Metastable zinc–nickel alloys deposited from an alkaline electrolyte

•Zn–Ni coatings with high corrosion resistance were prepared by electrodeposition.•The electrodeposited γ alloy is found to be different from the equilibrium γ phase.•A random atomic distribution is proposed for the electrodeposited alloy.•The calculated free energy function can explain the phase composition of Zn–Ni coatings. Zinc alloy offers superior sacrificial protection to steel as the alloy dissolves more slowly than pure zinc. The degree of protection and the rate of dissolution depend on the alloying metal and its composition. In this work, the physico-chemical characterization of zinc–nickel electrodeposits obtained from an alkaline bath is carried out and a description of the structural and thermodynamic properties of these alloys is proposed. Contrary to the common acceptance, XRD spectra and DSC thermal analysis show that the electrodeposited γ alloy has to be regarded as a metastable phase, whose atomic arrangement is different from that of the equilibrium γ intermetallic compound. A model for atomic distribution in the electrodeposited alloy is proposed. The Gibbs free-energy function for the electrodeposited phase has been evaluated and the metastable boundaries of the single-phase and two-phase fields have been calculated. Reasonable agreement is found with experimental values reported in the literature for Zn–Ni coatings with different composition.