Effects of TiO2 Nanoparticle Doping on the Micro-Arc Oxidation Coating Structure and Corrosion Resistance of 6061 Aluminum Alloy

To elucidate the effects of TiO₂ nanoparticles on the microstructure and corrosion resistance of micro-arc oxidation (MAO) coatings formed on 6061 aluminum alloy, MAO coatings were prepared in a silicate-based electrolyte with varying TiO₂ nanoparticle concentrations. The coating structure and properties were evaluated using a coating thickness gauge, surface profilometer, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and an electrochemical workstation. The results show that, with increasing TiO₂ content, both coating thickness and surface roughness gradually increase, while the surface porosity first decreases and then increases. An appropriate amount of TiO₂ effectively lowers the surface porosity and enhances coating compactness. The T₁ condition exhibited the least precipitation of corrosion products during immersion tests and thus the best corrosion resistance. Compared to the untreated 6061 aluminum alloy substrate, the optimized coating demonstrated a reduction in corrosion current density (<i>J</i>_corr) by more than one order of magnitude, reaching 1.127 × 10^-6 A·cm^-2, while its polarization resistance (<i>R</i>_p) increased by over one order of magnitude, attaining 3.558 × 10⁴ Ω·cm². Furthermore, relative to the TiO₂-free T₀ coating, the <i>J</i>_corr of the optimized coating was further reduced by approximately 2.5 times, with its <i>R</i>_p enhanced by about 2.3 times. XRD analysis indicated that the MAO coatings primarily consist of α-Al₂O₃ and γ- Al₂O₃. This study provides theoretical and experimental support for the application of TiO₂ nanoparticles in MAO processes.