CORROSION RESISTANCE OF ELECTRODEPOSITED ZINC-NICKEL COATINGS

摘要

The corrosion behaviour of commercial zinc-nickel coating (12%Ni) was compared with that of commercial prephosphated electrogalvanized steel and of bare electrogalvanised steel. Anticorrosive behaviour of such materials was evaluated by natural exposure in urban and marine-industrial atmospheres, by SEM/EDS, XRD and by EIS in sodium sulphate solution. The prephosphated zinc coating tended to corrode uniformly from the surface with the formation of zinc corrosion products and gradual consumption of zinc coating. In the Zn-Ni coating, the zinc started to dissolve from the cracks of the coating, and after some time the corrosion products tended to cover the surface uniformly. EIS monitoring of the Zn-Ni coated samples in Na_2SO_4 has shown that the sacrificial protection was maintained even after 1 year of exposure in a marine-industrial atmosphere, whereas the zinc coated samples seemed, for this exposure time, to have predominantly a barrier protection.