Effect of heat treatments on 8090 AlLi alloy pitting susceptibility in sea water

The pitting susceptibility of 8090 Al-Li alloy in sea water, after different heat treatments, was investigated. Free corrosion and electrochemical tests were carried out at 25 degrees C, in quiescent sea water at pH = 8.2 and dissolved oxygen = 6.5 ppm. The microstructure was examined by metallographic microscopy and by X-Ray microdiffractometry, while the corrosion layer was characterized by chemical methods and by Infrared and X-Ray photoelectron spectroscopies. The following was observed: aging treatments lead to a non homogeneous microstructure which increases the average corrosion rate as well as pitting susceptibility; heat treatments do not affect the average passive film composition; in all examined states, AI-Li alloy 8090 is subject to localized corrosion which takes place preferentially at the grain boundaries.