Influence of overaging on the mechanical properties and stress corrosion cracking behaviour of 7075 T6 aluminium alloy.

The effect of a reageing heat treatment following a T6 temper on the mechanical properties and the stress corrosion cracking behaviour (SCC) on the EN AW 7075 aluminium alloy is studied. The reageing time was 27 hours for all the temperatures used: 147,152 and 163degreesC; this last temperature is indicated in the MIL-H-6088F, standard to obtain the T73 temper from the T6 temper. The mechanical properties and the stress corrosion behaviour are evaluated and, compared with the T6 and T73 tempers. The evolution of the microstructure is analysed with transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) techniques, and related with the properties. The reageing following to the T6 temper made a more stable structure higher the temperature, and, consequently, lowing the stress corrosion susceptibility. For temperatures lower than 147degreesC, this diminution of stress corrosion susceptibility occurs without reducing the mechanical properties. So, the 147degreesC reageing heat treatment has better stress corrosion behaviour than the T6 temper, with similar mechanical properties. By the other hand, the stress corrosion susceptibility achieved with the 152degreesC reageing is slightly worse than the T73 one, but their mechanical properties are better.