The occurrence of the tensile yield plateau in Mg alloys is relatively rare and its underlying reasons have been controversial. In this study, we systematically investigated the deformation mechanism of an extruded Mg-4.83Gd-2.36Nd-0.21Zr alloy, which exhibited an obvious tensile yield plateau. Quasi-in-situ EBSD analysis revealed that basal slip was the predominant mechanism in the tensile yield stage, which was attributed to the weak rare earth texture that facilitated basal slip activation and the fine recrystallized grains that suppressed twinning. The yield drop resulted from the combined effects of the easy activation of basal slip and the dislocation pinning by solute atoms. Additionally, the random distribution of grain orientations, high grain boundary misorientation angles (GBMA), and small grain sizes hindered intergranular deformation transfer between neighboring grains. The weak deformation transfer contributed to the formation of yield point elongation. This work underscores the role of texture, grain orientations, and GBMA in determining the yield plateau, offering a new perspective on yield plateau formation in Mg alloys.

Due to the effective precipitation strengthening effect of the β′ phase, Mg-Gd alloys exhibit excellent room temperature mechanical behaviors. However, when served at high temperatures, the metastable β′ phase will transform to other phases, resulting in severe performance degradation. In this study, we investigated the effect of precipitation state achieved by different heat treatments on high temperature tensile and creep behaviors of the Mg-15Gd alloy by comparing the properties of the as-cast, solid-solutioned (T4) and peak-aged (T6) alloys. The results showed that the tensile mechanical properties of the T6 alloy were always highest from room temperature to 300 ℃, in spite of an abnormal strength increase with temperature existed in the T4 alloy. For tensile creep properties, the T6 alloy exhibited the lowest steady creep rate below 235 ℃ while the T4 alloy possessed the best properties above 260 ℃. Microstructure characterization revealed that the transition was caused by the stress-promoted precipitation of β′ phase in the T4 alloy and rapid phase transformation in the T6 alloy at high temperatures. At 260 ℃, the calculated stress exponent n was 3.1 and 2.8 for the T4 and T6 alloys, respectively, suggesting the creep deformation mechanism was dislocation slip, which was further confirmed by the microstructure after creeping. Our findings can provide new insights into the heat treatment process of Mg-Gd alloys served at high temperatures.