Effect of phase morphology on microscopic deformation behavior of Mg–Li–Gd dual-phase alloys

In present work, three dual-phase Mg–6Li–2Gd, Mg–7Li–2Gd and Mg–8Li–2Gd (wt.%) alloys, with different morphology of β-Li and α-Mg phases, were fabricated by hot extrusion and then in-situ tension tested at room temperature. Digital image correlation (DIC) technique and slip trace analysis were utilized to investigate the effect of phase morphology, including the size and configuration of β-Li and α-Mg phases, on the microscopic deformation behavior of Mg–Li-Gd dual-phase alloys. These alloys showed a lowest strain accommodation by α-Mg phase at the Li content of 7 wt%. In particular, the small α-Mg phase enclosed in a three-dimensional continuously connected network of β-Li phase in Mg–8Li–2Gd alloys was observed to be distributed homogeneously by fine slip traces and triggered a large amount of deformation. Interrupted load-unload-reload (LUR) tension tests confirmed the important role of hetero-deformation induced (HDI) stress. TEM analysis further revealed the existence of stress concentration sites in the α-Mg phase, induced by the pile-up geometrically necessary dislocations (GNDs) near phase boundary. The different microscopic deformation behaviors were thus attributed to the varying phase morphology which would affect the ratio of phase boundary-affected zone in two phases, rather than the orientation of α-Mg phase, even though it is critical to the activation of dislocation slip.