The effect of solution aggressiveness on the corrosion-induced degradation mechanism of Al-Cu-Li 2198 alloy

Investigation on the corrosion-induced degradation mechanisms of Al-Cu-Li 2198 alloy is critical for the aircraft maintenance protocol. This article aims to identify the corrosion-induced degradation mechanisms of aluminum alloy 2198-T8; three (3) different accelerated corrosion tests with electrolytes of various aggressiveness, namely sodium chloride (NaCl), Harisson's and exfoliation corrosion (EXCO) solution were exploited. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and immersion tests were used in this context. The EIS analyses revealed that exploitation of different electrolytes essentially affects corrosion-degradation mechanism. Intergranular corrosion attack was found to dominate in EXCO solution, while transgranular attack was evident in both, 3.5 wt% NaCl and Harrison's solutions. Severe localized corrosion in Harrison's solution led to higher degradation of elongation at fracture (Af) throughout immersion duration; EXCO exposure led to higher corrosion attack rate for the short exposure times (<= 6 h). Correlation between the different electrolytes regarding tensile ductility decrease was attempted through a linear coefficient for the initial, small exposure times; 1-hour EXCO exposure of AA2198-T8 was found to be equivalent to 107 h exposure to 3.5 wt% NaCl solution, while the respective correlation with Harrison's solution showed that 1-hour EXCO exposure is equivalent to 27 h Harrison exposure.