Influences of crystallographic texture and nanostructural features on corrosion properties of electrogalvanized and chromate conversion coatings

Abstract

Galvanized coatings are widely used in industry, but the influences of microstructure on corrosion behaviors have rarely been studied in these coatings. The present investigation aims to systematically analyze crystallographic texture and nanostructural features of galvanized coatings as well as their chromate conversion layers, and examines the relationship between their structures and corrosion properties. Three groups of electrogalvanized coatings fabricated with different types of plating additives are studied, using a series of complementary characterization techniques. The corrosion behaviors of the deposits are then analyzed with the potentiodynamic polarization technique and salt spray test, in light of their structural characteristics. The study reveals that the additives critically influence the microstructure of both the galvanized coatings and chromate layer. The corrosion resistance of the coatings can be enhanced by suppressing the {100} crystallographic planes of zinc and minimizing defects along the zinc/substrate interface, and by promoting formation of an amorphous-oxide layer in the chromate film.