Microstructure and Mechanical Properties of a Mg94Y4Ni2 Alloy with Long Period Stacking Ordered Structure

Microstructure and mechanical properties of the Mg₉₄Y₄Ni₂ alloy (at.%) during homogenization, extrusion, and aging processes were systematically investigated using x-ray diffractometer, optical microscopy, scanning electron microscopy, transmission electron microscopy, and electronic universal testing machine. The results showed that the morphology evolution of 18R LPSO structure during annealing in Mg₉₄Y₄Ni₂ alloy was different from that of Mg-Y-Zn systems. The 18R-type Mg₁₂YNi phase was thermal stable and was not transformed into 14H structure when annealed at 773 K. After solution treatment at 773 K for 10 h and aging at 498 K for 24 h (T6 treatment) of the extruded alloy, a great amount of fine β′ phases were precipitated dispersedly in the matrix. The tensile tests showed that the extruded Mg₉₄Y₄Ni₂ alloy after T6 treatment exhibited good tensile properties with ultimate tensile strength of 453 MPa and elongation to failure of 2.4% at room temperature. Thus, a high-strength Mg₉₄Y₄Ni₂ alloy, which is strengthened by the coexisted LPSO phases and β′ precipitates, can be prepared via simple hot extrusion and T6 treatment.