Regulation of ultrasonic atomization behavior and preparation of low-melting-point alloy powders.

Viscous damping and acoustic radiation pressure challenge the ultrasonic atomization of high-viscosity and high-surface-tension fluids. To address this issue and reveal the underlying mechanisms, a rotational ultrasonic atomization platform was developed. The effects of ultrasonic power, liquid viscosity, horn geometry, rotation speed, and initial momentum on atomization behavior were investigated using high-speed imaging. For low-viscosity liquids, increasing ultrasonic power elevated the Weber number, widened the spray angle from 63 degrees to 142 degrees, and shortened the atomization incubation period from 10.86 s to 8.15 s. For high-viscosity liquids, viscous damping suppressed the capillary wave pathway, making cavitation the dominant mechanism. Driven by the secondary Bjerknes force, cavitation bubbles bridged into branched, neural-network-like clusters. Their collective collapse overcame the viscous dissipation barrier, providing experimental validation for Boguslavskii's hypothesis. A critical rotation threshold of 60 revolutions per minute was identified. Below this threshold, acoustic pinning confined the liquid on the horn end-face; above it, centrifugal force forcibly thinned the liquid film, triggering atomization. Furthermore, horn geometry determined the atomization onset location, while increased initial momentum accelerated initiation. Experiments on Sn-58Bi melt verified that coupling optimized horn geometry with a centrifugal force field effectively overcomes the surface energy barrier. Based on these findings, a six-stage atomization model is proposed. The capillary wave mechanism primarily achieves initial film thinning by stripping large droplets, while cavitation dominates fine fragmentation. This work systematically investigates the atomization mechanism of high-resistance fluids and demonstrates the fabrication of metal powders via rotational ultrasonic atomization.