Improved Mechanical Properties of Mg–Ni–Y Alloys via Thermomechanical Processing

The microstructure and mechanical properties of hot extruded Mg99.5−xNi0.5Yx alloys containing 0, 0.5, 1, and 2 at% yttrium were systematically investigated. It was found that by addition of Y, the amount of the long period stacking ordered structures as the main strengthening phase increased, which were subsequently deformed by the kinking mechanism during the extrusion process. Dynamic recrystallization (DRX) was responsible for grain refinement, where the grain size was determined by the competition of particle stimulated nucleation (PSN) mechanism of the LPSO phase and the increase of the homologous temperature during hot deformation by Y addition. Accordingly, the finest DRX grain size of 2.5 μm was achieved at 1 at% Y addition. At 2 at% Y, some deformed grains formed in the microstructure due to incomplete DRX. Both tensile and shear punch testing revealed that the Mg98.5Ni0.5Y1 alloy exhibited the optimum mechanical properties and strength–ductility balance, which was attributed to the strengthening effect of the LPSO phase, grain refinement, and weakened basal texture. The tensile and shear behaviors were also correlated, revealing a dependency consistent with the von-Mises yield criterion.