Phase Transformations and Recrystallization in Cold-Rolled Al–Mn, Al–Sc–Zr and Al–Mn–Sc–Zr Alloy

Abstract

The effect of cold-rolling on mechanical and electrical properties, microstructure and recrystallization behaviour of the AlMn, AlScZr and AlMnScZr alloys was studied. The materials were investigated during isothermal annealing at 300, 400, 500 and 550°C and during step-by-step quasilinear annealing from 200°C up to 600°C with a heating rate of 100 K/h followed by subsequent isothermal annealing at 600°C/5 h. Precipitation reactions were studied by electrical resistometry and (micro) hardness measurements. The microstructure development was investigated by electron microscopy and electron backscatter diffraction examinations. The hardening effect is due to uniformly distributed Al3Sc and/or Al3(Sc,Zr) particles. The distinct changes in resistivity of the alloys above ∼ 300°C are mainly caused by precipitation of Mn-containing particles. It has a negligible effect on hardness. Phase transformations in the AlMn and AlMnScZr alloys are highly enhanced by cold rolling. The precipitation is dependent on the deformation degree – the more deformation the more intensive precipitation of the Mn-containing particles. The combination of Mn, Sc and Zr additions to Al substantially suppresses recrystallization at 550°C. A partial recrystallization was observed in the AlScZr alloy and AlMnScZr alloy after annealing 550°C/60 min and 550°C/760 min, respectively. The decomposition sequence of the supersaturated solid solution of the AlMnScZr alloy is compatible with the decomposition sequence of the AlScZr system accompanied and/or followed by the formation of Mn-containing particles.