Predicting Grain Boundary Segregation and Mobility in Magnesium Alloys

Grain boundary (GB) segregation and mobility play central roles in controlling grain growth and texture evolution in magnesium alloys. This work presents an integrated atomistic and data-driven framework to understand the thermodynamic and kinetic origins of GB behavior in Mg and Mg-based alloys. First, solute segregation thermodynamics are quantified using a spectral approach based on per-site segregation free energy distributions for yttrium in Mg symmetric tilt grain boundaries (STGBs). Thermodynamic integration combined with molecular dynamics reveals significant anharmonic and entropic contributions at processing-relevant temperatures, which are captured using surrogate models with physics-informed descriptors and uncertainty quantification, yielding segregation predictions consistent with experiments. Second, a comprehensive molecular dynamics survey of Mg STGB migration mechanisms demonstrates strong mobility anisotropy governed by GB geometry, disconnection characteristics, and slip-system anisotropy intrinsic to HCP crystals under different driving forces. Surrogate models using physically meaningful geometric features improve predictive capability for GB mobility. Finally, classical thermodynamic and solute-drag models are applied to ternary Mg–Ca–Zn alloys to assess co-segregation effects and their influence on GB mobility, providing mechanistic insight into rare-earth-free texture weakening. Together, these studies establish a multiscale, physics-guided framework for predicting GB segregation and mobility in Mg alloys.