Microstructure Evolution of Al-Mg-Si Alloy Sheets during Preparation

The grain, phase structur e and texture evolution of an Al-Mg-Si alloy used in automobile industry during casting, homogenization, hot rolling, annealing, cold rolling, solution and pre-aging were studied by OM, SEM and XRD.The results show that the as-cast grains are approximately equiaxed and become lamellar after hot rolling.Recrystallization occurs during annealing, but the orientation relationship is kept parallel to the rolling direction.After cold rolling, the grains become lamellar again, and complete recrystallization occurs after solution and pre-aging, forming equiaxed grains without distortion.The as-cast alloy mainly contains β-Fe-rich phase, α-Fe-rich phase, Mg₂Si phase and Q phase, which are distributed along the grain boundary.After homogenization, Mg₂Si phase and Q phase are dissolved, the thin β-Fe-rich phase changes into α-Fe-rich phase, and the thick β-Fe-rich phase does not change.After hot rolling, the amount of precipitated phase increases, and the distribution of precipitated phase and Fe-rich phase is parallel to the rolling direction.After annealing, the quantity and size of the precipitated phase increase further.After cold rolling, the precipitated phase tends to be fine and dispersed.After solid solution and pre-aging, the precipitated phase dissolves and only the Fe-rich phase remains in the matrix.In hot or cold rolling, the rolling textures of brass, S and copper are enhanced, but annealing or solution+pre-aging can weaken the rolling textures of brass, S and copper, and enhance the textures of cube and Goss.