Influence of Phase Composition of Zn–Ni Alloy Film on the Corrosion Resistance of Zinc Coating

Abstract

The effect of the phase composition of zinc-nickel alloy films electrodeposited on zinc-coated steel samples on their corrosion behavior was investigated. The alloys were electrodeposited from dilute ammonia-glycinate electrolytes. This type of electrolytes models the modified first bath in a rinsing system of the zinc plating line. It is shown that the galvanic displacement reaction at a level of 0.32 mA cm^–2 does not lead to a decrease of the adhesion of the alloy films to the zinc substrate. The best corrosion protection of a zinc coating is provided by a zinc-nickel alloy film, which additionally to the γ-phase also contains Ni or the amorphous β-phase. At the thickness of only approximately 1.5 μm, the Zn–Ni alloy shifts the corrosion potential of the galvanized steel by 100–150 mV in a positive direction and reduces the corrosion current density by 1.2–1.8 times.