Characterization of the Fe-Al Inhibition Layer Formed in the Initial Stages of Hot-dip Galvannealing.

Due to the lack of detailed information surrounding the inhibition phenomenon in hot-dip galvannealing, and the microstructure and morphology of the Fe-Al inhibition compounds, this study was initiated to investigate the inhibition layer formed under the low bath Al content, short-dipping-time conditions typical of commercial galvannealing. In this paper, Fe-Al inhibition layer formation on samples produced in a 0.14 mass% Al-bearing Zn bath on a Ti IF, Ti-Nb IF and a P-added Ti IF substrate was studied using a technique combining both SEM and TEM. The inhibition layer on the Ti IF and Ti-Nb IF substrates was composed of both Fe2Al5 and FeAl3. The inhibition layer on the P-added substrate was composed primarily of FeAl3 with individual grains of Fe2Al5 observed between the FeAl3 and the steel substrate. A possible formation mechanisms for the inhibition layer is speculated based upon the TEM observations of the morphology of the layer.