Effects of high-temperature ultrasonic melt treatment on microstructural evolution and precipitation kinetics in Al–Cu alloys

Abstract

Ultrasonic melt treatment (UST) has been proposed as a promising approach to engineer microstructures of metallic materials by injecting high-intensity ultrasonic waves into molten metal, enabling porosity control and refinements of grains and dendrites. Here, we show that applying high-temperature UST (∼100 °C above the liquidus) to Al–10 wt% Cu alloys—despite the absence of grain refinement—still altered dendritic evolution and downstream precipitation behavior by promoting extensive solute homogenization in the liquid. Under rapid quenching, UST produced uniform dendritic morphologies and precipitation behavior, with fine θ’ (Al2Cu) precipitates and a sharp aging peak. In contrast, non-UST alloys exhibited bimodal dendritic structures and broad aging responses. Even at slower cooling rates, UST further suppressed dendritic variability and improved precipitation-hardening uniformity. The observed changes in dendritic spacing and precipitation kinetics can be directly rationalized using the Al–Cu phase diagram together with classical nucleation theory. These findings emphasize the importance of molten-state solute homogenization induced by high-temperature UST, offering a scientifically grounded and industrially viable pathway to property-consistent aluminum castings within a short processing window.