Superplastic Deformation of Aluminum Systems at 500-650 °C with or without Presence of Liquid Phase

Abstract

Three aluminum base materials were studied over the high temperature range of 500-650 °C, in an attempt to examine the role of liquid phase on controlling deformation mechanisms based the observed m- and Q-values. For the two near-pure At systems, the 1050 At and AO, no solute-induced incipient partial melting was expected, and the solidus and liquidus temperatures should merge to near 655±5 °C. The m-values of these materials were consistently scattered with 0.1-0.25 up to the extrahigh temperature of 650 °C. The high activation energy in the A0 material at T>600 °C is postulated to be related to the load transfer effect or bubble-induced stress reduction, but not the liquid phase role in explaining the deformation mechanism. In the 6061A1, an appreciable amount of liquid should have been present at 590 and 610 °C. The low activation energy of 20 kJ/mole over the temperature range of 570-610 °C might reflect the transition of deformation mechanisms, though no pronounced increase in m-values was observed even at 610 °C. This result was controversial and needs future studies.