AA2618 and AA7075 alloys superplastic transition in isothermal hot-deformation tests

This work deals with the isothermal deformation behaviour of two aluminium alloys, AA2618 and AA7075. These materials were integrated by mechanical tests, differential thermal analysis (DTA), and metallographic examination. Stress-relaxation and compression tests confirmed that both alloys exhibit a superplastic behaviour, characterised by a large elongation before failure and at low flow stress. Ranges of temperature and strain rate, at which such a superplastic behaviour is predominant, are shown. In particular, temperatures at which the strain-rate sensitivity parameter m is higher than 0.7, as determined by the isothermal stress-relaxation tests, are defined. Finally, the relationship between the results of deformation tests and microstructural properties is discussed, considering the perspectives of utilising these alloys for industrial isothermal forging. (C) 2000 Elsevier Science Ltd. All rights reserved.