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Flow transitions and flow localization in large-strain deformation of magnesium alloy

2016-04-06
Sagapuram, Dinakar
Efe, Mert
Trumble, Kevin P.
Chandrasekar, Srinivasan
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 (similar to 1), under controllable strain rates (10-10(5)/s) and temperatures (80-300 degrees 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 degrees 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.