Characterization of hot deformation behavior of an extruded Mg–Zn–Mn–Y alloy containing LPSO phase

•Peak stress and Zener–Hollomon parameter increase with decreasing temperature.•Peak stress and Zener–Hollomon parameter increase also with increasing strain rate.•The presence of LPSO phase in the Mg alloy results in a higher activation energy.•LPSO kink bands form via the motion of dislocation pairs having opposite signs.•Highly-coherent interface between the LPSO phase and Mg matrix is observed. The hot deformation behavior of an as-extruded ZM31+6Y alloy containing 18R-LPSO (long-period stacking ordered) phase was studied via compression testing in the temperature and strain ranges of 200–400°C and 0.001–1.0s−1, respectively, with particular emphasis on the deformation mechanisms of LPSO phase. Both the peak stress and Zener–Hollomon parameter increased with decreasing temperature and increasing strain rate. At lower temperatures and higher strain rates an early shear fracture at ∼45° relative to the compression axis was observed. The activation energy evaluated using Sellars and McTegart equation was about 275.9kJ/mol, which was higher than that in the conventional magnesium alloys due to the presence of LPSO phase. A modified Sellars and McTegart equation was also used to identify the effect of temperature and strain rate on the deformation behavior. The activation energy appeared to decrease with increasing deformation temperature and strain rate. The microstructural change in different deformation conditions could be well understood in terms of dynamic recrystallization (DRX) and kink band formation in the LPSO phase due to the motion of dislocation pairs having opposite signs. The well-deformable LPSO phase was observed to experience thinning instead of coarsening due to kinking at elevated temperatures. The highly-coherent interface between the magnesium matrix and LPSO phase essentially eliminated the potential debonding or micro-cracking which was beneficial for ductility. These results revealed a good potential for the elevated temperature applications of ZM31+6Y alloy.