Variables affecting growth and morphology of the intermetallic layer (Fe2Al5)

A steel substrate containing 0.4% carbon was hot-dip aluminized in pure Al and Al–11 wt.% Cu alloy. During the aluminizing process, an intermetallic layer (Fe2Al5) was developed at the interface between the aluminizing metal and the steel substrate. The effects on its growth and morphology resulted due to variation in compositions of aluminizing metal, carbon content of the steel substrate, aluminizing temperatures (675–950 °C) and dipping times (1–10 min) were investigated. In pure Al, the intermetallic layer was thick and it showed a finger-like growth with the substrate. While in the Al–Cu alloy, it was thin enough and its growth was almost smoother. Its thinning was attributed to the formation of tetragonal intermetallic phases, Al2Cu and Al7Cu2Fe, on the surface of the aluminized steel. In both melts, its thickness increased with increasing aluminizing temperatures in the range 675–775 °C, while above this range it was found constant. Likewise, it increased rapidly with the increase of the dipping time up to 4 min, after that with increasing time it increased very slowly. Conversely, the variations in both the aluminizing temperature and the dipping time did not influence morphology of the intermetallic layer.

Research Highlights
► An intermetallic layer of Fe2Al5 phase grows in hot-dip aluminized steels.
► Aluminizing metal-composition, temperature and time affect its growth rate.
► The addition of 11% Cu by weight in Al decreases the growth rate up to 75%.
► The rise in temperature 675–775 °C increases, but above 775 °C it has no effect.
► For the shorter dipping time i.e. < 4 min the growth rate is fast, then very slow.