Exfoliation corrosion and electrochemical impedance spectroscopy of an Al-Li alloy in EXCO solution

摘要

The exfoliation corrosion and electrochemical impedance spectroscopy (EIS) of an Al-2.8%Cu-1.5%Li-0.3%Mg-0.3%Zn-0.3%Mn-0.15%Zr alloy with various aging states in EXCO solution were investigated. The equilibrium precipitates at grain boundaries are anodic to the alloy base at their adjacent periphery. With prolonging aging time, the amount and the size of the equilibrium precipitates at grain boundaries are increased, resulting in an enhanced susceptibility to exfoliation corrosion. At the beginning of immersion in EXCO solution, the EIS plot of the alloys is composed of a capacitive arc in the high frequency range and an inductive loop in the low frequency range. As immersion time is increased, two capacitive arcs appear in the high-mediate and mediate- low frequency ranges respectively and the appearance time of two capacitive arcs could be an indication of the speed of localized corrosion development in EXCO solution. The longer appearance time of two capacitive arcs of the under-aged alloy indicates its slower localized corrosion development.