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

Abstract

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.

Keywords

• Mg–Nd–Sc alloy
• isothermal section
• phase equilibria
• solid solubility