Cross-sectional observation of the intermetallic phase in a galvannealed steel

The coated zinc layer on the dual-phase steel can possess excellent anti-corrosion properties, and the continuous hot-dip process for the dual-phase steel is well known as galvannealed treatment. Since the coated layer is very thin, it is very difficult to acquire a thin foil for transmission electron microscopy by the traditional twin-jet method. The focused ion beam method was used in the present study to obtain high-quality specimens for investiging the details of the microstructure in the coated layer. It was found that a fully microalloying layer exists between the zinc layer and iron matrix. The zinc-rich phases ζ and δ can be observed in the coated layer. However, the Γ1 and Γ2 phases could not be detected in the present study, although they could be expected in parts of lower zinc content in the coated layer.