Characteristics of superplasticity domain in the processing map for hot working of as-cast Mg–11.5Li–1.5Al alloy

Abstract

Processing map for hot working of as-cast Mg–11.5Li–1.5Al alloy has been developed in the temperature range 200–450°C and strain rate range 0.001–100 s −1. The map exhibited a single domain with a peak efficiency of 65% occurring at 400°C and 0.001 s −1. Under these conditions, the material exhibited abnormal elongation. On the basis of the elongation, the grain structure, the apparent activation energy for hot deformation (95 kJ mole −1) and the peak efficiency of power dissipation (65% corresponding to a strain rate sensitivity of about 0.5), the domain is interpreted to represent superplasticity. At strain rates higher than about 10 s −1, the material exhibits microstructural instability, while at temperatures of 450°C and a strain rate of 0.001 s −1, grain boundary cracking is observed.