Superplasticity behavior of ZK60 alloy sheet prepared by high strain rate rolling process

The superplastic deformation characteristics of the high strain rate rolling ZK60 magnesium alloys at temperature ranging from 523 K to 673 K and at an initial strain rates ranging from 1×10-3 s-1 to 1×10-1 s-1 were investigated. The results show that the maximum elongation to failure of 650% is obtained at 648 K and the strain rate of 1×10-3 s-1 in the as-rolled ZK60 magnesium alloys and its strain rate sensitivity (m) is high up to 0.53. An excellent high strain rate superplasticity with the elongation to failure of 584.5% is obtained at 623 K and the strain rate of 1×10-2 s-1 and its strain rate sensitivity (m) is 0.47. The microstructure and theoretical analysis shows that, at temperature above 573 K, the dominant deformation mechanism in high strain rate superplasticity is grain boundary sliding (GBS), which was studied systematically. The dislocation creep controlled by grain boundary diffusion was considered the main accommodation mechanism, and high strain rate superplasticity was also accompanied by a certain degree of inter-granular liquid phase aiding mechanism, which was observed.