Study of cathodic reactions in defects of thermal spray aluminium coatings on steel in artificial seawater

Electrochemical and surface characterization techniques were used to study the corrosion protection provided by Thermal Spray Aluminium (TSA) coatings on carbon steel substrates with and without defects in artificial seawater. Results showed that the presence of defects accelerates the formation of a protective corrosion product layer on the TSA coating. Voltammetry and Electrochemical Impedance Spectroscopy (EIS) revealed that both calcareous deposits and aluminium corrosion products hindered diffusion of dissolved O2. Analysis of corrosion products by SEM-EDX, μ-Raman spectroscopy and XRD revealed Al oxides/hydroxides and hydrotalcite on top of TSA coating and a bilayer of calcareous deposits on the defect area.