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Aluminium alloys with higher content of alloying elements arevery susceptible to the emergence of crystal segregation thatsignificantly affects the mechanical, physical and chemicalproperties of these alloys. Crystal segregation is calledchemical heterogeneity in microscale and is formed duringcrystallization. Crystallization of alloys does not occur at aparticular temperature, as is the case of pure metals, but in acertain temperature interval. During cooling of the melt occursto formation of different regions within the dendritic cellthat differs in chemical composition. Generally is crystalsegregation defined as chemical heterogeneity formed duringalloy crystallization that is enriched or deprived of alloyingelements and impurities that segregate unevenly across thesurface of the dendrites. In the central area of the dendriticcells is alloy deprived of alloying elements, while the outerparts of dendritic cells and in space between dendrites is theconcentration of alloying elements richer. This concentrationhas a hyperbolic course, when the central region of dendriticcells has the lowest concentration of the alloying elements andthe outer part of dendrite boughs and interdendritic space havethe maximum. Distribution of individual elements has arecurring character and can be described by sine function. Thedistance between two main axes of dendritic cells is affectedby the temperature interval between the liquidus and solidusfor the given alloy, the cooling rate of the melt andtemperature gradient during solidification. Formation of thecrystal segregation in aluminium alloys rich in alloyingelement and additives cannot be prevented, it is possible onlyinfluence its scope and with the right choice of heat treatmentparameters can be suppressed. To suppress the crystalsegregation the castings are subjected to heat treatment whichis called homogenization annealing. It is the diffusion processin which there occurs to a balancing of chemical composition ofalloy and the uniformity of its structure.

The Use of Colour Metallography and EDS for Identification of Chemical Heterogeneity of Selected Aluminium Alloys Copper and Zinc Alloyed