Effect of a magnetic field on dendritic morphology in Al-Cu hypoeutectic alloy

Abstract

The effect of a high magnetic field on dendritic morphology in Al-10at%Cu alloy was investigated with help of differential thermal analysis (DTA). The DTA curves showed that nucleation temperature of primary α-Al phase was reduced and its growth rates increased in magnetic fields. The reduction of nucleation temperature was due to the increase of interfacial free energy between liquid and Al nucleus in a magnetic field, while imposition of a magnetic field modified the effective distribution coefficient and further altered the solutal and curvature undercooling, which made the driving force for dendritic growth becoming larger. It was shown that the dendritic morphology was changed from disordered dendrites to regular ones and the angle between preferred growth direction and magnetic field is about 55° in 12T. The formation of regular primary dendrites could be attributed to magnetic orientation and the suppression of free convection.