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Metals 2014, 4(4), 477-489; doi:10.3390/met4040477

Correlation vs. Causation: The Effects of Ultrasonic Melt Treatment on Cast Metal Grain Size

1
Materials Science and Engineering Department, University of Wisconsin-Milwaukee, 3200 N. Cramer St., Milwaukee, WI 53211, USA
2
Army Research Laboratory, Weapons and Materials Research Directorate, Aberdeen Proving Ground, MD 21005, USA
*
Author to whom correspondence should be addressed.
Received: 11 July 2014 / Revised: 16 September 2014 / Accepted: 22 October 2014 / Published: 29 October 2014
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Abstract

Interest in ultrasonic treatment of liquid metal has waxed and waned for nearly 80 years. A review of several experiments representative of ultrasonic cavitation treatment of Al and Mg alloys shows that the theoretical mechanisms thought to be responsible for grain refinement are (1) cavitation-induced increase in melting temperature predicted by the Clausius-Clapeyron equation and (2) cavitation-induced wetting of otherwise unwetted insoluble particles. Neither of these theoretical mechanisms can be directly confirmed by experiment, and though they remain speculative, the available literature generally assumes that one or the other or both mechanisms are active. However, grain size is known to depend on temperature of the liquid, temperature of the mold, and cooling rate of the entire system. From the reviewed experiments, it is difficult to isolate temperature and cooling rate effects on grain size from the theoretical effects. Ultrasonic treatments of Al-A356 were carried out to isolate such effects, and though it was found that ultrasound produced significant grain refinement, the treatments also significantly chilled the liquid and thereby reduced the pouring temperature. The grain sizes attained closely correlated with pouring temperature suggesting that ultrasonic grain refinement is predominantly a result of heat removal by the horn and ultrasonic stirring. View Full-Text
Keywords: ultrasonic cavitation; grain refinement; metals and alloys; nucleation ultrasonic cavitation; grain refinement; metals and alloys; nucleation
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Ferguson, J.B.; Schultz, B.F.; Cho, K.; Rohatgi, P.K. Correlation vs. Causation: The Effects of Ultrasonic Melt Treatment on Cast Metal Grain Size. Metals 2014, 4, 477-489.

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