The effect of combined cold rolling and homogenization on the microstructures and mechanical properties of twin-roll casted 8021 aluminum alloy

Abstract

The microstructures and mechanical properties of the twin-roll casting (TRC) 8021 alloy strip under different homogenization processes (direct homogenization, cold rolling + homogenization) have been systematically investigated by optical microscope, tensile testing, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) technique. It was revealed that due to the severe microstructural gradient throughout the full strip thickness, the coarse grain layer is readily formed in the strip surface due to the high stored energy involved. Although the introduction of cold rolling before homogenization reduces the strain inhomogeneity in the strip, the rather high deformation level produces fully recrystallized structures after homogenization at 580 °C. After cold rolling and final annealing, recrystallized grains are formed in the interior of the sheets for most the homogenization temperatures. Compared with direct homogenized samples, the average recrystallized grain sizes in the “cold-rolled + homogenized” samples are larger due to the small thickness reduction. Therefore, the combination of cold rolling and homogenization can improve the elongation and decrease the strength of the strip. Homogenization at 530 °C is selected as the optimum parameter for both the two homogenization processes as it provides a good combination of strength and elongation.