The effect of various anodic coatings on the creep behavior of a strong aluminum alloy

Abstract

Comparative creep tests were conducted on a strong creep-resistant aluminum alloy, uncoated and coated with thin, medium and thick anodic layers. None of the various anodic coatings exhibited any strengthening effect similar to that which strong adherent coatings or inherent surface layers have been observed to have on room or elevated temperature plastic deformation of annealed monocrystalline or polycrystalline metals and alloys. This lack of strengthening effect can be explained by the fact that coherent precipitates effectively impeded the motion of dislocations throughout the bulk of the creep-resistant alloy; thus the anodic coatings did not have the impact which strong surface layers and coatings have on annealed materials where theee layers or coatings are the main direct or indirect obstacle to the motion of dislocations and their egress to the surface. Cracks in the medium and heavy coatings served as surface stress raisers, thus resulting in faster secondary creep rates compared with those of the uncoated and thinly coated specimens.