Thermodynamics of Mg–Y–O Alloys and Segregation at the Mg/MgO Interface

Elemental segregation driven by the reduction of the total Gibbs energy of the system has been widely observed at the melt/substrate interfaces in various Al- and Mg alloys containing different inoculant particles. This study provides experimental observations, analyses, and identifications of the formation of Y-segregation 2DCs at the Mg/MgO interfaces in a solidified Mg–0.5Y (w%) sample. From an extended Gibbs adsorption isotherm, the interfacial segregation of solute Y in a dilute Mg alloy melt is quantitatively described. The thermodynamics of the elemental interactions, conditions for the formation of MgO and Y₂O₃ particles, and the contributions to the interfacial energy difference are detailed. A reasonable atomic segregation factor at the liquid/MgO interface from the bulk Mg–0.5Y melt is estimated. This changes the structural and chemical configuration at the interface, thus the nucleation potency of native MgO particles as well as the as-cast grain size.