AZ91D镁合金酸性钒/锆酸盐转化膜的制备

Preparation of Acidic Vanadium/Zirconate Conversion Coatings on AZ91D Magnesium Alloy

目的提高AZ91D镁合金的耐蚀性能。方法用新型的酸性钒/锆酸盐体系在镁合金表面制备化学转化膜,并研究转化膜的最佳工艺条件。选取偏钒酸钠、六氟锆酸以及氟化氢铵在镁合金表面制备钒/锆酸盐转化膜。使用电化学工作站,分别测试转化膜的电化学交流阻抗曲线(EIS)、Tafel极化曲线、腐蚀电流、极化电阻,使用X射线衍射仪(XRD)分析膜层的主要成分,通过扫描电子显微镜(SEM)对转化膜的微观形貌进行分析。结果在镁合金表面成功制备钒/锆酸盐转化膜,其膜层颜色为灰褐色且致密、光滑、平整。该转化膜使镁合金的耐盐雾时间从0.2 h增加到4.5 h,腐蚀电流降至1.883×10^(-5) A,极化电阻增加到2200?。钒/锆酸盐转化膜的主要组成为Zr(OH)_4、V_2O_5、VO_2、MgF_2。同时钒/锆酸盐转化膜的微观形貌显示出,该转化膜由两层膜层构成,底层为带有龟裂状的膜层,顶层是带有颗粒状的化合物。结论酸性钒/锆酸盐转化膜可以提高AZ91D镁合金的耐蚀性。

The work aims to improve corrosion resistance of AZ91D magnesium alloy. A new type of acidic vanadi- um/zirconate system was used to prepare chemical conversion coatings on the surface of magnesium alloy, and optimum technological conditions of conversion coatings were studied. The acid vanadate/zirconate conversion coatings were prepared on the surface of magnesium alloy by using sodium vanadate, hexafluorozirconic acid and ammonium fluoride. Electrochemical work- station was applied to evaluate electrochemical ac impedance curve （EIS）, Tafel polarization curve, corrosion current and polar- ization resistance of the conversion coatings. The main constituents of the coatings were analyzed with X-ray diffractometer （XRD）. Microstructure of the conversion coatings was analyzed with scanning electron microscope （SEM）. The vanadi- urn/zirconate conversion coatings were successfully prepared on the surface of magnesium alloy. The film layers were grayish, dense and smooth, which made salt fog resistance duration of magnesium alloy increase from 0.2 h to 4.5 h, corrosion current decrease to 1.883×10^-5A and polarization resistance increase to 2200Ω. The main constituents of vanadium/zirconate conver- sion coatings were Zr（OH）4, V205, VO2 and MgF2. Meanwhile, the microstructure of vanadium/zirconate conversion coatings showed that the conversion coatings were composed of two layers of films, the bottom layer was polygonal film layer, and top layer was granular compound. The acidic vanadate/zirconate conversion coatings can improve corrosion resistance of AZ91D magnesium alloy sucessfully.