COMPARATIVE INVESTIGATION OF THE EFFECT OF CHLORIDE IONS CONCENTRATION ON THE ELECTROCHEMICAL BEHAVIOUR OF 2024-T3 AND 7050-T7451 ALUMINIUM ALLOYS AND ITS RELATION WITH MICROSTRUCUTRAL CHARACTERIZATION

摘要

High-strength Al alloys (AA) used in the aerospace industry have a complex microstructure, which plays a key role in their corrosion resistance. Particularly, it is of foremost importance the electrochemical behavior of coarse intermetallics (IMs) present in their microstructure, and their galvanic interaction with the bulk matrix. In the literature, the corrosion studies of Al alloys in chloride solutions have been frequently performed in concentrated solutions. In the present work, the electrochemical behavior of high strength Al alloys, 2024-T3 and 7050-T7451, in solutions containing chloride in the concentration range from 10 to 500 mM was investigated and compared. The experimental techniques employed were: open circuit potential (OCP), anodic polarization curves, electrochemical impedance spectroscopy (EIS) and microstructural characterization by SEM/EDS. For both alloys, OCP results showed a logarithmic dependence on chloride concentration, with the 2024-T3 alloy always presenting nobler values. On the other hand, anodic polarization curves presented no defined passive region and showed depolarization with increasing chloride concentration. EIS experiments showed different responses for the two alloys. While a capacitive response was observed for the 2024-T3 alloy, a low frequency inductive loop was defined for the 7050-T7451 samples. Some hypotheses are presented which may explain these different impedance behaviors.