Improving Corrosion Resistance of Magnesium Alloys via Synergistic Action of TiO2 Superhydrophobic Coating and Micro-Arc Oxidation

To mitigate the intrinsic high corrosion susceptibility of AZ31B magnesium alloy, a three-step synergistic surface modification strategy was developed in this work: initially, a MgO ceramic coating was in situ fabricated on the AZ31B substrate via micro-arc oxidation (MAO); subsequently, a TiO2 sealing barrier layer was deposited on the MAO coating through a deep ultraviolet (DUV)-assisted sol–gel method; finally, a superhydrophobic top layer was constructed via fluoroalkylsilane (FAS) self-assembly. The microstructural characteristics, chemical compositions and corrosion resistance of the coatings at different modification stages were comprehensively characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), water contact angle (WCA) measurements and electrochemical tests. The results showed that the as-deposited TiO2 was predominantly anatase phase, and FAS molecules were firmly anchored on the coating surface via Si-O-Ti covalent bonds, endowing the composite coating with a WCA of up to 160°. Electrochemical tests demonstrated that the FAS-TiO2-MAO composite coating exhibited an ultra-low corrosion current density of 1.31 × 10−9 A/cm2 and a remarkably high charge transfer resistance (Rct) of 3.46 × 108 Ω·cm2. Compared with the bare AZ31B substrate, the corrosion current density was decreased by nearly four orders of magnitude, while the charge transfer resistance was enhanced by approximately six orders of magnitude, indicating a significant improvement in corrosion resistance. Moreover, the composite coating exhibited excellent interfacial adhesion, favorable mechanical durability, and outstanding chemical stability, confirming its reliable long-term corrosion protection and high practical application potential. This work provides a feasible strategy for fabricating high-performance superhydrophobic anticorrosive coatings on magnesium alloys.