热浸镀锌层氟钛酸转化膜的制备和耐蚀性能

摘要

以氟钛酸为成膜剂、磷酸二氢锰为促进剂对热浸镀锌层表面进行钝化处理，获得了氟钛酸转化膜。采用扫描电镜研究了不同处理时间所得转化膜的微观形貌；通过中性盐雾试验、电化学极化和电化学阻抗谱，研究了不同处理时间所得转化膜的耐蚀性。确定了氟钛酸转化膜的制备工艺条件为：H2TiF6(w=60%)5 mL/L，Mn(H2PO4)2·2H2O 15 g/L，pH 2.5，处理时间1 min。与未经处理的热浸镀锌试样相比，经氟钛酸钝化后的试样在中性盐雾试验中出现白锈的时间明显延迟，在5%NaCl溶液中的腐蚀电流密度明显降低，极化电阻和电化学阻抗显著增大。处理时间为1 min时所得转化膜的耐蚀性能最好。%Hot-dip galvanized coating was passivated in a bath consisting of fluorotitanic acid as film-forming agent and manganese dihydrogen phosphate as accelerator. The surface morphologies of the conversion coatings obtained by treating for different time were observed by SEM. The corrosion resistance of the conversion coatings was studied by neutral salt spray (NSS) test, electrochemical polarization method, and electrochemical impedance spectroscopy. The optimal process parameters were determined as follows:H2TiF6 (w = 60%) 5 mL/L, Mn(H2PO4)2·2H2O 15 g/L, pH 2.5, and treatment time 1 min. Compared to the as-prepared hot-dip galvanized coating, the sample passivated with fluorotitanic acid can endure longer time for white rusting in NSS test, and has lower corrosion current density and higher polarization resistance and electrochemical impedance in 5%NaCl solution. The conversion coating obtained by treating for 1 min has the best corrosion resistance.