Warm and Hot Deformation Behavior of As-Cast ZEK100 Magnesium Alloy

Abstract

Isothermal warm and hot deformation behavior of as-cast ZEK100 (Mg-1.2Zn-0.25Zr-0.17Nd, in wt.%) magnesium alloy was studied using the Gleeble® 3500 thermal-mechanical simulation testing system. The study was conducted over a wide range of temperatures (100 °C-500 °C) and strain rates (5.0 × 10−4 s−1–1.0 × 10 s−1), for a low true strain regime (i.e. 0.2) associated with general deformation level during twin roll casting process. For the range of studied strain, steady state flow stress was obtained at low strain rates (5.0 × 10−4 and 1.0 × 10−3 s−1) and high deformation temperatures (350, 400 and 450 °C). At medium strain rates of 1.0 × 10−2 and 1.0 × 10−1 s−1, steady state flow stress was observed for deformation temperatures of 400–450 °C and 450 °C, respectively. In the rest of conditions, strain hardening was the dominant deformation mechanism. A modified Ludwig equation was successfully used to develop constitutive model for the ZEK100. The model was validated by compression of material under continuous cooling or an abrupt change in the strain rate conditions. Deformed microstructure was consisted of twinning at low temperature deformation; while, at higher temperatures discrete regions of discontinuous dynamic recrystallization (by bulging at serrated boundaries) were observed. The former is associated with the strain hardening observed in the stress strain curves while the latter is the main reason of steady state flow stress. Strain hardening sensitivity and strain rate sensitivity exponents were also correlated to the deformed microstructure of the alloy.