Improved strength in wrought Mg–Y–Ni alloys by adjusting the block-shaped LPSO phase and plate-shaped γ′ phase

The microstructure and mechanical properties of two Mg–Y–Ni alloys with different volume fraction of block-shaped LPSO phase and different number densities of plate-shaped γ′ phase were investigated. The volume fraction of block-shaped LPSO phase increases with the content of Y and Ni in the Mg–Y–Ni alloys with Y/Ni atomic ratio of 1. The plate-shaped γ′ phase is formed in the matrix of the as-cast alloys and grows across the matrix during the preheating before extrusion, and its number density increases with increasing content of Y and Ni. After extrusion, the block-shaped LPSO phase is distributed along extrusion direction, and the plate-shaped γ′ phase can be observed in both non-dynamic recrystallized (non-DRXed) grains with strong basal texture and dynamic recrystallized (DRXed) grains with random texture. The increased volume fraction of LPSO phase improves the tensile yield strength of the as-extruded Mg–Y–Ni alloys, accompanied by the decrease in ductility. In addition to the obvious strengthening from the LPSO phase, the plate-shaped γ′ phase is also an effective strengthening phase which can hinder the movement of the slip systems in non-DRXed and DRXed grains of the Mg–Y–Ni alloys. The Mg94Y3Ni3 (at%) alloy containing the highest volume fraction of block-shaped LPSO phase and the highest number density of plate-shaped γ′ phase exhibits the superior tensile yield strength of 502 MPa after extrusion.