Passivation of zinc coatings in cerium-containing solutions

Process was developed for no-chromate passivation of zinc coatings in a solution containing 20-40 g L-1 of cerium nitrate, 5-25 mL L-1 H2O2, and 2-8 g L-1 of an additive (8-10 g L-1 of malic acid and 4-8 g L-1 of sodium nitrate) at a temperature of 40-60°C and pH 2.5-3.5. It was shown that cerium-containing passivating coatings on zinc-plated steel articles compare well in corrosion resistance and protecting capacity with iridescent chromate coatings. It was found that cerium-containing coatings are capable of self-healing and sustain a thermal shock without degradation of their characteristics.