Evaluation of the anticorrosive behaviour of organic coatings applied on a Zn-21Al-2Cu alloy

Painting of a Zn-21wt%Al-2wt% Cu alloy, with four different superficial conditions, was carried out without difficulties using conventional paint systems recommended for applications over galvanised steel and even a common system to paint steel. The preparation of the ternary alloy surfaces by means of two phosphating treatments led to a slight improvement in the performance of the paint systems in exposure tests to a NaCl solution, a SO2 atmosphere and to weathering. Hardly any difference was observed among the superficial conditions in the adhesion tests. After 11 years of atmospheric exposure, specimens of the ternary alloy coated with the epoxy-polyurethane or the chlorinated rubber paint systems did not present major symptoms of degradation.