On the activation energies observed in Al-based materials deformed at ultrahigh temperatures

Lou, B.Y., Wang, T.D., Huang, J.C. and Langdon, T.G. (2001) On the activation energies observed in Al-based materials deformed at ultrahigh temperatures. In, Chandra, Namas (ed.) Superplasticity in Advanced Materials - ICSAM-2000. (Materials Science Forum, 357-359) 2000 International Conference on Superplasticity in Advanced Materials (ICSAM-2000) (01/08/00 - 04/08/00) Switzerland. Trans Tech Publications Ltd, pp. 545-550.

Abstract

This study examines the exceptionally high activation energies estimated fi om data obtained from various composites exhibiting high strain rate superplasticity and loaded at ultrahigh temperatures near or slightly above the solidus. It is shown that the activation energies for the 6061 composite and for Al 6061 and 1050 alloys are below 200 kJ/mol at temperatures lower than the incipient melting temperature, T-i, but they become significantly higher at temperatures near or slightly above T-i and this increase is independent of the alloy system, the grain size, whether the material is superplastic and the dominant deformation mechanism at T<T-i. There is a transition from plastic flow in a solid state to a viscous-like flow behavior in the Al-6061 systems at T>610 degreesC and in the Al-1050 alloy at T>650 degreesC. It is concluded that the high values of Q(t) have no physical meaning in terms of the rate-controlling diffusive species.

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Contributors

Author: T.G. Langdon

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