Quasi-superplasticity in an Mg–Li–Al–Y alloy processed by rolling

In order to explore the high temperature ductility of ultra-light magnesium-lithium alloy, a new Mg-7.28Li-2.19Al-0.091Y (LAY720) alloy was prepared by casting and rolling. The microstructural evolution, mechanical properties, model, and deformation mechanism under hot tension were studied by optical microscope, X-ray diffraction, scanning electron microscope, energy dispersive spectroscopy, and tensile tester. Mechanical properties tests showed that the maximum elongation of 265.8% was achieved at 623 K and 5.0 × 10 −4 s −1 Microstructural examination found that the tensile alloy is composed of α-Mg + β–Li dual-phase banded grains under high strain rate condition, which disappears when the strain rate decreases and the temperature increases. Continuous dynamic recrystallization occurs at 473 and 523 K while dynamic grain growth occurs at 573 and 623 K under the other strain rates. The AlLi compound precipitation at the α-Mg grain boundary was discovered in LAY720 alloy at 523 K and 1.67 × 10 −4 s −1 . A critical strain and critical stress model for dynamic recrystallization of the alloy was obtained. Discontinuous dynamic recrystallization and dynamic grain growth were estimated by our models. A power-law constitutive analysis revealed that the stress exponent of 3 and the deformation activation energy of 138.35 kJ/mol confirmed that lattice diffusion controlled dislocation glide and dynamic grain growth are the deformation mechanism at 623 K and 5.0 × 10 −4 s −1 .