Constellation, le dépôt institutionnel de l'Université du Québec à Chicoutimi

Résumé

The precipitation behavior of Zr-bearing dispersoids is investigated in Al–Si–Mg 6xxx alloys with different Si levels (0.4, 0.7, and 1.0 wt%) at three homogenization temperatures (450, 500, and 550 °C). The hot deformation behavior is studied using uniaxial compression tests at different Zener–Hollomon parameters. The microstructure evolution during hot deformation and postdeformation annealing is evaluated using the electron backscatter diffraction technique. The results show a significant influence of the Si level and homogenization temperature on the precipitation of two types of Zr-bearing dispersoids. Si promotes the precipitation of both spherical L12–Al3Zr and elongated DO22–(Al,Si)3(Zr,Ti) dispersoids during low-temperature homogenization. However, it accelerates the transformation of Zr dispersoids from L12 to DO22 at high homogenization temperature. The flow stress is more influenced by the solid solution level and hot deformation parameters rather than by the dispersoid distribution. The fine dense L12–Al3Zr dispersoids provide higher recrystallization resistance during postdeformation annealing compared with the large elongated DO22–(Al,Si)3(Zr,Ti) dispersoids. Owing to the uniform distribution of dispersoids and limited dispersoid-free zones, the high Si alloy (1.0%) exhibits best recrystallization resistance among the three alloys studied.