Effects of deposition thickness on electrochemical behaviors of AZ31B magnesium alloy with composite coatings prepared by micro-arc oxidation and electrophoretic deposition

Two types of coatings with different deposition thicknesses were prepared on AZ31B Mg alloy by micro-arc oxidation (MAO) and micro-arc oxidation plus electrophoretic deposition (MAO/EPD) techniques. The surface morphology, cross section and phase composition of two type coatings were studied by scanning electron microscopy and X-ray diffraction. The corrosion performance of the coatings was investigated via electrochemical and immersion experiments. The results indicated that corrosion resistance of MAO coating did not monotonously enhance with the increase of the period of deposition time; instead, it displayed a close relation with the thickness of the coating dense layer. The corrosion resistance of MAO/EPD coating was upgraded with the composite coating. Compared with MAO coating, MAO/EPD coating was found more effective in isolating the substrate from the corrosive environment. It was attributed to EPD coating composite that greatly reduces the micro-porosity and microcrack defects of MAO coating.