Al-Mg-Mn alloy coating on steel with superior corrosion behavior

Hot-dip coating of steel sheets by a novel Al-Mg-Mn alloy, characterization and corrosion property evaluation of the coatings have been described in this article. Morphology and composition of coatings were investigated using SEM and EDS. GDOES sputtering was used for elemental depth profiling of the coating. Microstructural characterization has revealed that the coating consists of broadly two layers; soft Al-Mg-Mn alloy layer on the top and finger-like hard Fe-Al intermetallic layer underneath i.e. towards the steel substrate. The phase analysis carried out using XRD confirms that Fe-Al intermetallic layer consists of two intermetallic layers: outer thin FeAl3 with Mn-rich layer and inner tongue-like thick Fe2Al5 layer. The growth of the intermetallic layers was found to be governed by volume diffusion, which followed a parabolic rate law. Potentiodynamic polarization measurements in 3.5 wt.% NaCl solution show that the coating exhibits superior sacrificial properties compared to other aluminized steels which can be attributed to the presence of magnesium in the coating. Corrosion resistance of the coating was found to be six times better than that of galvanized (GI) coating with comparable sacrificial property.