Influence of thermal treatment on the corrosion resistance of electrolytic Zn–Ni+Ni composite coatings

Abstract

This study was undertaken in order to obtain and characterize the corrosion resistance of Zn–Ni+Ni composite coatings. The influence of thermal treatment on surface morphology, phase composition, and corrosion resistance of Zn–Ni+Ni coating was investigated. The Zn–Ni+Ni coating was deposited under galvanostatic conditions (j = 40 mA cm−2). Thermal treatment was carried out in argon atmosphere. The surface morphology of Zn–Ni+Ni coatings was carried using a scanning electron microscope (JEOL JSM-6480) and the surface chemical composition was determined by the EDS method. Structural investigations were conducted by X-ray diffraction method. The studies of electrochemical corrosion resistance were carried out in a 5% NaCl solution, using potentiodynamic and scanning vibrating electrode (SVET) methods. On the grounds of corrosion investigations, it was stated that thermal treatment improves both total and localized corrosion resistance of Zn–Ni+Ni coating in a 5% NaCl water solution. The higher corrosion resistance of the thermally treated Zn–Ni+Ni coating could be attributed to the increase in the amount of zinc bonded to nickel in the form of Ni2Zn11 and Ni5Zn21 intermetallic phases. The SVET analysis indicated that thermal treatment of Zn–Ni+Ni coating causes a decrease in the number of corrosion centers on their surface area.