LAUSR

Abstract The effects of Zr and Mn additions to Mg-15Gd-1Zn alloy on the formation of long period stacking ordered (LPSO) structure under solution-treated (T4-treated) condition and the dynamic recrystallization (DRX) behavior alloy during extrusion have been investigated. The underneath mechanisms have also been proposed. The results indicate that Zr hinders the formation of LPSO structure by consuming Zn, while the Mn promotes it. On the other hand, Zr suppresses the grain growth by introducing Mg(Zn, Zr) precipitates during the DRX, while Mn effectively hinders the recrystallization process due to increasing LPSO structure. As the LPSO structure has dissolved in recrystallized grains, Mn addition affects little on suppressing grain growth in the grain growth step. Zr addition improves the mechanical properties of both the casting and extruded Mg-15Gd-1Zn alloys by refining grains and introducing Mg(Zn, Zr) precipitates. By contrast, the Mn addition is beneficial for the tensile properties of casting Mg-15Gd-1Zn alloy because of the LPSO structure with high ductility but harmful for the properties of the extruded alloys due to the coarse un-recrystallized grains.