Growth of intermetallic layer in the aluminide mild steel during hot-dipping

Mild steel was coated by hot-dipping in a molten aluminum bath. The growth behavior in the intermetallic layer after various times of immersion in the hot-dip at 700 °C was analyzed by electron backscatter diffraction (EBSD). The results showed that the aluminide layer consisted of an outer aluminum topcoat, minor FeAl3 and major Fe2Al5, respectively. From another perspective, Fe2Al5 possessed a tongue-like morphology, which caused the corresponding serration-like morphology of the steel substrate. The Fe–Al/steel substrate interface of the Fe2Al5 phase, after removal of the steel substrate, displayed a columnar structure growing toward the steel substrate, implying that Fe2Al5 grew at a rapid rate along the diffusion direction. Moreover, the EBSD results revealed the Fe2Al5 phase was not only composed of columnar grains, but also possessed fine grains clustered around the peaks of the serration-like steel substrate.