Study on influence of Na2WO4/SDS composite corrosion inhibitors on microstructure and properties of plasma electrolytic oxidation composite coating on AZ31B

A corrosion-resistant plasma electrolytic oxidation (PEO) composite coating was fabricated on AZ31B magnesium alloy via incorporating a Na 2 WO 4 /SDS composite inhibitor, followed by silanization. The effects of the inhibitor on coating microstructure and corrosion resistance were investigated using XRD, FT-IR, XPS, SEM, potentiodynamic polarization and EIS. Silanization effectively sealed the PEO coating, increasing its thickness and compactness. Na 2 WO 4 and SDS further enhanced coating thickness and density, improving its physical barrier against corrosive media. The loaded Na 2 WO 4 reacted with dissolved Mg 2+ to form protective MgWO 4 , inhibiting substrate erosion. SDS's hydrophobic dodecyl chains adsorbed onto the coating, forming a directional hydrophobic layer that reduced water/Cl − contact and hindered corrosive media penetration. At the exposed substrate, SDS's hydrophilic end competed with adsorbed water via electrostatic attraction, suppressing hydrogen evolution and substrate corrosion. The P-W10S-SG coating (41.2 g/L Na 2 WO 4 , 10 g/L SDS) showed optimal performance. After 480 h immersion in 3.5 wt% NaCl, its |Z| 0.01Hz remained stable at 10 7 –10 8  Ω⋅cm 2 , representing five-order-of-magnitude improvement over pure PEO, and four orders over P-SG and P-W0S-SG coatings.