ABSTRACT Hexavalent chromium-based passivation treatments have been successfully used as promoters of conversion coatings for many years. Their effectiveness is without question although there are many problems with regard to their environmental suitability. Hexavalent chromium compounds are carcinogenic and toxic. These problems have lead researchers to evaluate other potential systems, with lower toxicity, to ascertain if they can replace chromates as effective passivators. Researchers have proposed several alternative passivation treatments; these are processes based on molybdates, permanganates, titanates, rare earth metal and Cr3+ (considered to be non-carcinogenic) compounds. In this work, zinc coatings obtained from free-cyanide alkaline bath and submitted to a Cr3+ based passivation treatment with different colors were studied. The corrosion behavior was studied by polarization measurements and mainly by electrochemical impedance spectroscopy in 0.6 N NaCl solution. Morphological observations on the coatings surface were also performed. The results indicate that the green-colored Cr3+ passivated coatings have a good corrosion resistance followed by yellow and blue-colored passivation respectively. They could be a less polluting alternative to the traditional chromated coatings.
Cite this paper
nullC. Tomachuk, A. Sarli and C. Elsner, "Anti-Corrosion Performance of Cr+6-Free Passivating Layers Applied on Electrogalvanized," Materials Sciences and Applications, Vol. 1 No. 4, 2010, pp. 202-209. doi: 10.4236/msa.2010.14032.
 N. Zaki, “Chromate Conversion Coating for Zinc,” Metal Fi-nishing, Vol. 86, No. 2, February 1988, pp. 75-78.
 P. L. Hagans and C. M. Haas, “ASM Handbook,” Surface Engineer-ing, ASM International, Vol. 5, 1994.
 F. Deflorian, S. Rossi, L. Fedrizzi and P. L. Bonora, “EIS Study of Organic Coating on Zinc Surface Pretreated with Environmentally Friendly Products,” Progress in Organic Coatings, Vol. 52, No. 4, 2005, pp. 271-279.
 R. Berger, U. Bexell, T. M. Grehk and S. E. H?rnstr?m, “A Comparative Study of the Corrosion Protective Properties of Chromium and Chromium Free Passi-vation Methods,” Surface and Coatings Technology, Vol. 202, No. 2, 2007, pp. 391-397.
 K. W. Cho, V. S. Rao and H. Kwon, “Microstructure and Electrochemical Characterization of Trivalent Chromium Based Conversion Coating on Zinc,” Electrochimica Acta, Vol. 52, No. 13, 2007, pp. 4449-4456.
 Y.-T. Chang, N.-T. Wen, W.-K. Chen, M.-D. Ger, G.-T. Pan and T. C.-K. Yang, “The Effects of Immersion Time on Morphology and Electrochemical Properties of the Cr(III)-Based Conversion Coatings on Zinc Coated Steel Sur-face,” Corrosion Science., Vol. 50, No. 12, 2008, pp. 3494-3499.
 X. Zhang, C. Van den Bos, W. G. Sloof, A. Hovestad, H. Terryn and J. H. W. de Wit, “Comparison of the Morphology and Corrosion Performance of Cr(VI)- and Cr(III)-Based Conversion Coatings on Zinc,” Surface and Coatings Technology, Vol. 199, No. 1, 2005, pp. 92-104.
 N. T. Wen, F. J. Chen, M. D. Ger, Y. N. Pan and C. S. Lin, “Microstructure of Trivalent Chromium Conversion Coating on Electrogalvanized Steel Plate,” Electrochemical Solid State Letter, Vol. 11, No. 8, 2008, pp. C47-C50.
 N.-T. Wen, C.-S. Lin, C.-Y. Bai and M.-D. Ger, “Structures and Characteristics of Cr(III)-Based Conversion Coatings on Electrogalvanized Steels,” Surface and Coatings Technology, Vol. 203, No. 3-4, 2008, pp. 317-323.
 B. Da Fonte, Jr. and M. C. Mich, US Patent 4.359.345, 1982.
 C. R. Tomachuk, C. I. Elsner, A. R. Di Sarli and O. B. Ferraz, “Morphology and Corrosion Resistance of Cr(III)- Based Conversion Treatments Applied on Electrogalvanised Steel,” Journal of Coatings Technology and Research, Vol. 7, No. 4, 2010, pp. 493-502.
 C. R. Tomachuk, C. I. Elsner, A. R. Di Sarli and O. B. Ferraz, “Corrosion Resistance of Cr(III) Conversion Treatments Applied on Electrogalvanised Steel and Subjected to Chloride Containing Media,” Materials Chemistry and Physics, Vol. 119, No. 1-2, 2009, pp. 19-29.
 E. Almeida, T. C. Diamantino, M. O. Figueiredo and C. Sá, “Oxidizing Alternative Species to Chromium VI in Zinc Galvanized Steel Surface Treatment. Part 1. A Morphological and Chemical Study,” Surface and Coatings Technology, Vol. 106, No. 1, July 1998, pp. 8-17.
 E. Almeida, L. Fedrizzi and T. C. Diamantino, “Oxidizing Alternative Species to Chromium VI in Zinc Galvanized Steel Surface Treatment. Part 2. An Electrochemical Study,” Surface and Coatings Technology, Vol. 105, No. 1-2, June 1998, pp. 97-101.
 G. D. Wilcox and D. R. Gabe, “Passivation Studies Using Group VIA Anions. V. Cathodic Treatment of Zinc,” British Corrosion Journal, Vol. 22, No. 4, 1987, pp. 254- 258.
 G. D. Wilcox, D. R. Gabe and M. E. Warwick, “The Development of Passivation Coatings by Cathodic Reduction in Sodium Molybdate Solutions,” Corrosion Science, Vol. 28, No. 6, 1988, pp. 577-585, 587.
