An investigation on the hot workability and microstructural evolution of a novel dual-phase Mg–Li alloy by using 3D processing maps

Abstract

Hot compression tests of a novel dual-phase Mg–Li alloy were performed in temperature range of 200–400 °C and strain rate range of 0.01–10s−1. 2D and 3D processing maps were established using Prasad's and Murty's instability criteria (methods) based on the dynamic materials model. It was found that one instability region obtained based on Prasad's instability criterion exist in the domain of power dissipation efficiency at a strain of 0.7. Prasad's and Murty's instability criteria are difficult to accurately characterize the instability characteristics of the alloy. The accuracy processing map rectified was obtained by means of Murty's and Prasad's instability criteria and microstructural analysis. On the basis of the processing map rectified, the optimum hot working parameters were obtained to be the temperature range of 320–400 °C and strain rate range of 0.01–0.4s−1 with the peak power dissipation efficiency. In this domain, the α phase undergone dynamic recrystallization (DRX) and dynamic recovery (DRV). The β-phase occurred DRX during the hot deformation. The instability regions lie in the temperature range of 200–250 °C with strain rate range of 0.01–1s−1 and the temperature range of 200–312 °C with strain rate range of 1–10s−1. Microstructural observations indicate that characteristics of the flow instabilities were flow localization, deformation twinning, the adiabatic shear bands and macro/micro cracking. The rectified processing map was successfully verified by the hot rolling test. The rectified processing map could accurately characterize workability characteristics of a novel dual-phase Mg–Li alloy and could be used for the optimization of hot working process parameters.

Keywords

• Mg–Li–Al–Zn–Y–Zr alloy
• Workability
• Instability criterion
• Processing map