A study on the process to control the cavity and the thickness distribution of superplastically formed parts

The use of superplastically formed Al alloy components could save cost and reduce weight in aerospace structures. However, problems related with non-uniform thickness and cavitation occur during superplastic deformation. In the case of hemisphere forming part, the thickness becomes much thinner and the cavitation increased exponentially as closed to the pole. In order to unify the thickness and to decrease the cavity, the thickness distribution of sheet was controlled by using the rotary forging. The sheet is preformed into the cone type and become the thickest in the center. The hemisphere formed part using the preformed sheet has uniform thickness and also lower cavity than that of original sheet. It is found that cavity is increased rapidly when the strain reaches the critical value. Also discussed are that the critical strain is closely related to shapes and positions in the vicinity of particles and at triple point of grain boundary.