无钴硫酸体系三价铬黑色钝化工艺

Process for trivalent chromium black passivation in cobalt-free sulfuric acid system

以过渡金属硫化物M替代钴(镍)盐作发黑剂,在镀锌层表面得到黑色钝化膜。钝化液的配方与工艺为:Cr2(SO4)335g/L,有机羧酸X6g/L,柠檬酸32g/L,过渡金属硫化物M2g/L,FeSO410g/L,NaNO37g/L,NaH2PO415g/L,pH=2.0,室温,时间30s。钝化膜层乌黑均匀、附着力合格;经封闭后的三价铬黑色钝化膜,其耐蚀性等级高于市售含钴盐发黑剂的三价铬黑色钝化膜,且达到六价铬钝化的耐蚀等级;钝化膜中不含六价铬;钝化液性能稳定。

A black passivation film was obtained on surface of zinc coating by using transition-metal sulfide （code： M） instead of cobalt or nickel salt as blackening agent. The bath composition and passivation process parameters are as follows： Cr2（SO4）335 g/L, organic carboxylic acid （code： X） 6 g/L, citric acid 32 g/L, transition-metal sulfide M 2 g/L, FeSO4 10 g/L, NaNO3 7 g/L, NaHzPO4 15 g/L, pH = 2.0, room temperature, and time 30 s. The obtained passivation film is black and uniform, and of qualified adhesion. The corrosion resistance of sealed black trivalent chromium passivation film is higher than that of passivation film prepared from commercial passivation solution containing cobalt salt, and is equal to that of hexavalent chromium passivation film. The black passivation film is free of hexavalent chromium. The passivation bath has stable performance.