Hot deformation behavior and workability characteristics of AZ91 magnesium alloy powder compacts-A study using processing map

This study examined the hot deformation behavior and workability characteristics of AZ91 Mg alloy powder compacts by performing hot compression tests with a Gleeble 3800 machine. To this end, powder compacts with a relative green density of 93% were hot-compressed at temperatures ranging from 150 °C to 500 °C and at true strain rates ranging from 0.001 s−1 to 10 s−1. The true stress-true strain curves peaked at low strains, after which the flow stress increased slightly or remained constant. The work hardening rate decreased with increasing deformation temperature or strain rate. Processing maps were developed for all of the hot compression tests at strains of 0.1, 0.5, and 0.8, which represented a safe deformation domain at deformation temperatures and strain rates in the ranges of 150-300 °C and 0.001-0.01 s−1. Kinetic analysis of the flow stress data for the safe deformation domain yielded an activation energy of 75 kJ/mol which is lower than those previously reported for the hot compression of bulk AZ91 Mg alloy. According to the developed processing maps and the microstructures of the hot-compressed specimens, the optimum hot working window for AZ91 Mg alloy powder compacts was determined to lie between 275-325 °C and 0.001-0.01 s−1.