Effect of dilute atom Gd on critical resolved shear stress and anisotropic deformation mechanism of Mg-Gd alloy

Abstract

Formability and ductility of Mg alloy are highly dependent on its mechanical anisotropy and are mainly dominated by the anisotropic deformations of basal slip, tension twining and non-basal slips. This work is engaged to measuring critical resolved shear stress (CRSS) for basal slip, twin nucleation/growth and pyramidal slip of a Mg-1 wt% Gd alloy by micropillar compressions. The effects of rare earth (RE) element, Gd, on the CRSS and the deformation mechanisms are discussed, and the mechanical anisotropy is determined. The results suggest that Gd atom is capable of balancing the anisotropy ratio of hard mode to soft mode, by triggering significant strengthening in basal slip of Mg alloy. The strengthening effect is related to the misfit-volume induced fluctuations in solute concentrations and the wavy solutes/dislocation interaction energies when Gd is added. As a result, Gd solute is advantageous to reduce the mechanical anisotropy, thus benefits to formability and ductility of Mg alloys. The presented results can provide a framework to understand basically the physical origin of mechanical anisotropy and formability of Mg-RE alloys and can be guidelines to design high ductility Mg alloys for next-generation lunar exploration.