Abstract:The variations of corrosion potential, electrochemical impedance and surface morphology of LY12 aluminum alloy with pH of simulated acidic rain solutions were investigated with EIS and SEM. It is found that corrosion potential shifts to less noble value with increasing pH in the solutions of pH lower than 3.1 and shifts to more noble value in the solutions of pH higher than 3.1. In the solutions of pH lower than 3.1,the electrochemical impedance diagram has a capacitive loop at higher frequency and an inductive loop at lower frequency and the magnitude of high frequency loop decreases with decreasing pH and increasing period of immersion. However, in the solutions of pH higher than 3.4 two capacitive loops appear and the magnitude of high frequency loops increases with pH and period of immersion. Observation of SEM shows that the pitting intensity increases with decreasing pH in the range of pH2.0~3.4, no evident pits are observed at pH higher than 3.4. The experiment results were discussed from resistance of oxide film and adsorption processes of anions in simulated acid rain solution.

Key words:  acid rain; aluminum alloy; impedance; SEM