Salt film formation during corrosion of aluminum

High-purity aluminium rods with 5 mm² cross-section were imbedded in epoxy resin and corroded from one end. Depths of these artificial pits were 0–1 mm. With concentrated aluminum chloride solution, > 80% of saturation, and high anodic potentials, it was possible to obtain a continuous salt film on the corroding surface and electropolishing. Current density under these conditions is mass transport controlled and increases with convective flow. At low salt concentrations and potentials the convection induced by simultaneous hydrogen evolution prevents continuous salt film formation.