Anomalous deformation behavior and underlying mechanisms of Mg-Nd-Zr-Ca alloy during low-temperature hot compression

Abstract

The anomalous deformation behavior of a Mg-1.8Nd-0.4Zr-0.3Ca (wt%) alloy during hot compression at low temperatures (180–330 °C) and strain rates of 0.001–10 s⁻¹ was systematically investigated. The flow stress exhibits an abnormal increase with decreasing strain rate at 180 °C, accompanied by negative strain rate sensitivity and pronounced Portevin–Le Chatelier (PLC) serrated flow, which are attributed to dynamic strain aging (DSA). The activation energy for serrated flow is determined to be 197.9 kJ/mol, matching the diffusion activation energy of Zr in Mg, confirming that Zr solute atoms are primarily responsible for dislocation pinning. At 230 °C and low strain rate (0.001 s⁻¹), DSA initially elevates the flow stress, but with increasing strain, dynamic precipitation of Zr-rich phases at twin boundaries and dynamic recrystallization (DRX) grain boundaries weakens the solute pinning effect, while dynamic recovery (DRV) and localized DRX become active, leading to post‑peak softening. Microstructural analysis reveals that basal slip and multiple twinning dominate low‑temperature deformation. Lamellar bands and coaxial grain boundaries (CGBs) formed by sequential twinning generate high densities of dislocations and stacking faults, promoting the activation of pyramidal slip and improving the strength-ductility matching under low-temperature deformation. At high strain rates (10 s⁻¹), kink bands formed by ordered dislocation arrangements further accommodate local strain and suppress microcrack nucleation. This work clarifies the low-temperature deformation mechanisms and provides a reference for optimizing their thermomechanical processing.