ABSTRACT
The corrosion behaviour of chromated zinc and chromated zinc alloy (Zn–Co, Zn–Fe and Zn–Ni) coatings, obtained from different industrial plants, was studied by means of accelerated corrosion tests (salt spray test and d.c. electrochemical techniques) and field tests. The morphology of corrosion attack in the salt spray tests is also reported. At almost neutral pH values, all the chromated zinc alloy coatings show a better corrosion resistance than the conventional chromated zinc coatings. Acidity causes a decrease in the corrosion resistance of both chromated zinc and chromated zinc alloys; at low pH values the corrosion resistance of zinc coatings is higher compared to the alloy coatings. The results show that the corrosion resistance of Zn–Co and Zn–Fe alloys mainly depends on the formation of a particularly protective chromate conversion layer, while the corrosion resistance of Zn–Ni alloys is due to the particular corrosion mechanism.
