Synergistic improvement of AZ31B magnesium alloy surface properties through PEO/hybrid sol-gel duplex coating

This study optimises hybrid sol–gel coating parameters on PEO-treated AZ31B magnesium alloy to enhance surface properties and protective performance. Magnesium alloys, despite their excellent strength-to-weight ratio, are limited in industrial applications due to their poor corrosion resistance. A systematic design of experiments approach was employed to investigate the effects of key processing conditions namely Methyltriethoxysilane/Tetraethyl Orthosilicate (MTES:TEOS) molar ratios (60:40–80:20), curing temperature (180–220°C), and cure time (10–20 min) on coating morphology and properties. Coatings were evaluated via FESEM, XRD, scratch/adhesion tests and wear tests. The optimised parameters (70:30 MTES:TEOS ratio, 200°C curing temperature, 15 min curing time) yielded superior coating performance. The hybrid coating developed an interpenetrating network as the sol–gel material infiltrated micropores, effectively sealing them and creating robust mechanical bonds. The optimised coating reduced the wear rate by 73% compared to the uncoated substrate and near-hydrophobic behaviour with a water contact angle of 89.3° through effective pore sealing and surface energy modification. The optimised duplex coating reduced the corrosion current density from 45.2 to 3.6 µA/cm² (≈92% reduction), clearly demonstrating the substantial enhancement in barrier protection.