Comparison of macrosegregation in titanium and aluminium alloy ingots

The existing information shows that positive zonal segregation appears in titanium alloy ingots under the conditions of vacuum are remelting. This segregation is characterized by enriching of central and upper ingot zones with elements having partition coefficient values noticeably less than unity (Cu, Ni, Cr, Fe, Si, Mn). Negative segregation (enriching of peripheral zones) of such elements as Cu, Mg, Zn. Si also having partition coefficient less the unity develops in continuous casting of aluminium alloy ingots. However, positive segregation also occurs in aluminium alloy ingots during vacuum are remelting or continuous casting accompanied by vigorous metal stirring in molten pool. Analysis of these data and the results of investigations concerning copper, magnesium, Ni superalloys and steel ingots allowed one to validate the general model of zonal segregation. Values of the partition coefficient and solidification shrinkage, sizes of the transition region and the rate of metal movement in the molten pool are of prime importance. Various relationships of these parameters governs development of a type of macrosegregation (positive or negative) or production of a rather homogeneous ingot. (C) 1999 Elsevier Science S.A. All rights reserved.