Influence of retrogression temperature and time on the mechanical properties and exfoliation corrosion behavior of aluminium alloy AA7150

The tensile properties, exfoliation corrosion behavior and microstructures of the retrogression and re-aging (RRA) treated aluminum (Al) alloy AA7150 were studied. AA7150 was retrogressed at different temperatures (175 °C, 185 °C and 195 °C) for various times. It is found that as the hardness of the retrogressed AA7150 approaches the near-peak condition, the corresponding RRA treated AA7150 possesses good exfoliation corrosion resistance without strength loss. By retrogressing at 175 °C, the retrogression time can be extended to 3 h, the RRA treated AA7150 possesses a strength as high as that of conventional AA7150-T6, and its exfoliation corrosion resistance is in the vicinity to that of AA7150-T73. This enhanced exfoliation corrosion resistance was associated with the more separated η precipitates at the grain boundary. AA7150-T6 is mainly strengthened by fine GP zones with high number density, while the intra-grain micro-structure of AA7150-RRA retrogressed at 175 °C for 3 h is characterized by relatively coarse η′ precipitates.