For 7475 Al alloy, there were micrographs showing filaments or whiskers formation during the separation stage of superplastic elongation. This indicates the presence of liquid phase which accommodates grain boundary sliding to reach superplasticity. On the other hand, there is no such phenomenon reported regarding Mg alloy in literatures. Scanning electron microscopic (SEM) fractography exceptionally exhibits a mark of grain boundary sliding and its accommodating mechanism of inter-granular liquid phase. Under the testing conditions of 350 degrees C and 1x10(-4) s(-1), the initially fine-grained structure (3.7 mu m) yields 642% superplastic elongation and exhibits fluffy appearance on the fractured surface. For other specimens showing less superplasticity, their fractured surfaces exhibit partial fluffy appearance.
TRANSACTIONS OF NONFERROUS METALS SOCIETY OF CHINA