Microsegregation, also known as interdendritic segregation and coring, occurs over short distances, often between small dendrite arms. The centers of the dendrites, which represent the first solid to freeze, are rich in the higher melting point element in the alloy. The regions between the dendrites are rich in the lower melting point element, since these regions represent the last liquid to freeze. The composition and properties of the solid portion of an alloy differ from one region to the next, and it is expected that a casting would have poorer properties as a result.
Microsegregation can cause hot shortness. Consider a Cu-40% Ni alloy. When it is heated to 1225°C, below the equilibrium solidus but above the nonequilibrium solidus, the low-nickel regions between the dendrites melt.