Abstract: The influence of yttrium (Y) content on the mechanical properties and deformation behavior of Mg-Y alloys at room temperature (RT) and cryogenic temperature (CT) was systematically clarified. Increasing Y from 0 to 1.0 at.% markedly enhances strength and ductility at both temperatures, with the Mg-1.0Y exhibiting nearly double the tensile yield strength (TYS) and ultimate tensile strength (UTS) and a more than fourfold increase in elongation to fracture (EF) at CT compared with pure Mg. At RT, deformation in the low-Y alloy is dominated by basal slip followed by {101¯2} tension twins, whereas higher Y content suppresses twinning and promotes the activation of non-basal slip, especially pyramidal 〈c + a〉 slip, leading to steadier lattice rotation and more homogeneous strain distribution. At CT, twinning and twin thickening are further promoted in the low-Y alloy, causing severe strain localization and early ductility loss, while the high-Y alloy retains a slip-dominated deformation mode with stable lattice rotation. Moreover, Y addition broadens slip transfer pathways from basal-basal to basal-prismatic/pyramidal slip transfers, enhancing intergranular strain compatibility and further improving ductility. These findings demonstrate that Y alloying shifts the deformation mechanism of Mg alloys from twinning-dominated to slip-dominated, providing a pathway to achieve superior mechanical properties.

Key words: Mg alloys, Cryogenic temperature, Strain distribution, Slip transfer, Deformation behavior