Effects of tensile stress on microstructural change of eutectoid Zn-AI alloy

Microstructural changes and phase transformations of eutectoid Zn-Al-based alloy ZnA120.2Cul.8 (wt pct) were studied under tensile stress by using X-ray diffraction and scanning electron microscopy (SEM) techniques. It was found that the lamellar microstructure of the heat-treated eutectoid Zn-Albased alloy changed partially into a spheroidized structure at the rupture part of the specimen after tensile testing, while the lamellar structure at the bulk part of the specimen remained stable in the original state. The X-ray diffraction identification results showed that two phase transformations,i.e., decomposition of metastable phase η′_T and a four-phase transformation, α+ ε → T + η, occurred during tensile testing. It was concluded that the tensile stress affected not only microstructural change but also phase transformation of the alloy. The SEM observation on the etched specimen showed clearly the morphology of the microstructural change.