Mg-Li alloys with high lithium concentrations possess a lightweight body-centered cubic (BCC) matrix structure (β-Li). Interspersed eutectics (primarily the reticulated I-phase) often form along phase boundaries (PBs) and grain boundaries (GBs) which strengthen the alloy but cause the loss of ductility due to the brittle behavior of I-phase. By modifying the Li content, we fabricated the (β+α) biphase Mg-Li alloy in which the α-Mg phase with a hexagonal close-packed structure (HCP) is embedded in β-Li matrix, significantly increasing interface density. The high-density interfaces mitigate the distribution and dimension of the I-phase along GBs and PBs. The alloy exhibits enhanced ductility (elongation (EL) = 17.8 %) compared with the alloy without the α-Mg phase (EL = 5.1 %). Structural characterizations unveil the strengthening mechanism of the nanoscale B2 (Li, Mg)Zn-type precipitates in conjunction with the microscale I-phase. The (Li, Mg) Zn nanophases augment the yield and ultimate tensile strength of the alloy without a discernible compromise in ductility, predominantly due to gliding dislocations cutting through the precipitates. In contrast, the microscale I-phase presents a formidable barrier to dislocation motion, facilitating dislocation pileups at interfaces and culminating in diminished ductility across the interface. In-situ stretching techniques were employed to scrutinize the microstructural evolution of alloys during tensile deformation, elucidating that the deformation compatibility of alloys correlates with the average size of the I-phase and their distribution along GBs and PBs. Corresponding to the orientation relationship (OR) between the α-Mg and β-Li phases {110}Li//{0001}Mg and <>Li //<>Mg, the slip continuity between α-Mg and β-Li on plane pairs of {123}Li-{}Mg and {112}Li-{}Mg assures the deformation compatibility through facilitating the deformation across interfaces. Simultaneously, during the stretching process, the dispersed I-phase instigates the emergence of sporadic microcracks, indicating gradual damage evolution. These discoveries offer novel insights into achieving exceptional strength-ductility amalgamations in Mg-Li alloys through microstructural adjustments.

中文翻译：

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通过分散的 α-Mg 相减轻沿晶界散布共晶的尺寸和分布，提高铸造 Mg-Li 合金的延展性

高锂浓度的镁锂合金具有轻质的体心立方（BCC）基体结构（β-Li）。散布的共晶（主要是网状 I 相）通常沿着相界 (PB) 和晶界 (GB) 形成，它们强化了合金，但由于 I 相的脆性行为导致延展性损失。通过改变Li含量，我们制备了(β+α)双相Mg-Li合金，其中具有六方密排结构(HCP)的α-Mg相嵌入β-Li基体中，显着增加了界面密度。高密度界面减轻了 I 相沿 GB 和 PB 的分布和尺寸。与不含 α-Mg 相的合金 (EL = 5.1%) 相比，该合金表现出增强的延展性 (伸长率 (EL) = 17.8%)。结构表征揭示了纳米级 B2 (Li, Mg)Zn 型析出物与微米级 I 相的强化机制。(Li, Mg) Zn 纳米相提高了合金的屈服强度和极限拉伸强度，而不会明显影响延展性，这主要是由于滑动位错切割了沉淀物。相比之下，微尺度 I 相对位错运动构成了巨大的障碍，促进了界面处的位错堆积，最终导致界面上的延展性降低。采用原位拉伸技术来研究合金在拉伸变形过程中的微观结构演变，阐明合金的变形相容性与 I 相的平均尺寸及其沿 GB 和 PB 的分布相关。对应于α-Mg和β-Li相{110}Li//{0001}Mg和<>Li //<>Mg之间的取向关系（OR），α-Mg和β-Li之间的滑移连续性{123}Li-{}Mg 和 {112}Li-{}Mg 平面对通过促进跨界面变形来确保变形兼容性。同时，在拉伸过程中，分散的 I 相促使出现零星的微裂纹，表明损伤逐渐演变。这些发现为通过微观结构调整实现镁锂合金卓越的强度-延展性融合提供了新颖的见解。