Formation and growth kinetics of the initial amorphous oxide film on the aluminum melt: A ReaxFF molecular dynamics simulation

Understanding on oxidation is critical for the improvement of aluminum melt quality which determines the properties of the aluminum alloy processed by casting. However, the oxidation mechanism of aluminum melt is still unclear in atomistic scale. In this work, we performed reactive molecular dynamics simulation to investigate the oxidation mechanism of aluminum melt on an atomic scale. Our results focus on the island-like nucleation on the melt surface and the following growth of the oxide film. The oxide grows via ion diffusion and the diffusion of O anions plays a greater effect. The evolution of the diffusion coefficient indicates an island-by-layer growth on the aluminum melt. Kinetically, the oxide growth obeys a linear law during the nucleation stage and switches to a logarithmic law after a closed oxide film forms. Besides, we emphasize the effect of oxygen content and ambient temperature on the formation of oxides. Our research can provide insights into the atomic-scale oxidation mechanism of aluminum melt which contributes to the better design for anti-oxidation methods during casting and the oxide-based functional materials.