FIELD AND LABORATORY CORROSION TESTS ON ZINC NICKEL-ALLOY COATINGS

Among the zinc alloy coatings, zinc-nickel is of particular interest because it seems to maintain very good corrosion resistance even when it is exposed to heating, as happens to components in car engine compartments. Chromated zinc and chromated zinc-nickel alloy coatings were placed on the underside and in the engine compartment of different cars subjected to field testing. The results were compared with those obtained in laboratory tests on the same materials, before and after heat treatment at 120-degrees-C for 1 h. The influence of heat treatment on the superficial morphology and corrosion resistance of the coatings was evaluated using scanning electron microscopy, salt spray tests and electrochemical tests. The results obtained in this work show that the heat treatment does not produce any remarkable modification of the behaviour of chromated zinc-nickel alloys whose corrosion protective properties remain almost unchanged, in contrast with the behaviour of chromated zinc.