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.