Effect of a magnetic field on the banding phenomenon in aluminium–silicon eutectic alloy

Abstract

The effect of a magnetic field on the frequency of transverse band formation in directionally solidified Al–Si eutectic alloy is investigated for a range of solidification speeds. The band spacing for both field and no-field ingots is found to be linearly dependent on the solidification rate, but for a given solidification speed a magnetic field of 30 000 Oe, applied perpendicular to the solidification direction, reduced the band spacing by approximately 35%. The results are explained in terms of the effects of the solidification rate and magnetic field on the impurity concentration ahead of the solid–liquid interface, a fluctuating impurity level being the direct cause of the banding phenomenon. It is shown that the magnetic-field effect on band spacing is consistent with the theories (previously published) developed to account for the observed effects of a magnetic field on alloy diffusion and solidification.