Cathodic Corrosion Protection of Steel with Electroplated Aluminum Alloys

Abstract

Aluminum has excellent corrosion properties due to the formation of a dense oxide layer. This layer spontaneously forms in contact with air and protects the bulk material from further oxidation. Unfortunately, the formation of the natural oxide layer renders pure aluminum passive so that it is not a good candidate for the corrosion protection of a more noble substrate like steel. Therefore, for applications as a corrosion protection layer aluminum should be alloyed with other elements to prevent complete passivation.Electrodeposition is an elegant and cost-efficient method to apply thin coatings on various substrates with complex geometries. The layer properties can be easily controlled by adjusting the deposition parameters (current density, temperature, electrolyte composition). Aluminum cannot be deposited from aqueous electrolytes because of its negative Nernst potential (-1.66 V vs. NHE). Ionic liquids (ILs) are suitable electrolytes for the deposition of reactive metals, such as Al, Nb and Ta. They have a broad electrochemical window (> 3 V) and high electrical conductivity, and show good solubility for many metal salts.This paper will discuss the deposition of binary aluminum alloys from imidazolium-based ILs and their corrosion behaviour. Results from potentiodynamic polarization experiments will be compared with results from salt spray tests and long-term environmental exposure experiments (> 1 year) to assess the suitability of the alloys for cathodic corrosion protection of steel.