In this study, we compared and examined the corrosion resistance of the magnesium alloy with the composite film of 2 kinds of coating on 3 kinds of surface treated film as the substrate treatment. 3 kinds of surface treated film stands for conventional DOW17 anodized film (DAF), chemical conversion treatment JISA3-type MX3 film (CCF), which contain hexavalent chromium, fluorine and phosphorus compounds, and environmentally friendly silicate anodized film (SAF) containing no hazardous substances and 2 kinds of coating stands for organic coating and electrodeposion coating. As a result of the analysis, we could observe that it was extremely effective for magnesium alloy AZ91D to apply the composite film of environmentally friendly SAF with cationic electrodeposition coatings to obtain superior corrosion resistance to that of the composite film of conventional DAF or CCF with organic spray coating. At the same time we could take an action for the environment countermeasure by using the environmentally friendly SAF with the water base cationic electrodeposition coatings as a countermeasure for VOC (Volatile Organic Compound) regulations.

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The magnesium anodizing treatment described in this paper is an environmentally friendly treatment which excludes the use of chromates, fluorine compounds, and phosphates. An alkali bath, which mimics conditions necessary to form naturally occurring magnesium salts, was selected as an electrolytic bath. The components of the electrolytic bath were optimized, and the samples were evaluated by salt spray test. The results suggest that the anodizing treatment with the optimized conditions on the surface of magnesium alloys AZ91 can achieve a higher level of corrosion resistance than the traditional chemical conversion and anodizing treatments which use chromates, fluorine compounds, and phosphates.

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