First-principles surface interaction studies of aluminum-copper and aluminum-copper-magnesium secondary phases in aluminum alloys

Abstract First-principles density functional theory-based calculations were performed to study θ-phase Al 2 Cu, S-phase Al 2 CuMg surface stability, as well as their interactions with water molecules and chloride (Cl − ) ions. These secondary phases are commonly found in aluminum-based alloys and are initiation points for localized corrosion. Density functional theory (DFT)-based simulations provide insight into the origins of localized (pitting) corrosion processes of aluminum-based alloys. For both phases studied, Cl − ions cause atomic distortions on the surface layers. The nature of the distortions could be a factor to weaken the interlayer bonds in the Al 2 Cu and Al 2 CuMg secondary phases, facilitating the corrosion process. Electronic structure calculations revealed not only electron charge transfer from Cl − ions to alloy surface but also electron sharing, suggesting ionic and covalent bonding features, respectively. The S-phase Al 2 CuMg structure has a more active surface than the θ-phase Al 2 Cu. We also found a higher tendency of formation of new species, such as Al 3+ , Al(OH) 2+ , HCl, AlCl 2+ , Al(OH)Cl + , and Cl 2 on the S-phase Al 2 CuMg surface. Surface chemical reactions and resultant species present contribute to establishment of local surface chemistry that influences the corrosion behavior of aluminum alloys.