Solidification characteristics of Pb-Sb hypereutectic alloy within ultrasonic field

The solidification of Pb-16%Sb hypereutectic alloy is investigated within ultrasonic field with a frequency of 15 kHz. It is found that the ultrasonic field promotes crystal nucleation and terminates the further bulk undercooling of the alloy melt. Theoretical analysis shows that the cavitation effect and the forced bulk vibration are the main factors that reduce the undercooling level. With the increase of ultrasound intensity, the primary (Sb) phase experiences a growth mode transition from faceted to non-faceted branched growth, and the macrosegregation of primary (Sb) phase is gradually suppressed. In addition, the microstructures of Pb-Sb eutectic exhibit a conspicuous coarsening with increasing ultrasound intensity, and a structural transition of "lamellar eutectic-anomalous eutectic" occurs when ultrasound intensity rises up to 1.6 W/cm². The ultrasonic field also changes the solute distribution adjacent to the solidification front, which lowers the Pb contents in primary (Sb) phase.