Microstructural changes inside the lamellar structures of alloy ZA27

The microstructural changes inside the lamellar structure of the cast and aged alloy ZA27 were studied using TEM, XRD and SEM techniques. Using TEM, the network of transitional phase ηm′ was determined to be of an fcc crystal structure inside the lamellae η phase during ageing at 150 °C. The mechanism of the decomposition of the η phase lamellae can be summarized as follows: η → ηm′ + η′ → α + η. The adjacent co-existence of the ε phase and the T′ phase inside the α phase lamellae confirmed that a four phase transformation, α + ε → T′ + η, had occurred during the prolonged ageing.