Computer-aided cooling curve thermal analysis technique was used to investigate microstructure and phase evolutions in Mg–5Zn alloy containing 0–1.5 mass% yttrium (Y) solidified at 0.7 C s-1 cooling rate. Optical and field emission scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction analysis were performed to characterise microstructure of the cast alloys. The observations revealed that a considerable refinement, calculated as over 74%, was occurred in the alloys with increasing Y content to 1.5 mass%. The first derivative curves revealed two peaks corresponding to aMg and Mg7Zn3 for the binary Mg–5Zn alloy. The results also showed the evolution of three peaks related to the aMg, W-phase (Mg3Zn3Y2) and I-phase (Mg3Zn6Y) in the Mg–5Zn–xY alloys. The nucleation temperature of both aMg and I-phase decreased slightly by increasing Y content. In addition, the solidification range and total solidification time increased by 44.4 and 50% with increasing Y content
