Synergistic corrosion protection for AZ31 Mg alloy by anodizing and stannate post-sealing treatments

Stannate post-treatment of as-anodized AZ31 Mg alloy was carried out in 0.4 M sodium stannate 3-hydrate (Na2SnO3·3H2O) at 350 K. It effectively leveled the porous anodized coating by depositing a SnO2 superficial layer with a thickness of 0.4 μm. After the surface sealing, the mass transport impedance at low frequency was controlled by the ideal capacitance dispersion during the initial immersion; thus, slow corrosion kinetics was achieved. This impedance behavior might account for the ideally polarizable cathodic behavior of the electrode with overpotential. As a consequence, the stannate post-treatment afforded higher Rp, Ecorr, and Epit values throughout the immersion in 0.1 M NaCl.