Unraveling the mechanisms of aluminum solidification under hyper-gravity condition from molecular dynamics simulations

Gradient materials show excellent performance in combining strength, ductility, and fatigue resistance. In the present work, we proposed a novel hyper-gravity loading method and applied it to the solidification of aluminum using molecular dynamics simulation. A gradient structure is obtained after solidification, which is consistent with the experimental studies. The hyper-gravity-induced gradient pressure is identified as the main factor making the melting point, nucleation, and grain growth unevenly in the model, which leads to the decreased grain size along the hyper-gravity direction. Three solidification behaviors are observed in one solidification, i.e., homogenous nucleation initiates first at the bottom of the model, where it undergoes the highest pressure; then heterogeneous solidification combined with homogenous solidification appears in the middle; finally, directional solidification dominates because the insufficient undercooling makes the nucleation difficult. Moreover, the gradient structure and grain refinement are further enhanced with increasing gravity intensity.