Abstract: Different pre-deformations (0%-10%) were performed on the naturally aged 2195 aluminum-lithium alloy. The effect of pre-deformation on the microstructure and mechanical properties of the 2195 aluminum-lithium alloy after stress relaxation aging was studied by means of stress relaxation aging test at 180 ℃ under initial loading stress of 250 MPa, mechanical tensile test at room temperature and scanning electron microscope observation. The results show that as the pre-deformation increases, the residual stress after stress relaxation of the alloy generally decreases and then increases. The alloy with 4% pre-deformation has the lowest residual stress, which is more conducive to the accumulation of creep strain. The stress relaxation curve of the alloy without pre-deformation shows four-stage characteristics, while that of the alloy with pre-deformation show two-stage characteristics, which is attributed to the difference in evolution of microstructure of the alloy with or without pre-deformation. The yield strength and tensile strength of the stress relaxation aged alloy increase with the increase of pre-deformation. The elongation after fracture of the stress relaxation aged alloy without pre-deformation is the smallest, while that of the stress relaxation aged alloy with 4% pre-deformation is the largest. The intrinsic reason for the superior comprehensive mechanical properties exhibited by stress relaxation aged alloy with 4% pre-deformation is the uniform distribution of small-sized T₁ strengthening phases within the grains and the relatively narrow precipitation free zones at the grain boundaries. The fracture mechanism of stress relaxation aged alloy without pre-deformation treatment is intergranular fracture, while under 4% and 10% pre-deformation conditions, the fracture mechanism is transgranular ductile fracture and transgranular cleavage fracture, respectively.

Key words: 2195 aluminum-lithium alloy, pre-deformation, stress relaxation aging, precipitate, precipitation free zone