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

• Published in: Applied surface science 2018-05, Vol.439, p.910-918
• Main Authors: da Silva, Thiago H., Nelson, Eric B., Williamson, Izaak, Efaw, Corey M., Sapper, Erik, Hurley, Michael F., Li, Lan
• Format: Article
• Language: English
• Subjects: Aluminum alloys; Chloride ions; Density functional theory; Localized corrosion; S-Phase Al2CuMg; θ-Phase Al2Cu
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2017.12.256

•First-principles to predict corrosion mechanisms of (0 0 1) θ-phase Al2Cu and (0 0 1) S-phase Al2CuMg surfaces in presence of water and Cl− were performed.•Atop Al sites are more energetically favorable for Cl− and water interactions than Cu sites.•S-phase is more reactive than the θ-phase surface, suggesting more susceptibility to surface interaction.•The S-phase Al2CuMg interaction with Cl− and water results in multiple new species formation.•θ -phase Interlayer spacing and topological partial charge density distribution may result in a more charge-stable structure. First-principles density functional theory-based calculations were performed to study θ-phase Al2Cu, S-phase Al2CuMg 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 Al2Cu and Al2CuMg 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 Al2CuMg structure has a more active surface than the θ-phase Al2Cu. We also found a higher tendency of formation of new species, such as Al3+, Al(OH)2+, HCl, AlCl2+, Al(OH)Cl+, and Cl2 on the S-phase Al2CuMg surface. Surface chemical reactions and resultant species present contribute to establishment of local surface chemistry that influences the corrosion behavior of aluminum alloys.