Extrusion ratio-induced microstructural disparity and plastic deformation behavior in dual-phase Mg-Li-Zn-Y alloys

This study systematically investigates the influence of extrusion ratio on the microstructure and mechanical properties of a dual-phase Mg-10.16Li-2.63Zn-0.08Y (wt.%) alloy, with Visco-plastic Self-consistent modeling incorporating Predominant Twin Reorientation (VPSC-PTR) modeling employed to quantitatively elucidate the distinct deformation mechanisms of the α-Mg and β-Li phases. The results demonstrate that increasing the extrusion ratio enhances interphase deformation compatibility and significantly suppresses {10-12} extension twinning in the α-Mg phase, owing to elevated deformation heating. Marked disparity in microstructural evolution is observed between the two phases: the α-Mg phase exhibits only limited recrystallization (with a recrystallized fraction of merely ∼36%), whereas the β-Li phase transitions from partial to complete recrystallization followed by pronounced grain growth, which may be attributed to the higher atomic diffusivity in the BCC β-Li phase than in the HCP α-Mg phase. These microstructural changes are accompanied by markedly enhanced ductility but a marginal reduction in strength as the extrusion ratio increases. The alloy with an extrusion ratio of 25 (E25) achieves optimal ductility, with an elongation (EL) of 49.6%, while retaining moderate strength (yield strength (YS) of 141 MPa and ultimate tensile strength (UTS) of 177 MPa). Such ductility improvement is primarily attributed to the drastically reduced twin density within the α-Mg phase, which alleviates twin-matrix interfacial incompatibility and mitigates stress concentration, thereby suppressing intraphase crack initiation. VPSC-PTR simulations further reveal that plastic deformation is dominated by the soft β-Li matrix via {110}<111> slip (supplemented by {112}<111> slip), accommodating the majority of strain, while the hard α-Mg phase primarily provides load-bearing capacity.