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 H2 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 Hh, Hh1h and Hh1o. The results show that the adsorption areas are maximum for Hh1o, followed by Hh1h and Hh. The diffusion ability of Hh1o is the strongest whereas Hh 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 Hh and Hh1o, and constrains Hh1h which accumulates around it and forms gas porosities in aluminum. Hh1o is the most dispersive in aluminum melt, moreover, the distance of Al-Hh1o is shorter than that of Al-Hh1h, both of which are detrimental to the removal of Hh1o. 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.