Exceptional mechanical properties by enhanced dislocation behaviors and solute segregation at lamellar structures via rotary swaging and aging treatment in Mg-Y-Zn-Mn alloy

Mechanisms behind the exceptional mechanical properties achieved by controlled rotary swaging (RS) and aging treatment are elaborated in Mg-Y-Zn-Mn alloy. While the RS deformation is shown to increase the strength significantly, the followed aging treatment can further improve ultimate tensile strength (UTS) and ductility simultaneously. Optimal comprehensive mechanical properties, with the tensile yield strength (TYS) of ∼286 MPa, UTS of ∼440 MPa, and the elongation of ∼7.3%, are achieved by a combination of 4-pass RS deformation and aging treatment. The TYS and UTS are further increased to ∼341 MPa and 477 MPa, respectively, by the increased RS deformation (10-passes) and aging treatment. The improved TYS by the RS deformation is primarily attributed to the high dislocation density and the formation of basal texture, while the refined nano-lamellar structure and grain size yield sizable contributions. Furthermore, co-segregation of Y and Zn at nano-lamellar structures, including γ’ precipitates and 14H-LPSO (long period-stacking order) phase, is obviously enhanced by the aging treatment, owing to the promoted segregation conditions benefited from the high dislocation density induced in the RS deformation. The co-segregation of alloying species stabilizes the nano-lamellar structures and enhances their interactions with <c+a> dislocations by forming dislocation jogs during slipping. In addition, the activation of <c+a> slip between nano-lamellar structures is enhanced within the plasticity domain owing to the enriched local chemical composition. The UTS and ductility are thus improved simultaneously by the aging treatment after RS deformation.