Abstract: Microstructure and mechanical behavior of the 7175 aluminum alloy during aging process at 120 ℃ for different time were systematically studied by means of OM, SEM, TEM, Vickers hardness tester and universal tensile testing machine. The results show that after solution treatment and aging, the microstructure of 7175 aluminum alloy is typical fibrous structure, with no obvious recrystallization occurring, and there is no obvious difference in grain morphology and second phase during aging. As the aging time increases, the size of precipitated phase at the grain boundary gradually increases, the particle size of precipitated phase in the grain increases, with the average particle size changing from 5.87 nm to 8.38 nm. When aged at 120 ℃, the hardness of 7175 aluminum alloy reaches the peak at 16 h, and the peak hardness is 196.5 HV. When aged at 120 ℃ for 16 h, the precipitated phase in the grain is much quantity, small and evenly distributed, which effectively improves the hardness of the alloy. At the same time, the yield strength of the alloy increases rapidly from 471 MPa to 490 MPa, when the aging time is 10-16 h, and the change of yield strength tends to be flat when the aging time is greater than 16 h.

Key words: aluminium alloy, aging time, microstructure, precipitated phase, hardness