Abstract
A superplastic aluminum-zinc eutectoid alloy was fatigue tested at 100 °C and 200 °C at different constant plastic strain amplitudes and strain rates. During fatigue deformation, the average peak stress increased with increasing strain rate and grain size and decreasing temperature. It was almost independent of the plastic strain amplitude. To detect interfacial sliding, interphase boundary migration, and intergranular cracking, selected areas on surfaces were examined before fatigue deformation and re-examined after fatigue deformation. Interface sliding, which was almost reversible, occurred on (Al)/(Al) and (Zn)/(Zn) grain boundaries and on (Al)/(Zn) interphase boundaries. Grains appeared to slide in groups. Cracks followed grain and interphase boundaries. Along an intergranular crack, most interfaces were (Zn)/(Zn) grain boundaries and (Al)/ (Zn) interphase boundaries. Grains deformed to accommodate interfacial sliding. The absence of slip lines suggested that diffusional creep made a significant contribution to deformation in grains of the zinc-rich phase. Deformation of the aluminum-rich phase involved the glide and climb of dislocations.
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