Effect of Li content on microstructure, texture and mechanical behaviors of the as-extruded Mg-Li sheets

The microstructures, texture and mechanical behaviors of as-extruded Mg-xLi sheets (x = 1, 2, 3; wt%) were investigated by the optical microscope, X-ray diffraction (XRD), electron back scattered diffraction (EBSD) and uniaxial tension test. The results showed that the as-extruded Mg-3Li sheet possessed a bimodal microstructure with two different grain sizes of 9.6 mu m and 3.7 mu m, respectively. Even the coarse grains of Mg-3Li were finer than the grains of Mg-(1,2)Li sheets. Meanwhile, the as-extruded Mg-3Li sheet showed higher strength and ductility compared to other two sheets. Especially, as the Li content increased from 2 wt% to 3 wt%, the ultimate tensile strength (UTS), the elongation to failure and the strain hardening exponent (n-value) along the transverse direction (TD) were enhanced by similar to 16%, 70% and 17%, respectively. The macro-texture and the orientation distribution characteristic implied that large amounts of prismatic and pyramidal slips were activated in the Mg-3Li alloy during the extrusion process, while only basal slip was observed in the Mg-(1,2) Li alloys. The non-basal slips led to more potential nucleation sites and a better coordination for the deformation, resulting in the bimodal fine microstructure and better comprehensive mechanical properties of the as-extruded Mg-3Li sheet.