UC Irvine

Liquid-state Ultrasonic Treatment (UST) is an emerging industrial liquid-processing method to enhance the quality and microstructure of cast parts while eliminating the need for chemical modifiers. The effects of liquid-state UST on the solidification chronology, grain refinement, and the morphology of secondary phases of commercial A380 aluminum alloy are systematically investigated to identify the limiting processing conditions and elucidate the underlying mechanisms. Multifrequency Multimode Modulated (mf-UST) is a novel impartment method that eliminates intensity decay via frequency-swept ultrasonics. Trials were completed in commercial A380 aluminum alloy using mf-UST impartment method above the liquidus temperature. A380 was chosen to observe the effectiveness of treatment on the modification of Fe-containing intermetallics such as β-Al5FeSi and α-Al15(Fe, Mn)3Si2 which appear frequently in recycled aluminum compositions. Samples were produced from trials at three treatment temperatures (700 °C, 680 °C, 660 °C) and three treatment times (5, 10, 15 min). Liquid state mf-UST modified the formation and morphology of the α-Al15(Fe, Mn)3Si2 intermetallic phase and could be tailored via changing treatment time. mf-UST provoked the production of an unusually stable modified Si within the hypoeutectic alloy which nucleates on AlP and AlP/cavity combinations. The maximum observed grain refinement was found within 5 min of mf-UST at 680 °C displaying an 85.8% reduction in grain size. Results demonstrate that mf-UST applied in the liquid state influences solidification chronology and thus impacts the resultant intermetallic morphology. These new primary intermetallic morphologies likely affect the degree of Al grain refinement, in addition to the pre-existing ‘oxide refinement’ theory.