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

Abstract

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 [Zn5(OH)8Cl2·H2O], zinc aluminum hydrotalcites [Zn0.71Al0.29(OH)2(CO3)0.145·xH2O, Zn0.70Al0.30(OH)2(CO3)0.15·xH2O, Zn6Al2(OH)16CO3·4H2O] and aluminum chloride hydroxide hydrate [Al5Cl3(OH)12·4H2O]. 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.