Effects of aging on mechanical properties and microstructure of multi-directionally forged 7075 aluminum alloy

The effects of natural aging for a long period of time (2.4 years) and as well as artificial aging on the mechanical properties and microstructure of multi-directionally forged (MDFed) 7075 aluminum alloys were systematically investigated. MDFing up to a cumulative strain of 0.7 increased yield strength (+96MPa) and ultimate tensile strength (+94MPa) mainly due to work hardening. The addition of both natural aging at ambient temperature for 7800 ks and artificial aging at 393K for 26 ks of the MDFed samples further increased yield strength (+190MPa) and (+293MPa), respectively. The microstructure and mechanical properties derived by MDFing were stably maintained for a long period of time during natural aging, even while distinct softening took place soon after the commencement of artificial aging. The number of precipitates in the MDFed samples after natural aging was notably smaller compared with that introduced by artificial aging. The achieved strengths after aging were, therefore, almost comparable.