The hot compressive deformation behavior of cast Mg-Gd-Y-Zn-Zr alloys with and without LPSO phase in their initial microstructures

Samples of Mg-8.2Gd-3.8Y-1.1Zn-0.4Zr alloy with and without an intragranular lamellae-shaped long period stacking ordered (LPSO) phase were prepared through heat treatment and a series of hot compression tests on these materials were conducted to examine and evaluate the influence of LPSO on the hot compressive deformation behavior and deformation mechanisms at a given alloy composition. The values of activation energy for plastic flow (Q_c) of the solution treated (without LPSO phase) and annealed alloys (with intragranular LPSO phase) were larger than that for pure Mg, indicating that the presence of a high amount of rare earth (RE) elements and LPSO in the Mg matrix significantly increases Q_c. The Q_c value of the annealed alloy was larger than that of the solution treated alloy at all the strain levels (223.3 vs. 195.5 kJ/mol in average) and the largest difference in Q_c between the two alloys was recorded at the smallest strain of 0.1 where precipitation of LPSO during deformation was limited in the solution treated alloy. These observations imply that the formation of LPSO phase out of the RE-rich solid solution matrix during deformation increases Q_c, but the increment is not so large. Analysis of the hot compressive data of the alloys with LPSO phase and the alloys with RE-rich solid solution matrix in literatures indicates the similarity of the effect of the LPSO and RE-rich solid solution matrix phases on Q_c and high-temperature strength.