Surface characteristics of anodized AZ91D with potassium permanganate in alkaline by various time

Magnesium is demanded increasing in aerospace, electronics industry and medical field requires the surface treatment method. That allows increasing the corrosion resistance in order to put to practical use as products. The spark anodized treatment method in this study used was anodized depending on the various times to 1-4 minutes with a current density of 300 mA/cm2 in the constant-current mode that duty cycle is 50% and frequency is 125 Hz by a bipolar pulse power. And the characteristics of the film were evaluated. This treatment method is to obtain the uniform film by reducing the applied voltage on the surface by adding 0.1 M Sodium silicate (Na₂SiO₃) in the mixed solution of 2.0 M Sodium hydroxide (NaOH) and 0.1M Sodium phosphate (Na₃PO₄). It aims to express brown or dark brown color by adding Potassium permanganate, and to improve the corrosion resistance. After anodization treatment, the surface characteristics were analyzed using SEM, XRD and illuminance meter, and Vickers hardness was measured. In order to evaluate of corrosion resistance, the corrosion potential and corrosion current were measured by potentiodynamic method in 3.5 wt. % NaCl electrolyte. The critical voltage required to generate the oxidized layer could be lower depending on the addition of (Na₂SiO₃) and (KMnO₄). The size of a pore was reduced depending on the processing time, and the thickness of the film was grown in proportion to it. As the result of XRD, a new peak of Mg0.9Mn0.1O was formed, and the peak of parent metal was reduced by the increase of the oxide. By the potentiodynamic polarization behavior, the value of corrosion potential was increased and the corrosion current density was decreased and the corrosion resistance was improved.