Study on oxidation mechanism of aluminum surface under applied electric field

Abstract

The oxidation behavior of aluminum alloy has a significant impact on its industrial application of aluminum alloy, and studying how aluminum alloy oxidizes in electrolyte solutions is crucial. However, current research predominantly focuses on aluminum anodization at higher voltages and the second-phase corrosion behaviors in halide ion-containing solutions. The research on the formation mechanism of the oxide film on the aluminum surface lacks in-depth analysis, and there is no unified opinion on the method of oxygen invasion into the oxide film. This study establishes an experiment on the corrosion of aluminum alloy in an oxygen-free water environment. By scrutinizing the oxidation behaviors of aluminum surface under conditions of no voltage and low voltage, we investigate the effect of applied electric field on the mode of oxygen invasion in alumina. The findings reveal that under the condition of no external voltage and an alkaline environment, self-passivation products of aluminum undergo a transformation from AlO(OH) to Al(OH)3 as the pH value increases. At a pH of 10, complete transformation into Al(OH)3 occurs. When external voltage is applied, Al(OH)3 is initially formed on the aluminum surface with an increase of potential. As the potential reaches a certain value, the potential energy barrier for the reaction of H and O in OH− is disrupted, leading to the reaction of Al3+ replacing H+ and generating an Al2O3 film, with the current on the membrane surface changes unevenly during this process, resulting in the emergence of a double-layer film structure on the aluminum surface. Therefore, under the electrochemical environment of applying a small current, the film formation process on the surface of aluminum alloy is carried out under the action of OH− heterocracking in water, and the O in the water molecule forms two distinct oxide films with the Al matrix in the form of O2− and OH−.