Evolution of intermetallics between solid Fe-Cr/Fe-Ni alloys and molten aluminium

Abstract

Investigations of the evolution of intermetallic compounds (IMCs) at the interface between iron-based alloys and molten aluminium have important technical and scientific significance in many key areas. Most previous studies of IMCs formed at molten aluminium/solid steel interfaces have been focused on relatively long reaction times, but less research has been performed on the evolution of IMCs at the aluminizing interfaces of Fe-Cr and Fe-Ni alloys within a few seconds. In this study, hot-dip aluminizing experiments under natural convection conditions were employed to study the evolution of two interfacial IMCs (Fe-15Cr alloy and Fe-35Ni alloy with molten aluminium) at 700–900°C within 30 s. The IMCs for Fe-15Cr consisted of an Fe4Al13 layer next to the aluminium and an Fe2Al5 layer adjacent to the steel. In contrast, only one layer of Fe4Al13 was detected at the interface between the Fe-35Ni alloy and molten aluminium. The growth of Fe2Al5 was described by a parabolic rate law. An activation energy of 7.53 kJ/mol was determined for the temperature range of 700–900°C. The evolution of Fe4Al13 for the two alloys was similar: their thicknesses decreased anomalously with increasing dipping temperature, and their kinetics were controlled by both diffusion and dissolution. In this study, based on reaction-diffusion theory, growth and dissolution equations of the IMCs were established, and the diffusion coefficients of Al atoms in Fe2Al5 and Fe4Al13 were obtained for the first time. The similarities and differences in the IMCs for the two alloys were explained mainly by the different diffusion coefficients.