Superplasticity in a two-phase Mg–8Li–2Zn alloy processed by two-pass extrusion

Tensile tests on a two-pass extruded Mg–8Li–2Zn alloy are conducted at 473–593 K, and an initial strain rate of 1.5 × 10−4–7.5 × 10−3 s−1. The two-pass extruded alloy has refined structure and excellent superplastic properties, with a maximum recorded elongation of 758% at 563 K under an initial strain rate of 1.5 × 10−4 s−1. The value of the strain rate sensitivity under the optimum superplastic condition is 0.55, and the activation energy is 90 kJ/mol. These indicate that the dominant deformation mechanism in the two-pass extruded alloy is grain-boundary sliding controlled by grain-boundary diffusion. Coalescence and interlinkage of cavities are the reasons for tensile failure.

► High-ratio (100:1) through a two-pass extrusion was implemented on a LZ82 alloy.
► Microstructure and mechanical properties under elevated temperatures was studied.
► The alloy has superplasticity with an elongation of 758% at 563 K and 1.5 × 10−4 s−1.
► The m value is ∼0.55 and the Q value is ∼90 kJ/mol.
► The deformation mechanism is GBS controlled by grain boundary diffusion.