Effect of electrolyte layer thickness on atmospheric corrosion of Al–1Si–O·SCu

Abstract

Atmospheric corrosion of Al–1Si–0·5Cu has been studied during the thinning of the electrolyte layer. It was shown that the electrolyte layer behaves as a thin film when it is less than about 1 mm thick. Under an electrolyte containing chloride, the galvanic current passed through a peak as the film thickness diminished and the peak height increased with chlorideion concentration. A decrease in galvanic current with the thinning of the electrolyte layer is characteristic of distilled water films. The change in the galvanic current during thinning revealed that anodic dissolution from the aluminium alloy took place up to the current peak, after which the alloy was passivated by the precipitation of corrosion products in chloride solutions and by the formation of a passivating oxide film in distilled water. The anodic dissolution rate up to the current peak is determined by diffusion controlled oxygen reduction on a palladium counter electrode.