Superplasticity in an AZ80 magnesium alloy subjected to friction stir processing (FSP) has been investigated. FSP was carried out at two traveling speeds of 150mm/min and 300mm/min for grain refinement. Optical microscopy on cross section of processing direction revealed an obvious difference in size and feature between the stir zones at the two traveling speeds. The hardness after FSP at a room temperature was about 30HV higher than as-received sample. The maximum stress of the FSPed sample lowered remarkably at lower strain rates compared with that of the as-received one at 573K and 673K. On the other hand, the elongation to failure of the FSPed sample showed ten to thirteen times larger than that of the as-received one at 573K and low strain rates. Further surface morphology near the fracture tip was observed by scanning electron microscopy to discuss deformation mechanism at high temperatures.
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