Influence of surface plastic deformation on the microstructure evolution and corrosion behavior of the new generation of high-strength Al-Zn-Mg-Cu alloy

Al-Zn-Mg-Cu alloys inevitably undergo surface plastic deformation during application, which significantly alters their surface properties, particularly corrosion resistance. In this work, multiple microstructural characterization methods and corrosion electrochemical testing technologies were employed to comprehensively investigate the influence of surface plastic deformation on the microstructure and corrosion behavior of the Al-Zn-Mg-Cu alloy's surface layer. The results indicate that a disturbed surface layer (DSL), characterized by ultrafine recrystallized grains and a thickness of approximately 350 nm, is formed on the alloy surface induced by surface plastic deformation. The original Mg (Zn, Al, Cu)₂ phase within the DSL dissolves accompanied by redistribution of alloying elements. The AlCu phase precipitates, and the Mg and Zn elements segregate at the recrystallized grain boundaries. In the DSL-affected zone, subgrain boundaries with continuous precipitates form within the original grains, and the grain boundary precipitates transform the Mg (Zn, Al, Cu)₂ phase into the Al₂Cu phase. Meanwhile, high-density dislocations are also observed in the grains. Compared with the matrix, the DSL exhibits higher corrosion susceptibility, manifested as a lower corrosion potential and a larger corrosion current density. Therefore, uniform corrosion is more likely to occur in the DSL.