Surface Protection of Friction Stir Welding Joint for AZ31 Magnesium Alloy Coated by Microarc Oxidation
XUE Wen-bin1,2, CHEN Ting-fang1,3, LI Yong-liang3, ZOU Zhi-feng1,2, LIU Xiao-long1,2, ZHAO Yan-hua4
1. Key Laboratory of Beam Technology and Materials Modification(Ministry of Education),College of Nuclear Science and Technology,Beijing Normal University,Beijing 100875,China;
2. Beijing Radiation Center,Beijing 100875, China;
3. Analytical and Testing Center,Beijing Normal University,Beijing 100875,China;
4. Capital Aerospace Machinery Company,Beijing 100076,China
Abstract：A uniform ceramic coating on friction stir welding (FSW) joint of AZ31 magnesium alloy was fabricated by microarc oxidation (MAO) in silicate electrolyte. Microstructure, phase constituent and microhardness profile of the MAO coating at the different zones of FSW joint were analyzed. The influence of microarc oxidation surface treatment on corrosion behaviors of FSW joint was evaluated by immersion and potentiodynamic polarization tests. The results show that hardness of stir zone is higher than that of base alloy, but the hardness of heat-affected zone is lower than that of base alloy. However, the microhardness of MAO coating at different zones of FSW joint is the same, which is about seven times higher than that of AZ31 base alloy. After immersion test in 3.5%NaCl(mass fraction) solution, the serious pitting corrosion on heat-affected zone takes place, but no pitting corrosion is observed on the MAO coating surface. In addition, the heat-affected zone of FSW joint has a lower corrosion potential and higher corrosion current density, but the corrosion current density of MAO coating at different zones is very close, which is much lower than that of bare AZ31 magnesium alloy. So the MAO surface treatment can significantly improve the corrosion resistance of FSW joint of AZ31 magnesium alloy.
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