Structure, Composition and Corrosion Resistance of Zn-Ni-P Alloys Electrodeposited from an Ionic Liquid Based on Choline Chloride

Ternary Zn-Ni-P alloy coatings were electrodeposited from electrolytes based on choline-chloride ionic liquid. Their phases, microstructures, chemical compositions and corrosion behaviors were characterized as a function of electrodeposition current density. Varying the deposition current density has an influence on the composition and corrosion resistance of the obtained amorphous Zn-Ni-P deposit. The chemical composition results show that during electrodeposition from ionic liquids, P is incorporated into the Zn-Ni alloy through an indirect mechanism. The amount of phosphorus and nickel of the alloy decreases with an increase in the deposition current density while that of zinc increases, which corresponds to normal co-deposition mechanism. From the two electrolytes considered, the morphology of the Zn-Ni-P alloy electrodeposited evolved from a superficial network of fine cracks to larger cracks with an increase of the deposition current density. From polarization curves of coatings in 3.5% NaCl, it is shown that the P incorporated Zn-Ni alloy coatings exhibit a remarkably enhanced corrosion resistance and barrier properties, and the protective ability increases with decrease in the deposition current density. (C) 2014 The Electrochemical Society. All rights reserved.