Microstructure and Corrosion Behavior of ZnO-Mg Coating on AISI 4140 Steel Fabricated by Spray Coating
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JMEPEG https://doi.org/10.1007/s11665-020-05099-9
Microstructure and Corrosion Behavior of ZnO-Mg Coating on AISI 4140 Steel Fabricated by Spray Coating T. Ramkumar, M. Selvakumar, M. Mohanraj, P. Chandramohan, and P. Narayanasamy (Submitted April 13, 2020; in revised form July 12, 2020) This paper aims to investigate the corrosion behavior of ZnO-Mg coatings on AISI 4140 steel using spray coating technology. Three different coating thicknesses of approximately 30, 60 and 90 lm are considered in this study. The structural and morphological properties of the coated samples are characterized using optical microscope, scanning electron microscope (SEM), x-ray diffraction analysis, atomic force microscope and energy-dispersive spectroscopy analysis. The corrosion behavior is evaluated in a chloride environment by Tafel and electrochemical impedance spectroscopy (EIS) techniques as a function of coating thickness. The acquired results exhibit that the introduction of ZnO-Mg coating improves corrosion resistance of AISI 4140. ZnO-Mg coating acts as a stabilizer in the electrolyte and maintains electrochemical stability. After prolonged polarization, the coating exhibits higher impedance in the subsequent EIS results compared to that of the substrate. The corroded surfaces of AISI 4140 are analyzed using SEM for surface morphological changes. Keywords
AISI-ZnO-Mg, AFM, electrochemical impedance, Tafel
1. Introduction Mild steel and its derivatives have been used since ages in various applications due to distinct structural characteristics and coat. Automobile applications are significant because of easy availability, ease of fabrication, low cost and good tensile strength among others (Ref 1-4). Specifically, multilayered thin film coatings find excellent engineering applications owing to admirable mechanical properties. ZnO coatings enhance mechanical properties, if coated over steel. Substantial emphasis has been placed on evolving replacements for ZnO-based coatings for the above reason. ZnO-Mg coatings have the potential to act as protective coatings for steel, since they have excellent corrosion resistance. Many coating approaches are applied commercially to offer protection from corrosive environments and for properties enrichment and thus to increase the life span of mild steel base infrastructure. Mg is anodic to mild steel; it protects the base material even when it is deposited in porous condition. However, Mg has limited application as structural material because of its high chemical reactivity and shrinkage on solidification. In order T. Ramkumar, Department of Mechanical Engineering, Dr. Mahalingam College of Engineering and Technology, Pollachi 642003, India; M. Selvakumar, Department of Automobile Engineering, Dr. Mahalingam College of Engineering and Technology, Pollachi 642003, India; M. Mohanraj, Department of Mechanical Engineering, Hindusthan College of Engineering and Technology, Coimbatore 641032, India; P. Chandramohan, Department of Mechanical Engineering, Sri Ramakrishna Engineering College, Coimb
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