The determination of types of defects that may be present in aluminum alloys has been a long-going discussion. Porosity has been held responsible for many of the failures in cast aluminum alloys. Due to the dramatic decrease in the solubility of hydrogen from liquid to solid aluminum, hydrogen is believed to be released from the solidification front and nucleate to form porosity. In this work, the diffusivity of hydrogen at different temperatures were investigated by means of Molecular Dynamic (MD) simulations. Dislocation density, crystal lattice deformation, and related changes in the tensile properties were determined in the presence of hydrogen for mono and nanocrystalline aluminum structures. The findings were correlated with the experimental and simulation data found in the literature where different tensile results were reported at different casting conditions.