The effect of retrogression and reaging on the resistance to stress corrosion of an 8090 type aluminium alloy

The influence of retrogression and reaging (RR) treatment on the resistance to stress—corrosion cracking of a commercial AlLi 8090 alloy was investigated. The retrogression was performed for various times at temperatures in the range 200–260°C. The reaging treatment was carried out at 170°C. Stress corrosion tests were performed using C-ring specimens and by alternate immersion. Changes in the microstructure of the material near the grain boundaries were studied by transmission electron microscopy. It was shown that RR treatment substantially improved the resistance to SCC of the alloy. As with 7000 type Al alloys, the RR treatment brings about the dissipation of dislocations; the greater the extent of dissipation of dislocations, the greater the resistance to SCC. Another factor which, possibly, affects the sensitivity to stress—corrosion in this alloy is the presence of the δ′ precipitates near the grain boundaries. The best results on SCC resistance were obtained for retrogression performed for 30 min at 260°C followed by reaging. For such treatment a zone completely free of δ′ precipitates was developed near the grain boundaries.