Exfoliation corrosion testing of aluminium alloys

Abstract

The exfoliation corrosion behaviour of sheet and plate materials of various conventional aluminium and Al–Li alloys has been evaluated using accelerated tests. Results are .compared with atmospheric exposure data published in the literature to assess the applicability of the testing techniques employed. For damage tolerant Al–Li based sheet and plate, the cyclic acidified salt fog (Mastmaasis) test according to ASTM G85, Annex A2 indicated susceptibility to exfoliation corrosion, reproducing the limited outdoor corrosion data for the Al–Li alloys 8090–T81 and 2091–T84 as well as marine exposure results reported for the conventional alloys 2024–T351 and 7075–T7351. Therefore, it appears to be a promising testing technique for predicting the service performance of high strength aluminium alloys. Compared with the ratings determined following the cyclic acidified saltfog tests, the standard Exco test according to ASTM G34 indicated better exfoliation corrosion behaviour of the alloys investigated, except for 8090–T6 sheet and 7075–T7351 plate, which exhibited severe and mild exfoliation respectively. In the modified Exco test suggested by Lee and Lifka, 7075–T7351 panels were susceptible to pitting, whereas the other alloys studied generally suffered more severe exfoliation than in the standard Exco test.