Fabrication and Properties of Micro-arc Oxidation/Polyimide/CeO2 Composite Coating on Mg Alloys
Micro-arc oxidation (MAO) coatings on magnesium alloys exhibit inherent micro-pores and micro-cracks that serve as corrosive pathways, limiting long-term corrosion and wear resistance. This study fabricates a polyimide (PI)/CeO2 composite coating to seal MAO defects and enhance protective performance. CeO2 particles were dispersed in a polyimide solution and applied to MAO-treated surfaces. Scanning electron microscopy, X-ray diffraction, electrochemical testing, salt spray testing, and friction-wear testing characterized microstructure, corrosion resistance, and wear resistance. Microstructural analysis shows the PI layer completely fills MAO pores, forming a dense, smooth, hydrophobic surface with contact angles of (114.6±4.2)° and (110.1±3.3)°. Electrochemical tests reveal the MAO/PI-CeO2 coating exhibits the most positive corrosion potential and lowest corrosion current density in 3.5 wt.% NaCl, far superior to single MAO and MAO/PI coatings. Salt spray testing confirms only slight local corrosion after 40 days, demonstrating excellent long-term stability. CeO2 doping densifies the PI matrix; dissolved Ce3+/Ce4+ reacts with OH– to form precipitates that seal micro-defects and inhibit cathodic reactions. The introduction of CeO2 reduces wear depth and width, significantly enhancing wear resistance. PI provides self-lubrication, while CeO2 enhances load-bearing capacity and structural integrity, reducing plastic deformation during sliding contact. The composite coating successfully seals MAO defects and significantly improves long-term corrosion resistance, wear resistance, and hydrophobicity of MAO-coated magnesium alloys.