An optimized constitutive model and microstructure characterization of a homogenized Al-Cu-Li alloy during hot deformation

The quenching expansion tests in the temperature range 350-500 degrees C and isothermal compression tests in the range 350-500 degrees C & 0.01-10 s-1 of a homogenized Al-Cu-Li alloy were conducted to investigate the flow behavior and thermal expansion behavior. The corresponding microstructures of the tested specimens were characterized by back-scattered electron-scanning electron microscope (BSE-SEM), electron back-scattered diffraction (EBSD) and transmission electron microscope (TEM). Coarse secondary phases including Al2CuLi (T1), Al2(Cu-Ag)(Li-Mg) (omega), Al2Cu (theta), Al2CuMg (S) dissolve with increasing temperature, which is likely to increase the coefficient of thermal expansion. The temperature rising induced by deformation heat varies from 2.29 degrees C to 38.32 degrees C with increasing strain rate and decreasing temperature. Three different constitutive models were calculated, evaluated and optimized, based on which, the two-step optimized Johnson-Cook model showed the highest precision. At the temperature <= 400 degrees C, the existences of undeformable coarse phases (especially T1 or omega phase) promote particle stimulated nucleation (PSN), which pronouncedly increases the volume fraction of dynamic recrystallization (DRX) and decreases the flow stress. At temperature of 450 degrees C, most of undeformable coarse phases dissolved, cutting-off mechanism of S and theta phase was observed, which is no longer beneficial to PSN, and CDRX becomes the main DRX mechanism. (c) 2022 Elsevier B.V. All rights reserved.