The superplasticity of as-extruded magnesium alloy was examined with strain rate of 10-2

1

0-4s-1 at 400

4

40℃. The results reveal that necking contract is dominant in tensile fracture of the specimens with a higher strain rate. With increasing in temperature

m value （strain rate sensitivity index） and elongation of the alloy are increased. With a lower strain rate

tensile fracture mechanism is controlled by cavity expansion

resulting in the decrease of elongation with increasing in temperature. Superplasticity deformation mechanism map was drawn by analyzing deforming mechanism. The results indicate that

with a low strain rate

at 400℃ or 420℃

deformation mechanism is characterized by dislocation creep controlled by the solute drag

while with a higher strain rate

it is characterized by the dislocation creep controlled by climb. At 440℃

deformation mechanism of the as-extruded alloy is accordant with the dislocation creep controlled by lattice diffusion.