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 T610 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.