极低锡量镀锡板铬−磷复合钝化及其膜层性能

Preparation and properties of chromate-phosphate composite passivation coating on ultralow-tin tinplate

为提高极低锡量(1.1 g/m^(2))镀锡板的耐蚀性,采用由16 g/L铬酸酐、2 g/L磷酸二氢铝和2 mL/L磷酸组成的溶液对镀锡板进行阴极电解钝化。通过正交试验得到较优的工艺条件为:pH 2.6,温度50℃,电流密度1 A/dm^(2),时间8 s。通过中性盐雾(NSS)试验、电化学阻抗谱(EIS)和Tafel曲线测试对比了六价铬钝化和铬−磷钝化镀锡板的耐蚀性。结果表明,铬磷钝化试样的耐蚀性优于六价铬钝化试样,在NSS试验3 h后的保护等级为5级。

In order to improve the corrosion resistance of tinplate with ultralow tin content(1.1 g/m^(2)),the tinplate was passivated by cathodic electrolysis in a bath comprising chromic anhydride 16 g/L,aluminum dihydrogen phosphate 2 g/L,and phosphoric acid 2 mL/L.The passivation process parameters were optimized by orthogonal test as follows:temperature 50℃,pH 2.6,current density 1 A/dm^(2),and time 8 s.The corrosion resistance of chromated tinplate and chromate–phosphate passivated tinplate was primarily compared by neutral salt spray(NSS)test,electrochemical impendence spectroscopy(EIS),and Tafel plot measurement.The results showed that the chromate–phosphate passivated tinplate showed better corrosion resistance than the chromated tinplate due to the fact that its protection level was 5 after NSS test for 3 hours.