Construction of hot processing map, dynamic recrystallization critical conditions and kinetic model of AZ61 alloy

Abstract

Under temperature of 300–450 °C and strain rates from 0.003 s−1 to 1 s−1 and deformation of 70 %, hot compression experiments of AZ61 magnesium alloy were carried out on Gleeble-1500 test machine, to study its thermal deformation behavior. Based on the dynamic material theory model, a three-dimensional hot working map was obtained. Based on the work hardening rate curves inflection point, the critical strain model was built. Subsequently, the dynamic recrystallization kinetics model was constructed according to critical conditions. The findings showed that at low strain rates and high temperatures, materials with larger power dissipation factors exhibit better processability, and at high strain rates and low temperatures, materials are more prone to instability with the increase of strain. Considering the connection between peak strain εp and critical strain εc, it is observed that εc precedes εp, indicating that dynamic recrystallization occurs before reaching the peak strain. Based on the kinetics model, observed the dynamic recrystallization volume fraction curves follow a “slow-fast-slow” changing trend, exhibiting an “S” shaped growth, which was agreed with the kinetics curve in classical dynamics.