通过电解在AZ91D镁合金表面得到均匀的转化膜。采用硫酸铜点滴腐蚀试验,研究了电解液成分及工艺参数对转化膜耐蚀性的影响。结果表明,在含有磷酸二氢锰45 g/L、硝酸锌50 g/L、硝酸钠3.0 g/L、硫酸铜1.00 g/L和EDTA 0.5 g/L的电解液(pH=2)中以电流密度1.3 A/dm²常温电解10 min所得到的转化膜耐蚀性能最好。通过盐水浸泡试验、极化曲线测量、电化学阻抗谱、扫描电镜、能谱等方法,比较了电解转化膜与化学转化膜之间的差异。X射线衍射分析表明,电解转化膜主要由Zn₃(PO₄)₂、Zn_2P_2O₇、ZnO、Mg_2P_2O₇和MgO组成。

A uniform conversion coating was prepared on the surface of AZ91 D magnesium alloy by electrolysis. The effects of the electrolyte composition and processes conditions on corrosion resistance of the conversion coating were studied by copper sulfate dropping corrosion test. The conversion coating obtained by electrolysis in a bath containing manganese dihydrogen phosphate 45 g/L, zinc nitrate 50 g/L, sodium nitrate 3 g/L, copper sulfate 1.00 g/L and EDTA 0.5 g/L at room temperature, pH 2, and current density 1.3 A/dm² for 10 min has the optimal corrosion resistance. The differences between electrolytic and chemical conversion coatings were compared by salt water immersion test, polarization curve measurement, electrochemical impedance spectroscopy, scanning electron microscopy, and energydispersive spectroscopy. The result of X-ray diffraction analysis showed that the electrolytic conversion coating is mainly composed of Zn₃(PO₄)₂, Zn_2P_2O₇, ZnO, Mg_2P_2O₇ and MgO.