Grain refinement of commercial magnesium alloys for high-strain-rate-superplastic forming

Superplasticity usually occurs when grain size is small, typically less than similar to 10 mum In this study, the deformation mechanisms at elevated temperatures in magnesium alloy with different grain sizes are discussed. From the discussion, the grain requirement for high strain rate superplasticity (10(-2) similar to 10(0) s(-1)) is derived. The strain rate range is chosen because it corresponds to the forming rate in commercial mass-production. Four different processing routes for grain refinement are presented and the developed grain structures are compared. Finally, a fine-grained magnesium alloy fabricated by commercial extrusion route is selected to demonstrate the proposed high strain rate superplastic forming at a strain rate of similar to 10(-2) s(-1).