Electrodeposition of single gamma phased Zn–Ni alloy coatings from additive-free acidic bath

Abstract Zn–Ni alloy coatings were electrodeposited on mild steel substrate from acidic sulphate bath. The effect of different electrodeposition parameters including temperature, current density, agitation speed and Ni2+/Zn2+ ion ratio on the Zn–Ni coating's physical, chemical and mechanical properties has been studied. Results show that Ni content of coatings has a strong effect on the structure, morphology and microhardness of coatings. Increasing Ni2+/Zn2+ ratio in the bath, higher temperature and higher deposition current density increased the Ni content of coatings. However, higher agitation speed increased the Zn electrodeposition and the anomaly of deposits. The phase structure of the coatings was strongly affected by the Ni content in the coatings. It changed from Zn rich η phase to Ni5Zn21 γ phase. Weak signal of δ-Ni3Zn22 phase was rarely observed for some coatings deposited at different parameters. Single γ phase coatings with optimum properties were electrodeposited at 40 °C and 80 mA/cm2, under 600 rpm agitation speed from the bath with Ni2+/Zn2+ ratio equals 1. Wear resistance of coatings were also improved by Ni doping.