Microstructure and corrosion resistance of Fe-Al intermetallic coating on Mild steel synthesized by Hot-dip Aluminizing

The present study deals with the surface modification of steel base through diffusion of aluminium by hot dip aluminizing, for improving wear and corrosion resistance. The material chosen for study is mild steel. Effect of varying dip times at different diffusion temperatures and times on the microstructure and corrosion behavior of aluminized and diffused specimens was studied. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), were followed to observe the cross-section and the distribution of the elements. Several samples of mild steel strips were aluminized by dipping in molten aluminium for different dipping times. An intermetallic compound (IMC) is rapidly developed and grown in the steel-liquid interface. It has been usually reported that the IMC was formed by the dissolution of iron in the steel substrate toward the melt and the diffusion of aluminum in an opposite direction.The reaction between the steel and the molten aluminum leads to the formation of Fe-Al intermetallic compounds on the in the surface layer (essentially consisted of orthorhombic Fe2Al5), which could be instrumental in the significant increase in surface hardness. The thickness and the morphology of the interlayer vary with the temperature of the molten aluminum, the interlayer is 'thick' and exhibits a finger-like growth into the steel. The potentiodynamic polarization for the coated samples reveals that the corrosion rate is lowest at an optimum dipping time of 3 min at which the SEM showed that the coat is free of cracks. A critical dipping time is about 3 min at which the corrosion rate is minimum.