Effect of anodizing potential on the surface morphology and corrosion property of AZ31 magnesium alloy

Abstract

Anodizing is a functional method for coating magnesium alloys and improves its corrosion resistance. The anodizing process was performed on AZ31 magnesium alloy in 1 M NaOH alkaline solution at various applied potentials. The surface morphology and phase structure of the anodic film were analyzed using optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion property of the anodic film was characterized using potentiodynamic polarization measurement, electrochemical impedance spectroscopy (EIS) and salt spray test. The anodic film is composed of two phases, magnesium hydroxides and magnesium oxides. At low anodizing potential, the main constituent of the anodic film is magnesium hydroxide. By increasing the anodizing potential, magnesium oxide grows to be the main constituent of the film. The results show that the anticorrosion property was enhanced by anodizing and the film formed at 100 V has the best corrosion resistance. ©2010 The Japan Institute of Metals.