| Title |
Blow Forming of Superplastic 7475 aluminum Alloy Sheets |
| Authors |
정성규(S . K . Jeong); 최준환(J . H . Choi); 이동녕(D . N . Lee); 이혁모(H . M . Lee); 홍순형(S . H . Hong); 홍성석(S . S . Hong); 이종수(J . S . Lee) |
| Abstract |
The 7475 aluminum alloy sheets were subjected to a thermornechanical treatment to have superplastic characteristics. The superplastic specimens were tested in an Instron testing machine at constant cross head speeds to obtain a constitutive equation for an optimum superplasticity. The constitutive equation which offers the reference data for a constant-apex-strain-rate blow forming was established at 516℃ in the form of 0=K·ε˙^m. The equation was applied to the analyses of blow forming into cylinderical and conical dies. The theoretical models mainly followed Ragab`s analytic model about a constant-pressure blow forming but were modified into the models relevant to a constant-apex-strain-rate blow forming. A number of experiment have been conducted, involving the blow forming of superplastic 7475 Al alloy sheets into cylinderical and conical dies at 516℃ with the apex-strain-rate, 1.15 × 10^(-3)/sec. The theoretical results and experiments were compared and the problems such as cavity occurrence and dynamic grain growth were discussed. |