Behavior of Alloying Elements during anodizing of Magnesium Alloys

摘要

Recent work has shown the feasibility of forming uniform barrier-type anodic films on magnesium alloys by use of a glycerol-based electrolyte containing fluoride ions. The films contain significant amounts of oxide and fluoride species, as well as species derived from the alloy substrate. The formation of such films appears to give rise to the enrichment of certain alloy elements in an alloy layer located immediately beneath the anodic film. The enrichment process is possibly similar to that occurs during the formation of anodic films on aluminium alloys, which has been extensively studied. The enrichment of aluminium alloys can significantly affect the composition of the film and the film morphology. Further, enrichment occurs not only beneath anodic films of aluminium alloys but also beneath other types of film on the alloys, such as ones generated by etching and electropolishing, and the enrichment can subsequently affect the corrosion potential and behaviour of the alloy during conversion treatments. In contrast to aluminium alloys, enrichment of magnesium alloys has received comparatively little attention.In the present work, the enrichment of alloying elements due to formation of anodic films on magnesium alloys is examined by glow discharge optical emission spectroscopy and ion beam analysis. The study focuses on the thickness of the enriched alloy layers, the rate of accumulation of the enriching element, and the behaviour of the alloying element once it is oxidized and incorporated into the anodic film.