Superior mechanical properties and microstructual evolution of 2195-T6 Al-Li alloys at a high strain rate

In this study, AA2195-T6 exhibited a superior plasticity while maintaining a high strength under high strain rate deformation. Superior total elongation (17%) was achieved at 2000 s-1, reflecting a 79% increase relative to that at 0.001 s-1. Ultimate tensile strength was 610 MPa observed at 2000 s-1, which was 602 MPa at 0.001 s-1. Meanwhile, an abnormal work hardening effect with a local maximum of 5740 MPa was also observed at 2000 s1. As the strain rate increased, the mechanism of fracture changed from brittle fracture to a combination of ductile fracture and intergranular delamination fracture. Microstructural evolution and the interaction between the dislocations and the T1 phase (Al2CuLi) were explored. The dislocation density around the T1 phase was quantified. The dislocation density around the T1 phase was 1.4 x 1017 m-2 at 0.001 s-1, which was much higher than that 1.6 x 1016 m-2 at 2000 s-1. It caused a markedly uneven dislocation distribution and high stress concentration around the T1 phase at 0.001 s-1. At 2000 s-1, a process ranging from stress concentration to stress release occurred around the T1 phase, which maintained the movement of dislocations and improved the plasticity of AA2915-T6. The ultrahigh work hardening effect at 2000 s-1 was attributed to the peak interaction between the dislocations and the T1 phase, which caused the T1 phase to appear bowed. This study renders feasible the direct formation of aerospace components at the highest strength of the thermal treatment (T6 temper).