Composition: Zinc impurified with Cadmium.

Processing: Sand casting.

Etching: cotton impregnated with a diluted solution of HCl (50%) until the macrostructure is revealed. For revealing the microstructure, immersion in 2% nital for 30-120 s.

The presence of Cd as an impurity promotes the formation of equiaxial grains. The latter show different brightness depending on their crystallographic orientation. Lenticular twins can be seen within the interior of some grains. The dendritic morphology becomes visible after longer etching times. This is associated with Cd segregation. As shown in the last two micrographs, dendrites, grain boundaries and Cd segregation (darker regions) are better discerned if a polished specimen is etched with nital. This lack of homogeneity in solid solutions is known as coring or microsegregation, which is favoured under non-equilibrium cooling conditions.

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