Hot compression behavior of the 1 wt% calcium containing Mg–8Al–0.5Zn (AZ80) alloy fabricated using electromagnetic casting technology

Abstract

An AZ80 alloy containing 1wt% Ca (1wt% Ca-AZ80 alloy) was fabricated using a combination of electromagnetic casting and electromagnetic stirring. Due to the beneficial effects of reduction in the temperature gradient in the melt and refinement of dendritic structure by enhanced fluid motion, the fine and homogeneous microstructure could be obtained in the billets. Compression tests were performed on the cast 1wt% Ca-AZ80 alloy to examine its hot deformation behavior in the temperature range of 523–693K and the strain rate range of 10−3–101s−1. The analysis of the deformation behavior indicated that the lattice diffusion controlled Garofalo׳s hyperbolic sine creep with stress exponents of 6–7 dictates the plastic flow at the given testing conditions. The size of the dynamically recrystallized (DRX) grains and the volume fraction of the DRX grains decreased as the Zener–Hollomon parameter increased. A comparison of the processing maps of the cast 1wt% Ca-AZ80 alloy with those of the conventionally processed cast AZ80 alloy studied by other investigators at strains of 0.2–0.5 indicated that the former exhibits a better hot workability over a wider range of temperatures and strain rates. This may be attributed to the microstructural refinement and homogeneity of the present alloy achieved by a combination of EMC and EMS, which is superior to those of the magnesium alloys obtained by conventional casting process, and the additional presence of thermally stable Al2Ca phase in the 1wt% Ca-AZ80 alloy.