Low temperature superplasticity of ultrafine grained Mg–9.25Zn–1.66Y alloy with an icosahedral quasicrystalline phase

•The UFG I-phase Mg-9.25Zn-1.66Y exhibited low temperature superplasticity.•Thermal stability of the UFG microstructure was high below 473 K.•Its thermal stability sharply decreased from 523 K.•A criterion for achieving low temperature superplasticity was calculated.

The ultrafine grained Mg–9.25Zn–1.66Y alloy sheet with I-phase prepared by directly applying high-ratio differential speed rolling to the as-cast microstructure exhibited excellent low-temperature superplasticity (386–888% at 443–473 K) at a moderately high strain rate of 10−3 s−1. A criterion for achieving low temperature superplasticity was proposed.