TENSILE CREEP DEFORMATION AND MICROSTRUCTURAL CHANGE IN CAST ZN-AL ALLOY

Phase transformation and microstructural change of an as-cast eutectoi d Zn-Al alloy specimen Zn-76-Al-22-Cu-(2) (mass%) were investigated du ring tensile creep testing by using scanning electron microscopy (SEM) and X-ray diffraction techniques. Creep induced decomposition of a me tastable eta(T)' phase and a four-phase transformation, alpha + epsilo n --> T' + eta, occurred during the creep testing. Also the detailed m icrostructural change from decomposed dendritic structure into spheroi dized structure was observed in the neck zone and the rupture part of the specimen. The rupture was initiated within the spheroidized struct ure and developed along the grain boundaries of the fine lamellar stru cture and the decomposed eta(T)' phase.