Constructing bimodal grain structure is a promising approach to achieve the high strength-ductility synergy in Mg alloy. Formation of bimodal grain is closely related to the dynamic and/or static recrystallization process, which has not been fully understood in the typical Mg-RE based alloy. In this work, it is claimed for the first time that the minor Ce addition (∼0.3 wt%) into Mg matrix significantly promotes the pyramidal <c+a> and non-basal <a> dislocations at the early stage of extrusion, which consequently enhances the formation of sub-grain boundaries via the movement and recovery of pyramidal II-type <c+a> dislocations. At this stage, fine sub-grain lamellae are widely observed predominantly due to the low migration rate of sub-grain boundary caused by the limited mobility of <c+a> dislocations. At the later stage, the sub-grains continuously transform into dynamic recrystallized (DRXed) grains that have $〈10\overline{1}0〉$ Taylor axis and also strong fiber texture, indicating substantial activation of pyramidal II-type <c+a> dislocation. The low mobility of <c+a> dislocations, accompanied with the solute drag from grain boundary (GB) segregation and pinning from nano-phases, cause a sluggish DRX process and thus a bimodal microstructure with ultra-fined DRXed grains, ∼0.51 µm. The resultant texture hardening and grain refinement hardening effects, originated from bimodal microstructure, result in a yield strength of ∼352 MPa, which is exceptional in Mg-Ce dilute alloy. This work clarifies the critical role of Ce addition in tuning recrystallization behavior and mechanical property of magnesium, and can also shed light on designing the other high-performance Mg alloys.

构建双峰晶粒结构是实现镁合金高强塑性协同作用的一种很有前景的方法。双峰晶粒的形成与动态和/或静态再结晶过程密切相关，这在典型的 Mg-RE 基合金中尚未完全理解。在这项工作中，首次声称在 Mg 基体中添加少量 Ce（~0.3 wt%）显着促进了挤压早期的锥体<c+a>和非基底<a>位错，这因此，通过锥体 II 型<c+a>的运动和恢复来增强亚晶界的形成位错。在这个阶段，由于<c+a>位错的有限迁移率导致亚晶界迁移率低，因此广泛观察到细小的亚晶层。在后期，亚晶粒不断转变为动态再结晶（DRXed）晶粒，具有$〈10\overline{1}0〉$泰勒轴和强纤维质地，表明锥体 II 型<c+a>位错的显着激活。<c+a>位错的低迁移率，伴随着晶界（GB）偏析的溶质阻力和纳米相的钉扎，导致缓慢的 DRX 过程，从而形成具有超细 DRX 晶粒的双峰微观结构，~0.51 µm . 由此产生的织构硬化和晶粒细化硬化效应源自双峰微观结构，导致屈服强度约为 352 MPa，这在 Mg-Ce 稀合金中非常出色。这项工作阐明了添加 Ce 在调节镁的再结晶行为和力学性能中的关键作用，也可以为设计其他高性能镁合金提供启示。