Unveiling anomalous strengthening and deformation mechanism evolution in a Mg-Gd-Y-Zr alloy under rate-temperature coupling effects

Abstract

• Lower strain rates (10 s⁻¹ to 10⁻³ s⁻¹) increase peak stress but reduce ductility around 150 °C. • Strength anomaly at 150 °C arises from strain aging, precipitation, and dislocation structures. • High strain rates significantly postpone the occurrence of softening and twinning termination. • High strain rates increase recrystallization temperature, enhancing efficiency and homogeneity. While the deformation behavior of rare-earth magnesium alloys at high temperatures has been extensively studied, the deformation mechanisms under moderate-to-low temperatures and high strain rates remain insufficiently understood. To address this gap, hot compression tests were conducted on a Mg-11Gd-3Y-0.5Zr (wt.%) alloy over a temperature range of 150 °C–450 °C under strain rates of 10⁻³ s⁻¹ (low strain rate (LSR)) and 10 s⁻¹ (high strain rate (HSR)) to explore the strain rate-temperature coupling effects during hot deformation. The results revealed an anomalous increase in peak stress at 150 °C–250 °C as the strain rate decreased, attributed to the combined effects of nano-precipitates, dislocation cell structures, and serrated flow induced by dynamic strain aging. At higher temperatures, strain rate influences softening pathways: under HSR at 450 °C, the effect of twinning shifts from strengthening to facilitating dynamic recrystallization (DRX), resulting in substantial grain refinement (∼4 µm, 81% area fraction at a strain of 0.6). In contrast, at LSR, softening is dominated by dynamic recovery at 350 °C, with limited DRX (∼4 µm grains, 10% area fraction at a strain of 0.6) occurs at 400 °C. These findings clarify the dual role of twinning and its interaction with rate-temperature conditions, providing valuable insights into optimizing the hot processing of rare-earth magnesium alloys.

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