Effects of vibration during solidification

Abstract

A review of the literature on the effects of vibration on solidification is presented in terms of a unifying concept, the frequency–amplitude f-a map. Some theoretical models are assessed in relation to data from the literature summarized on the f-a map, revealing a mechanical-fragmentation model as a best fit for dendritically solidifying alloys. For materials such as pure metals solidifying on a planar front the f-a map shows a close correlation between the theoretical threshold for cavitation and the onset of grain refinement. In general, there seems little evidence to suggest fundamental differences between ultrasonic, sonic, and subsonic vibration. The undoubted improvements to mechanical, corrosion, and other properties appear to be countered to date by troublesome side effects such as ejection of liquid from the melt (which is satisfactorily predicted and avoidable); occasional porosity when vibrating in a cavitation regime (predictable and potentially avoidable); coarsening of dendrite structure and second phases (explainable but unavoidable); and hot tearing (for which neither explanation nor avoidance seems yet to have been attained).