The identification of improved Johnson-Cook constitutive model in a wide range of temperature and its application in predicting FLCs of Al–Mg–Li sheet

For the Al–Mg–Li alloy sheet, a series of uniaxial tensile tests are firstly carried out under different temperatures (25–450 °C) and strain rates (0.00025–0.01 s−1). Then, to describe the flow behavior of the sheet, the improved Johnson-Cook constitutive model (hereinafter abbreviated as ‘improved J-C model’) is employed, in which the coefficients are respectively determined in different temperature ranges of 25–150 °C, 200–300 °C and 350–450 °C. Afterwards, the improved J-C model is introduced into the modified M-K model to predict the FLCs of the sheet, which are finally compared with the experimental FLCs obtained by Nakazima tests. It is found that the improved J-C model can accurately describe the stress-strain relationship for the Al–Mg–Li alloy sheet in a wide temperature range within 25–450 °C and give an accurate prediction of FLCs under 25 °C and 150 °C. However, the predicted FLCs are much lower than the experimental ones when the forming temperature is equal or greater than 250 °C and the reasons that may cause this great difference are analyzed in detail.