Effect of pre-strain rolling path on abnormal grain growth in friction-stir welded Al-Mg-Si alloy

Abstract

The fine-grained microstructures evolved during friction stir welding of aluminum alloys often exhibit abnormal grain growth during post-weld heat treatment. To avoid this undesirable phenomenon, a pre-strain rolling approach has been employed in the present study. The proposed method was based on the idea that the pre-strain rolling would promote recrystallization instead of the abnormal grain growth during the subsequent heat treatment. To validate this concept, the produced welds were cold rolled in two different directions - either parallel or perpendicular to the weld path - prior to the standard T6 tempering. In both cases, the pre-strain rolling was found to be effective for suppression of the abnormal grain growth. Moreover, the revealed effect was sensitive to the rolling path. Specifically, the pre-rolling along the weld line resulted in the finest final grain size in treated-treated welds. This observation was explained in the terms of relatively high Taylor factor, which enhanced recrystallization behavior during subsequent annealing.