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

摘要

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, Al_(0.403)Zn_(0.597) and Al_9Si 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)_8Cl_2·H_2O], zinc aluminum hydrotalcites [Zn_(0.71)Al_(0.29)(OH)_2(CO_3)_(0.145)·xH_2O, Zn_(0.70)Al_(0.30)(OH)_2(CO_3)_(0.15)·xH_2O, Zn_6Al_2(OH)_(16)CO_3·4H_2O] and aluminum chloride hydroxide hydrate [Al_5Cl_3(OH)_(12)·4H_2O]. 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.