Co-doping strategy enables stably spontaneous nanocrystal passivating film for extraordinary corrosion resistance in high-strength aluminum alloy

As a natural barrier, the spontaneous passive film on aluminum alloy surfaces is critical for the corrosion resistance to chloride ions in marine environments. However, this anti-corrosion ability of the passive film is severely limited by its highly defective amorphous structure and non-uniform distribution caused by the multiphase microstructure in high-strength aluminum alloys. In this study, the co-doping strategy is proposed to engineer an anti-corrosion spontaneous passive film with uniform distribution and stable nanocrystal structure, effectively suppressing chloride ion-induced degradation on the high-strength aluminum alloy surface layer, achieving a corrosion inhibition efficiency of 78.5% and decreased pitting corrosion depth of 94%. Based on this engineering strategy, the stable nanocrystal passive film was achieved through co-doping Zn and Zr, exhibiting twice the thickness and a ∼79.5% reduction in defect density. The Zn segregates around the Al 2 Cu strengthening phases, forming a ZnO-rich interfacial protection layer that mitigates localized current leakage, and Zr inhibits the penetration of chloride ions through the nanocrystal boundary channels by forming Zr-O-Al bonds at the nanocrystal boundary. This study provides new insights for designing the highly stable passive films for anti-corrosion and provides a paradigm-shifting approach to integrate spontaneous passivation and structural reinforcement in corrosion-resistant metallic material design.