Superplasticity in a fine-grained Mg-Zn-Y-Zr alloy containing quasicrystalline particles

A Mg-Zn-Y-Zr alloy sheet containing icosahedral quasicrystalline particles and Zr-rich particles has been developed by the thermomechanical processes, i.e. hot extrusion and hot rolling. The grain size is found to be 5 μm. The superplastic deformation behavior of the alloy has been investigated. Under the test condition in the strain rate range of 5 × 10^-4 to 5 × 10^-2 s^-1 and the temperature range between 300°C and 450°C, large elongation to failures are observed, especially around 600% at 450°C (5 × 10^-4 s^-1). During superplastic deformation, the concurrent grain growth rate is significantly retarded by the presence of I-phase particles, thermally stable at the temperature up to around 500°C. In addition, the formation of cavities is found to be negligible because of interfacial coherency between icosahedral quasicrystalline particles and the α-Mg matrix. Although superplastic deformation could be relatively prevented by the pinning effect of the distributed particles, microstructure stability can provide large elongation to failure in such an alloy.