Flow stability of binary Al–Li alloys

The constitutive stress–strain behavior of extruded Al–1 wt.% Li and Al–2 wt.% Li has been characterized in the temperature range 573–823 K between strain rates of 5×10−4 and 1 s−1. These results together with dynamic materials modeling (DMM) were utilized to establish strain rate–strain-temperature processing maps. Stable regions, defined on the basis of two mechanistic stability criteria, 0<m<1 and δ log(m)/δ log(ε̄̇)<0, and two thermodynamic criteria, s>1 and δ log(s)/δ log(ε̄̇)<0, were found to be associated with dynamic recovery (DRC) at low temperatures and dynamic recrystallization (DRX) at higher temperatures. Unstable flow was observed at both low temperatures (573–623 K)/high strain rates (10−1 s−1) and at high temperatures (773–823 K)/low strain rates (10−3–5×10−4 s−1), these instabilities being associated, respectively, with macroscopic shear band formation and dynamic grain growth.