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

Abstract:

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° 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. RD has the highest strength, the highest hardening rate and the lowest elongation. 45° direction has the lowest strength and 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 T₁ phase. The strength in 45° direction has been greatly improved to the level same as TD. And the hardening rate was significantly reduced. TD becomes the direction with the largest hardening rate. The anisotropy of elongation and fracture shape did not change. It can be seen that the T1 phase caused the anisotropic strengthening of the 2198 Al-Li alloy sheet but it has little effect on the anisotropy of fracture behavior. The purpose of this study is to clarify the effect of heat treatment on the anisotropic mechanical behaviors of 2198 Al-Li alloy sheet, to provide a theoretical basis for the development of its plastic forming process and to help to propose new ideas for strengthening and toughening of 2198 Al-Li alloy sheet.

Key words:Al-Li alloy; heat treatment; anisotropy; mechanical properties; microstructure