Mechanical properties, corrosion behaviors and microstructures of 7075 aluminium alloy with various aging treatments

The influence of two novel aging treatments, T6I6 (130 °C, 80 min + 65 °C, 240 h+130 °C, 18 h) and high-temperature pre-precipitation(HTPP) aging (445 °C, 30 min+120 °C, 24 h) on the tensile properties, intergranular corrosion, exfoliation corrosion behaviors and microstructures of 7075 Al alloy was studied, which were compared with the T6, T73 and RRA treatments. Fine η′ precipitate with high density was obtained in the alloy with the T6 and RRA treatments. The η′ precipitate density in the HTPP aged alloy is decreased due to the formation of coarse particles during the pre-precipitation process at high temperature of 445 °C. The 7075-T6I6 alloy possesses higher precipitate density and whole precipitate volume fraction within the grain than the 7075-T73 alloy, and its whole precipitate volume fraction is even greater than that of the 7075-T6 alloy. Compared with T6 treatment, the RRA, T73, T6I6 and HTPP aging treatments cause the discontinuous distribution of the η precipitates at the grain boundary, which decreases the intergranular corrosion and exfoliation corrosion susceptibility of the alloy. Meanwhile, the T6I6 and RRA treatments can keep the high strength of the 7075 Al alloy, but the studied HTPP aging and T73 treatments lower its strength.