MACROSEGREGATION DURING DENDRITIC ARRAYED GROWTH OF HYPOEUTECTIC PB-SN ALLOYS - INFLUENCE OF PRIMARY ARM SPACING AND MUSHY ZONE LENGTH

Thermosolutal convection in the dendritic mushy zone occurs during dir ectional solidification of hypoeutectic lead tin alloys in a positive thermal gradient, with the melt on the top and the solid below. This r esults in macrosegregation along the length of the solidified samples. The extent of macrosegregation increases with increasing primary dend rite spacings for constant mushy zone length. For constant primary spa cings, the macrosegregation increases with decreasing mushy zone lengt h. Presence of convection reduces the primary dendrite spacings. Howev er, convection in the interdendritic melt has significantly more influ ence on the spacings as compared with that in the overlying melt, whic h is caused by the solutal buildup at the dendrite tips.