Corrosion behaviour of chromated Zn and Zn alloy electrodeposits

The influence of a chromate film on the corrosion behaviour of Zn, Zn–Co and ZnFe coatings was investigated. XPS, AES techniques were applied for characterisation of the iridescent chromate films, while the XRD method was used for the corrosion product analysis. Atmospheric field (4 years data), accelerated (neutral salt spray and SO2 cabinet) tests and electrochemical measurements were applied for the corrosion resistance studies. The beneficial influence of alloying for chromated Zn electrodeposits was observed under the conditions, where Cl− ions were the dominant pollutant (marine test site, Cl− cabinet, Cl− aqueous solution). The degree of protection from the chromate film, in spite of their lower thickness, was detected to be higher for the alloyed samples. A higher concentration of Cr(VI) compounds in the passive chromate layers of alloyed samples may be the reason of their superior corrosion resistance.