Micromechanical origin of the enhanced ductility in twinless duplex Mg-Li alloy

Unlike many Mg alloys that exhibit limited ductility, duplex Mg-Li alloys possess enhanced ductility but the underlying mechanisms are unclear. Using real-time in situ neutron diffraction measurements, we show that the underlying deformation modes in this duplex microstructure include an early yield of body-centered-cubic (BCC) beta-Li phase and the later elevated hardening in this phase at large macroscopic plastic strain, and the sequential activation of basal and pyramidal a slip systems in hexagonal-close-packed (HCP) alpha-Mg phase. The latter relieves the Mises constraint for deformation compatibility, and the successive yielding sequence promotes the overall work hardening rate, both of which are beneficial for ductility enhancement. No obvious twinning activities were found and correspondingly the hysteresis loops were symmetric upon a full loading cycle within +/- 1% applied strain.