Microstructure and Corrosion Behavior of ZnO-Mg Coating on AISI 4140 Steel Fabricated by Spray Coating

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 approximate to 30, 60 and 90 mu m 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.