Study on Polydopamine‐Densified Waterborne Polyurethane Coatings and Their Corrosion Protection Performance on Al Alloy 3003

Abstract Al alloys are widely used, primarily due to their excellent electrical conductivity, thermal conductivity, formability, and weldability. However, corrosion issues have limited their further development. Organic coatings are an important means of corrosion protection, yet as environmental awareness grows, waterborne anticorrosion coatings (e.g., waterborne polyurethanes) are gradually replacing traditional organic coatings. Compared with solvent‐based organic coatings, however, waterborne coatings still face shortcomings in their protective performance and require modification. This study used polydopamine (PDA) to modify a waterborne polyurethane (WPU) coating. Samples were immersed in a 3.5 wt.% NaCl solution, and the properties of the coatings before and after modification were evaluated by electrochemical impedance spectroscopy (EIS). After 30 days of immersion in 3.5 wt.% NaCl, the maximum |Z| 0.01 Hz of PDA‐modified WPU was more than 8.0 × 10 5 Ω∙cm 2 , which is significantly higher than the |Z| 0.01 Hz of 1.0 × 10 5 Ω∙cm 2 for the unmodified WPU. Various characterization techniques demonstrated that PDA successfully addressed defects in the WPU coating, improving its overall density. This densification effectively slowed the diffusion of chloride ions and other corrosive species, thereby enhancing the coating's anti‐corrosion performance. This work introduces a new strategy for enhancing waterborne polyurethane coatings and enriches corrosion protection methods for aluminum alloys.