Corrosion Behavior and Microstructure of the Al-Al2O3 Coatings Produced by Low Pressure Cold Spraying

Low Pressure Cold Spray was used to produce Al based powder coatings on low carbon steel, 2024 Al alloy and AZ31 Magnezium alloy  substrates. The corrosion protection provided by these coatings were evaluated by electrochemical measurements (polarization curves, electrochemical impedance spectroscopy) in 5% NaCl electrolyte, and accelerated  salt spray  tests. The microstructures, mechanical properties, electrochemical and salt spray (fog) corrosion behavior of the Al based coatings were investigated comparing with pure Al. Electrochemical measurements showed that cold sprayed Al-Al₂O₃ coatings  exhibit: (i) corrosion potential of the Al coating is similar to solid Al, (ii) corrosion potential of the Al-Al₂O₃ coatings is comparable as Al, and (iii) change of  polarization processes occurs for Al-Al₂O₃ coatings. The accelerated salt spray tests revealed dependence of corrosion resistance on Al₂O₃ content. The electrochemical corrosion mechanisms of the coatings and microstructure were discussed. The coatings show a typical layered cold sprayed material structure.