Influence of aging on corrosion resistance and structure of the passive film formed on Al−2Li binary alloys

Al−Li alloys have the advantage of low density, high strength and toughness, and low corrosion fatigue rate. This combination of properties has led to their use in aerospace. Al₃Li（δ′）phase is one of main strengthening phases of Al−Li alloys. The higher chemical reactivity of Li clearly influences its corrosion behavior. In order to explain the effect of δ′ phase in the Al−Li alloy electrochemical corrosion process, an Al−2Li binary alloy was prepared by vacuum melting. Aging treatment of Al−2Li alloy at 180 ℃ followed by solution treatment were carried out. A potentiodynamic polarization plot of the alloy was tested in a 3.5% (mass fraction) NaCl solution. Phase composition of all samples was determined by X-ray diffraction (XRD). Passive film was formed on this alloy at a passivation potential of −0.85 V vs SCE. Corrosion resistance of the passive film on the surface of the Al−2Li binary alloy was tested by electrochemical impedance spectroscopy (EIS). Structure of the passive film was analyzed by potentiostatic polarization and the Mott−Schottky (M−S) approach. Results show that the corrosion potentials of Al−2Li alloy initially move toward the positive, then toward negative, along with increasing aging time. EIS spectra of the passive films on the solution treatment and aging have two capacitive impedance arcs; the corrosion mechanism is not changed by the aging treatment. Corrosion resistance of the passive film is, in order from high to low, aged 20 h > solution treatment > aged 40 h > aged 1 h, and is related to the compactness and acceptor concentration of the passive film.