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SUMMARY
The morphologies and corrosion resistance of electrodeposited zinc-cobalt compositionally modulated alloy multilayer coatings produced from a sulphate bath have been investigated and reported in this paper. Various current density waveforms were designed using a computer-aided pulse plater unit to deposit zinc-cobalt alloy layers of alternate compositions from 10% cobalt to 70% cobalt. Different numbers of layers with different thicknesses were deposited by designing a variety of current density waveforms. It was shown that designing waveforms with steps to produce a gradual increase or decrease in current densities can prevent crack formation and improves the quality of Zn/Co CMAM coatings. Neutral salt spray corrosion tests showed that Zn/Co CMAM coatings have better corrosion resistance than single layer Zn-Co alloy coatings. Effects of bath temperature and agitation on the corrosion resistance of these CMAM coatings were also investigated. It was found that the best corrosion protection could be achieved for a two layered Co/Zn CMAM coating deposited at 25–30 °C from a bath with a high rate of agitation.