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 (Jcorr) by more than one order of magnitude, reaching 1.127 × 10-6 A·cm-2, while its polarization resistance (Rp) increased by over one order of magnitude, attaining 3.558 × 104 Ω·cm2. Furthermore, relative to the TiO2-free T0 coating, the Jcorr of the optimized coating was further reduced by approximately 2.5 times, with its Rp 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.