Pulse plating of Zn-Ni alloy coatings

Abstract

In this work the electrodeposition of Zn-Ni alloy coatings from a chloride-based electrolyte using a square-wave current pulse-plating technique was investigated. The effects of the pulse plating variables (peak current density, on-time and off-time) and some important bath conditions (ZnC1₂ and NiCl₂.6H₂O concentrations in the bath as well as bath temperature) on the chemical composition, surface morphology, grain size, phase distribution and preferred orientation of the deposits were studied. The bath temperature had a very strong effect on the composition of the deposits which, in turn, had very strong effects on the phases present, surface morphology and grain size. The peak current density was found to have little effect on the composition and phases present, but had considerable effect on grain size. The on-time and off-time had no significant influence on the characteristics of the deposits, except for slight grain refinement observed with increasing off-time. Only the η, γ and α crystal phases were found in the deposits while other intermediate phases such as β and δ were not found in any of the deposits produced in this work. Grain refinement of the deposits down to the nanocrystalline range can be achieved by increasing the Ni content of the deposits.