Using friction stir processing to augment corrosion resistance of cold sprayed AA2024/Al₂O₃ composite coatings

In this study, the feasibility of employing friction stir processing (FSP) as a post-spray method to augment the corrosion resistance of cold sprayed (CS) AA2024/Al₂O₃ metal matrix composites (MMCs) was investigated. The effect of the FSP passes on the electrochemical properties of composites in a 3.5 wt.% NaCl solution was studied with cyclic polarization and electrochemical impedance spectroscopy (EIS). Microstructural evolution were employed to analyze and identify the corrosion mechanisms of the CSed and FSPed composites. Results demonstrated an improvement of the corrosion resistance of the AA2024/Al₂O₃ coatings for the low pass number FSP (1 and 2 passes), with the best corrosion performance occurring at 2-pass FSP. The improved surface condition is the main improvement mechansim of corrosion resistance. Whereas for the high pass number FSP (4 passes), the corrosion resistance was reduced due to the combined effect of the improved surface condition and deteriorated interfaces of inside coatings.