Quantitative evaluation of creep strain distribution in an extruded Mg–Zn–Gd alloy of multimodal microstructure

Abstract

The creep behavior of an extruded Mg–Zn–Gd alloy with a long-period stacking ordered (LPSO) phase is investigated at 473K under applied stress ranging from 150 to 270MPa. The microstructure of the extruded alloy is characterized by a multimodal microstructure consisting of three main regions: dynamically recrystallized (DRXed) α-Mg grains with random orientation; worked α-Mg grains with 〈101¯0〉 fiber texture; and fiber-shaped LPSO phase grains. Creep behavior of the extruded alloy shows a high stress exponent of n≈11. Local creep strain distribution in the alloy creeping under 210MPa is evaluated based on distortion/displacement observed with micro-grid markers. The share contributed to total creep deformation by intra-grain sliding (IGS) in the DRXed and textured grain regions and grain boundary sliding (GBS) is determined methodically in this study. Rates of contribution are ∼79% and ∼21% with IGS and GBS, respectively. To be exact, the shares contributed by IGS are ∼21% and ∼58% in the DRXed and the fiber-textured grain regions, respectively. The greater part of GBS with small strain occurs in the DRXed grain region, but the rest of GBS trailing large local strain is detected at the grain boundary between the DRXed grain and the worked grain showing a high Schmid factor. The magnitude of the slip-induced GBS that occurs at grain boundaries around the worked grain is dependent on two discrete parameters: angle of grain boundary; and Schmid factor of the worked grain.