Experimental investigation of phase equilibria in the Mg-rich corner of Mg-Nd-Sc system

Phase equilibria in the Mg-rich corner of Mg–Nd–Sc ternary system was studied by using the equilibrated alloys method. The partial isothermal sections at 500 °C, 530 °C, and 550 °C were constructed by analyzing the phase constitution and the chemical compositions of the present phases in 19 alloy samples. The Mg 3 (Mg, Nd, Sc) phase exhibited noticeable ternary solubility introduced by the solid solution of Mg and Sc in the Mg 3 Nd lattice. (Mg_hcp) showed a narrow homogeneity range paralleling to Mg–Sc binary boundary, whereas Mg 41 Nd 5 showed negligible ternary solubility at all three temperatures. The three-phase equilibrium region of (Mg_hcp) + Mg 41 Nd 5  + Mg 3 (Mg, Nd, Sc) dominated the Mg-rich corner and was surrounded by three two-phase equilibrium regions constituted by any two of above three phases. The primary crystals and the solidification pathways of alloys in the Mg-rich corner were analyzed via the as-cast microstructure. The matrix phases of (MgSc_bcc) and/or (Mg_hcp) together with the precipitations of Mg 3 (Mg, Nd, Sc) and other ordering structures could provide additional space to optimize microstructure and properties of Sc-alloyed Mg–Nd alloys.