Effect of NH4Cl on the microstructure, wettability and corrosion behavior of electrodeposited Ni–Zn coatings with hierarchical nano/microstructure

Abstract

In this study, nickel‐zinc (Ni–Zn) superhydrophobic coatings with a hierarchical nano/microstructure were deposited through a two-step electrodeposition process on the copper substrate. The effect of adding NH4Cl crystal modifier concentration on the composition, surface morphology, roughness and wettability of coatings were evaluated by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), scanning electron microscopy (SEM), laser confocal scanning microscopy (LCSM) and contact angle measurements. Additionally, the corrosion behavior of selected coatings was investigated using potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) techniques. The results showed that adding NH4Cl could affect the composition and surface morphology of the Ni–Zn coatings. A transition from a Zn-rich Ni–Zn coatings with polyhedral shape to the Ni-rich Ni–Zn coatings with hierarchical nano/mico-conical structure was taken place through adding NH4Cl as a crystal modifier. The Ni–Zn coating prepared with 400 g·L−1 NH4Cl showed superhydrophobic behavior with the highest water droplet contact angle of ~155°. The confocal microscopy results confirmed this coating has the highest roughness and power spectral density (PSD) values at entire spatial frequencies. In addition, the superhydrophobic coatings exhibited higher corrosion resistance compared to the other coatings.