Post-treatment of 85Zn-15Al coating deposited by arc thermal spray process and its corrosion characteristics in 3.5 wt.% NaCl solution

Abstract

Al and Zn are used to protect the steel structures from corrosion. In the present studies, 85Zn-15Al alloy wires has been used for the deposition of coating by are thermal spray process. Moreover, this process of coating exhibited severe defects formation, therefore, this coating was post-treated with different concentrations i.e. 0.05, 0.1 and 0.5M sodium hexa meta phosphate (Na| (POs)]: SHIMP) to fill to defects of deposited coatings and accessed their corrosion resistance in 3.5 wt.% NaCI solution with exposure periods. After the treatment, the porosity of the coating reduced significantly by formation of composite oxide films onto the coating surface. Initially, 0.5 M SHIMP treated coating exhibited highest in total impedance due to significant reduction of porosity but once the exposure periods are extended, the composite oxides are dissolved, thus, total impedance is decreased. Alternatively, 0.05 M SHMP was not able to fill the defects of coating completely, therefore, it also exhibited lower in impedance. In the case of 0.1 M SHIMP, the total impedance with exposure periods is increased and found to be highest due filling of porosity and formation of stable corrosion products.