High-intensity ultrasound can effectively improve the grain structure and element distribution uniformity of industrial large-scale Al alloy ingots. In this paper, ultrasonic-assisted casting of 2219 Al alloy ingots (Ф630 mm×4500 mm) was carried out to compare the microstructure differences between the two ingots. The results indicate that the core of the conventional ingot is predominantly composed of coarse dendrites. After ultrasonic treatment, the α-Al grains in the ingot are refined, with refinement rates of 27.7%, 31.4%, and 24.2% at the edge, R/2, and core positions, respectively. The area fractions of the coarse Al₂Cu eutectic phase are 15.18%, 8.42%, and 5.3%, respectively, which represent relative reductions of 21.1%, 31.6%, and 30.4% compared to the ingot without ultrasonic treatment. The tensile strength, yield strength, and elongation of the ultrasonically treated ingot are significantly improved compared to those of the untreated ingot. Specifically, the tensile strength at the center, R/2, and edge positions is relatively increased by 18.2%, 24.2%, and 11.1%, respectively. This study validates that ultrasonic cavitation and acoustic streaming promoting heterogeneous nucleation are the dominant mechanisms for modifying Al alloy melts, and by establishing a quantitative relationship with the undercooling required for nucleation, it provides a precise basis for process control in industrial applications of this mechanism.