Deformation behavior of an extruded Mg-Dy-Zn alloy with long period stacking ordered phase

Deformation behavior of an extruded Mg-2Dy-0.5Zn (at%) alloy was investigated under uniaxial tensile test at a range of strain rates of 3×10−5-3×10−1 s−1 and temperature ranging from room temperature (RT) to 300 °C. The microstructure of the alloy was mainly composed of α-Mg, (Mg, Zn)xDy particle phase and a large number of long period stacking ordered (LPSO) phases. The tensile testing results indicated that strain rate sensitivity exponent (m) generally increased with increasing temperature and decreasing strain rate. Interestingly, m exhibited two different values in logσ−logε̇ curves at 300 °C, indicating that the plastic deformation mechanism of the alloy occurred to change. The surface and microstructure observations of the tensile specimens after tension revealed that the deformation behavior of the alloy was similar to that of the metal matrix composites, where the load transferred from the Mg matrix to the LPSO phase at low temperatures (RT~200 °C) under different strain rates and at 300 °C under high strain rates, while the grain boundary sliding accommodated by dislocation slip dominated the whole deformation behavior at 300 °C under low strain rates. The alloy exhibited a quasi-superplastic deformation with an elongation-to-failure of 105% at 300 °C and 3×10−5 s−1. The quasi-superplastic deformation was attributed to the stable grains retained by the precipitation of the LPSO phase with good thermal stability in grain interior at an elevated temperature.