Microstructure and Yield Plateau of an Annealed Extruded Mg-Y-Cu Alloy

The microstructure and yield plateau of an annealed extruded Mg-6.8Y-2.5Cu alloy were investigated. During the annealing process, the 18R-LPSO phase transformed into a 14H-LPSO phase. With increasing annealing time, the grain size increased while the number of dislocations decreased in the extruded alloy. Uneven plastic deformation occurred in the annealed alloy during the yield stage, accompanied by Lüders band formation. The yield strain significantly decreased with extended annealing time. Dislocation multiplication and interactions between dislocations and solute atoms or second phases led to the formation of yielding phenomenon in both extruded and annealed alloys. The grain size and dislocation density affected the yield strain of the annealed alloy, and their corresponding influence mechanisms were evaluated for different annealing time.