传统AZ91镁合金存在强度与塑性难以同时提高的矛盾。为解决此问题，本工作在AZ91镁合金中构建了两种不同的异构组织：由变形粗晶和动态再结晶细晶交替分布的层状晶粒异构组织、完全由再结晶晶粒组成的双峰晶粒异构组织。力学性能测试结果表明，层状晶粒异构组织的AZ91镁合金具有更好的强塑性匹配。利用SEM滑移迹线表征技术和数字-图像相关(DIC)技术等测试手段，对两种异质结构AZ91镁合金的塑性变形行为进行了研究。结果表明：两种异构组织合金的细晶中均激活了基面滑移和非基面滑移，部分晶粒间发生滑移传递，有效减缓了晶间应力集中。粗晶区具有较高的位错存储能力，变形后期粗晶内产生孪晶，协调其在c轴方向的变形，抑制裂纹扩展，使得两种异构组织AZ91镁合金均表现出较高的加工硬化能力和均匀延伸率。双峰晶粒异构组织AZ91镁合金的室温屈服强度(YS)约234.5 MPa，抗拉强度(UTS)约337.5 MPa，延伸率(EL)约23.8%，层状晶粒异构组织合金得益于变形粗晶区位错密度更高、细晶区晶粒尺寸更小，在保持高塑性(EL ≈ 21.3%)的同时，其强度显著提升(YS ≈ 274.9 MPa，UTS ≈ 377.1 MPa)，展现出更为优异的强塑性结合。
Magnesium alloys have attracted significant attention
owing to their low density and high specific strength, offering broad
application prospects in lightweight aerospace and automotive components.
However, the limited number of activatable slip systems inherent to their hexagonal
close-packed structure severely restricts ductility and work-hardening
capacity, posing a persistent challenge in achieving a synergy between strength
and ductility. Heterogeneous structure design is considered an effective
strategy for attaining such a balance in metallic materials. In this work, AZ91
magnesium alloys with a lamellar grain structure (LGS) and a bimodal grain
structure (BGS) were fabricated via thermomechanical processing combined with
controlled annealing, achieving a synergistic enhancement of strength and
ductility. The LGS was produced by rapid extrusion, resulting in a lamellar
microstructure characterized by alternating dynamically recrystallized (DRX)
fine grains (average ~3.6 µm) and deformed coarse grains (average ~24.0 µm). The
BGS was obtained by annealing the extruded alloy, leading to fully statically
recrystallized coarse grains (average ~13.0 µm) coexisting with DRX fine grains
(average ~5.2 µm). Mechanical testing showed that both heterogeneous structures
exhibited pronounced work-hardening capability and improved uniform elongation.
The BGS alloy demonstrated a yield strength (YS) of ~234.5 MPa, an ultimate
tensile strength (UTS) of ~337.5 MPa, and elongation (EL) of ~23.8%. In
contrast, the LGS alloy exhibited significantly higher strength (YS ≈ 274.9
MPa; UTS ≈ 377.1 MPa) while maintaining excellent ductility (EL ≈ 21.3%). This
improvement is attributed to the combined effects of higher dislocation density
in the deformed coarse-grained regions and the finer grain size in the
fine-grained domains. In this study, multi-scale characterization techniques,
including SEM-based slip trace analysis and digital image correlation, were
employed to elucidate the deformation mechanisms. The results indicate that, at
the early stage of deformation (~8% strain), both basal and non-basal slip
systems were activated in the fine-grained regions of the two heterostructured
alloys. In addition, basal-to-basal and basal-to-non-basal slip transfer
occurred between adjacent grains, effectively alleviating intergranular stress
concentration. Meanwhile, the coarse-grained regions exhibited a high
dislocation storage capacity, and deformation twinning was activated at later
deformation stages to accommodate c-axis strain. As a result, both heterostructured
alloys (LGS and BGS) demonstrated strong work-hardening behavior, with the LGS
alloy achieving a superior combination of strength and ductility. The findings
contribute to a deeper understanding of the plastic deformation mechanisms in
heterostructured magnesium alloys and provide a feasible pathway for enhancing
their mechanical performance.
