Optimization of hot extrusion process parameters of Mg-4Y-2Nd-1Gd-1Ag-0.5Zr alloys based on processing map and dynamic recrystallization model

Abstract The hot‐deformation behavior and extrusion response of a rare‐earth–containing Mg-4Y-2Nd-1Gd-1Ag-0.5Zr alloy were systematically investigated to establish processing guidelines for high-strength magnesium components. Cylindrical billets were homogenized, subjected to isothermal compression at 350–500 °C and strain rates of 0.001–1 s −1 , and analyzed using a dynamic materials model to construct constitutive equations and hot-processing maps. The alloy exhibits an activation energy of ∼229 kJ mol −1 , close to the diffusion energy of Y in Mg, and a stress exponent n ≈ 5.0, confirming that high-temperature deformation is governed by dislocation glide and climb in the climb-controlled regime. Flow-stress curves reveal typical dynamic recrystallization (DRX) features, with higher temperatures and lower strain rates promoting extensive DRX and grain refinement. The instability regions predicted by the processing maps expand with strain from low-temperature/high-rate to high-temperature/high-rate conditions. Extrusion experiments validated the modelling results and identified an optimal processing window near 425 °C, yielding defect-free rods with a fine recrystallized grain size (∼4.4 µm), a yield strength of 289 MPa, an ultimate tensile strength of 335 MPa, and an elongation of 10.6 %. These findings provide a mechanistic basis for the design of magnesium alloys combining high strength and ductility, and demonstrate the effectiveness of processing-map-guided extrusion for rare-earth-modified Mg systems.