Ageing characteristics of furnace cooled eutectoid Zn-Al based alloy

Phase transformations and microstructural changes of a furnace cooled eutectoid Zn-Al based alloy were studied during ageing at 100 and 170°C using X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Three phase transformations occurred in the furnace cooled eutectoid Zn-Al alloy. The metastable η′_FC phase decomposed during isothermal ageing. The four-phase transformation, α + ε → T′ + η followed the discontinuous decomposition of the η′_FC phase. Typical morphologies of the decomposition of the η′_FC and ε phases were observed in scanning electron microscopy. Decomposition of Al-rich α phase was observed during the prolonged ageing by transmission electron microscopy. The different types of decomposition of the different metastable phases dominated at different stages of ageing.