Modeling the formability of aluminum alloys at elevated temperatures using a new thermo-elasto-viscoplastic crystal plasticity framework

Industrial processes often use high temperature forming of alloys such as aluminum that have unsatisfactory room temperature formability. Accurate forming models to integrate warm forming in production environment have been hampered by a lack of constitutive relations at elevated temperatures, forcing one to rely on experimental data for such integration. In this paper, the new thermo elastoviscoplastic (TEV) crystal plasticity constitutive framework developed by Cyr et al. [1] is implemented in an Marciniak-Kuczynski [2] analysis to predict the forming limit diagrams (FLDs) of the M5754 and AA3003 aluminum alloys at elevated temperatures. The model takes into account the temperature dependence of the single crystal elastic coefficients, single slip hardening parameters, thermal softening, slip rate sensitivity, and the total deformation. Temperature dependent hardening parameters have been determined through curve fitting the simulated stress-strain response with experiments during uniaxial tension at room and elevated temperatures. The calibration of the TEV model for the single slip parameters in uniaxial tension is shown to provide accurate predictions of the experimental forming limit diagrams (FLDs) without the need for further curve fitting. The effects of elastic constants and thermal softening on FLD prediction are discussed, and equations are developed to predict the temperature dependence of single-slip hardening parameters and so-called initial imperfection parameter employed in the Marciniak-Kuczynski (M-K) analysis. The predictive capability of the new model is then demonstrated by FLD simulations for various elevated temperatures. (C) 2017 Elsevier Ltd. All rights reserved.