 The distribution of the two elements within the grains is nonuniform, a phenomenon termed 'segregation'; that is, concentration gradients are established across the grains.As a casting having a cored structure is reheated, grain boundary regions will melt first inasmuch as they are richer in the low-melting component.This produces a sudden loss in mechanical integrity due to the thin liquid film that separates the grains.Furthermore, this melting may begin at a temperature below the equilibrium solidus temperature of the alloy.