Application Example 9: Cross-Sectional Examination of a Painted Steel

Abstract

The cross-section of a painted steel is presented. Over the galvanized steel substrate, with a Zn layer of ~5 μm thick, a paint layer is observed clearly (Fig. E9.1a); the paint layer appears to consist of two layers, an inner layer, with anticorrosion pigments, and an outer, the so-called “clear paint layer” with color pigments. In between these two major layers, a thin paint layer, ~1 μm thick, is observed where the pigments are not visible. Close examination of the interface between the inner paint layer and Zn in the high-angle BSE imaging mode reveals successfully a chromate layer (indicated by the arrows) that had been applied over the galvanized steel (Fig. E9.1b). The chromate layer acts as a keying layer to promote the adhesion between the paint and galvanized steel. It also improves corrosion resistance of the painted steel.