Preparation and Corrosion Resistance of Trivalent Chromium Passivation Agent on Hot Dipped Galvanized Steel

Objective To study the preparation of trivalent chromium passivation agent and its corrosion resistance. Methods A kind of trivalent chromium passivation agent was prepared on the surface of galvanization with background film-former( a chromium anhydride),reducing agent( tartaric acid sodium),additive( inorganic mixed acid) and hole sealing agent( nano silica). The corrosion resistance of the passive film was studied by neutral salt spray test( NSS),tafel polarization and ac impedance( EIS) tests; and the surface morphology and elemental composition of passive film were analyzed by scanning electron microscopy( SEM) and energy spectrum analyzer( EDS). Results The results showed that the corrosion area of 120 h NSS experiment was below 5%. Compared with the corrosion potential( 1. 015 V) of the galvanized sheet without passivation,the self-corrosion potential( 0. 965 V) had positive displacement,and the corrosion current density decreased by about two orders of magnitude,from 8. 458 × 10- 4A / cm2to 6. 356 × 10- 6A / cm2. The corrosion resistance of galvanized sheet after passivation was greatly increased. SEM test showed that membrane surface was smoother with white particle deposition; EDS experiment indicated that passivated membrane mainly contained C,O,Si,Cr and Zn. XPS showed the Cr compounds were mainly trivalent and hexavalent,while the zinc compounds were mainly bivalent. Conclusion The passivation agent could improve the corrosion resistance of the galvanized sheet and has great industrial value.