<p>Aluminum alloys serve as crucial materials in transportation, aerospace, new energy, and other domains. Ultrasonic welding, recognized as an efficient and environmentally friendly solid-state joining technique, has demonstrated significant potential in addressing the connection issues of aluminum alloys, particularly in the joining of dissimilar materials such as steel, copper, magnesium, titanium, and nickel. This paper conducts a systematic review of the global research progress on ultrasonic welding of aluminum alloys over the past 15 years. It encompasses both aluminum/aluminum homojunctions and five typical dissimilar material systems, namely, aluminum/steel, aluminum/copper, aluminum/magnesium, aluminum/titanium, and aluminum/nickel. The study comprehensively summarizes the research accomplishments regarding the microstructure evolution, microhardness distribution, interfacial temperature field, and mechanical properties of the welded joints. It emphasizes that the core mechanism of ultrasonic welding resides in the intense interfacial plastic deformation and dynamic recrystallization induced by high-frequency vibration, thereby attaining metallurgical bonding. For combinations with a tendency to form intermetallic compounds, such as aluminum/steel, aluminum/copper, and aluminum/magnesium, the morphology and thickness of the interfacial compound layer exert a decisive influence on the joint performance. In systems like aluminum/titanium and aluminum/nickel, the bonding primarily depends on mechanical interlocking and solid-state diffusion. Innovative processes like interlayer introduction have proven effective in enhancing interfacial bonding quality. Based on the existing achievements, this review aims to offer a systematic theoretical foundation and technical guidance for the in-depth research and industrial promotion of ultrasonic welding technology for aluminum alloys.</p>