Evaluation of aluminum coatings in simulated marine environment

Corrosion of steel in marine environment induces great financial losses. One of the methods used to reduce the corrosion of steel is surface coating by appropriate materials. In this study, steel has been coated with aluminum by using the electric arc spray process. Samples were then submitted to heat treatments in air between 200 and 600 °C. They were then submitted to corrosion tests by immersion in synthetic sea-water (3.5% NaCl at pH = 8). The aluminum coatings are characterized by scanning electron microscopy (SEM) coupled with energy dispersive analysis (EDS) and X-ray diffraction (XRD). XRD and EDS results indicated that the coatings consist essentially of pure Al. An amorphous phase of Al2O3 was detected on the surface of the samples treated above 200 °C. SEM investigations combined to EDS analysis of the interfaces revealed the formation of two kinds of alloys: an FeAl in the range 200–400 °C and an Fe2Al5 above 400 °C. Dissolution tests showed that iron dissolution, through the coating, decreases with increasing annealing temperature.