Resonant pulsed electromagnetic stirring of melt for effective grain fragmentation

Abstract

The paper describes the results of an experimental research, demonstrating and explaining the effect of grain fragmentation, caused by pulsed resonant electromagnetic stirring. In the experiments, 6082 aluminium alloy melt was directionally solidified under the influence of continuous (AMF) and pulsed application (PMF) of an alternating magnetic field. The frequency of applied PMF was in accordance to the low-frequency circulation of the melt, causing the resonant increase of a pulsed component of the melt velocity. The structure of electromagnetically stirred specimens was compared to those, solidified without a magnetic field. A strong fragmentation effect (decrease of an average grain size on 51%, comparing with the solidification in natural conditions) for the case of resonant EM stirring was stated. Further, to analyse the influence of the flow, appearing due to the resonant stirring, we observed the formation of solid/liquid interface and a macro-crystalloid structure during solidification of continuously and pulsed stirred melt by applying the novel method of neutron radiography. The results confirmed the strong influence of the pulsed component of velocity on thermal conditions during solidification and, consequently, the metal structure.