Influence of potassium hydrogen tartrate on anodized film formed in environmental‐friendly electrolyte on AZ91D magnesium alloy

Abstract

Anodizing of AZ91D magnesium alloy in the alkaline borate-potassium hydrogen tartrate (PHT) environmental friendly electrolyte was studied. The effect of PHT on the anodizing process and anodic film properties was investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrometry (EDS), and potentiodynamic polarization. The results showed that the anodizing parameters, surface morphology, thickness, phase structure, and corrosion resistance of the anodic film were strongly dependent on the concentration of PHT. Moreover, the anodizing mechanism of the AZ91D magnesium alloy in the presence of PHT was also studied. That is, by adsorption on the surface of magnesium alloy, PHT decreases the anodizing current density and make the anodizing condition moderate, which is conducive to the performance improvement of the anodic film. Experimental Materials and specimen preparationPrior to PEO treatment, the AZ91D magnesium alloy (chemical composition see Table 1) sheets with a size of 0.50 cm 2 were polished up to 2000 grit, degreased with acetone, and washed with distilled water successively. The power supply was an AC power supply (120 V, 50 Hz) and the duration of the PEO process was 3 min. The anodic electrolyte was composed of 60 g/L NaOH, 25 g/L Na 2 B 4 O 7 , 20 g/L H 3 BO 3 , and 0.0-7.2 g/L of PHT (chemical structure formula see Fig. 1). The temperature of the electrolyte Materials and Corrosion 2014, 65, No. 7