Abstract
The adhesion of electrodeposition (ED) paint on steel sheets for automobiles is highly influenced by the properties of the zinc phosphate coating which is used to improve its corrosion resistance. In the present study, a steel surface was pretreated with two types of zinc phosphate formulations followed by ED painting. The surface morphology, crystal plane, and porosity properties of phosphate coating on steel samples were studied by scanning electron microscope, X-ray diffraction, and electron probe microanalyzer, respectively. The corrosion resistance of painted samples was evaluated by an accelerated corrosion test as well as by electrochemical techniques like cathodic disbonding and AC–DC–AC tests. The phosphate coating enriched with a phosphophyllite structure showed small globular crystals with less porosity, whereas a hopeite structure showed coarse crystals with high porosity and comparatively thicker coating. The maximum corrosion resistance was observed in the painted sample, where the phosphate coating comprised a phosphophyllite structure. On the other hand, the painted samples phosphated with a predominantly hopeite structure showed inferior corrosion resistance performance. The unphosphated sample showed severe degradation in paint adhesion and corrosion resistance, which substantiates the importance of phosphate pretreatment.
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References
Gibson, A, “Dip, Barrier, and Chemical Conversion Coatings - Phosphate Coating.” In: Mooney, T (ed.) ASM Metals Handbook, Vol. 5, 9th ed., pp. 378–404. ASM International Publishing, Materials Park, 1994
Tegehall, PE, Vannerberg, NG, “Nucleation and Formation of Zinc Phosphate Conversion Coating on Cold Rolled Steel.” Corr. Sci., 32 635–652 (1991)
Maeda, S, “Steel Surface Chemistry Affecting the Performance of Organic Coatings.” Prog. Org. Coat., 11 1–18 (1983)
Yoshihara, T, Okita, H, “Phosphate Coating Techniques for Car Bodies.” Trans. ISIJ, 23 985–993 (1983)
Satoh, N, “Effects of Heavy Metal Additions and Crystal Modification on the Zinc Phosphating of Electrogalvanized Steel Sheet.” Surf. Coat. Technol., 30 171–181 (1987)
Lakeman, JB, Gabe, DR, Richardson, MOW, “Physical Properties of Phosphate Coating and Their Correlation with Potential.” Trans. IMF, 55 47–53 (1977)
Sankara Narayanan, T, “Influence of Various Factors on Phosphatibility—an Overview.” Rev. Adv. Mater. Sci., 9 130–177 (2005)
Amiruddin, A, Thierry, D, “Corrosion Mechanisms of Phosphate Zinc Layers on Steel as Substrates for Automotive Coatings.” Prog. Org. Coat., 28 59–76 (1996)
Tang, N, van Ooij, WJ, Gorecki, G, “Comparative EIS Study of Pretreatment Performance in Coated Metals.” Prog. Org. Coat., 30 255–263 (1997)
Yin, KM, Lu, LI, “Parametric Study on the Electrochemical Impedance Spectroscopy of Organic-Coated Steels in Hydrochloric Acid Solutions.” J. Coat. Technol., 75 65–72 (2003)
Inone, PC, Gracia, CM, Ruvolo-Filho, A, “Evaluating Barrier Properties of Organic Coatings by Water Permeation and Electrochemical Methods.” J. Coat. Technol., 75 29–35 (2003)
Zhang, SL, Chen, HH, Zhang, XL, “Corrosion and Protection Characteristics of Phosphate Coatings on Aluminium Alloy 6061 Using Yttrium Oxide as Additive.” Corrosion, 64 30–34 (2008)
Suay, JJ, Rodriguez, MT, Izquierdo, R, Kudama, AH, Saura, JJ, “Rapid Assessment of Automotive Epoxy Primers by Electrochemical Techniques.” J. Coat. Technol., 75 103–111 (2003)
Freeman, DB, Phosphating and Metal Pretreatment. Woodhead-Faulkner Ltd, England, 1986
Biestek, T, Weber, J, Electrolytic and Chemical Coatings, 1st ed. Portcullis Press Ltd., Redhill, 1976
Harun, MK, Marsh, J, Lyon, SB, “The Effect of Surface Modification on the Cathodic Disbondment Rate of Epoxy and Alkyd Coatings.” Prog. Org. Coat., 54 317–321 (2005)
Suzuki, I, Corrosion-Resistance Coating Technology. Marcel Dekker Inc, New York, 1989
Weng, D, Jokiel, P, Uebleis, A, Boehni, H, “Corrosion and Protection Characteristics of Zinc and Manganese Phosphate Coatings.” Surf. Coat. Technol., 88 147–156 (1996)
Geenen, FM, De Wit, JHW, “An Impedance Spectroscopy Study of the Degradation Mechanism for a Model Epoxy Coating on Mild Steel.” Prog. Org. Coat., 18 299–312 (1990)
Loveday D, Peterson P, Bob Rodgers-Gamry Instruments, “Evaluation of Organic Coatings with Electrochemical Impedance Spectroscopy; Part 3: Protocols for Testing Coatings with EIS.” JCT Coat. Tech. 22–27 (2005)
Mahdavian, M, Attar, MM, “Electrochemical Behaviour of Some Transition metal Acetylacetonate Complexes as Corrosion Inhibitors for Mild Steel.” Corr. Sci., 51 409–414 (2009)
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Rani, N., Singh, A.K., Alam, S. et al. Optimization of phosphate coating properties on steel sheet for superior paint performance. J Coat Technol Res 9, 629–636 (2012). https://doi.org/10.1007/s11998-012-9395-9
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DOI: https://doi.org/10.1007/s11998-012-9395-9