Increased recyclingRecycling share in aluminum productionAluminum production increases impurityImpurities content, resulting in a higher risk of stabilizing primary intermetallicsPrimary intermetallics. Having precise thermodynamic databases is crucial for forecasting and avoiding primaries during solidificationSolidification. In this work, we evaluate experimentally the Al-rich liquidus lines of Al–Ti and Al–Zr phase diagramsPhase diagram, using direct analysis of dilute molten alloys with laser-induced breakdown spectroscopySpectroscopy (LIBSLIBS). The liquid alloys are cooled at different rates and the concentration of dissolved elements is measured continuously using LIBSLIBS. The results at a cooling rateCooling rate of 1 °C/min show that concentration measurementsMeasurements follow the predicted liquidus lines of the phase diagramsPhase diagram, albeit not always in full agreement with available thermodynamic databases. LIBSLIBS measurementsMeasurements at faster cooling ratesCooling rate (5, 10, and 20 °C/min) show clear signs of nucleation undercooling, which depend on the cooling rateCooling rate and the initial composition of the alloys. Comparing the undercooling of different alloy concentrations at different cooling ratesCooling rate reveals that for the same mass composition in Ti or Zr, the Al3Ti-D022Al3Ti-D022 phase nucleates at lower undercooling than the Al3Zr-D023AlZr-D0 phase.