An E(3)-equivariant interatomic potential uncovers the atomistic origin of solute and LPSO strengthening in Mg–Y–Zn alloy

The absence of a reliable interatomic potential for the Mg–Y–Zn ternary system has long hindered atomistic understanding of its strengthening mechanisms, where solid-solution hardening, dislocation–interface interactions, and LPSO kink deformation operate concurrently across multiple length scales. Here, we develop an E(3)-equivariant Allegro machine-learning interatomic potential that combines computational efficiency with near-DFT accuracy, validated against an extensive set of benchmarks, particularly the properties most critical to dislocation-mediated plasticity, including generalized stacking-fault energies, dislocation core structures, and Peierls stresses. This potential enables a large-scale framework that treats, within a single description, dislocation glide in the α-Mg matrix, basal-dislocation transmission across the α-Mg/LPSO interface, prismatic slip and its role as a dislocation source for kink boundaries in the LPSO structure. The simulations reveal that short-range ordered Y–Zn clusters impede basal ⟨ a ⟩ dislocation glide more effectively than isolated solutes. Meanwhile, both Y solute atoms and short-range ordered Y–Zn clusters are observed to promote cross-slip of pyramidal I ⟨ c+a ⟩ screw dislocations possessing a non-planar core structure. The semi-coherent α-Mg/LPSO interface impedes basal dislocations effectively, with a barrier governed by the dislocation orientation, the polytype (14H vs 18R), and the hard-layer spacing, largely suppressing their transmission into the LPSO. We further trace the origin of the basal dislocations that populate the LPSO kink boundaries to prismatic ⟨ a ⟩ slip. Prismatic dislocation shear simulations distinguish kink-pair formation from propagation and identify the LPSO hard layer as a character-selective filter that promotes the conversion of prismatic screw segments into basal ⟨ a ⟩ dislocations.