Corrosion of an Advanced Al-Cu-Li Alloy for Aerospace Applications

This paper discusses two Al-Cu alloys for aerospace applications, one which has a high concentration (>1.8 wt.%) of Li. These alloys are AA2024-T3 (Al-Cu) and AA2099-T8E77 (Al-Cu-Li) and are both in the plate format. Anodic polarisation and immersion in a 3.5 wt.% NaCl solution have been carried out and a comparison of the corrosion mechanisms have been made. Both alloys showed extensive corrosion over the surface, AA2024-T3, however, had areas of pitting that had joined together forming large corrosion regions, whereas AA2099-T8E77 had numerous corrosion pits that had not merged. The pits on AA2099-T8E77 propagated to a depth 120 gm whereas on AA2024-T3 the maximum depth was similar to 85 mu m. Intergranular and transgranular corrosion was also observed on the AA2024-T3 alloy following anodic polarisation. AA2099-T8E77 had reduced corrosion resistance with regards to E-pit-E-corr. values. For both alloys, dissolution of matrix material surrounding the Cu-rich intermetallic particles was observed, highlighting the particles' cathodic nature.