Effect of floating grains on the deformed microstructure of Mn- and Cr-containing Al-Mg-Si-Cu alloys

The effects of floating grains on the deformed microstructure of a Mn-and Cr-containing Al-Mg-Si-Cu alloy were first clarified based on a comparative study of the dispersoid precipitation and recrystallization behavior with and without floating grains. The presence of floating grains in the direct-chill casting billets resulted in inho-mogeneous and sparse precipitation of the alpha-Al(Mn,Cr)Si dispersoids after homogenization. In response, the Zener drag force was significantly reduced and severe localized recrystallization occurred in the specimen containing floating grains after hot working. Whereas, the specimen without floating grains, which had dense and fine dispersoids, still had an ideal recovery microstructure after solution soaking. The innate reason consists in the special microscale features of floating grains, which significantly decreased the nucleation rate of the dispersoids-forming beta ' precipitates.