Abstract: Since the development of the aviation industry, improving the flight performance and reducing the weight of aircrafts has always been the goal pursued by aviation designers. Therefore, it becomes increasingly important to develop a new alloy material with high hardness, high strength, and light weight. To obtain excellent mechanical properties and good corrosion resistance, a new kind of alloy material, ZL205A alloy, was developed by the Beijing Institute of Aerial Materials (BAM) in the 1960s. Owing to its favorable mechanical properties and excellent corrosion resistance, ZL205A alloy has been well applied in the aviation industry. However, this kind of Al alloy still possesses some undesirable solidification defects: shrinkage, porosities, coarsening grains, and solute segregation. Ultrasonic melt treatment (UST) provides a means to eliminate or modify these defects. In the present work, the effects of UST on ZL205A alloy were investigated for two conditions, i.e., before casting and during solidification in ambient environment. Then, the effects of ultrasonication on the as-cast microstructures and the tensile properties were accordingly characterized and analyzed. For the case in which UST was only introduced before casting (holding temperature at 750℃), degassing and the distribution of secondary phases were modified. For the case in which UST was only introduced when cooling from 750℃ for 7 min 10 s to about 650℃, grain refinement and reduced porosities were generated. When UST was continuously employed for both conditions, the above properties were further improved compared with those of ingots without ultrasonic treatment. The mechanical tensile test results show that the improvement of the ingot internal structure can improve the ingot mechanical tensile properties, which proves the correctness of the above research results. Thus, UST carried out at two different conditions induced different regulatory functions and influencing mechanisms. This study shows that the UST of ZL205A aluminum alloy in different melt states has different emphases on improving the internal structure of the ingot.