Mechanical properties, microstructures and process windows of 2195 Al–Li alloy processed by cryogenic deformation and heat treatment

The mechanical properties and microstructure of 2195 Al–Li alloy sheets processed via three cryogenic deformation and heat treatment paths were systematically investigated. The mechanical properties of the specimens after processing were tested through room temperature (RT) uniaxial tensile, and the microstructures were characterized by electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and observation on metallographic (OM). The critical strain was determined to be 8 % for the specimens by deformation before solution treatment (Process A). The optimized mechanical properties were achieved by improving the strain and aging process matching for the specimens by deformation after solution treatment (Process B). The optimized strain matchings were obtained for the specimens by deformation before and after solution treatment (Process C). The ultimate tensile strength (UTS) increases as strain decreases before solution treatment and increases as strain increases after that. Comparing the three processes under 10 % total strain, Process B has the highest UTS with 574 MPa. For Process B, the appropriate aging parameters are 170°C-72 h for strains of 0, 5 %, 10 %, and 155°C-32 h for 15 %. The microstructure results indicate that the optimal strain and aging process window should ensure the volume fraction (fv) of the T1 phase to be between 4.0 % and 8.2 %. The appropriate strengthening precipitate type is either a mixture of the T1 and θ′ phases or just the T1 phase. This study provides certain theoretical guidance for the formulation of process parameters for cryogenic deformation and heat treatment of Al–Li alloys.