Investigation of nanocrystalline zinc–nickel alloy coatings in an alkaline zincate bath

Nanocrystalline zinc–nickel alloy coatings obtained from an alkaline zincate bath containing a laboratory-made additive were investigated in this paper. The effects of the additive content and the cathode current density on the grain sizes of the coatings were studied. SEM and TEM observations and XRD analysis were performed to examine the microstructure (grain size) and phase composition of the coatings. The experimental results indicated that the addition of the additive leads to a much brighter and a more uniform nanocrystalline deposition with the grain sizes varying from 14 to 33 nm. The Hull cell test was used to determine the optimum ranges of both the cathode current density and the additive content. Salt spray tests and polarization measurements indicated that the nanocrystalline zinc–nickel alloy coatings have a better corrosion resistance than the zinc coatings deposited from a simple alkaline zincate bath.