Cavitation characteristics of a superplastic 8090 Al alloy during equi-biaxial tensile deformation

Cavitation behavior of a superplastic 8090 Al alloy during equi-biaxial tensile deformation has been investigated by deforming the sheet into a right cylindrical die. Cavitation characteristics could be separated into two stages. In stage I, the sheet deformed freely as part of a spherical dome, and the cavity volume increased exponentially with deformation. The evolution of cavity volume was due to both nucleation and growth of cavities. In the second stage, the surface friction would restrict thinning of the sheet, and the cavity volume first increased and then decreased with forming time for all test strain rates. Decrease in cavity volume in the later stage could be related to the cavity shrinkage that resulted from the sintering effect. A higher imposed pressure during forming leaded to a greater average cavity shrinkage rate. The cavitation level could be effectively reduced by a post-sintering procedure. (C) 2000 Elsevier Science S.A. All rights reserved.