Flow transitions and flow localization in large-strain deformation of magnesium alloy
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2016 Elsevier B.V. Understanding transitions from homogeneous to localized flow, and mechanisms underlying flow localization, is of paramount importance for deformation processing of magnesium. In this study, a shear-based deformation method is utilized for imposing large strains (~1), under controllable strain rates (10-105/s) and temperatures (80-300 C), in order to examine flow patterns in a magnesium alloy. Based on microstructure characterization, deformation twinning is suggested to contribute to the localized flow at temperatures below 200 C and at low strain rates. The transition from the localized to homogeneous flow with increasing temperature is due to reduction in twinning activity, and enhanced strain-rate sensitivity. At constant temperature, an increase in the strain rate decreases the propensity for flow localization. A model is presented for characterizing the maximum uniform strain as a function of temperature and deformation state (simple shear, plane-strain compression). The model incorporates temperature-sensitive microstructural changes and flow properties of magnesium into a classical framework to capture the flow localization phenomena at low temperatures and strain rates.