Dilute Al-Cu and Al-Mg alloys were solidified unidirectionally upward under transverse magnetic field and the solute distribution in the grown solid was analyzed by emission spectrometer for macro-segregation. A non-steady state solidification was observed where the solute concentration in the grown solid decreased with the progress of solidification, when a dilute Al-Cu alloy was solidified with positive axial temperature gradient. This was caused by sedimentaion of Cu-rich melt during melt-down of the bar stock.
In the case of Al-Mg alloy, the solute concentration in the grown solid increases with the progress of solidification because of solutal or thermosolutal convection. Reduction of convection intensity in the melt and therefore the reduction of axial macro-segregation in all of dilute Al-Cu and Al-Mg alloys were achieved by the presence of a transverse magnetic field. The character of the convection was discussed in view of solutal and thermosolutal convection and convection criterions are proposed to combine the solutal Rayleigh number, $Ra_S$ and the thermal Rayleigh number, $Ra_T$. For the estimation of the effect of the magnetic field the solutal Grashof number, $Gr_S$ and the square of the Hartman number were combined.
