Current work outlines the thermodynamic prediction of Mg–Zn–X (X = Sn, Y) alloys amenable for both semi-solid metal (SSM) processing and age hardening treatment. Semi-solid processing capability of Mg–Zn–X (X = Sn, Y) alloy has been evaluated by measuring the metallurgical parameters such as ‘solidification interval’, ‘temperature liquid fraction sensitivity’ and ‘highest knee point’ from non-equilibrium Scheil solidification curve. According to thermodynamic prediction, binary Mg–Zn and ternary Mg–Zn–Sn alloys are suitable for heat treatment; however, wide solidification intervals in these systems restrict their SSM processing ability. Formation of binary Zn2Y and ternary W-Mg3Zn2Y3 intermetallic phases in Mg–Zn–Y alloy has been predicted to improve their SSM processing potential and at the same time Mg–Zn–Y alloy is found to be suitable for heat treatment process. © 2015, The Indian Institute of Metals - IIM.