The role of magnesium segregation in the intergranular stress corrosion cracking of aluminium alloys

Stress corrosion susceptibility of aluminium alloys has been related to the grain boundary segregation of magnesium. In this paper segregation mechanisms are reviewed and examined with reference to both direct and indirect experimental evidence for magnesium segregation. Important parameters considered are the solution heat treatment temperature and the effect of grain boundary precipitation. Evidence to support both equilibrium and non-equilibrium segregation of magnesium is presented. Significantly magnesium segregation promotes hydrogen entry into aluminium but in isolation is not responsible for cracking susceptibility which depends on a critical grain boundary precipitate/hydrogen interaction.