Thermosolutal convection and convective instability during unidirectional solidification of Al-Mg alloys in vertical Bridgman furnace were investigated. The furnace was modified to give the same growth rate of the solidification front as the furnace moving rate. The morphology of solidification interface was revealed by quenching method, and the result was in agreement with the constitutional supercooling criterion.
The solute distribution in the solid was analyzed by EDX, SIMS and spectrometer and the temperature fluctuation in the melt ahead of solidification front was measured by DTA for Al-Mg and Pb-Sn alloys. There was no detectable temperature fluctuation and microsegregation. But the macrosegregation in the axial direction was confirmed and was in the range between the cases of no convection and complete convection.
Consequently, the flow pattern of thermosolutal convection is estimated to be a very weak laminar flow.
The macrosegregation in axial direction increased as velocity decreased in the planar solidification range which is consistent with the computational analysis about thermosolutal convection and convective instability.
