Hot Deformation Behavior and Constitutive Analysis of As-Extruded Mg–6Zn–5Ca–3Ce Alloy Fabricated by Rapid Solidification

The plasticity of Mg–6Zn–5Ca–3Ce alloy fabricated by rapid solidification (RS) at room temperature is poor due to its hexagonal-close-packed (HCP) structure. Therefore, hot deformation of RS Mg–6Zn–5Ca–3Ce alloy at elevated temperature would be a major benefit for manufacturing products with complex shapes. In the present study, hot deformation behavior of as-extruded Mg–6Zn–5Ca–3Ce alloy fabricated by RS was investigated by an isothermal compression test at a temperature (T) of 573–673 K and strain rate ($\dot{\epsilon }$) of 0.0001–0.01 s⁻¹. Results indicated that the flow stress increases along with the declining temperature and the rising strain rate. The flow stress behavior was then depicted by the hyperbolic sine constitutive equation where the value of activation energy (Q) was calculated to be 186.3 kJ/mol. This issue is mainly attributed to the existence of fine grain and numerous second phases, such as Mg₂Ca and Mg–Zn–Ce phase (T’ phase), acting as barriers to restrict dislocation motion effectively. Furthermore, strain compensation was introduced to incorporate the effect of plastic strain on material constants ($\alpha$,$Q$,$n$,$\ln A$) and the predicted flow stresses under various conditions were roughly consistent with the experimental results. Moreover, the processing maps based on the Murty criterion were constructed and visualized to find out the optimal deformation conditions during hot working. The preferential hot deformation windows were identified as follows: T = 590–640 K, $\dot{\epsilon }$ = 0.0001–0.0003 s⁻¹ and T = 650–670 K, $\dot{\epsilon }$ = 0.0003–0.004 s⁻¹ for the studied material.