Effects of deposition temperature on chemical composition, hardness, morphology and corrosion behavior of Zn-Ni alloy coatings

Zn–Ni alloy coatings were electrodeposited from acidic sulphate bath. In this study effect of plating bath temperature on hardness, morphology, chemical composition of the coating and cathodic current efficiency was investigated. The morphology and chemical composition of the coatings were investigated using Scanning Electron Microscopy (SEM) equipped with EDX analyzer. X-ray diffraction (XRD) technique was used to analyze the structure of the coatings. To investigate the corrosion properties of the coatings, Tafel Polarization experiments and electrochemical impedance spectroscopy (EIS), were used. Results showed that the amount of nickel in the coating increased by increasing deposition temperature. The amount of nickel had a great effect on structure, morphology and hardness of the coatings. In addition, as deposition temperature increased cathodic current efficiency reduced which in turn led to reduction of hardness. SEM results showed that at low temperatures the structure had fine grains and with increasing temperature, the structure became coarser. Coatings with 14 wt% Ni, had maximum corrosion resistance among all the coatings with different chemical composition. This coating had a  phase hexagonal structure and this was the main reason for the increased corrosion resistance of the coatings.