Effect of homogenization annealing on microstructure evolution and homogeneity of twin-roll casting Al-Mg-Si plate

The effects of homogenization annealing processes on twin-roll casting (TRC) Al-Mg-Si plates have been studied, the transformation of β-AlFeSi phase to α-AlFeMnSi phase and the recrystallization behavior have been discussed, and the uniformity of the plate has been evaluated. The results show that the hardness from the surface to the center is wildly fluctuating in the TRC plate, the recrystallization level and the morphology of second phases are different between the surface and the center. It indicates that the uniformity of TRC plate needs to improve. After the homogenization annealing process, the uniformity of the plate improves observably. When the homogenization annealing process is 540°C×7 h, the microstructure and properties of TRC Al-Mg-Si plate are uniform, the hardness from the surface to the center fluctuates smoothly, coarse lamellar β-AlFeSi phases have basically transformed into spherical α-AlFeMnSi phase, recrystallization level in the surface is in consistent with that in the center basically. As homogenization annealing temperature rises, the hardness from the surface to the center starts to fluctuate unsteadily. It is concluded that spherical α-AlFeMnSi phases initiate to coarsen, resulting in obvious fluctuations of Mg, Si and Fe elements. the recrystallization levels of the surface and the center are approximate when the process is 560°C×7 h, but the grains have significantly coarsened.