Influence of Heat Treatment on the Anisotropic Mechanical Behavior of 2198 Al-Li Alloy Sheet

The application of Al-Li alloy sheet with high specific strength and low fatigue crack growth rate for large thin-walled structural parts such as skin is an important way to reduce the weight of aeroplane. The mechanical behaviors of 2198 Al-Li alloy sheet along the rolling direction (RD), 45 degrees and transverse direction (TD) were tested using unidirectional tension. The effect of heat treatment on its anisotropy was studied. The crystallographic texture, aging precipitate and fracture morphology were analyzed for the micro mechanism. It was found that the new -quenched and naturally aged 2198 Al-Li alloy sheet has similar anisotropy. The alloy along RD has the highest strength, the highest hardening rate and the lowest elongation. The alloy along 45 direction has the lowest strength, the lowest hardening rate and the highest elongation. The main reason is the strong < 112 >{110} texture in the rolled sheet. However, the anisotropy of the 2198 Al-Li alloy sheet after artificial aging has changed significantly due to the inhomogeneous precipitation of the T-1 phase. The strength in 45 degrees direction has been greatly improved to the level as same as that along TD. And the hardening rate is significantly reduced. TD becomes the direction with the largest hardening rate. The anisotropy of elongation and fracture shape does not change. It can be seen that the T-1 phase causes the anisotropic strengthening of the 2198 Al-Li alloy sheet but it has little effect on the anisotropy of fracture behavior.