Before the surface treatment of magnesium alloy, it is necessary to consider the degree of electrical resistance, the apparent surface condition, and the degree of corrosion resistance, so that the most appropriate method could be used for the surface to be treated. Magnesium alloy also follows the basic rule of metal, and the best method is to process after mechanical and chemical cleaning.

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-In this study low voltage Plasma Electrolytic Oxidation (PEO) was utilized to eliminate high voltage PEO drawbacks such as high cost, dimensional deformation and porosity. Low voltage PEO produces a thin coating which causes low corrosion resistance. In order to solve such problem, 0.1~0.6M pyrophosphates were added in a bath containing 1.4M NaOH, and 0.35M Na 2 SiO 3 . 70 V PEO was conducted at 25℃ for 3 minutes. Chemical composition, morphology and corrosion resistance of the anodized coating were analyzed. The anodized film was composed of MgO, Mg 2 SiO 4 , and Mg 2 O 7 P 2 . The morphology of film showed appropriately dense structure and low porosity in the anodized layers. It is found that low voltage Plasma Electrolytic Oxidation in cooperation with phosphating treatment can provide a good corrosion protection for the AZ31B magnesium alloy.

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