Hot tensile deformation behavior and microstructural evolution of a Mg–9.3Li–1.79Al–1.61Zn alloy

Abstract

To explore the nature of hot plastic deformation, the microstructures and hot tensile deformation modeling in a rolled Mg–9.3Li–1.79Al–1.61Zn alloy were investigated. Microstructural study reveals that at the temperatures of 473 and 523K with strain rates of less than 1.67×10−4s−1, partial dynamic recrystallization (DRX) or continuous DRX takes place, whereas at the temperatures of 573 and 623K at most strain rates, complete DRX and pronounced dynamic grain growth occur. The maximum superplasticity of 566.7% was demonstrated in the present alloy at the temperature of 573K and the strain rate of 1.67×10−4s−1. A constitutive equation was established by regression analysis of Arrhenius type hyperbolic sine function and the activation energy for deformation of the present alloy was calculated as 141.12kJ/mol. The critical parameters at the characteristic points of flow stress curves were determined and the relationship between DRX volume fraction and strain was established by Avrami type equation. Finally, the relationship between dislocation density and Zener–Hollomon parameter was modeled and the conditions of critical peak dislocation density and critical peak stress for the initiation of DRX were derived. The theoretical prediction is consistent with the experimental result.