Abstract: Stress relaxation aging tests were conducted on 2195 Al-Li alloy under a loading stress of 250 MPa, with aging at different temperatures (160, 170 and 180 ℃) for 17 h. The effect of aging temperature on the stress relaxation behavior, mechanical properties, and precipitates of the alloy was investigated by using MTS CMT5205 universal material testing machine and scanning transmission electron microscope (STEM). The results show that the stress relaxation curves exhibit two distinct stages: a stage of decreasing stress relaxation rate followed by a stage of constant stress relaxation rate. As the aging temperature increases, both the initial stress relaxation rate and creep strain are enhanced. Specifically, the creep strain after stress relaxation at 180 ℃ for 17 h is approximately 62% higher than that at 160 ℃, indicating that increasing the aging temperature can accelerate the stress relaxation process and the accumulation of creep strain. Furthermore, the tensile strength of the alloy increase with the rising of aging temperature. Under the aging condition of 180 ℃, the yield strength and tensile strength of the alloy are approximately 20% and 10% higher, respectively, than those at 160 ℃. Meanwhile, the elongation after fracture decreases as the temperature rises, and that under the aging condition of 180 ℃ is about 27.6% lower than that at 160 ℃. At different aging temperatures, the precipitated phase in the alloy is always the T₁ phase. Moreover, as the aging temperature increases, the T₁ phase becomes more dispersedly distributed, with a larger quantity and smaller size, which is beneficial for enhancing the strength of the alloy.

Key words: 2195 Al-Li alloy, aging temperature, stress relaxation, precipitated phase