Journal of Metals, Materials and Minerals

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Multilayer Zn-Ni alloy coating was developed on mild steel from acid chloride bath containing thiamine hydrochloride, as additive. Composition modulated multilayer alloy (CMMA) coatings, or simply, multilayer coating with gradual change in composition were developed galvanostatically using triangular current pulses from single bath technique. CMMA coatings of Zn-Ni were developed under different conditions, such as cyclic cathode current densities (CCCDs) and a number of layers, and their corrosion behaviors were evaluated by potentiodynamic polarization and electrochemical impedance spectroscopy method. Optimal configuration, (Zn-Ni)2.0/4.0/600 was found to exhibit ~50 times better corrosion resistance compared to monolayer (Zn-Ni)3.0 alloy, deposited from the same bath for the same time. The corrosion resistance of CMMA coatings was observed to be better, and results were discussed. Further, decrease of corrosion rate at high degree of layering was found, and was explained by less relaxation time for redistribution of solutes at diffusion layer during plating. The better corrosion resistance of the CMMA coating, developed using triangular current pulses, have been discussed in relation to those obtained by square current pulses. Both formation of multilayer and corrosion mechanisms were analyzed using scanning electron microscopy (SEM).

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