Salt Spray (Fog) Corrosion Behavior of Cold-Sprayed Aluminum Amorphous/Nanocrystalline Alloy Coating

Aluminum amorphous alloys gained interest in aerospace, automobile and marine industry due to their high specific strength, better wear and corrosion resistances. In the present work, a gas-atomized aluminum amorphous/nanocrystalline alloy powder was deposited on Al-6061 alloy using cold spray technique. The as-sprayed coatings were heat treated at 573K (just below the glass transition temperature, 593K) to obtain a homogenized microstructure. The corrosion behavior of as-sprayed and heat-treated coatings was evaluated under potentiodynamic polarization (ASTM G59-97) and salt fog (ASTM B117) in NaCl medium. The potentiodynamic polarization study revealed a lowest corrosion rate of Al amorphous/nanocrystalline coating in the heat-treated condition than the as-sprayed condition due to reduction in coating defects like porosity and weaker inter-splat regions. The thickness of reaction layer formed during salt fog corrosion tests is 2 to 3 times lower in the case of cold-sprayed Al amorphous/ nanocrystalline coatings as compared to the Al-6061 substrate. The heat-treated coatings have demonstrated a further reduction in the reaction layer thickness. Pitting corrosion forming a porous oxide layer on the surface of bare substrate while a uniform, dense and thin corroded layer was noticed in as-sprayed and heat-treated coatings.