Hot deformation behavior and processing map development of Mg/Al2O3 composite: A case study of extrusion ratio effects

The hot deformation behavior of 2.5 wt.% submicron alumina reinforced magnesium composite manufactured by a new casting method was examined to assess the impact of extrusion ratio and initial microstructure on the hot workability of Mg/Al2O3 composite. The thermomechanical experiments were performed at strain rates from 0.001 s−1 to 0.05 s−1 and the temperature ranging from 523 K to 673 K. The processing map was developed using power dissipation efficiency in terms of temperature and strain rate. Results revealed that the higher extrusion ratio yields finer grain size and a more homogenous distribution of alumina particles resulting in lower flow stress and activation energy. Stable regions with more power efficiency (57%) and less instability were observed in materials that experienced higher strain. Based on the microstructural observation, dynamic recrystallization as the main restoration mechanism occurred at composite with a higher extrusion ratio and finer grains in all conditions. It was deduced that the enhanced workability of fine-grain material is confirmed by steady flow stress and safe zones of the processing map. It was also revealed that twinning–twinning intersection and flow localization are the main reasons for unstable flow in both samples with unlike grain sizes.