Role of Y in High-Strength Mg–Y–Cu–Ni Alloy System with Long-Period Stacking Ordered Phase

This study has systematically investigated the effect of Y content on the microstructural evolution and mechanical properties of the Mg–Y–Cu–Ni alloy system. Four alloys, Mg_(98−x)Y_xCu₁Ni₁ (x = 1, 2, 3, and 4 at.%), were fabricated and compared in various aspects for this purpose. Increasing Y content gave rise to an increasing fraction of long-period stacking ordered (LPSO) phases, and gradually changed their morphology from massive islands to lamellae. The alloying addition also induced an effective grain refinement, while inhibiting the dynamic recrystallization. When the Y content exceeded 3 at.%, a unique phase formed due to a mechanical mixture of the LPSO phase, the peritectic reaction product of Cu, and the eutectic reaction product of Ni. The mechanical properties were explained in light of the LPSO dispersion parameter. The extruded Mg₉₅Y₃Cu₁Ni₁ alloy exhibited excellent mechanical properties combining a yield strength of 381 MPa, tensile strength of 458 MPa, and elongation-to-failure of 6.7%.