Molecular mechanics and dynamics simulation of hydrogen diffusion in aluminum melt

The main impurities in aluminum melt are hydrogen and Al2O3, which can deteriorate melt quality and materials performance. However, the diffusion process of H atoms in aluminum melt and the interactions among Al atoms, Al2O3 and hydrogen have been studied rarely. Molecular mechanics and dynamics simulations are employed to study the diffusion behaviors of different types of hydrogen, such as free H atoms, H atoms in H-2 and H+ ions in H2O using COMPASS force field. Correspondingly, force field types h, h1h and h1o are used to describe different types of hydrogen which are labeled as H-h, H-h1h and H-h1o. The results show that the adsorption areas are maximum for H-hlo, followed by H-h1h and H-h. The diffusion ability of H-h1o is the strongest whereas H-h is hard to diffuse in aluminum melt because of the differences in radius and potential well depth of various types of hydrogen. Al2O3, cluster makes the Al atoms array disordered, creating the energy conditions for hydrogen diffusion in aluminum melt. Al2O3 improves the diffusion of H-h and H-h1o, and constrains H-h1h which accumulates around it and forms gas porosities in aluminum. H-h1h is the most dispersive in aluminum melt, moreover, the distance of AI-H-hlo is shorter than that of Al-H-hlh both of which are detrimental to the removal of Ho. The simulation results indicate that the gas porosities can be eliminated by the removal of Al2O3, inclusions, and the dispersive hydrogen can be removed by adsorption function of gas bubbles or molten fluxes.