Features of intermetallic compounds in aluminized steels formed using aluminum foil

Foil aluminizing of steel, wherein Al diffuses to the base steel material by diffusion treatment after hot pressing of the aluminum foil at a lower temperature than the melting point, was performed in this study. Alloy layers formed by diffusion at temperatures ranging from 700 to 1000 °C were investigated, and their features were compared with those of hot-dip aluminized steel. In hot-dip aluminizing, an intermediate Fe2Al5 layer was formed between the aluminum layer and the base steel during aluminum coating before the diffusion treatment. In contrast, the coating layer of the foil-aluminized steel specimen after diffusion bonding of the aluminum foil consisted only of the Al layer. An Fe2Al5 layer, an FeAl layer and an Al diffused layer were formed in both the aluminized specimens subsequent to the diffusion treatment. The numbers of voids formed in the Fe2Al5 layer and at the FeAl/Al diffused layer interface of the foil-aluminized specimens are smaller than those for hot-dip aluminizing. Moreover, the FeAl and Al diffused layers are formed with a greater thickness in the foil-aluminized steel under identical diffusion conditions. The Al concentration in hot-dip aluminized steel decreased in stages from the surface to the base steel, whereas, in the foil-aluminized steel, it decreased gradually. The Fe2Al5/base steel interface in the foil-aluminized steel was thus indistinct, and cross-sectional hardness also decreased gradually.