Abstract
The influence of retrogression and reaging (RRA) treatments on high strength aluminium alloy 7075 was studied using hardness and tensile testing and by measuring the stress corrosion crack growth rate using double-cantilever-beam specimens. Transmission electron microscopy was used to study the microstructures at both the matrix and the grain boundary. The RRA treatments result in a significant improvement of the stress corrosion resistance of aluminium alloy 7075-T651 without sacrificing its maximum strength. The crack velocity decreases to a level comparable with that of the T73 structure as a result of the optimum RRA treatments. The initial strength decrease during the retrogression treatment is mainly due to a dissolution of small η′ particles. The coarsening of grain boundary precipitates occurs during the retrogression treatment. The steady state crack velocity decreases logarithmically with increase in the volume fraction of grain boundary precipitates.
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