AZ91镁合金钼酸盐转化膜的制备及耐蚀性研究

Studies on Preparation and Corrosion Resistance of Molybdate Conversion Coating Formed on AZ91 Magnesium Alloy

采用化学转化法在AZ91镁合金基体表面制备一种环境友好型的钼酸盐转化膜。通过对溶液pH、温度以及Na2MoO4质量浓度等因素的控制并进行单因素试验和正交试验,确定化学转化的最佳工艺条件:30～40g/L Na2MoO4,pH为3.5,θ为70℃,t为50min。采用优化后的工艺能够在镁合金表面获得微黄致密,微细裂纹的膜层,X-射线衍射测试表明,钼酸盐转化膜的主要成分Mg2Mo3O8和MgMoO4。极化曲线测试表明钼酸盐转化膜能有效提高镁合金的耐蚀性能,自腐蚀电位提高,自腐蚀电流密度降低2个数量级。

An environmental friendly molybdate conversion coating was prepared on AZ91 magnesium alloy by chemical conversion method. The factors such as pH value, temperature and mass concentration of Na2MoO4 were investigated by single factor experiment and orthogonal experiments, and the optimum conditions of chemical conversion were determined as following ： pH 3.5, temperature 70 ℃, 30 - 40 g/L Na2 MoO4 and chemical conversion time 50 min. The macro surface morphology of as-prepared coating on Mg-based substrate was compact and yellowish, while presenting microscopic small cracks. XRD showed that main component of the molybdate conversion coating were MgaMo3O8 and MgMoO4. Electrochemical polarization test analysis showed that the molybdate conversion coating could effectively improving the cor- rosion resistance of magnesium alloy and increasing the self-corrosion potential, and the self-corrosion current density was decreased by two orders of magnitude.