According to the different introduction times in the deformation process and the different purposes of the heat treatment process, heat treatment can be divided into intermediate thermo-mechanical treatment (ITMT) and final thermo-mechanical treatment (FTMT). In the ITMT process, the precipitated phases exist as auxiliary phase particles. These precipitated phases can be used as recrystallization inhibitors to pin the grain boundaries, or play a core role in particle induced recrystallization nucleation [12,14–16]. In the FTMT process, the precipitated phase exists as a strengthening phase, directly participating in the aging strengthening behavior, and improving the mechanical properties of the deformed alloy [6,12]. Yang et al. [12] investigated the microstructure evolution and mechanical properties of an AZ91 alloy processed by equal channel angular pressing (ECAP) combined with prior and post aging treatment. Both the strength and ductility of AZ91 alloy were enhanced and flexibly managed through ECAP with a combination of prior or post aging treatment. The prior aging treatment process was benefited for the occurrence of dynamic recrystallization (DRX) during subsequent ECAP pro cessing, and post aging treatment was beneficial for improving the yield strength (YS). Jung et al. [15] reported that the tensile strength and ductility of an AZ80 alloy were improved simultaneously by aging prior to extrusion treatment compared to those of a directly extruded alloy. The enhanced strength was attributed to the reduced grain size and increased fraction of precipitates. Due to the accu mulation of a large number of dislocations around the dispersed large-size particles, a local deformation zone is formed, which re sults in a significant increase in the storage energy. Therefore, re crystallized grains preferentially nucleate in these large particles and their surroundings, thereby promoting dynamic recrystallization (DRX) behavior. For dispersed small-sized particles, these particles slow down the recrystallization speed by applying resistance to the grain boundaries or sub-grain migration, have a certain pinning ef fect on the grain boundaries, and restrict and hinder grain boundary migration. To a certain extent, the growth of recrystallized grains is restricted. Under the joint action of large and small particles, re crystallization and grain refinement can be achieved at the same time. However, the plasticity of Mg alloys, especially rare earth (RE) Mg alloys is very poor, and the ingot cannot be directly used as a high bearing component after machining as a blank to face a harsh service environment. At present, the plastic processing of ingots and en hancing the mechanical properties of alloys by improving the mi crostructure of Mg alloy have become an effective means of strengthening and toughening. General plastic processing tech nology due to the small amount of deformation generated during the deformation process, and the limited ability to refine the grains, often cannot meet the high-performance requirements for Mg alloy components. At the same time, traditional plastic processing tech nology will also have the problems of an uneven deformed micro structure and obvious anisotropy. Therefore, severe plastic deformation (SPD) methods, such as equal channel angular pressing (ECAP) [5,17,18], accumulative roll bonding (ARB) [19,20], cyclic ex trusion compression(CEC) [21,22], high-pressure torsion (HPT) [23,24], multi-directional forging (MDF) [25,26] and other technol ogies have been widely used to effectively refine grains, improve the mechanical properties of RE Mg alloys and eliminate anisotropy. Among these SPD methods, MDF technology is favored by scholars due to its relatively simple mold and low cost. Compared with the as-cast billet, the mechanical properties of the alloy after multiple deformation passes and MDF are significantly improved. However, the existing technology increases the number of deformation passes and obtains a larger accumulated strain to improve the UTS and YS of the deformed alloy at room temperature (RT). Jiang et al. [27] conducted isothermal MDF deformation at 300 °C on the as-cast AZ61 Mg alloy. The results showed that with the increase of the deformation passes, the grain size of the alloy was refined from 320 µm in the initial state to 3.7 µm after 180 passes, and the YS and UTS of the alloy increased from 169 MPa and 224 MPa in the initial state to 245 MPa and 265 MPa after 180 passes, respectively. Nie et al. [28] studied an as-cast AZ91 Mg alloy at 350 °C via isothermal MDF, and the results showed that the grain size of the alloy was reduced from 175 µm in the as-cast state to 7.2 µm after 6 passes. After 3 passes, the alloy obtained the highest YS of 158 MPa and UTS of 235 MPa, which were approximately 140% and 95.8% higher than that of the as-cast alloy, and the elongation was also doubled. However, in the actual production process, as the deformation passes increa