Direct observation of solute atom diffusion dynamics towards {101¯2} twin boundary in a magnesium alloy

Understanding solute segregation at twin boundaries (TBs) is essential for tailoring the microstructure and properties of magnesium alloys. Using in situ scanning transmission electron microscopy, we directly observe the diffusion behavior of Y atoms at a {101¯2} TB in a Mg-Y alloy. Atomic-resolution imaging reveals a metastable segregation structure with alternating Y concentration levels in the basal planes. Time-resolved images further trace the diffusion paths of Y atoms. Density functional theory calculations determine the diffusion energy barriers and preferred segregation sites. Our findings provide direct insights into solute-TB interactions, guiding TB engineering and heat treatment strategies in magnesium alloys.