Corrosion behavior of arc sprayed Al-Zn-Si-RE coatings on mild steel in 3.5 wt% NaCl solution

Al-Zn-Si-RE coating was deposited on mild steel by arc spraying Al-Zn based alloy wire with a high Al content. The corrosion behavior of Al-Zn-Si-RE coating was investigated by corrosion morphologies and electrochemical measurements. The results indicated that Al-Zn-Si-RE coating exhibited homogeneous distributions of elements and a dense homogeneous lamellar microstructure with good scale adhesion. The phases of the coatings are Zn-rich phase, Al-rich phase, Al0.403Zn0.597 and Al9Si phase. Corrosion products had been deposited in the defects, which caused self-sealing behavior and hindered further corrosion. Corrosion products formed on Al-Zn-Si-RE coating surface consisted mainly of simonkolleite [Zn-5(OH)(8)Cl-2 center dot H2O], zinc aluminum hydrotalcites [Zn0.71Al0.29(OH)(2)(CO3)(0.145)center dot xH(2)O, Zn0.70Al0.30(OH)(2)(CO3)(0.15)center dot xH(2)O, Zn6Al2(OH)(16)CO3 center dot 4H(2)O] and aluminum chloride hydroxide hydrate [Al5Cl3(OH)(12)center dot 4H(2)O]. Corrosion products had been deposited in the defects, which caused self-sealing behavior and hindered further corrosion. Furthermore, sacrificial anodic protection played a dominant role during the corrosion process. There were different corrosion stages of the coating in sodium chloride solution, such as pitting-dissolution-redeposition, active dissolution, cathodic protection and physical barriers caused by corrosion products. Finally, schematic model of the protective mechanisms of Al-Zn-Si-RE coating during immersion in sodium chloride solution was given. (C) 2013 Published by Elsevier Ltd.