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

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 ℃–450 ℃ 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 ℃–250 ℃ 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 ℃, 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 ℃, with limited DRX (~4 µm grains, 10% area fraction at a strain of 0.6) occurs at 400 ℃. 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.