Al-Cu alloys exhibit promising industrial applications owing to their low density and superior mechanical properties. However, their widespread adoption is severely limited by high hot tearing susceptibility. Hot tearing is closely related to the stress change and fluidity of the intergranular liquid films during the final stage of solidification. Due to the influences of grain size, liquid film thickness, and various defects, conventional polycrystalline samples cannot accurately reflect the stress-strain characteristics of the liquid films. To circumvent these inherent limitations in polycrystalline samples, a custom-designed device was developed to investigate the stress-strain behavior of monocrystalline intergranular liquid films. The effect of Sc on stress-strain of liquid films at the end of Al-Cu solidification was investigated using the self-made device. Meanwhile, combining the T-shaped mold experiment and differential thermal analysis, the relationship between the stress-strain of the liquid films and hot tearing susceptibility was analyzed. The temperature and stress fields during solidification were simulated using ProCAST. The results indicate that the addition of Sc refines the dendrites, modifies the morphology of θ-Al2Cu, alleviates the stress concentration during the solidification process, and prolongs the liquid feeding duration, thereby reducing the hot tearing susceptibility of the alloys. Numerical simulation results of temperature field, stress field, and hot tearing indicator of T-shaped mold are in good agreement with the experimental observations.