This study investigates the effects of fine and coarse undissolved particles in a billet of the Mg–7Sn–1Al–1Zn (TAZ711) alloy on the dynamic recrystallization (DRX) behavior during hot extrusion at low and high temperatures and the resultant microstructure and mechanical properties of the alloy. To this end, partially homogenized (PH) and fully homogenized (FH) billets are extruded at temperatures of 250 and 450 °C. The PH billet contains fine and coarse undissolved Mg₂Sn particles in the interdendritic region and along the grain boundaries, respectively. The fine particles (<1 μm in size) retard DRX during extrusion at 250 °C via the Zener pinning effect, and this retardation causes a decrease in the area fraction of dynamically recrystallized (DRXed) grains of the extruded alloy. In addition, the inhomogeneous distribution of fine particles in the PH billet leads to the formation of a bimodal DRXed grain structure with excessively grown grains in particle-scarce regions. In contrast, in the FH billet, numerous nanosized Mg₂Sn precipitates are formed throughout the material during extrusion at 250 °C, which, in turn, leads to the formation of small, uniform DRXed grains by the grain-boundary pinning effect of the precipitates. When the PH billet is extruded at the high temperature of 450 °C, the retardation effect of the fine particles on DRX is weakened by their dissolution in the α-Mg matrix and the increased extent of thermally activated grain-boundary migration. In contrast, the coarse Mg₂Sn particles in the billet promote DRX during extrusion through the particle-stimulated nucleation phenomenon, which results in an increase in the area fraction of DRXed grains. At both low and high extrusion temperatures, the extruded material fabricated using the PH billet, which contains both fine and coarse undissolved particles, has a lower tensile strength than that fabricated using the FH billet, which is virtually devoid of second-phase particles. This lower strength of the former is attributed mainly to the larger grains and/or absence of nanosized M₂Sn precipitates in it.

这项研究调查了Mg-7Sn-1Al-1Zn（TAZ711）合金钢坯中细小和粗大的不溶颗粒对低温和高温热挤压过程中动态重结晶（DRX）行为的影响，以及由此产生的显微组织和力学性能合金。为此，在250和450°C的温度下挤压部分均质（PH）和完全均质（FH）的钢坯。PH坯料含有细和粗的未溶解的Mg ₂分别在枝晶间区域和沿晶界的Sn粒子。细颗粒（尺寸<1μm）会通过齐纳钉扎效应在250°C的挤压过程中延迟DRX，并且这种延迟会导致挤压合金动态再结晶（DRXed）晶粒的面积分数降低。此外，PH钢坯中细小颗粒的不均匀分布会导致形成双峰DRXd晶粒结构，在颗粒稀少的区域中晶粒会过度生长。相比之下，在FH钢坯中，许多纳米Mg ₂在250°C的挤压过程中，整个材料中都会形成Sn析出物，这又会由于析出物的晶界钉扎效应而导致形成小的均匀的DRXd晶粒。当PH坯料在450℃的高温下挤出时，细粒对DRX的阻滞作用由于它们在α- Mg基体中的溶解和热活化的晶界迁移程度的增加而减弱。相反，粗镁₂坯料中的锡颗粒通过颗粒刺激的成核现象在挤压过程中促进DRX，导致DRX晶粒的面积分数增加。在低挤出温度和高挤出温度下，使用PH坯制造的挤压材料（同时包含细颗粒和粗颗粒未溶解颗粒）的拉伸强度要比使用FH坯制造的挤出材料低，而FH坯实际上不含第二相颗粒。前者的较低强度主要归因于较大的晶粒和/或其中不存在纳米级M ₂ Sn沉淀物。