Study on Thermo-Mechanical Treatment for Strength-Toughness Regulation in Aerospace Al-Li Alloys

Abstract

Aluminum-lithium (Al-Li) alloys have emerged as critical structural materials for airframe lightweighting, fuel efficiency improvement, and flight performance enhancement due to their exceptional combination of low density, high strength, and superior toughness. Thermo-mechanical treatment plays a pivotal role in tailoring the service performance of Al-Li alloy components, with cold deformation being a key factor determining their strength-toughness balance. This study systematically investigates the effects of cold rolling reduction (0%, 1%, 3%, 5%) and artificial aging (160°C/x h) on the microstructure and mechanical properties of an Al-Li alloy through cold-rolling thermo-mechanical treatment experiments. The results demonstrate that cold rolling significantly accelerates aging kinetics, suppresses the competitive precipitation of δ′ and σ phases during aging, and promotes T1 phase nucleation. With increasing cold rolling reduction, the precipitation density of T1 phase increases while its size decreases, accompanied by a gradual transition from transgranular fracture to intergranular fracture. The optimal strength-toughness combination is achieved in the Al-Li alloy subjected to 1% cold rolling followed by aging at 160°C for 20-24 h, exhibiting tensile strength of 594 MPa, yield strength of 552 MPa, and elongation of 7.2%.