Coarse-grained superplasticity and gas blow forming of commercial AZ31 magnesium alloy sheet

Superplasticity of commercial AZ31 magnesium alloy sheet has been investigated at strain rate range of 0.7 x 10(-3)-1.4 x 10(-1) s(-1) and temperature range of 523-673 K. Hot uniaxial and equibiaxial tensile tests are carried out. The maximum elongation of 362% has been obtained at the temperature of 673 K and strain rate of 0.7 x 10(-3) s(-1). The calculation of activation energy Q and examination of microstructures show that the deformation mechanism of commercial AZ31 magnesium alloy is dissimilar at different conditions. With the decreasing of temperature and increasing of strain rate, the deformation mechanism is converted from grain boundary sliding controlled by grain boundary diffusion to the mix of grain boundary sliding and plastic or/and creep deformation controlled by lattice diffusion. In the free bulging tests, the hemisphere has been formed successfully and for the components, the failure reason is the growing and connecting of the cavities.