Investigation of deformation and failure features in hot stamping of AA6082: Experimentation and modelling

This paper introduces a set of coupled viscoplastic constitutive equations for deformation and damage in hot stamping and cold die quenching of AA6082 panel parts. The equation set can be used to predict viscoplastic flow and plasticity-induced damage of AA6082 under hot forming conditions. Deformation and damage depend upon a coupled set of evolving internal state variables, e.g. dislocation density, which in turn is affected by thermally activated and deformation-dependent recrystallisation and recovery. A phenomenological description of damage is derived based on the expected physical scaling with temperature, strain and strain rate. The resulting equations were implemented in the commercial software ABAQUS via the user-defined subroutine VUMAT for carrying out forming process simulations. An experimental programme was designed, and specialised testing facilities developed for calibrating and validating the FE process modelling results. A good agreement between the process simulation and the experimental results has been achieved. This confirms that the physical dependencies in the constitutive equations are correctly formed, and that the equations and FE model can be calibrated and used for hot stamping of AA6082 panel parts. Further, forming process optimisation was carried out using the model to identify the optimal forming parameters for a basic panel part with a circular hole in the middle. The study concludes with a discussion of the potential impact of the constitutive model, experimental characterisation and modelling results on AA6082 panel parts manufacture.

► Failure features of AA6082 in hot stamping are found to be forming rate dependent.
► A calibrated viscoplastic damage constitutive equation set is presented for AA6082.
► A forming process window for AA6082 hot stamping was determined by FE simulation.