Effects of medium-frequency electromagnetic field on solidification process of semi-continuous casting AZ31 magnesium alloy

Abstract

Billets of AZ31 magnesium alloy with and without middle-frequency electromagnetic field were investigated. Within the framework of classical solidification theories, the effects of medium-frequency electromagnetic field on the as cast billets were studied. Compared with microstructures and mechanical properties of the direct chill casting (DC) billet, the medium-frequency electromagnetic continuous casting (MFEMC) billet shows refined and even microstructures throughout the whole section of the billet and improved mechanical properties. The refined microstructure is in connection with increased nuclei which are likely to be as a result of electromagnetic undercooling which decreases the free energy barrier of nucleation and increases the nucleation tendency by an induced undercooling ΔT and forced convection. The differences between grain sizes of different locations in the billet are a result of particles' forced movements with particles in the inner area moving outward and particles in the border area moving inward. The former movement contributes to slightly coarser grains in outer areas of the billet while finer grains are obtained in the centre area of the billet by mutual collisions due to the latter movement.