Movement behavior and separation of Al2O3 from Al melt under rotating magnetic field

The effect of a rotating magnetic field (RMF) on the distribution of Al2O3 particles with an Al melt was studied by means of simulation and experiment. The results show that Al2O3 particles (diameter of 1–10 µm, 1wt.%) are significantly agglomerated at the top of ingots when subjected to an RMF, and their distribution is influenced by both the intensity and the duration of RMF application. The optimal separation efficiency is achieved with the magnetic intensity of 12 mT for 120 s. The number of the particles at the bottom and the middle decreases by 64.5% and 69.7%, respectively, while that at the top increases by 242.5% compared to the condition without an RMF. However, if further increase the intensity or the duration of RMF, it can induce turbulent flows that draw some of the separated Al2O3 particles back into the melt, reducing separation efficiency. The calculation results show that as the magnetic intensity increases from 6 mT to 18 mT, the velocity difference between the particles and the Al melt flow quadruples, increasing from 0.013 m·s−1 to 0.066 m·s−1. Driven by this velocity difference, centrifugal motion, and secondary circulation, Al2O3 particles tend to migrate upwards within the melt, facilitating the separation of impurity particles and enhancing the purity of the melt.