Processing Map of AZ31-1Ca-1.5 vol.% Nano-Alumina Composite for Hot Working

A processing map for extruded AZ31-1Ca-1.5NAl composite has been developed, which exhibited four important domains for hot working. The corresponding temperatures and strain rates associated with these domains are: (1) 250-350°C and 0.0003-0.01 s^-1; (1A) 350-410°C and 0.0003-0.01 s^-1; (2): 410-490°C and 0.002-0.2 s^-1; and (3) 325-410°C and 0.6 s^-1 to 10 s^-1. Dynamic recrystallization (DRX) occurred in all the four domains although different slip mechanisms and recovery processes are involved. Basal slip and prismatic slip dominates deformation in Domains 1 and 1A, respectively, with recovery occurring by climb that is lattice self-diffusion controlled. However, because of the high strain rates in Domain 3, recovery occurs through a climb process, controlled by grain boundary self-diffusion. The recovery mechanism in Domain 2 is cross-slip assisted by pyramidal slip along with basal and prismatic slip. The grain size has a linear relation with Zener-Hollomon parameter in all the domains. At high strain rates, the composite undergoes shear fracture at lower temperatures and intercrystalline fracture at higher temperatures. All of the identified DRX domains are suitable for conducting bulk metal forming processes although the one with the highest strain rates (Domain 3) is preferred for achieving high productivity.