The influence of electromagnetic stirring (EMS) on grain refinement has been studied for two copperbase alloys (Cu-1 wt pct Ni-1 wt pct Pb-0.2 wt pct P and Cu-4 wt pct Zn-4 wt pct Sn-4 wt pct Pb) solidified in a Bridgman furnace. Metallographic inspection of the specimens, temperature measurements during solidification, and numerical simulations performed with CALCOSOFT revealed that the efficiency of EMS is strongly dependent upon the penetration of the liquid in the mushy zone and therefore upon the position of the convection vortices with respect to the liquidus front. In particular, the low-concentration alloy could be grain refined only at high power and when the coil was moved close to the liquidus front. These results were analyzed on the basis of a dendrite fragmentation criterion similar to Flemings' criterion for local remelting of the mushy zone. Considering that the component of the fluid flow velocity along the thermal gradient, u l,G ϭ , must be larger than the casting speed, V c , dendrite fragmentation occurs if at some depth within the mushy zone where dendrite arms are sufficiently developed, typically 8 2 , where 2 is the final secondary dendrite arm spacing, K is the permeability of the mushy zone, g l is the volume fraction of liquid, is the dynamic viscosity, B 0 is the magnetic field, 0 is the permeability of vacuum, and d ind is the distance between the inductor and the liquidus front.

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Single pan thermal analyses (SPTA) have been performed on Cu-14.5 wt.% Sn, Cu-21.3 wt.% Sn and Cu-26.8 wt.% Sn peritectic alloys. For this purpose, a SPTA assembly has been built and calibrated. As the latent heat is a function of temperature and composition during solidification of alloys, a new heat flow model coupled to a Cu-Sn thermodynamic database has been defined for the calculation of the corresponding evolutions of the solid mass fraction, f s ðT Þ. To verify the accuracy of this model, a close comparison with a microsegregation model that includes back-diffusion in the primary a-solid phase has also been conducted successfully. The thermal analyses have finally shown that the Cu-Sn phase diagram recently assessed in the review of Liu et al. is the most reliable.

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