Development of microstructure of asymmetrically rolled AA3003 aluminium sheets with Zr addition

Abstract

Asymmetric rolling is a method of severe plastic deformation, which can produce large volumes of deformed material and is easy to implement for industrial use. Asymmetric rolling with different circumferential velocities of rolls gives rise to intense plastic shear strains, resulting in grain refinement and improving mechanical properties. An aluminium alloy from AA3003 series enhanced by 0.16 wt% Zr was produced by twin-roll casting in industrial conditions. A part of specimens was annealed at 450∘C in order to precipitate fine dispersion of Al3Zr particles, which may enhance recrystallization resistance at elevated temperatures. Materials were subjected to cold rolling and to asymmetric rolling in several steps. Both methods result in a substantial elongation and fragmentation of grains. The grain refinement is more distinctive after asymmetric rolling. During isochronal annealing Vickers microhardness of materials decreases. The main drop occurs in the asymmetrically rolled material between 400 and 450∘C. In the annealed material the main drop connected with recrystallization is shifted by 50∘C to higher temperatures due to the presence of Al3Zr particles. Recrystallization occurs in the cold-rolled material between 450 and 500∘C. The imposed deformation by rolling is lower in this specimen and hence the driving force for recrystallization is also lower than in the asymmetrically rolled material. After recrystallization, the grain size of both cold-rolled and asymmetrically rolled materials is comparable. However, grains are still elongated in the rolling direction.