Protection of Aluminium Alloys against Stress Corrosion Cracking in Saline Water by Properly Oriented Anodic Coatings: II. Influence of γ 1 -oxide thickness

Abstract

This work is a continuation of that published as Part I under the same title, in which a method was suggested for protecting Al–2·5 wt-% Mg alloy specimens against SCC in saline waters by using, for the first time, suitably oriented anodic films of γ₁-, and γ₂-A1₂O₃ and their hydrates, prepared under severe acid anodising conditions. In order to optimise the performance of the γ₁-Al₂O₃ =film (that is, one with the oxide grains oriented in a direction perpendicular to thefuture stress direction, this having been shown to give the best protection), a further study has been made, under the same accelerated laboratory stress corrosion conditions. It was shown that the protective properties increased as the oxide thickness decreased. A more detailed study was also made of the influence of the anodic current density, and a photograph is presented showing oxide grain orientation.