钝化液中金属杂质对镀锌层三价铬钝化的影响

Effects of metal impurities in passivator on trivalent chromium passivation of electroplated zinc coating

[目的]研究金属杂质离子对镀锌三价铬钝化效果的影响,为钝化液中金属杂质离子含量的控制提供参考。[方法]采用添加不同质量浓度的Fe^(2+)、Cu^(2+)和Zn^(2+)的三价铬钝化液对镀锌层进行钝化处理。通过三维视频显微镜、动电位极化曲线测试等研究了上述3种金属杂质离子对钝化膜外观及耐蚀性的影响。[结果]钝化液中Fe^(2+)的质量浓度超过0.1 g/L或Cu^(2+)的质量浓度超过0.03 g/L时即可导致钝化膜不均匀、颜色变暗甚至起粉,以及耐蚀性显著变差。钝化液中Zn^(2+)质量浓度小于2 g/L时对钝化膜外观和耐蚀性影响不大,但不小于4.0 g/L时会导致钝化膜耐蚀性严重下降,因此钝化液中Zn^(2+)的质量浓度应控制在4.0 g/L以内。[结论]3种金属杂质均会导致钝化膜性能下降,必须严格控制三者在钝化液中的含量。

[Introduction]The effects of metal impurity ions on trivalent chromium passivation of electroplated zinc coating need to be studied to provide reference for controlling the concentration of metal impurity ions in passivator.[Method]Trivalent chromium passivation was conducted on the surface of electroplated zinc coating in a passivator with different mass concentrations of Fe^(2+),Cu^(2+),or Zn^(2+).The effects of the above three kinds of metal impurity ions on the appearance and corrosion resistance of passivation film were studied by three-dimensional video microscopy and potentiodynamic polarization curve measurement.[Result]When the mass concentration exceeded 0.1 g/L for Fe^(2+)or 0.03 g/L for Cu^(2+)in passivator,the passivation film became ununiform,dark,or even powdering,as well as showed a significant deterioration in corrosion resistance.Zn^(2+)had little effect on the appearance and corrosion resistance of passive film when the mass concentration of Zn^(2+)was lower than 2 g/L.The mass concentration of Zn^(2+)should be controlled lower than 4.0 g/L,or else the corrosion resistance of passive film would be seriously degraded.[Conclusion]The three kinds of metal impurities studied in this paper can lead to a decrease in properties of trivalent passive film,it is necessary to strictly control their concentrations in passivator.