Corrosion Resistance of Zn-Ni Alloy Films Electroplated from Alkaline Zincate Solution Containing Brightener

Zn-Ni alloys were electroplated on an Fe plate with thicknesses of 40 mu m at 500 A center dot m(-2) and 293 K in unagitated zincate solutions. The reaction product of epichlorohydrin and imidazole (IME) was added in the solution as a brightener at the concentration of 0-5 ml/dm(-3). The corrosion resistance of the obtained Zn Ni alloys films was investigated from the polarization curve in 3 mass% NaC1 solution before and after the corrosion treatment (formation of corrosion products) in NaCI solution for 48 h. Before the corrosion treatment, the corrosion current density of plated films rarely changed regardless of addition of IME into the zincate solution because the reduction reaction of dissolved oxygen rarely changed. However, in films plated from the solution containing IME, the anode reaction was suppressed and the corrosion potential shifted to noble direction. The suppression of anode reaction with an addition of IME in plating solution is attributed to the increase in gamma-phase in plated films. On the other hand, after the corrosion treatment, the morphology of Zn chloride hydroxide of corrosion product was uniformly formed on the surface with increasing the concentration of IME. The reduction reaction of dissolved oxygen was suppressed with increasing the concentration of IME, resulting in