PULSE PLATING OF ZN-NI ALLOY COATINGS

In this work the electrodeposition of Zn-Ni alloy coatings from a chlo ride-based electrolyte using a square-wave current pulse-plating techn ique was investigated. The effects of the pulse plating variables (pea k current density, on-time and off-time) and some important bath condi tions (ZnCl2 and NiCl2.6H(2)O concentrations in the bath as well as ba th temperature) on the chemical composition, surface morphology, grain size, phase distribution and preferred orientation of the deposits we re studied. The bath temperature had a very strong effect on the compo sition of the deposits which, in turn, had very strong effects on the phases present, surface morphology and grain size. The peak current de nsity was found to have little effect on the composition and phases pr esent, but had considerable effect on grain size. The on-time and off- time had no significant influence on the characteristics of the deposi ts, except for slight grain refinement observed with increasing off-ti me. Only the eta, gamma and alpha crystal phases were found in the dep osits while other intermediate phases such as beta and delta were not found in any of the deposits produced in this work. Grain refinement o f the deposits down to the nanocrystalline range can be achieved by in creasing the Ni content of the deposits.