Effect of Two Different Immersion Periods and Surface Oxide Film Formation Upon the Corrosion Behavior of Pure Al and Zn Samples in NaCl Solution

摘要

The corrosion behavior in some metallic materials can be changed through active to passive due to surface oxide film formation. For instance, pure Aluminum and Zinc present spontaneously oxide film formation at the sample surface when immersed in the corrosive environment. It is suggested that the corrosion performance of these passive materials involve simultaneous chemical dissolution and formation of the oxide at the oxide/environment and oxide/metal interfaces. The aim of the present work is to investigate the effect of oxide films upon the electrochemical corrosion response for both pure metals, presenting different grain morphologies, immersed in two different periods. The specimens were immersed in a 3% NaCl solution and monitored for two different periods: 7 days (about 168 hours) and 15 days (about 360 hours). The electrochemical impedance spectroscopy and polarization methods were performed after the immersion period. Specimens were also examined by scanning electron microscopy to reveal the oxide film. It was found that Zn and Al samples were, respectively, corroded by general and pitting dissolution. Measurements of the solution pH values are also discussed. It was found, that the electrochemical resistance decreases with increasing immersion time along a certain initial period, increasing again after that.