镀锌钢表面有机酸/硅酸盐钝化及钝化膜的耐蚀性能

Passivation of Galvanized Steel by Organic Acid /Silicate Solution and Corrosion Resistance of the Passivation Film

为加强环保，进一步提高镀锌铜彩色钝化膜的耐蚀性能，采用硅酸盐和有机酸单宁酸对镀锌钢板表面进行复合钝化，采用醋酸铅点滴试验和中性盐雾试验研究了钝化膜的耐蚀性能，并对复合钝化液的组分及工艺条件进行优选。结果表明：优选工艺为35g／LNa2SiO3，10mL／LH2O2（30％），5mL／LH2SO4（98％），2g／LCuSO4，5g／L单宁酸，10g/LNaNO3，pH值为2．0，温度为50℃，钝化时间30s，钝化封闭后于60—70℃老化5-10min；钝化膜外观为均匀彩色，与基体附着力良好，耐醋酸铅点滴腐蚀时间为79S，耐中性盐雾腐蚀时间达128h，其耐蚀性能虽不及六价铬钝化膜，但优于三价铬钝化膜。

Galvanized steel was passivated in the passivation fluid consisting of silicate and tannic acid. The corrosion resistance of as-obtained passivation film was evaluated by lead acetate dripping test and neutral salt-spray test,and the composition of the passivation fluid and the passivation condition were optimized. Results indicated that passivation fluid with the optimal composition consisted of 35 g /L Na2SiO3,10 mL /L H2O2( 30%,volume fraction),5 mL/L H2SO4( 98%,mass fraction),2 g /L CuSO4,5 g/L tannic acid,and 10 g/L NaNO3; and the optimal passivation parameters were suggested as pH value of 2. 0,temperature of 50 ℃,passivation time of 30 s,and aging time of 5 ~ 10 min( 60 ~ 70 ℃) after passivation and sealing. Resultant passivation film had uniform colored appearance and good adhesion to substrate. Besides,the passivation film could endure 79 s of lead acetate dripping corrosion and 128 h of neutral salt-spray corrosion,showing better corrosion resistance than trivalent Cr conversion coating( though its corrosion resistance was poorer than that of hexavalent Cr conversion coating).