STRESS-CORROSION CRACKING OF AGED AL-CU-MG ALLOYS IN NACL SOLUTION

Pitting potentials and stress corrosion life-times of AlCuMg alloys (mainly 2024 alloy) with various ageing structures have been measured in a de-aerated 1M NaCl solution under conditions of controlled potential. The aged alloy, which has the higher susceptibility to stress-corrosion cracking, showed two pitting potentials corresponding to pitting at the grain boundaries and within the grains. The susceptibility of the alloys to intergranular stress-corrosion cracking occurred at potentials above the pitting potential of the grain boundaries. The intergranular stress-corrosion cracking is caused not by the dissolution of the grain boundary precipitates (S phase) but by the pitting dissolution of the solute-denuded zones along the grain boundaries. Aspects of SCC in the alloys are similar to those in the Al-4%Cu alloy without Mg. © 1979.