Hot working mechanisms in DMD-processed versus cast AZ31-1 wt.% Ca alloy

The hot deformation behavior of AZ31-1Ca magnesium alloy prepared by disintegrated melt deposition (DMD) technique is compared with that in as-cast (AC) condition. The microstructure of the DMD-processed material exhibited fine grain structure with fibering and intense basal texture along the extrusion direction unlike the AC material which had large grains and near random orientation. The processing maps developed on DMD-processed alloy exhibited three domains within the following ranges of temperature/strain rates: (1) 250-360°C/0.0003-0.01s^-1, (2) 430-500°C/0.0003-0.1s^-1; (3) 325-400°C/0.3-10s^-1. In the map for the AC alloy, Domain 1 occurred at higher temperature and Domain 3 was absent. Domain 1 in both conditions represents dynamic recrystallization (DRX) which is nucleated by basal+prismatic slip along with simultaneous recovery by dislocation climb controlled by lattice self-diffusion. In Domain 2 of DMD-processed alloy, grain boundary sliding and wedge cracking occurred leading to intercrystalline fracture in tension while in the AC alloy DRX has occurred to enhance the workability. In Domain 3 of DMD-processed alloy, DRX is nucleated by basal+prismatic slip with climb occurring via grain boundary self-diffusion. In the AC alloy, Domain 3 is absent since the large grain size reduced the grain boundary self-diffusion. Hot working DMD-processed alloy is best done at lower temperatures and higher strain rates (350°C and 10s^-1) while the AC alloy may be processed at higher temperatures and lower strain rates (475°C and <0.1s^-1).