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对热镀锌钢板先进行硅酸钠(水玻璃)预处理再镧盐钝化,以进一步提高镧盐转化膜的耐蚀性。用扫描电镜、能谱仪、盐雾腐蚀试验、塔菲尔极化曲线等方法研究了硅酸钠预处理对热镀锌层镧盐转化膜微观形貌和耐蚀性的影响。结果表明,硅酸钠预处理使得镧盐转化膜成膜均匀,膜层增厚且耐蚀性明显提高。通过正交试验得到最佳工艺为:先在室温下于0.5g/L的硅酸钠溶液中预处理1min,随后在70°C下于含La(NO3)3.6H2O9g/L和H2O210mL/L的溶液中钝化处理10min。与未经硅酸盐处理所得镧盐转化膜相比,经硅酸盐处理后,镧盐转化膜极化电阻提高了1倍,腐蚀电流密度减小了1个数量级。
Hot-dip galvanized steel sheet is subjected to sodium silicate (water glass) pretreatment followed by lanthanum salt passivation to further improve the corrosion resistance of lanthanum conversion coating. The effects of sodium silicate pretreatment on the microstructure and corrosion resistance of lanthanum conversion coatings were investigated by SEM, EDS, salt spray corrosion test and Tafel polarization curves. The results show that sodium silicate pretreatment makes the lanthanum conversion coating film uniform, the film thickening and corrosion resistance improved significantly. The optimum conditions were as follows: pretreatment with 0.5g / L sodium silicate for 1min at room temperature, followed by pretreatment with La (NO3) 3.6H2O9g / L and H2O210mL / L at 70 ° C Passivation solution for 10min. Compared with the lanthanum conversion coating without the silicate treatment, the polarization resistance of the lanthanum conversion coating was doubled and the corrosion current density was reduced by one order of magnitude after silicate treatment.