Plastic Flow Characteristics of an Extruded Mg-Li-Zn-RE Alloy

Abstract:

The flow behavior of an extruded Mg-7.8Li-4.6Zn-0.96Ce-0.85Y-0.30Zr alloy was investigated by a thermo-mechanical simulator in the temperature range from 250 to 450 °C and the strain rate range from 0.001 to 10 s-1. The results indicate that the flow stress-strain curves of the alloy are characterized by an increase of the flow stress until a maximum stress value followed by the flow softening being observed. Such flow behavior is a characteristic for hot working accompanied by dynamic recrystallization. The flow behavior of the alloy can be represented by a hyperbolic sine type equation during the whole deformation temperature; however, it is not proper to fit the flow stress equation using the power and the exponential equation. The stress exponent n in the hyperbolic sine equation is high and increases with increasing of deformation temperature. The hot deformation process of the alloy is mainly controlled by dislocation climb. The average hot deformation activation energy Q of the alloy is 148 kJ/mol, which is higher than both the self-diffusion activation energy of Mg (135 kJ/mol) and the lattice diffusion activation energy of β-phase (103 kJ/mol). The results discussed above can be attributed to the addition of rare-earth (RE)

Key words:Mg-Li alloy; hot deformation behavior; kinetic analysis