THE EFFECT OF ELECTROMAGNETIC STIRRING ON MACROSTRUCTURE AND MACROSEGREGATION IN THE ALUMINUM-ALLOY-7150

Ingots of aluminium alloy 7150 (Al-Zn-Mg-Cu) were unidirectionally sol idified vertically downwards under conditions of natural convection an d electromagnetic stirring of the bulk liquid. Increased fluid flow in the bulk liquid was found to promote the formation of equiaxed grains and hence the columnar-equiaxed transition (GET). Increased fluid flo w was also associated with an increase in macrosegregation of the allo ying elements. The extent of segregation was greatest for Cu and least for Zn. The experimental observations suggest that macrosegregation i n the ingots was caused by the displacement of solute-enriched liquid from the mushy zone as a result of the electromagnetically stirred bul k liquid being driven into the solidification front.