This study investigated the solidification behaviour of recycled aluminium alloy with varying gadolinium (Gd) content through cooling curve thermal analysis and microstructural characterisation. An Al–Fe–Si alloy was melted in an electrical furnace at 800 °C and then alloyed with different amounts of pure Gd (0.1, 0.3, 0.5, 0.8, and 1 mass%). The molten material was cast into a thin-walled mould for thermal analysis using the two-thermocouple technique. After data smoothing, two distinct phases were identified in the base alloy: aluminium and Al3Fe. The addition of Gd induced two new phases, clearly discernible at concentrations exceeding 0.3%. The phase formation sequence was Al, Al3Gd, followed by Al3Fe, and finally Al3(Gd, Fe, Si). The addition of Gd resulted in a reduction of both the temperature and time ranges of solidification. Moreover, the peak on the first derivative curves associated with the precipitation of Al3(Gd–Fe–Si) demonstrated a strong relationship between peak magnitude and the amount of Gd. While the formation temperature of the Al phase remained relatively unchanged, the solidification rate exhibited an initial increase followed by a decrease. Coherency point analysis revealed a decreased solidification rate during the coherence region, suggesting a grain refinement effect of Gd, confirmed by microstructural observation.
