Quantitative study on the evolution of geometrically necessary dislocation density and anomalous twinning behavior during tensile deformation of Mg-2Y alloy

Mg-RE (magnesium-rare earth) alloys exhibit excellent room-temperature ductility, significantly broadening their potential applications. A comprehensive understanding of their plastic deformation mechanisms is essential for developing new processing technologies. However, the evolution of geometrically necessary dislocation (GND) densities and the anomalous twinning behavior during plastic deformation in Mg-RE alloys remain poorly understood. In this work, the microstructural evolution of the Mg-2Y (wt.%) alloy under tensile deformation was tracked via quasi-in-situ electron backscattered diffraction (EBSD) observation. GND analysis based on lattice curvature tensor and variant identification method were utilized to quantitatively study the activation behavior of slip and twinning, respectively. The experimental results indicated that the GND density for basal slip remained the highest throughout the straining process while non-basal slip, prismatic and pyramidal slip, exhibited an increasing contribution to the total GND density. Some tension twinning variants with Schmid factor (SF) approaching zero or even negative SF were still activated. The evolution mechanism of GND density and the activation mechanisms of anomalous twinning were systematically discussed. The enhanced activity and increased GND contribution of non-basal slip could be attributed to two key mechanisms: the decrease in SF ba (SF for basal slip) coupled with the increase in SF pr and SF py (SF for prismatic and pyramidal slip) driven by twinning and grain rotation; the reduction in the critical resolved shear stress (CRSS) ratio of non-basal to basal slip resulting from twinning-induced grain refinement. Local stresses generated by dislocation slip at grain boundaries, combined with a homogeneous distribution of grain boundary misorientation angles (GBMA), served as the principal drivers for anomalous twinning activation.