Kinetics of intermetallic compound layers during initial period of reaction between mild steel and molten aluminum

Abstract

Hot dip aluminizing of mild steel at different temperatures was conducted to reveal the influence of reaction temperature and time on interfacial intermetallic compounds (IMCs). Scanning electron microscopy, energy dispersive X-ray spectrometry and X-ray diffraction were employed to investigate the interfacial microstructures. The IMCs of the dipping interface consisted of a thick layer of η-Fe ₂Al ₅ between 4.2–132.2 μm next to the steel and a thin layer of θ-Fe ₄Al ₁₃ between 0–5.5 μm close to the aluminum. With increasing dipping temperature and time, the total thickness of IMCs (Fe ₂Al ₅ plus Fe ₄Al ₁₃) increased. Specifically, the growth of the Fe ₂Al ₅ layer can be described by parabolic rate laws. An activation energy of 93 kJ mol ⁻¹ was obtained, combining both the results from the present work and previous studies in the temperature range of 675–900°C. The change in Fe ₄Al ₁₃ thickness is not significant compared with the Fe ₂Al ₅. However, the decrease in IMC thickness of the Fe ₄Al ₁₃ with dipping temperature was observed for the first time and had never been reported before. Moreover, it can be clearly observed that the thickness of the Fe ₄Al ₁₃ decreased with dipping time based on the linear fitting results by excluding the result of the initial 1 s. A possible mechanism is that interfacial dynamics and thermodynamics work for the dissolution and decomposition of the Fe ₄Al ₁₃ layer. Higher temperature accelerates the dissolution of the θ layer.