Improved Corrosive Resistance of Micro-Arc-Oxidation Coating on 6063 Aluminum Alloy by Co-Doping with Graphite and Sodium Tungstate

The present study investigates the effect of different concentrations of Na₂WO₄ and graphene oxide dispersed composite additives on the structure and corrosion resistance of 6063 aluminum alloy micro-arc oxidation (MAO) coatings in a silicate electrolyte. The characterisation of the microstructure, cross-sectional morphology, elemental distribution, and phase composition of the films was conducted utilising scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), and X-ray diffraction (XRD). The corrosion resistance of the films was tested by prolonged immersion for 24 h, 72 h, 168 h, and 240 h, with measurement of kinetic potential polarisation curves and impedance modulus in a 3.5 wt.% NaCl solution. The densification of the films was enhanced with increasing mass concentration of Na₂WO₄ and dispersed graphene oxide in the electrolyte, and the thickness initially increased and then decreased. The film containing 6 g of Na₂WO₄ and 10 mL of graphene oxide dispersion (G10-6) exhibited optimal densification and thickness, with an I_corr value of 3.01 × 10^-6 A·cm^-2 and a low-frequency impedance film value of 10⁸ Ω·cm², thereby demonstrating the most advanced corrosion resistance among the films. The densification and corrosion resistance of the films were enhanced by the incorporation of Na₂WO₄ and graphene oxide dispersion into the alkaline electrolyte.