The anodizing process of aluminum and its alloys: A historical and electrochemical approach

Abstract

Al and its alloys are found in several industrial applications. However, like most metals, this material is not immune to corrosion, being necessary to be protected against corrosion. One of the methods most commonly employed to improve the corrosion resistance of Al alloys is the anodizing process, which consists of thickening of the natural oxide (Al2O3) presents in Al through anodic oxidation. The anodizing process is accomplished by immersion of the Al alloy into an acid bath and passing an electric current through it. This process produces two layers: a barrier layer thicker than the natural oxide and a layer with regular arrangement of nanopores (porous layer). This duplex structure forms the anodized layer with a large specific surface area. With the advent of nanotechnology, this layer has been applied in other areas due to its low cost, stability, absence of toxicity, and biocompatibility. In this context, this paper addresses a historical and electrochemical review of the anodizing process of Al and its alloys, presenting the main events that culminated in the development of the current processes and the understanding of the relationship between the chemical reactions and the mechanisms that occur during nucleation and development of the oxide layer.