Simultaneously improved strength and ductility in a Ce-doped dual-phase Mg–9Li alloy

Rare earth metals are commonly added into Mg–Li alloys for strength or ductility improvement. In this paper, rare earth element Ce was incorporated into a Mg–Li alloy to modify its mechanical properties. It is found that the addition of small amount Ce (0.6 wt%) improves over 13% tensile strengths of the Mg–Li alloy without expense of ductility, owing to the formation of Mg₁₂Ce precipitates. To illustrate the toughening mechanism, an in-situ tensile experiment was performed focusing on crack initiation and fracture behavior at local regions such as phase boundaries. It is found that the deformation incompatibility occurs between the α-Mg and β-Li phases in Mg–9Li, and local strain analysis suggested that the β-Li phase contributes more than the α-Mg phase to the plasticity. However, the incorporation of Ce enhances the deformability of the α-Mg phase by weakening its basal texture, which alleviates the strain incompatibility along the phase boundaries. That is why the strength-ductility dilemma is overcome in the Ce-doped Mg–Li alloy. Besides, microcracks mostly generate within fine strips of α-Mg phase for the Ce-free alloy, while for the Ce-doped alloy both the fine α-Mg phase and precipitate strips serve as crack initiators.