微弧氧化-水滑石复合涂层的制备及其在AZ91镁合金防腐蚀中的应用

Fabrication and Corrosion Resistance of MAO-LDH Composite Coating on AZ91 Mg Alloy

针对镁合金耐蚀性差的缺点,结合微弧氧化(MAO)、共沉淀和水热技术在AZ91镁合金表面构建了具有主动防护功能的微弧氧化-水滑石(MAO-LDH)复合涂层,以改善镁合金的耐蚀能力。利用SEM、XPS和XRD等方法对涂层的表面形貌和化学成分进行了表征;采用ICP研究了插层MoO4^2-的释放行为;通过Tafel曲线和EIS考察了涂层的防腐蚀性能。结果表明:通过共沉淀法成功合成了MoO4^2-插层的MgAl-LDH浆料;将MAO试样在MgAl硝酸盐浆料中水热36 h,其表面即可沉积均匀连续的LDH膜,该膜可有效封闭MAO膜表面的微孔。在含有Cl^-的腐蚀介质中,插层的MoO4^2-能够与Cl^-发生置换而释放。在3.5%(质量分数)NaCl溶液中的浸泡试验表明:MAO-LDH复合涂层具有优异的防腐蚀能力,144 h后仍能为镁合金基体提供有效的防护。

In order to improve the corrosion resistance of Mg alloy,the micro-arc oxidation(MAO)layered double hydroxide(LDH)composite coating with active protection function was fabricated on AZ91 Mg alloy by combining MAO,co-precipitation and hydrothermal techniques.The surface morphology and chemical composition of the coating were characterized by SEM,XPS and XRD.In addition,the release behavior of intercalated MoO4^2-was studied by ICP,and the corrosion resistance of the coating was investigated by Tafel polarization and EIS.Results showed that MgAl-LDH slurry intercalated with MoO4^2-was synthesized through co-precipitation method.After hydrothermal treatment for 36 h in Mg-Al nitrate slurry,a continuous LDH film was deposited on the surface of MAO film,and the micropores were also effectively sealed.In the corrosive medium containing Cl^-,the intercalated MoO4^2-could be released through the exchange with Cl^-.The MAO-LDH composite coating exhibited excellent corrosion resistance,which could still provide effective protection for Mg alloy substrate even after 144 h of immersion in 3.5%(mass fraction)Na Cl solution.