show that abnormal grain growth (AGG) region of heattreated samples decreased significantly with titanium powder addition as compared with that without titanium powder addition. The results further suggest that AGG after heat treatment can be restrained by introducing second phase particles into the nuggets zone. Meanwhile, it is found that with the increase of FSW passes, titanium powders are dispersed more homogeneously and the AGG region deceases, thus the thermal stability of grain structure in weld nugget is improved.