Comparison of the Corrosion Behavior of Cold Sprayed and Thermal Sprayed Al Coatings in Seawater

Aluminum coatings are extensively used for protection of steel structures in marine environment because of their corrosion resistance as well as the cathodic protection effect to steel. In this paper, Al coatings were deposited on Q235 carbon steel substrates by Cold Spray and traditional Arc Spray techniques respectively, in order to study their marine corrosion and protection behavior.

Seawater immersion test and electrochemical measurements including open-circuit potential, polarization and impedance measurement were carried out to understand the marine corrosion performance and protection mechanism of Cold Sprayed Al coating, compared with Arc Sprayed coating and Al bulk metal. Their microstructures were observed by Scanning Electron Microscopy(SEM), Optical Microscopy(OM) and Scanning Acoustic Microscopy(SAM) characterization before and after the immersion corrosion.

The corrosion results revealed that cold sprayed Al coatings have higher corrosion resistance and can offer better protection effect than arc sprayed Al coatings in seawater. The SEM and SAM observations showed that thermal sprayed Al coatings have relative looser and defective microstructures which make it easier for penetration of medium into coating interior and lead to localized corrosion. The cold-sprayed Al coating has the similar corrosion behavior with the bulk aluminum in seawater, which can not only provide effective cathodic protection to substrate for their negative potential, but also prevent further seawater corrosion effectively with steady corrosion product due to its self-passivation. The corrosion process of cold sprayed Al coating in seawater can be understand to (1) Product film formation period, (2) Local film invalidation period and (3) Coating localized corrosion period.