ELECTROCHEMICAL CHARACTERIZATION OF THE CORROSION-RESISTANCE OF ALUMINUM-LITHIUM ALLOYS

The corrosion resistance of several promising new aluminum-lithium all oys has been characterized using electrochemical noise and impedance s pectroscopy 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 pre pared so that they were exposed on only one surface for each of the th ree orthogonal planes that are related to the rolling direction of the sheet. The measurements were made for each of the alloys while expose d to a synthetic marine environment. An automatic statistical analysis performed on electrochemical spectroscopy (EIS) data permitted the es tablishment of the relationship between the measured polarization resi stance and the corrosion resistance of aluminum alloys. Detection of a ny difference in intergranular corrosion (exfoliation) as a function o f orientation has been accomplished by simultaneous analysis of the EI S data for the deviation from the semicircle of a Nyquist representati on. The conclusions from the electrochemical noise and EIS data analys es were confirmed by optical and scanning electron microscopy examinat ion and compared to results obtained during the exposure of the same a lloys to seawater.