 V. I. Korobov, Y. M. Loshkarev and O. V. Kozhura, “Cathodic Treatment of Galvanic Zinc Coatings in Solutions of Molybdates,” Russian Journal of Electrochemistry, Vol. 34, No. 11, 1998, pp. 1154-1157.
 P. D. Deck and D. M. Reichgott, “Characterization of Chromium-Free No-Rinse Prepaint Coat-ings on Aluminium and Galvanized Steel,” Metal Finishing, Vol. 90, No 9, 1992, pp. 29-35.
 B. R. W. Hinton, “Corrosion Prevention and Chromates, the End of an Era?” Metal Finishing, Vol. 89, No. 9, 1991, pp. 55-61.
 B. R. W. Hinton, “Corrosion Prevention and Chromates, the End of an Era?” Metal Finishing, Vol. 89, 1991, pp. 15-20.
 A. Barbucci, M. Delucchi and G. Cerisola, “Study of Chromate-Free Pre-treatments and Primers for the Protection of Galvanized Steel Sheets,” Progress in Organic Coatings, Vol. 33, No. 2, 1998, pp. 131-138.
 G. D. Wilcox and J. A. Wharton, “A Review of Chromate Free-Passivation Treatments for Zinc and Zinc Alloys,” Transactions of the Institute of Metal Finishing, Vol. 75, No. 4, 1997, pp. B140-B146.
 T. F. Child and W. J. van Ooij, “Application of Silane Technology to Prevent Corrosion of Metal and Improve Paint Adhesion,” Transactions of the Institute of Metal Finishing, Vol. 77, No. 2, 1999, pp. 64-70.
 S. González, M. A. Gil, J. O. Hernández, V. Fox and R. M. Souto, “Resistance to Corrosion of Galvanized Steel Covered with an Epoxy –Polyamide Primer Coating,” Progress in Organic Coatings, Vol. 41, No. 1-3, March 2001, pp. 167-170.
 M. F. Montemor, A. M. Sim?es, M. G. S. Fer-reira and C. B. Breslin, “Composition and Corrosion Behavior of Galvanized Steel Treated with Rare-Earth Salts: The Effect of the Cation,” Progress in Organic Coatings, Vol. 44, No. 2, 2002, pp. 111-120.
 “Standard Practice for Operating Salt Spray (Fog) Apparatus,” ASTM B 117 Review A07.
 “Testing in a Saturated Atmosphere in the Presence of Sulphur Dioxide,” DIN 50018, 1997.
 “Atmospheres and their Technical Application Condensation Water Test Atmospheres,” DIN 50017, 1982.
 J. R. Mac Donald, “Impedance Spectroscopy Emphasizing Solid State Materials,” John Wiley & Sons, New York, 1987.
 F. Mansfeld, “Models for the Impedance Behavior of Protective Coatings and Cases of Localized Corrosion,” Electrochimica Acta, Vol. 38, No. 14, 1993, pp. 1891- 1897.
 P. Carbonini, T. Monetta, L. Nicodemo, P. Mastronardi, B. Scatteia and F. Bellucci, “Electrochemical Characterization of Multilayer Organic Coatings,” Progress in Organic Coatings, Vol. 29, No. 1-4, 1996, pp. 13-20.
 L. de Rosa, T. Monetta, D. B. Mitton and F. Bellucci, “Monitoring Degradation of Single and Multilayer Organic Coatings. I. Absorption and Transport of Water: Theoretical Analysis and Methods,” Journal of the Electrochemical Society, Vol. 145, No. 11, 1998, pp. 3830- 3838.
 A. Boukamp, “Equivalent Circuit,” Report CT88/265/128, CT89/214/128, University of Twente, The Netherlands, 1989.
 N. M. Martyah and J. E. McCaskie, “Corrosion Behavior of Zinc Chromate Coatings,” Metal Finishing, Vol. 94, No. 2, 1996, pp. 65-67.
 C. Delouis, M. Duprat and C. Tournillon, “The Kinetics of Zinc Dissolution in Aerated Sodium Sulphate Solutions. A Measurement of the Corrosion Rate by Impedance Techniques,” Corrosion Science, Vol. 29, No. 1, 1989, pp. 13-20.
 B. Del Amo, L. Véleva, A. R. Di Sarli and C. I. Elsner, “Performance of Coated Steel Systems Exposed to Different Media. Part 1: Painted Galvanized Steel,” Progress in Organic Coatings, Vol. 50, No. 3, 2004, pp. 179-192.
 E. P. M van Westing, G. M. Ferrari, F. M. Geenen and J. H. W. de Wit, “In Situ Determination of the Loss of Adhesion of Barrier Epoxy Coatings Using Electrochemical Impedance Spectroscopy,” Progress in Organic Coatings, Vol. 23, No. 1, 1993, pp. 89-103.
 G. G. Nascimento, O. R. Mattos, J. L. C. Santos and I. C. P. Margarit, “Impedance Measurements on Lacquered Tinplate: Fitting with Equivalent Circuits,” Journal of Applied Electrochemistry., Vol. 29, No. 3, March 1999, pp. 383-392.
 F. Mansfeld, “Use of Electrochemical Impedance Spectroscopy for the Study of Corrosion Protection by Polymer Coatings,” Journal of Applied Electrochemistry, Vol. 25, No. 3, March 1995, pp. 187-202.
 R. L. Zeller and R. F. Savinell, “Interpretation of AC Impedance Response of Chromated Electrogalvanized Steel,” Corrosion Science, Vol. 26, No. 5, 1986, pp. 389- 399.