Effect of Scanning Path on the Surface Microstructure and Corrosion Resistance of 7075 Aluminum Alloy During Femtosecond Laser Cleaning

To investigate the effect of femtosecond laser scanning path on the surface integrity of 7075 aluminum alloy after paint removal, parallel, Z-shape, and loop-shape scanning were compared in terms of surface morphology, microstructure, chemical composition, roughness, wettability, and corrosion resistance. Parallel scanning effectively removed the paint while maintaining a surface roughness of 0.27 μm, close to that of the original substrate. The resulting regular unidirectional laser-induced periodic surface structures (LIPSS) yielded a water contact angle of 85°, consistent with the Wenzel wetting model. X-ray photoelectron spectroscopy (XPS) showed the lowest C 1s and O 1s peak intensities, the lowest lattice-oxygen fraction in Al2O3, the strongest metallic Al0 signal, and limited thermal oxidation. Electrochemical measurements showed the most positive corrosion potential (−0.974 V), the highest film resistance and charge-transfer resistance, and the best corrosion resistance for parallel scanning. By contrast, energy accumulation at the ends during Z-shape scanning and thermal accumulation at the corners and center during loop-shape scanning increased pit and recast-defect densities, oxidation, and corrosion degradation. Loop-shape scanning produced a surface roughness of 3.60 μm and a contact angle of 140.7°, indicating superhydrophobicity, but also the highest corrosion current density and the poorest corrosion resistance, showing that superhydrophobicity does not necessarily correspond to high corrosion resistance. The results show that scanning path affects LIPSS evolution, oxide-film integrity, and corrosion resistance through the spatial distribution of laser energy and thermal accumulation. Among the three paths, parallel scanning provided the best combination of paint removal, low substrate damage, and corrosion resistance, supporting its use in femtosecond-laser paint removal from aircraft aluminum alloy skins.