Morphology and Corrosion Performance of Chromate Conversion Coatings on Different Substrates

The aqueous corrosion resistances of galvalume (FeAl+Zn) and steel galvanized (Fe-Zn) alloys, passivated by immersion in chromating solution with different immersion times (0, 10, 30 y 60 s) are compared. The electrochemical behaviour of various chromated and non-chromated coatings was investigated in 3 wt-% NaCl solution using polarization techniques. For comparison, AISI 1010 carbon steel substrates were also analyzed. The characterization measurements and polarization curves revealed that textural properties of Fe alloys influence the growth of the films and both the cathodic and anodic reactions. An optimum anticorrosive protection was obtained at 30 s. CCCs treatments inhibited the corrosion of zinc to a significant degree, but less effectively than coatings formed with aluminium-zinc alloys. The difference in the corrosion protection given by the two substrates types was attributed to the structural properties, thickness coating, grain size and roughness observed, which affect oxygen diffusion.