Forming limit diagram for a superplastic 5083 aluminum alloy

The superplastic blow forming limits for a 5083 aluminum alloy were investigated at a strain state from the plane strain to the balanced biaxial at a temperature of 773 K and a strain rate of about I X 10(-3) s(-1). It was discovered that the equivalent strain at the forming limit was in a range of 1.3 +/- 0.1 for every strain state and was consistent with that obtained by the uniaxial tensile tests. Namely, the forming limit for the blow forming could be estimated from the equivalent strain-to-fracture in the uniaxial tensile test. The cavity volume fraction and the cavity growth rate at the forming limit, however, increased by changing the strain state from uniaxial to balanced biaxial through a plane strain. The relationship between the forming limit and the cavity volume fraction is dependent upon the strain state.