Optimizing hot workability regions for a novel TZ73 magnesium alloy: a processing map approach

Abstract

Newly developed Mg‒based alloy with composition of Mg–7Sn–3Zn (wt.%) (TZ73) was prepared by the squeeze casting technique and homogenized at 300 °C for 24 h. A processing map approach was adopted to identify safe hot workability regions. Hot compression tests were conducted in the range of T = 200 – 450 °C and \(\dot{\varepsilon }\) = 10^‒3 – 10 s^‒1, and a processing map was constructed by combining the strain rate sensitivity (m) and instability parameter ξ \(\left(\dot{\upvarepsilon }\right)\). High m‒value suggests better processability, and ξ \(\left(\dot{\upvarepsilon }\right)\)< 0 is considered an “unsafe” region for the hot deformation processes. Instability in the microstructure was identified by flow localization and crack initiation. Four distinct domains obtained from the processing map were analyzed based on microstructural and crystallographic texture evolution. Domain‒II within the temperature range of 200 – 300 °C and \(\dot{\varepsilon }\) = 10^‒1 – 10 s^‒1 was identified as ‘instability region’ with the lowest m < 0.01. Domain‒III, with T = 300 – 400 °C and \(\dot{\upvarepsilon }\) = 10^‒3 – 10^‒2 s^‒1 was identified as ‘safe region’ with the highest m > 0.20. The crystallographic texture was investigated using pole figures (PFs) and inverse pole figures (IPFs), which revealed that the basal texture weakened with increasing temperature and m‒values. The average stress exponent (n) was estimated to be 5.30, and the activation energy (Q) was estimated to be 148 kJ.mol⁻¹. Based on the deformation curves, a mathematical equation for the peak stress (\({\sigma}_{p}\)) dependence on T and \(\dot{\varepsilon }\) was obtained, which illustrates the hot deformation behavior and kinetics of a newly developed TZ73 Mg alloy.

Graphical Abstract