Low temperature superplasticity in a ZK60 magnesium alloy

Low temperature superplastic behavior of a magnesium alloy, ZK60, was investigated at about half the absolute melting point. The grains were equiaxed with an average size of 6.5 mu m. The tensile tests revealed that the material exhibited low temperature superplasticity (LTSP) with elongation-to-failure of over 400%. Microstructural observations suggested that grain boundary sliding (GBS) made a substantial contribution to the total strain. The stress exponent, grain size exponent and activation energy for superplastic flow were also characterized. The strain rate was inversely proportional to the cube of the grain size and to the second power of stress. The activation energy was close to that for grain boundary diffusion in magnesium. It is suggested that the deformation mechanism for LTSP is GBS accommodated by dislocation movement controlled by grain boundary diffusion.