Constitutive behavior of a SIMA processed magnesium alloy by employing repetitive upsetting-extrusion (RUE)

Thixotropic compression tests were carried out on a repetitive upsetting-extrusion (RUE) processed AZ91D magnesium alloy at temperatures ranging from 500 degrees C to 550 degrees C by using a Gleeble-1500 thermal-mechanical simulator. Semi-solid stress-strain data were obtained. A modified constitutive model was established to describe the thixotropic behavior of the RUE strained alloys. The results revealed that three stages of elastic-like deformation, strain hardening deformation and rheological viscoplastic deformation were involved in the thixoforming process. Furthermore, the compressed microstructures in semi-solid state were investigated with referring to microstructure observation. Dominant deformation mechanisms during the thixotropic compression were considered as the slipping or rotating mechanism of the solid particles along the liquid films, the slipping mechanism between the solid particles, the plastic deformation mechanism of the solid particles and the DRX behavior of the solid particles, whose function varied with the change of temperature and strain rate. (C) 2018 Elsevier B.V. All rights reserved.