The effect of frequency on solidification characteristics of AZ80 alloy during electromagnetic DC casting

The effects of electromagnetic frequency on solidification characteristics of AZ80 magnesium alloy billet during electromagnetic Direct-chill (DC) casting were investigated experimentally. The billet with diameter 320 mm was solidified in an oscillation electromagnetic field (EMF) with the imposition of a pulse current at the frequency of 20 Hz, 30 Hz, and 40 Hz when the time-averaged current intensity was 80 A and duty cycle was 20%, from which pulse electromagnetic force was yielded. The macrostructure evolution was quantitatively examined based on the grain size and its distribution, and the conductivity was measured to evaluate the characteristics of solidified structures. The effects of electromagnetic frequency on macro- and microstructure evolution, phase composition, element segregation, and conductivity distribution were discussed in detail. It was observed that the solidified structure under pulse oscillation electromagnetic field is sensitive to the electromagnetic frequency, and there is an effective frequency range for the refinement of solidified structures. The grain size range decreases from 815 μm ∼ 951 μm (without EMF) to 408 μm ∼ 612 μm (EMF-30Hz). The segregation ratio reduced evidently at the frequency of 30 Hz. As the frequency further decreases or increases, the grain size and segregation ratio increase. Moreover, the conductivity distribution on the cross section of the billet is more uniform in the presence of EMF, which is closely related to the solidification structures. (paper)