A modified Johnson-Cook model of as-quenched AA2219 considering negative to positive strain rate sensitivities over a wide temperature range

In order to establish the constitutive model to predict deformation behavior during quenching process, uniaxial tension behaviors of an as-quenched AA2219 sheet were investigated over a wide temperature range (298-773K) at different strain rates (0.001-1s-1) in quasi-static regime. The experimental results show that the flow stress is closely related to temperature and strain rate. The material exhibits negative strain rate sensitivity (SRS) that the flow stress decreases with increase of strain rate below a critical temperature of Tc. A model established by Kabirian et al. (Kabirian, F., Khan, A.S., Pandey, A. Int. J. Plast. 2014, 55) based on the KHL model considering the negative to positive SRS shows successful prediction of the flow stress in a temperature range of 296-473K. However, at higher temperatures (473-773K) the measured SRS deviates from the calculated values of Sigmoidal function given by Kabirianet al. with the increase of temperature. Therefore, in this paper, based on an extended Sigmoidal function and a proposed relation between flow stress and the coupling effects of strain and temperature, a modified Johnson-Cook model is proposed to describe the quasi-static stress-strain responses over a wider temperature range. Correlations using the modified model show good agreement with the experimental results.