Influence of Superplastic Forming Conditions of 7475 Alloy on Its Microstructure

This study concerns the superplastic forming process of 7475 aluminum alloy sheets. The objective is to define the interaction between the plastic strain and the evolution of the grain size of parts obtained by superplastic inflation. These parts are specially designed to show significant strain gradients. The rheological parameters of the sheet aluminum under conditions of superplastic forming are experimentally characterized by inflation tests on a conical die with a varying angle. The forming pressure for the standard part is determined by numerical simulation (Code FORGES 2®). The parts were formed at three different strain rates and a fixed temperature (510°C). The evolution of the grain size is measured along a radial section of each part. The numerically calculated plastic strain distribution is compared to the experimental results. The influence of the plastic strain and the strain rate on the evolution of the size and the morphology of the grains is analyzed and discussed.