Abstract
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.
Highlights
The dynamic solidification of Sn-38.1% Pb eutectic alloy within an ultrasonic field is investigated at a frequency of 35 kHz
A “dendritic-equiaxed” structural transition occurs in the primary (Sn) phase, and its grain size is significantly reduced within the ultrasonic field
A “dendritic-equiaxed” structural transition occurs to the primary (Sn) phase, and its grain size is significantly reduced by the ultrasonic field
Summary
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. Campell [2] reviewed the effects of various kinds of vibration on solidification, and summarized that sound intensity, frequency and vibration mode are the three key factors Another important parameter, the critical size of alloy sample within which ultrasound can function, has been neglected by most researchers. The mutual motion between growing solid phases and liquid alloy induces sound attenuation because the propagation distance increases [10] These result in the weakening of both the cavitation effect and acoustic streaming [11]. The mechanism of Sn-Pb eutectic growth within an ultrasonic field is discussed
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