Effects of metal impurities in passivator on trivalent chromium passivation of electroplated zinc coating
[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 Fe2+,Cu2+,or Zn2+.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 Fe2+or 0.03 g/L for Cu2+in passivator,the passivation film became ununiform,dark,or even powdering,as well as showed a significant deterioration in corrosion resistance.Zn2+had little effect on the appearance and corrosion resistance of passive film when the mass concentration of Zn2+was lower than 2 g/L.The mass concentration of Zn2+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.
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