First-principles study of the influence of typical alloying elements on corrosion behavior of Aluminum alloys

Aluminum (Al) alloys, especially the 5xxx and 7xxx series, are widely used in various applications due to their excellent mechanical properties achieved through alloying. Exploring the effect of alloying elements on the corrosion resistance of Al alloys is an important step in the development of high-performance Al materials. In this work, Density Functional Theory (DFT) calculations were utilized to examine the role of alloying elements on galvanic corrosion behavior in 5xxx and 7xxx series Al alloys, and the impact of aggressive ions on the protective properties of their passive films. According to the DFT calculation results, the potential difference between the Al matrix and Mg2Al₃ shows an initial decrease followed by an increase as the concentration of Mg increases in 5xxx series alloys (Al-Mg). For 7xxx series alloys (Al-Zn-Mg-Cu), increasing Cu content enhances the susceptibility to galvanic corrosion. Additionally, competitive adsorption diagrams of various ions on the passive film of the alloyed Al in chloride-containing solutions were plotted. The Si-additive in the film promotes the adsorption of hydroxide ions (OH⁻) on the passive films, thus effectively blocking the penetration of harmful Cl^- ions. However, when passive films are modified by Mg, Zn or Cu additives, the film degradation is accelerated. This study explains the mechanisms of micro-galvanic corrosion and ions adsorption on the passive film of Al alloys, thereby providing the theoretical basis for designing corrosion-resistant alloys.