Boron treatment of aluminum alloysAluminum alloy removes peritectic impurities (e.g., V, Ti, and Zr) by forming stable borides in the melt, commonly achieved through the addition of Al-B master alloysMaster alloy. Hence, accurate thermodynamicThermodynamics modelingModeling of Al-rich regions is essential for developing impurity control strategies. Although phase stability data of the Al-B system is available in commercial thermochemical packages, recent liquid composition monitoring via laser-induced breakdown spectroscopy (LIBSLaser-Induced Breakdown Spectroscopy (LIBS)) revealed discrepancies with thermodynamicThermodynamics databases. In this work, the binary Al-B system is assessed via the CALculation of PHAse Diagrams (CALPHADCALPHAD) method. The compound energy formalism (CEF) is used to describe the solid phases, while the modified quasichemical model (MQM) is employed for the liquid phase. The formation enthalpy and heat capacity (Cp) of the AlB2 intermetallicIntermetallics compound were estimated using density functional theory (DFTDensity Functional Theory (DFT)) calculations, whereas the Cp of AlB12 was obtained employing the modified Neumann-Koop rule (modified NKR), informed by the DFTDensity Functional Theory (DFT)-derived data for AlB2. Al-rich Al-B liquidus temperature projections were experimentally validated using differential scanning calorimetry (DSCDifferential Scanning Calorimetry (DSC)) and LIBSLaser-Induced Breakdown Spectroscopy (LIBS). Finally, the precipitates formed during LIBSLaser-Induced Breakdown Spectroscopy (LIBS) experiments are characterized by energy dispersive spectroscopy (EDS). The combined computational and experimental results are used to refine and improve the Al-B thermodynamicThermodynamics description, giving particular attention to the Al-rich region devoted to boron treatment of aluminum alloysAluminum alloy.