<p>The nucleation and growth of hydrogen bubbles in molten aluminum are key processes affecting the quality of aluminum products and foams. Classical nucleation theory does not adequately explain bubble formation at typical hydrogen concentrations, prompting the use of the molecular cluster model, which accounts for gas molecule aggregation under supersaturated conditions. This study applies the molecular cluster model to analyze hydrogen bubble formation during aluminum casting, using the experimental conditions of Sahu et al., who added 0.5, 1.0, and 1.5 wt% TiH₂ to aluminum melts at 700 °C. Assuming full dissociation of TiH₂, hydrogen concentrations and corresponding saturation pressures were estimated, and nucleation rates were calculated. The model predicts a significant increase in bubble formation at 1.5 wt% TiH₂, assuming a lost degree of freedom (f_L) of 2.31 for hydrogen molecules in the melt. The nucleation period of critical clusters was extremely short, less than a millisecond. Final bubble diameters reached approximately 1.0~1.45 mm, and growth rates increased with hydrogen concentration. The total time from critical cluster to fully grown bubble ranged from 32 to 436 milliseconds, depending on the hydrogen concentration level. These results demonstrate the effectiveness of the molecular cluster model in describing hydrogen bubble nucleation process in aluminum melts. The findings provide valuable insights for controlling bubble formation in aluminum foam production, emphasizing the importance of hydrogen concentration and flow conditions for achieving desirable microstructures.</p>