Corrosion Resistance Properties of Sodium Hexametaphosphate (SHMP) Treated Arc Thermal Sprayed Al Coating in Artificial Sea Water

Abstract

Arc thermal spray coating process is popular and convenient to apply on steel substrate to protect steel from corrosion in different environment. However, porosity is common in coating process, and it is important to reduce the porosity for better corrosion resistance properties. Here in our research, Al coating was deposited on mild steel substrate by arc thermal spray process and different concentrations (0.05M, 0.1M, 0.5M) of Sodium Hexametaphosphate (Na6[(PO3)6]) solution was used as pore sealing agent to treat the applied Al coating and their corrosion studies were evaluated in artificial sea water. In this study, the treated samples were dried for 2 days at room temperature. Then kept in the humidity chamber for 6 days (different humidity and same temperature) to deposit uniform oxide films. Different experiments: X-ray diffraction (XRD), field emission-scanning electron microscopy (SEM), electrochemical impedance spectroscopy (EIS) was carried out to study the performance of both Al coating and SHMP treated samples. Electrochemical results show higher impedance value when samples are treated with 0.05M SHMP concentration solution. At the same time, Al coating and samples treated with higher concentration solution show almost same impedance value which is considerably lower comparing with 0.5M SHMP treated samples.