Zinc-iron phases formed on galvannealed steel

Moessbauer spectroscopy has been used to identify the zinc-iron intermetallic phases present in the coating of three galvannealed steels, two of which were produced on commercial galvanizing lines and one in the laboratory. Both CEMS and XMS have been used in order to determine the depth dependence of each phase. Three main zinc-iron phases have been identified with the proportion of each dependent on the preparation conditions. In the commercially produced coatings, CEMS, probing near the top of the coating, indicates that the zinc rich ξ-FeZn13 and δ-FeZn10 alloys are present. XMS indicates the presence of some Γ-Fe3Zn10 closer to the steel. In contrast, the laboratory produced sample contains nearly pure ξ-FeZn13 through the entire coating thickness. Subphases of the delta and gamma alloys were also identified. These subphases appear to be mixed with a preference for the higher zinc subphase of each to form closer to the surface of the coating. (orig.)