Zincnickel alloys were electrodeposited on steel from chloride bath by direct and pulse current. Some electric variables Žaverage current density, pulse frequency, duty cycle. and some important bath conditions Žratio of Ni2Zn2 in bath, temperature. on chemical compositions, current efficiency, microhardness and surface appearance of coatings were studied. At low current densities, transition from anomalous to normal co-deposition was observed for both direct and pulse current. Pulse current seems to increase brightness of the coating and to decrease the precipitation of zinc hydroxide at the cathode surface. In addition, applied pulse current increases the percentage of nickel in deposits. Pulse frequency and duty cycle had little effect on the chemical composition of deposits. The polarization curve of zincnickel deposition with pulse current is shifted to positive potentials in comparison with direct current curves. The temperature of the plating bath had a very strong effect on the composition of the deposits. This is primarily the result of intrinsically slow nickel kinetics. The hardness of ZnNi alloy coatings (approx. 220 VHN. was greater than the hardness of zinc coating (approx. 161 VHN.. The hydroxide suppression mechanism for ZnNi co-deposition has been confirmed.
کلید واژگان :Electrodeposition of ZnNi alloys; Pulse plating
ارزش ریالی : 600000 ریال
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