Improvement of corrosion resistance of Mg by rare earth elements〜Development of low nvironmental-burden material and investigation into mechanism

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Surface oxide film containing rare earth elements(REs)was formed on Mg materials by chemical conversion and anodization to improve their corrosion resistance. Analysis of the film was carried out and the corrosion resistance against salt water was examined. Co-deposition of REs with magnesium metal in molten salt electrolysis was also studied in this study, and the influence of REs on the electrolysis efficiency was discussed.The corrosion resistance of common magnesium alloys, such as AZ31, AZ61, AZ91 and AM60, was particularly improved by chemical conversion coating in solution containing both magnesium nitrate and RE nitrates, and the suitable coating condition for each alloy was clarified. The results from XRD, EPMA and XPS analyses indicated that the surface film consisted of complex oxides of magnesium and RE, and that the improvement of the corrosion resistance was affected by the distribution of the elements in the film.Oxide film was formed on Mg alloy by anodization in solution containing RE nitrate. The corrosion resistance was bettered consequently, but particular results by the treatment with both magnesium and REs was hardly seen.Magnesium metal containing REs was directly electrodeposited in a molten MgCl_2-NaCl-CaCl_2 bath with RECl_3.The morphology of the deposit strongly depended on the co-deposition of RE, and the electrochemical responses were remarkably changed. These results suggested a possibility that the electrolysis efficiency of magnesium deposition was improved by the co-deposition of REs