Influence of Y content on thermal expansion and mechanical properties of Mg-Gd-Y alloys

The influence of Y content on coefficient of thermal expansion (CTE) and mechanical properties for Mg-10Gd-xY (x = 0.5, 2.5, 4.5, and 6.5 wt%) alloys are elaborated through first-principle calculations and experimental characterizations. Alloying Y is demonstrated to obviously decline the CTE and enhance the strength. The theoretical predictions of thermal expansion of Mg-Gd-Y solid solutions demonstrate that, the significant reduced contribution of lattice vibration resulted from the reduced Grüneisen parameter upon alloying with Y primarily contributes to the decline of CTE. The obviously improved strength is associated strongly with the solid solution strengthening and grain refinement caused by the segregation of alloying elements at grain boundary, the pinning effect and particle-stimulation nucleation of Mg₅(Gd, Y) particles. In addition, the relatively good ductility with the elongation being above 10 % can be achieved at relatively low Y content below 2.5 wt% owing to the enhanced activation of pyramidal <c+a> slips. Nevertheless, the ductility deteriorates with further increasing Y content due to the increased fraction and size of Mg₅(Gd, Y) phase.