Evolution of Phases, Microstructure, and Surface Roughness during Heat Treatment of Aluminized Low Carbon Steel

Diffusion processes for aluminum-silicon coatings on low carbon sheet steels during austenizing have been investigated. Temperature profiles were imposed with closed-loop control of a motorized linear slide that moves samples through a tube furnace. Heat treatment variables were heating rate, hold temperature, and hold time. Subsequent analysis included scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and surface roughness measurements. The evolution of the coating was tracked by following the formation of seven main microstructural regions. In order to observe the cross-sectional microstructure without any mechanical influence of the preparation process, a focused-ion beam (FIB) was used. The effects of the various heat treatment parameters were evaluated. The resulting observations and data enhance the understanding of the diffusion process and provide information needed to optimize the heat treatment.