Electrochemical characterization of the corrosion resistance of aluminum-lithium alloys

Abstract

The corrosion resistance of several promising new aluminum-lithium alloys has been characterized using electrochemical noise and impedance spectroscopy measurements. Corrosion of ALCAN 8090-T8 was compared with that of its conventional counterpart, aluminum alloy AA2024-T3. ALCAN and Kaiser 2090-T8 were compared with AA7075-T6. The samples were prepared so that they were exposed on only one surface for each of the three orthogonal planes that are related to the rolling direction of the sheet. The measurements were made for each of the alloys while exposed to a synthetic marine environment. An automatic statistical analysis performed on electrochemical spectroscopy (EIS) data permitted the establishment of the relationship between the measured polarization resistance and the corrosion resistance of aluminum alloys. Detection of any difference in intergranular corrosion (exfoliation) as a function of orientation has been accomplished by simultaneous analysis of the EIS data for the deviation from the semicircle of a Nyquist representation. The conclusions from the electrochemical noise and EIS data analyses were confirmed by optical and scanning electron microscopy examination and compared to results obtained during the exposure of the same alloys to seawater.