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

• Published in: Electrochimica acta Vol. 115; pp. 644 - 656
• Main Authors: Jiang, Qiong, Miao, Qiang, Liang, Wen-ping, Ying, Feng, Tong, Fei, Xu, Yi, Ren, Bei-lei, Yao, Zheng-jun, Zhang, Ping-ze
• Format: Journal Article
• Language: English
• Published: 01.01.2014
• Subjects: Alloy steels; Aluminum; Aluminum base alloys; Coatings; Corrosion; Corrosion products; Deposition; Mathematical models; Phases
• ISSN: 0013-4686
• DOI: 10.1016/j.electacta.2013.09.156

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 sub(0.403)Zn sub(0.597) and Al sub(9)Si 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 sub(5)(OH) sub(8)Cl sub(2)[middot]H sub(2)O], zinc aluminum hydrotalcites [Zn sub(0.71)Al sub(0.29)(OH) sub(2)(CO sub(3)) sub(0.145)[middot]xH sub(2) O, Zn sub(0.70)Al sub(0.30)(OH) sub(2)(CO sub(3)) sub(0.15)[middot]xH sub(2)O, Zn sub(6)Al sub(2)(OH) sub( 16)CO sub(3)[middot]4H sub(2)O] and aluminum chloride hydroxide hydrate [Al sub(5)Cl sub(3)(OH) sub(12)[middot]4H sub(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.