Abstract
Scaling up ultrasonic cavitation melt treatment (UST) requires effective flow management with minimised energy requirements. To this end, container dimensions leading to the resonance play a crucial role in amplifying pressure amplitude for cavitation. To quantify the importance of resonance length during the treatment of liquid aluminium, we used calibrated high-temperature cavitometers (in the range of 8–400 kHz), to measure and record the acoustic pressure profiles inside the cavitation-induced environment of liquid Al and deionized water (used as an analogue to Al) excited at 19.5 kHz. To achieve a comprehensive map of the acoustic pressure field, measurements were conducted at three different cavitometer positions relative to the vibrating sonotrode probe and for a number of resonant and non-resonant container lengths based on the speed of sound in the treated medium. The results showed that the resonance length affected the pressure magnitude in liquid Al in all cavitometer positions, while water showed no sensitivity to resonance length. An important practical application of UST in aluminium processing concerns grain refinement. For this reason, grain size analysis of UST-treated Al-Cu-Zr-Ti alloy was used as an indicator of the melt treatment efficiency. The result showed that the treatment in a resonance tank of L=λAl (the wavelength of sound in Al) gave the best structure refinement as compared to other tested lengths. The data given here contribute to the optimisation of the ultrasonic process in continuous casting, by providing an optimum value for the critical compartment (e.g. in a launder of direct-chill casting) dimension.
Highlights
Ultrasonic cavitation melt treatment (UST) is an environmentally friendly, economical and sustainable technique [1,2,3] that has been shown to benefit the microstructure and mechanical properties of metallic alloys upon casting
We measured experimentally the acoustic pressure induced by ultrasonic processing in both liquid Al and DI water with a broad frequency-calibrated cavitometer (8–400 kHz) for different tank lengths – in both resonant and non-resonant conditions – keeping all other dimensions constant and for various positions of the sensor
The effect of the ultrasonic treatment on liquid Al was verified by metallographic examination
Summary
Ultrasonic cavitation melt treatment (UST) is an environmentally friendly, economical and sustainable technique [1,2,3] that has been shown to benefit the microstructure and mechanical properties of metallic alloys upon casting. Optimisation requires deep understanding of the parameters affecting the process. Inherent difficulties such as the opacity of the liquid metals and (until recently) lack of high temperature experimental tools that enable direct measurement of cavitation activity, limited the understanding of acoustic bubble dynamics and associated flow field effects. This imposes difficulties in process optimisation and control and eventually scaling up for adoption by industry. The effec tiveness of UST is assessed through indirect post-process observations, Sonotrode Cavitometer
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