Evolution of Zr-Bearing Dispersoids during Homogenization and Their Effects on Hot Deformation and Recrystallization Resistance in Al-0.8%Mg-1.0%Si Alloy

The precipitation behavior of Zr-bearing dispersoids in an Al-0.8%Mg-1.0%Si alloy was investigated for different homogenization treatments (450-550 °C). The effect on the recrystallization resistance of the alloy was also studied during post-deformation annealing. With an addition of 0.2 wt.% Zr, two different Zr-bearing dispersoids were observed depending on the homogenization conditions. Homogenization at 450 °C for 2 h resulted in the precipitation of fine and dense L12-Al3Zr dispersoids (8-10 nm), which were found to be coherent with the matrix. In contrast, extended homogenization times, such as 12 h at 450 °C, or increasing the homogenization temperature to 500-550 °C produced elongated DO22-(Al,Si)3Zr dispersoids with a larger size. During hot compression testing, the addition of 0.2 wt.% Zr combined with homogenization at 450 °C increased the high-temperature flow stress by 20% relative to the base alloy free of Zr, revealing their potential to inhibit dislocation motion and dynamic recovery. Both dispersoids were found to have positive impact on the retardation of recrystallization during post-deformation annealing, but the fine and coherent Al3Zr dispersoids were more effective than the coarse and incoherent (Al,Si)3Zr dispersoids.