FORMING-LIMITS ANALYSIS OF THE SUPERPLASTIC 2A97 Al-Li ALLOY

摘要

The superplastic formability of the as-rolled 2A97 Al-Li alloy was studied under various stress states with the use of both tensile tests and bulge tests deformed at 350-430 degrees C. The flow stress curves of the 2A97 alloy at the test temperature with an initial strain rate ranging from 1x10(-3) s(-1) to 3x10(-2 )s(-1) were characterized by the modified Hooke equation and the Grosman equation. The bulge tests were performed under four different strain paths, ranging from equi-biaxial to approaching plane strain. The effects of temperature and bulge-tool aspect ratio on the dome height, forming pressure, thickness distribution, and cavitation were investigated. Dome height and forming pressure appear to be more sensitive to tool ratio than temperature. Increasing the temperature in bulge forming was found to improve the thickness distribution in the formed parts, but it may lead to excessive cavitation. The results of the forming-limit diagram show significant scatter in terms of failure strain. It indicates that a determination of the forming limits of superplastic 2A97 cannot be represented with a simple forming-limit diagram and additional metrics for internal cavitation need to be considered.