Complex microstructural changes in as-cast eutectoid Zn-Al alloy

Phase transformations and microstructural changes of an as-cast eutectoid Zn-Al alloy (ZnAl₂₂Cu₂) were investigated during isothermal holding. The typical dendritic structures consisted of _s phase as a core with the edge of decomposed _s phase and decomposed _s in the interdendritic regions. A series of complex phase transformations was observed. Both decompositions of _s and _s were determined at an early stage of ageing and a four-phase transformation, _f+T+, was observed at the boundaries of _f phase and the phase, instead of clearly observed at the boundaries of phase, in a solution-treated Zn-Al alloy during prolonged ageing.