Molecular dynamics simulation of deformation and failure in magnesium bicrystals containing preexisting voids

Abstract

Magnesium and its alloys have broad application prospects due to their lightweight and high specific strength. However, their hexagonal close-packed crystal structure results in poor room-temperature ductility and low damage tolerance, which are critical bottlenecks limiting engineering applications. In actual magnesium crystals, initial defects such as micropores are commonly present. Yet the coupling effects between such defects and grain boundaries (GBs) on plastic deformation evolution and failure mechanisms at the atomic scale remain insufficiently understood. This study employs molecular dynamics simulations to construct magnesium bicrystal models with a preset void. The deformation and failure responses under uniaxial tension are systematically examined for five distinct GB angles, namely 14.52°, 34.54°, 53.14°, 71.74°, and 90° asymmetric boundary. The synergistic regulatory mechanisms of GB geometry and internal defects are revealed. The results demonstrate that the mechanical behavior is dominated by the GB angle. Low-angle symmetric tilt GB (14.52°) possess both high yield strength and favorable plastic stability, whereas high-angle and asymmetric GBs are prone to inducing stress concentration. Voids act as stress concentrators and interact differently with various GBs to regulate dislocation evolution, twin nucleation, and crack initiation. Particularly, the special GB angle of 53.14° can effectively retard crack propagation via twinning. This study elucidates the interaction mechanisms between GBs and preexisting defects at the atomic scale, revealing the dual role of voids as stress concentrators at the early deformation stage and damage nucleation sites during plastic deformation. The findings provide a theoretical foundation for GB engineering design and damage tolerance optimization of magnesium alloys.