Microstructural and Corrosion Behavior Analysis of Zn-Co-Al2O3 Coatings Deposited on St37 Steel by Electroplating in Electrolytes with Different pH Values

Document Type : Original Article

Authors

1 Department of Materials Engineering and Metallurgy, Faculty of Engineering, Shahid Bahonar University of Kerman, Kerman, Iran

2 Department of Materials Engineering, Faculty of Mechanical and Materials Engineering, Graduate University of Advanced Technology, Kerman, Iran

3 Mechanical Engineering Department, Faculty of Engineering, Higher Education Complex of Bam, Bam, Kerman, Iran

Abstract

In the present study, by varying the pH of the electroplating electrolyte, different Zn-Co-Al2O3 composite coatings were deposited on an St37 steel substrate. After coating at pH values of 4.5, 5, and 5.5, the microstructure of the coatings was examined using a scanning electron microscope (SEM). The corrosion behavior of the test samples in 3.5 wt% sodium chloride solution was also evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results showed that increasing the pH led to finer crystallite size and a higher amount of alumina particles in the coatings. Polarization data analysis also revealed that applying the coating reduced the corrosion current density of steel, with the coating deposited at pH=5.5 exhibiting the most significant reduction compared to the other coated samples. Furthermore, EIS results indicated that the charge transfer resistance of the coatings formed at pH values of 4.5, 5, and 5.5 was approximately 345, 547, and 682 Ω.cm2, respectively. These values confirm that the coating deposited at pH=5.5 has superior corrosion resistance compared to the others.

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Applied Chemistry Today
Volume 21, Issue 78
May 2026
Pages 77-90

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