Effect of anodizing temperature and organic acid addition on the structure and corrosion resistance of anodic aluminum oxide films

Abstract

Anodic aluminum oxide films, industrially produced by anodizing aluminum alloys under the galvanostatic mode at a relatively low temperature of 20°C (electrolyte bath temperature), present the reliable anticorrosive effect for numerous applications. For fabricating anodic aluminum oxide films with the promising corrosion resistance as well as high growth rate in a wide temperature range, the effect of anodizing temperatures on the structure and growth mechanism of anodic aluminum oxide films was investigated. As the temperature increases up to 30°C, the stress-driven breakdown of porous-type anodic aluminum oxide layers induced by their thinner pore walls was estimated. This phenomenon is interpreted by an increase of electronic current and thus a strong scour effect of O2 bubbles on the porous-type anodic aluminum oxide layers. Moreover, with the addition of composite organic acid into the sulfuric acid-based electrolyte solution, the anions (C6H5O73−,C4H4O62−) that incorporated into the anodic oxide contribute to lowering the electronic current and thus suppressing the formation of oxygen bubbles, resulting in a thicker barrier-type anodic aluminum oxide layer. This is assumed to be responsible for the enhanced corrosion resistance of anodic aluminum oxide films prepared at 30°C with 50 g/L organic acid addition.