The dynamic deformation mechanisms of materials, especially the relationship between microstructural evolution and mechanical response under extreme strain rates, are a core issue in impact engineering and materials design. This study employs molecular dynamics simulations to systematically investigate the deformation behavior of an Al–Mg–Ti alloy under ultra‐high strain rates (5 × 10 8 ~ 1 × 10 10 s −1 ). The simulations reveal for the first time a chain‐reaction mechanism leading to a bimodal stress–strain response. In the early stage of deformation, dislocation slip and the phase transformation from FCC to hexagonal HCP structures jointly contribute to the first stress peak. Subsequently, the local accumulation of the HCP phase triggers an amorphization transformation within shear bands. The load‐bearing capacity of the newly formed amorphous regions is identified as the direct cause of the second stress peak, representing a previously unrecognized key mechanism. Further analysis shows that when the strain rate exceeds 5 × 10 9 s −1 , insufficient time for atomic rearrangement significantly suppresses the HCP phase transformation, limiting its volume fraction to below 4%, thereby clarifying the atomic‐scale origin of the strain‐rate effect.
Zhang et al. (Mon,) studied this question.