<p>Iron impurities in molten zinc can significantly affect its mechanical properties and corrosion resistance. This research has identified iron phases in both the binary Zn-Mg and ternary Zn-Mg-Cu systems using the cooling curve thermal analysis (CCTA) technique. These findings have practical implications for the manufacturing and quality control of zinc-based alloys and serve as a valuable resource for ensuring optimal performance. The study uses optical microscopy, scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) to examine the microstructure and phase composition. Furthermore, the hardness of these alloys was evaluated using the Vickers method. The results indicate significant peaks at 476.8 °C and 435.2 °C, which occur before the dendritic zinc peak in the cooling and first-derivative curves of iron-containing alloys—a feature absent in iron-free alloys. In addition to the Zn matrix, the Zn₁₁Mg₂ and Zn₄(Cu, Mg) phases, an L-shaped FeZn₁₃ phase is identified, supported by EDS and XRD analyses. Although there are no notable changes in cooling and solidification rates, the iron phase expands the mushy zone during solidification, which is crucial for semisolid processing. This study highlights the potential of CCTA as an effective initial screening and process control tool for identifying iron impurities in zinc-based alloys, with direct implications for the development of high-quality zinc alloys.</p>