In this work the deformation mechanisms which operate in several superplastic aluminum alloys during tensile straining have been investigated by means of texture analysis via x-ray diffraction (macrotexture) and electron diffraction (microtexture). Tensile tests have been performed at different temperatures and strain rates with the aim of studying the deformation behavior outside and within the superplastic regime. Special attention has been paid to the alloy Al-5%Ca-5%Zn (fine-grained alloy, d ≈ 2-3 μm, with 20%vol. of second phase, Al3CaZn) and the main conclusions obtained have been generalized to other superplastic aluminum alloys: 2090, 8090, Supral 2004 and ski5083. The main original contribution of this work is the following: it has been found that in some superplastic aluminum alloys crystallographic slip operates even under optimum superplastic conditions, where this mechanism competes with grain boundary sliding. This behavior seems to be characteristic of alloys which recrystallize in a continuous way. As such, this observation could explain why "continuous" alloys undergo superplastic deformation at relatively high strain rates and are therefore extremely interesting for their potential applications in industry. Alloys which recrystallize in a discontinuous way follow the pattern of behavior traditionally accepted for superplastic alloys.

Peer reviewed