Superplasticity of Mg-5.8Zn-1Y-Zr alloy sheet fabricated by combination of extrusion and hot-rolling processes

Superplastic behaviors of quasicrystal phase containing Mg-5.8Zn-1Y-0.48Zr alloy sheets fabricated by combination of extrusion and hot-rolling processes have been investigated at temperature ranging from 623 to 753 K and at the strain rates ranging from 10⁻⁴ to 10⁻² s⁻¹ by uniaxial tensile tests. An excellent superplasticity with the maximum elongation to failure of 1020% was obtained at 753 K and the strain rate of 1.04×10⁻³ s⁻¹ and its strain rate sensitivity, m, is as high as up to 0.75. The microstructure was stable during superplastic deformation due to the uniformly distributed fine quasicrystal particles. In addition, micro-cavities and their coalescences were observed in the superplastic deformation of the ZW61 magnesium alloy. Grain boundary sliding (GBS) was considered to be the main deformation mechanism during the superplastic deformation. Dislocation creep controlled by atom diffusion through grain boundaries or interior grains is suggested mainly to accommodate the GBS in superplastic deformation. Supported by the National Basic Research Program of China (“973”) (Grant No. 2007CB613704)