Study of Microstructure and Corrosion Resistance of Zinc Electrodeposits before and after Black Chromating

Abstract:

In this work, microstructure and corrosion properties of zinc electroplated steel before and after black chromating was investigated. The test samples were prepared by electrodeposition process, using a commercially-available alkaline electrolyte. Subsequently, the galvanized samples were applied with a black chromate-based passivation layer and a clear top-coat layer. Their microstructures were examined using X-ray diffractometry and scanning electron microscopy. The corrosion resistance of the samples was assessed with the salt spray test, following the ASTM B117, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization in 5 wt.% NaCl solutions. The study showed that zinc electroplated steels exhibit (110) crystallographic orientation. The passivation and top-coat layers did not affect the microstructure of the zinc layer, and covered uniformly on the zinc layer for all sets of samples. The corrosion resistant results obtained from salt spray testing and electrochemical testing revealed that the microstructure of zinc coatings prepared by using different applied current did not influence on their corrosion resistance markedly. While black passivation followed by top coating provided a significant improvement on corrosion resistance of the coatings.

• Periodical: Key Engineering Materials (Volume 751)
• Pages: 119-124
• DOI: https://doi.org/10.4028/www.scientific.net/KEM.751.119
• Online since: August 2017
• Authors: Kanokwan Saengkiettiyut*, Pranee Rattanawaleedirojn, Adisak Thueploy, Jumpot Wanichsampan, Yuttanant Boonyongmaneerat
• Keywords: Chromating, Corrosion Resistance, Electrodeposition, Zinc

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