Dynamic solidification of Sn-38.1% Pb eutectic alloy within ultrasonic field

The dynamic solidification of Sn-38.1% Pb eutectic alloy within an ultrasonic field is investigated at a frequency of 35 kHz. As the sample height H is reduced, the effect of ultrasound on macrosegregation becomes more prominent, and the volume fraction of spherical eutectic cells increases correspondingly. When H equals the wavelength λ in liquid alloy, the introduction of ultrasound enlarges the distribution region of the primary (Sn) phase, but reduces the domains of the Sn-Pb eutectic and primary (Pb) phases. Meanwhile, a "dendritic-equiaxed" structural transition occurs in the primary (Sn) phase, and its grain size is significantly reduced within the ultrasonic field. Once H decreases to λ/2 and λ/4, the ultrasonic field promotes crystal nucleation and suppresses further undercooling of the bulk liquid alloy. Theoretical analyses indicate that the local high pressure induced by the cavitation effect and the stirring effect due to acoustic streaming are the main factors dominating the eutectic growth mechanism during dynamic solidification.