Anodic Layer Growth on 1050 and 2024 Aluminium Alloys in Presence of Etidronic Acid : Changes in Morphology and Structure

Abstract

Anodic layer growth during anodization is a well-known phenomenon, used to increase the thickness of the natural layer present on the surface of metals for corrosion resistance. In the case of pure aluminum and its alloys, the porous oxide layer leading to a regular structures with nanopores arrangements, which provides interesting corrosion resistance and mechanical performances. The most frequent electrolytes (sulfuric, oxalid or phosphoric acid) induce low current/voltage at direct or pulsed modes to elaborate the oxide layer according to the different electrochemical windows. If the anodic oxide film elaborated in the first moment is soluble into the electrolyte, a porous structure take place with pores oriented perpendicular to the metal surface. The formation of the barrier layer occurs at the interface between the metal and the porous layer, but is thin enough to allow a continuous ionic flow which lead to a continuous film growth.The present work deals with aluminum anodization in etidronic acid (HEDP) at very high voltages for aluminum 1050 and 2024 alloys. It appears that the oxide layer growth, studied by XRD and SEM pictures of cross section obtained by ionic polishing, differs clearly for the reason that pores formations not only starts from the barrier layer, but also at different locations such as the oxide layer/electrolyte interface. The final result consist in an oxide layer with excellent functional properties.