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

Abstract

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 α′_s phase as a core with the edge of decomposed β′_s phase and decomposed η′_s in the interdendritic regions. A series of complex phase transformations was observed. Both decompositions of β′_s and η′_s were determined at an early stage of ageing and a four-phase transformation, α_f+ɛ→T′+η, was observed at the boundaries of α_f phase and the ɛ phase, instead of clearly observed at the boundaries of ɛ phase, in a solution-treated Zn-Al alloy during prolonged ageing.