Effect Of Thermo-mechanical Treatment On The Microstructure And Properties Of AA7085 Aluminum Alloy

The final thermo-mechanical treatment is an effective way to improve the comprehensive mechanical properties of alloy through combining the strain strengthening and phase strengthening in the final stage, which is already applied to Al-Zn-Mg, A1-Zn-Mg-Cu and Al-Mg series alloy. As a new type of aluminum alloy that possesses high strength, fracture toughness and low quenching sensitivity, AA7085 aluminum alloy was developed by increasing Zn/Mg ratio and has promising application in the area of aviation used as thick aluminum alloy plate.In this paper, AA7085 aluminum alloy(Al-7.16Zn- 1.69Mg- 1.59Cu- 0.10Zr) was studied by means of OM, SEM, TEM, tensile test, conductivity test, et al to investigate the effect of homogenization and solution treatment, pre-aging processes, predeformation processes and final aging processes on the aging precipitation and comprehensive mechanical properties. The results show that:① Localized recrystallization and deformation band did not appear within the alloy homogenized at 400 oC for 12 h and 460 oC for 12 h with 70% rolling reduction at 420 oC. The peak hardness was reached after solution treated at 465 oC for 1h and aging treat at 120 oC for 24 h. The tensile strength, yield strength and elongation of peak-aged alloy were 634.2 MPa, 551 MPa and 11.5%, respectively and the TEM microstructure of peak-aged alloy show that a large amount of GP zones and η′phases with 6~10 nm in the size and 1.1×104μm2 of number density appeared within the grain, meanwhile continuous distribution of η phase in the grain boundary, narrow precipitate free zone(PFZ) lead to localized brittle fracture;② After the introduction of 19.3% warm deformation, the tensile strength and elongation of the final aged alloy were improved by 2.6% and decreased by 18.3% respectively compared with the conventional peak aged alloy. TEM results show that dislocations within the warm deformed alloy distributed more uniform and the density of precipitates after the final aging was improved, however, the size of the precipitates and the width of precipitate free zone(PFZ) also increased;③ The distribution uniformity of dislocation was improved and the difference of dislocation density nearby the grain boundary also decreased by introduction of pre-aging at 120 oC for 10 h, which promoted the increase of precipitates density and made the distribution of precipitate more uniform and finer. The tensile strength, yield strength and elongation of the alloy processed by the final thermo-mechanical treatment of 465 oC/1 h+120 oC /10 h+Warm-rolled 20%+120 oC /15 h reached 682.7 MPa, 600.7 MPa and 12.4%, respectively and the strength and elongation improved by 7.7% and 7.8% compared with the conventional peak aged alloy.