Multi-dome forming test for determining the strain rate sensitivity index of a superplastic 7075Al alloy sheet

• Higher strain rate sensitivity of 0.49 at the forming parameters has been achieved.
• When the temperature is high, the thinning is less.
• At high annealing time, the strain rate sensitivity index value will be low.

Superplasticity is a phenomenon indicating exceptional ductility that certain metals and alloys exhibit, when deformed under specific conditions. The tensile elongation of superplastic materials typically exceed 400%, elongations exceeding 5000% having been achieved. Superplasticity in sheet metals offers unique advantages for forming complex shapes easily, as a regular production process. In pressure thermo forming, the applied gas pressure deforms the sheet continuously, until it matches the shapes of the female die. The present study is about a technique to assess the strain rate sensitivity of a 7075 Al alloy sheet by a multi-dome forming test, under different forming pressures, temperatures and annealing times. This study considers mainly the thickness at dome apex, cavity volume fraction and assessment of the strain-rate sensitivity index. It was found that the material after 30 min annealing acquired a higher strain rate sensitivity of 0.49 and a pole thickness of 1.33 mm in diameter of a 15 mm dome, under the forming parameters of 0.5 MPa pressure, a forming time of 60 min and temperature of 530 °C.