Synergistic effects of solutes on active deformation modes, grain boundary segregation and texture evolution in Mg-Gd-Zn alloys

Abstract

Synergistic effects of rare earth elements (RE) and Zn have a major impact on the properties of ternary Mg-RE-Zn alloys. This study illuminates their dependence on the solute ratio by comparing texture evolution, solute segregation, and active deformation modes of three Mg-Gd-Zn alloys with a varying Gd:Zn ratio of 2:1, 1:1 and 1:2. A low Gd:Zn ratio led to a texture featuring a pronounced TD-tilted basal pole spread alongside a magnified solute segregation at grain boundaries, indicating a significant impact of solute-boundary interactions on RE-texture formation. Atom probe tomography revealed major alterations of the segregation energy of both Gd and Zn, depending mainly on the solute ratio rather than the absolute solute concentration. Additionally, the alloy with the smallest Gd:Zn ratio, i.e. Gd:Zn = 1:2, showed the highest direction dependent anisotropy of the yield stress under tensile strain, which was attributed to a magnified anisotropy of twinning depending on the Gd:Zn ratio. EBSD assisted slip trace analysis showed that the occurrence of non-basal slip systems could be increased by reducing the Gd:Zn ratio. Synergistic solute effects were found to be crucial for the activation of non-basal slip, solute segregation, as well as the formation of RE-texture components and proven to be highly sensitive to the solute ratio.