Corrosion Resistance of Zn-Ni Alloy Films Electroplated in Alkaline Zincate Solutions Containing a Brightener

Zn-Ni alloys were electroplated on a Fe plate with a thickness 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 to the solution as a brightener at concentrations of 0-5 mL dm(-3). The corrosion resistance of the obtained Zn-Ni alloy films was investigated from the polarization curve in 3 mass% NaCl solution before and after the corrosion treatment (formation of corrosion products) for 48 hours. Before the corrosion treatment, the corrosion current density of plated films rarely changed, regardless of the 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 toward the noble direction. The suppression of the anode reaction with an addition of IME into the plating solution is attributed to the increase in. -phase in the plated films. After the corrosion treatment, Zn chloride hydroxide of the corrosion product uniformly formed on the surface when increasing the concentration of IME. The reduction reaction of dissolved oxygen was suppressed by increasing the concentration of IME, resulting in a decrease in corrosion current density.