Application Example 27: Cross-Sectional Examination of a Galvanized Steel for Car Bodies

Abstract

Through examination of the cross-section of a galvanized steel prepared in the manner described in the previous section, the power of follow-up treatment by rf-GD sputtering for sample surface preparation for SEMis now demonstrated. The galvanized layer is of the composition of Zn-0.2wt% Al which is widely used for car bodies. Here, detailed information on the Zn/steel interface is of key importance for both steel and car industries. The cross-section of the galvanized steel is shown in Fig. E27.1a. A zinc layer, ~20 μm thick, is observed over the steel substrate, as indicated by the arrow. Examination of the Zn/steel interface at an increased magnification of about 30,000× reveals a layer of Fe₂Al₅ (Fig. E27.1b, c). Fig. E27.1b is the cross-section before rf-GD sputtering. For preparation of cross-section, a diamond knife with its edge damaged slightly, not extensively, was employed deliberately to demonstrate the power of follow-up treatment by rf-GD sputtering. By the use of a damaged knife, knife marks are observed everywhere in the section along the direction parallel to the cutting direction. Further, deformation of relatively soft zinc layer is evident. At the location indicated by the arrows, fine aluminum particles, <100 nm in diameter, are present, but these particles are not revealed readily due to deformation of the zinc matrix.