Comparison study of hot deformation behavior and processing map of AZ80 magnesium alloy casted with and without ultrasonic vibration

In order to compare the workability of AZ80 magnesium alloy casted with and without variablefrequency ultrasonic field (VUF), uniaxial hot compression tests were carried out in the temperature range of 523-673 K and the strain rate range of 0.001-1 s(-1) on a Gleeble-3500D thermo-mechanical simulator. The flow stress, constitutive relation, DRX kinetic model and processing map were analyzed based on the experimental data. The results show that, the VUF samples have lower peak stress and peak strain than DC samples at low strain rates, while the opposite situation can be observed at high strain rate. The calculated activation energy Q and stress exponent n for DC samples are 192.38 kJ/mol and 7.30158, which are higher than the calculated values for VUF samples, showing the figures of 165.30 kJ/mol and 7.30158, respectively. The VUF casted samples start DRX earlier and easier, and can obtain complete DRX structure at high strain rate. The VUF samples have larger workability range but smaller instability region than DC samples. Dense and irregular bulges can be observed on side surfaces of DC samples after compression, while surfaces of VUF samples are smooth. (C) 2019 Elsevier B.V. All rights reserved.