Atmospheric acid rain significantly accelerates the deterioration of aluminum alloys used in outdoor structures, emphasizing the importance of optimized anodic oxide coatings for AA6005 aluminum alloy. This study investigated the corrosion behavior of uncoated and anodized AA6005 specimens with coating thicknesses of 10 μm and 14 μm in a simulated acid rain solution using electrochemical techniques combined with post-exposure surface characterization. Open circuit potential (OCP), electrochemical impedance spectroscopy (EIS), and Tafel polarization tests revealed that anodizing markedly enhanced the corrosion resistance, increasing the total polarization resistance from 73.65 kΩcm2 for the bare alloy to 7597 kΩcm2 for the 14 μm coating and reducing the corrosion current density from 19.10 to 7.88 nAcm2. Scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) revealed that the uncoated alloy experienced active dissolution and heterogeneous corrosion product formation, whereas the anodized samples formed a uniform, oxygen-enriched oxide layer that acted as an effective barrier against aggressive acidic species despite the presence of microcracks in the anodic layer. Atomic force microscopy (AFM) results further showed that increasing coating thickness decreased the surface roughness, with the Ra value decreasing from 50.213 nm for the bare alloy to 24.073 nm for the 14 μm coating, indicating improved surface stability under acidic conditions.
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