Abstract
A Zn-22wt%Al alloy was superplastically compressed with or without ultrasonic oscillations under various deforming conditions. The nominal stress (σ) increases with increasing strainrate (e) and strain (e) especially in a higher strain range. σ remarkably reduces and specimen temperature during compression elevates with increasing ultrasonic amplitude by applying ultrasonic oscillations. A decrease in σ by applying ultrasonics (Δσ) is more significant as e and. e increase and the initial specimen has less heights. The specimen temperature rapidly rises after appliciation of ultrasonics and saturates with increasing e. The visioplasticity analysis shows that the restrained zone of superplastic flow is formed due to the friction across the die and that application of ultrasonics is effective to reduce the frictional restraint during deformation in the lower strain rate range and to accelerate the superplastic flow in the higher strain rate range. The decrease of frictional constraint and temperature rise contribute to the decrease of σ with application of ultrasonics. Improvement of the superplastic deformability in connection with grain boundary and phase boundary relaxation also contribute to the decrease of σ.
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