Nanosecond Laser Texturing of Triple-Scale Surface Structuring for Robust Pitting Corrosion Resistance in AA6061

Aluminum alloys such as AA6061 are widely deployed in marine and chloride-containing environments but remain vulnerable to localized pitting corrosion once the native oxide film is destabilized. This work presents a scalable, PFAS-free surface engineering strategy that suppresses pitting corrosion through nanosecond laser manufacturing of triple-scale hierarchical architectures combined with siloxane-based chemical functionalization. Nanosecond IR laser texturing generates fully covered grid and grid-plus-double-diagonal (G+DD) patterns consisting of micron-scale trenches and ridges, submicron resolidified features, and nanoscale cauliflower-like structures enriched with aluminum oxide. This multiscale roughness increases the effective surface area, enhances oxide density, and promotes robust chemical anchoring of a non-fluorinated OTS–PDMS hybrid layer, which lowers surface energy while maintaining mechanical stability. The optimized (LT (GDD) + CT) surface exhibits stable Cassie–Baxter wetting behavior with a static water contact angle of ~158°, advancing and receding angles above 159°, a roll-off angle of ~2°, and an ultra-low normalized surface free energy of ~5.6 mN m^-1, indicating strong suppression of polar interactions and reduced electrolyte affinity. Electrochemical characterization in 0.6 M NaCl reveals a pronounced positive shift in pitting potential and orders-of-magnitude increases in low-frequency impedance magnitude and polarization resistance relative to bare, chemically treated-only, and laser-only controls. Time-dependent electrochemical impedance spectroscopy conducted over 17 days demonstrates sustained high corrosion resistance and minimal degradation of the hierarchical morphology. Post-immersion microscopy confirms limited localized attack and preserved surface features on the fully textured and functionalized surface, whereas partial-coverage or single-treatment samples exhibit evident pitting and surface breakdown. The results demonstrate that process-driven nanosecond laser texturing coupled with PFAS-free siloxane functionalization provides a manufacturable, industry-compatible route to durable, non-wetting, highly robust, and sustained corrosion-resistant aluminum surfaces suitable for aerospace, marine, and transportation applications without reliance on fluorinated chemistry.