Multi-stage heat treatment of aluminum alloy AA7049

High strength 7xxx series aluminum alloys in the T6 temper are known to be highly susceptible to stress corrosion cracking (SCC). Retrogression and re-aging (RRA) is a heat treatment by which the resistance to SCC is enhanced without losing yield or tensile strength. The influence of multi-stage heat treatment on the properties and microstructure of AA7049 aluminum alloy was investigated. The microstructure of the alloy in various temper conditions was correlated to the electrical conductivity measurements, DSC analysis and TEM observation. The DSC analysis shows that RRA treatments lead to significant change in the microstructure and the resultant RRA precipitate microstructure is significantly different from both the T6 and T73 microstructures and is able to retain the strength of T6 temper while attaining the thermodynamic stability of the T73 temper.