轻质铝锂合金1420是替代常规铝合金的理想材料, 在民用和军工领域都具有广阔的市场空间。针对常规试验手段难以实现金属板材在热成形过程中的曲线应变路径，无法获取成形过程中真实应力应变状态的材料力学行为和成形极限等难题，采用十字形试件高温环境双向拉伸的试验方法开展研究。通过光学散斑应变测量和控制技术，实现不同应变速率和不同双曲线应变路径加载的双向拉伸试验，测试板材在超塑温度下应力应变关系和成形极限应变，研究应变速率和变曲线加载路径对塑性变形行为、破裂、微观组织及损伤的影响，基于试验数据和Drucker理论选取正确的屈服模型，对比塑性应变矢量增量与屈服轨迹外法线方向，推导成形极限应力图，建立应变速率相关的屈服准则和本构方程，结合UPFs子程序的仿真分析选取韧性断裂准并预测成形极限。该项目为工业化铝锂合金1420板材复杂型面钣金件超塑成形工艺提供理论依据。

Lightweight Al-Li alloy 1420 is an ideal material to replace conventional Al alloys, and has broad market space in both civil and military fields. In order to overcome the difficulties of conventional test methods in realizing the curve strain path of sheet metal in hot forming process and obtaining the material mechanical behavior and forming limit of the true stress-strain state in forming process, the cruciform biaxial tension testing in high temperature environment is employed for the research. Through optical speckle strain measurement and control technology, biaxial tension tests with different strain rates and different hyperbolic strain paths are conducted to investigate stress-strain relationship and forming limit strain of sheet metal at superplastic temperature, to evaluate the effects of strain rate and variable curve loading paths on plastic deformation behavior, fracture, microstructure and damage, to confirm yield model based on experimental data and Drucker theory, to compare incremental plastic strain vectors with the outward normals to the yield criteria, to deduce the forming limit stress, to establish the yield criterion and constitutive equation related to strain rate, and to select the ductile fracture based on the simulation analysis of UPFs subroutine for the prediction of forming limit. The project provides a theoretical basis for superplastic forming process of complex profile sheet of industrial Al-Li alloy 1420.