Phase formation at the interface between a boron alloyed steel substrate and an Al-rich coating

Al-base coating (AlSi10Fe3) was applied to a steel substrate (22MnB5) by hot dipping. The coated steel substrates were austenitized at 920 °C for several dwells, and phase formation at the steel/coating interface was investigated by means of ex-situ phase analysis with synchrotron radiation and EBSD. Phase identification by EBSD and XRD confirmed the formation of Al-rich intermetallics during austenitization. Increasing the dwell time led to Fe diffusion into the Al-base coating as well as Al diffusion into the substrate. As a result of the diffusion processes, Al-rich intermetallics in the coating transformed to more Fe-rich intermetallics. Simultaneously, Al diffusion into the substrate changed the microstructure of the steel substrate near the coating interface. Formation of FeAl intermetallics and thus the mechanical properties of the AlSi10Fe3 coating can be influenced by heat treatment. Higher austenitization temperatures and longer dwell times support the formation of more ductile FeAl intermetallics but also lead to grain growth; thus having a negative effect on the mechanical properties of the steel.