Improvement of electrochemical corrosion uniformity in AA2024 FSW joints by laser shock peening

ABSTRACT This study systematically investigates the residual stress distribution, microstructural evolution, and corrosion behavior in friction stir welded AA2024 joints, focusing on the nugget zone (NZ), heat-affected zone (HAZ), thermo-mechanically affected zone (TMAZ) and base metal (BM) before and after laser shock peening (LSP) treatment. Electrochemical characterization revealed significant variations in corrosion resistance prior to LSP treatment, with the BM and NZ exhibiting 1.5-fold and 1.9-fold higher corrosion resistance, respectively, compared to the HAZ. Notably, LSP effectively homogenized the electrochemical response across these regions, reducing inter-regional disparities in corrosion current density through microstructural modification. Residual stress analysis and microstructural characterization demonstrated that surface compressive residual stresses followed the hierarchical order: HAZ > TMAZ > NZ. In contrast, grain refinement through dislocation mechanism is more pronounced in the NZ. These findings demonstrate that compressive residual stresses introduced by LSP play a more dominant role in enhancing corrosion resistance of FSW joint under the present LSP conditions. LSP-induced compressive stresses reduce macro- and microscopic defects, thereby diminishing initiation sites for localized corrosion, while the associated grain refinement may introduce localized electrochemical heterogeneity. The synergistic interplay of these opposing regulatory effects contributes, to some extent, to enhancing the electrochemical corrosion uniformity of the welded joint. This study provides critical insights for optimizing post-weld surface treatments of aluminum alloys in engineering applications.