Ultrasonic Treatment (UST) is a novel and nascent liquid processingProcessing method with potential as a sustainable castingCasting technology for use in the treatment and refinement of scrap and downcycled aluminum alloyAluminum alloy systems. UST is the application of ultrasonic energy into a liquid metalMetals which induces modification and refinement in the solidified microstructureMicrostructure. The two frequency modalities through which UST is imparted into the liquid metalMetals, i.e.—fixed frequency and multifrequencyMultifrequency, dictate the effectiveness of treatment. Applying a multifrequencyMultifrequency ultrasonic wave increases the efficiency, intensity, and depth of treatment. Downcycled and scrap aluminum alloysAluminum alloy contain an increased presence of detrimental intermetallicIntermetallic phases whose morphologies have a negative impact on mechanical performance, making them unfit for cast products. MultifrequencyMultifrequency UST demonstrates the ability to modify the intermetallicIntermetallic phases and grain size through liquid-state application. Changes to the microstructureMicrostructure in an Al–7.8%Si–1.27%Fe will be discussed and briefly compared with changes seen in a complimentary study of A380. MultifrequencyMultifrequency UST exhibits a time-dependent behavior. UST produced a 51.5% decrease in the grain size of Al–7.8%Si–1.27%Fe and primary Si formed in a hypoeutectic system.