Effect of high strain rate on dynamic behavior and deformation mechanism of Mg-Nd-Zr-Ca alloy

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The flow stress crossover behavior and its mechanisms in a Mg–1.8Nd–0.4Zr–0.3Ca alloy were systematically investigated through uniaxial compression tests conducted at 330–430 °C with high strain rates of 1 and 10 s -1 . The results demonstrate a distinct strain rate dependence of the flow behavior: at 1 s -1 , the flow stress curve exhibits steady-state characteristics without a distinct peak, whereas at 10 s -1 , it shows a single-peak feature with significant dynamic softening. Microstructural analysis reveals that plastic deformation at 1 s -1 primarily controlled by the coordinated interplay between twinning and dislocation slip, accompanied by minor continuous dynamic recrystallization (CDRX) and twin-induced dynamic recrystallization (TDRX), forming a necklace-like structure. At the higher strain rate of 10 s -1 , twinning activity is significantly reduced. Enhanced dislocation accumulation coupled with adiabatic heating promotes the dominance of CDRX, which raises the recrystallized fraction substantially from 14.9% to 35.1%. As strain accumulates, the operative deformation mechanism shifts from dislocation slip to grain boundary sliding, causing a drop in the flow stress. Furthermore, both increased strain rate and higher strain levels facilitate the activation of pyramidal slip and the dynamic precipitation of fine Mg 41 (Nd, Ca) 5 phases. Such precipitates act as effective obstacles to dislocation motion and grain boundary migration, inhibiting the growth of dynamically recrystallized (DRX) grains. This investigation provides a comprehensive understanding of the deformation mechanism in Mg-RE alloys subjected to high-strain-rate loading, providing theoretical guidance for optimizing their high-speed thermomechanical processing.