DECOUPLING GEOMETRIC AND INTRINSIC CONTRIBUTIONS TO PRECIPITATION STRENGTHENING IN MAGNESIUM ALLOYS: A DISCRETE DISLOCATION DYNAMICS STUDY

Magnesium alloys, as lightweight structural materials, rely primarily on precipitation strengthening to enhance their mechanical properties. However, the low symmetry of the hexagonal close-packed (HCP) structure in magnesium matrix leads to complex influences of precipitate morphology, number density, volume fraction, and crystallographic orientation on strengthening efficiency. Traditional experiments struggle to isolate these variables. This study employs discrete dislocation dynamics simulations based on the ParaDiS platform, extended for HCP lattices, to systematically investigate precipitation strengthening mechanisms. Simulation results show that, at constant volume fraction, rod-like precipitates provide superior strengthening compared to plate-like or spherical ones, mainly due to reduced effective obstacle spacing on slip planes. Increasing number density and volume fraction further elevates yield strength, with nonlinear multi-body interactions prominent at high volume fractions. The intrinsic strength of precipitates governs deformation mechanisms, transitioning from shearing-dominated mechanism to bypassing-dominated mechanism. Crystallographic orientation effects reveal that precipitate morphology modulates slip system activation, with rod-like precipitates more effective in suppressing basal slip and mitigating mechanical anisotropy. A modified geometric model is proposed based on simulation data, quantitatively linking macroscopic precipitate parameters to microscopic strengthening increments, consistent with experimental observations. This work provides theoretical insights for optimizing precipitation strengthening in magnesium alloys.