<p>The nature of the morphologies forming in the microstructure of the hypoeutectic Al-Cu alloys exposed to rapid undercooling has been investigated. Experimental and simulation works were carried out using Al-4.6wt.%Cu and Al-8wt.%Cu hypoeutectic alloys. The experimental results show that pure aluminum, FCC Al phase, and AlCu_theta phase are the microstructural features forming the microstructure of quenched hypoeutectic Al-Cu alloys. A microstructure analysis was carried out using stereo-light optical and scanning electron (SEM) microscopes. The molecular dynamics simulation using Lammps software was employed to study the redistribution of the aluminum and copper atoms to understand the nucleation phenomena and the microstructure forming during the quenching process. The molecular dynamic method successfully predicts the nature of the microstructural feature forming in the microstructure, wherein Cu-Cu, Al-Al, and Al-Cu atoms aggregate to make fluctuation in the concentration of the high undercooled molten alloy. The simulation results also show that the AlCu_theta phase nucleates in the higher copper concentration area and pure aluminum and FCC_Al phase nucleates in the lower copper concentration area.</p>