Electrochemical analysis of molybdate conversion coating on hot‐dip galvanized steel in various growth stages

The electrochemical behavior of molybdate conversion coatings in various growth stages was investigated by electrochemical impedance spectroscopy and equivalent circuits. The chemical composition and microstructure were characterized by SEM/energy dispersive spectroscopy, atomic force microscopy, an...

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Bibliographic Details
Published in:Surface and interface analysis 2017-08, Vol.49 (8), p.698-704
Main Authors: Zhang, Shuang‐hong, Yang, Bo, Kong, Gang, Lu, Jin‐tang
Format: Article
Language:English
Subjects:
Atomic beam spectroscopy
Atomic force microscopy
Chemical composition
Conversion coating
Conversion coatings
corrosion
Crack propagation
Cracks
EIS
Electrochemical analysis
Electrochemical impedance spectroscopy
Equivalent circuits
Galvanized steel
Galvanized steels
Hot dip galvanizing
Immersion coating
Microstructure
molybdate coating
Protective coatings
Salt spray tests
Scanning electron microscopy
Spectrum analysis
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Summary:The electrochemical behavior of molybdate conversion coatings in various growth stages was investigated by electrochemical impedance spectroscopy and equivalent circuits. The chemical composition and microstructure were characterized by SEM/energy dispersive spectroscopy, atomic force microscopy, and AES. Neutral salt spray tests complemented the information. The results indicated that the growth process of the molybdate conversion coating was accompanied by the growth of micro cracks, consisting of three stages: in the early and middle stages, the protective property of the coatings increased with increasing treatment time and then decreased when the cracks developed in the last stage. On the basis of the observation of the microstructure and the analysis of the electrochemical impedance spectra of the coatings in various stages, a simplified growth process model of the molybdate conversion coating on hot‐dip galvanized steel was created. Copyright © 2017 John Wiley & Sons, Ltd.
ISSN:0142-2421
1096-9918
DOI:10.1002/sia.6210