Achieving ultra-high tensile yield strength over 400 MPa in RE modified Mg–Zn-based alloys using conventional thermomechanical processing is a challenging task. In this study, we successfully produced a Mg–7Zn–2Gd–0.5Zr (wt. %) alloy with exceptional strength through traditional hot-extrusion techniques. This alloy exhibits a tensile yield strength of 440 MPa and an acceptable ductility of 4.5%, surpassing a majority of previously reported Mg–Zn-RE-based alloys. Our findings demonstrate that the addition of Gd in Mg–Zn-based alloys effectively retards dynamic recrystallization (DRX) during extrusion, leading to the formation of a distinctive bimodal structure comprising approximately 13.8% coarse un-recrystallized (unDRXed) grains and about 86.2% fine DRXed grains. Furthermore, the alloying effect of Gd enhances particle density, including micron-sized particles and dynamic nano-precipitates. These dynamic precipitates play a crucial role in impeding dislocation movement during extrusion, thereby contributing to the formation of bimodal structure. Additionally, both nano-precipitates and segregation of Zn and Gd atoms towards grain boundaries facilitate the formation of fine DRXed grains through pinning effect. Consequently, the significantly increased tensile yield strength observed in our Gd-modified alloy can be attributed to multiple strengthening mechanisms: fine DRXed grains, strong texture exhibited by unDRXed grains, numerous dynamic precipitates, high-density residual dislocations, and co-segregation of solutes. However, the formation of bimodal structure worsens the yield asymmetry of the Gd-modified alloy due to its strong basal texture. These results provide a valuable insight for further development efforts aimed at achieving ultra-high-strength Mg–Zn-RE-based alloys.

中文翻译：

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通过添加 Gd，挤压 ZK70 合金中双峰结构的演化和实现超高屈服强度

使用传统热机械加工在稀土改性镁锌基合金中实现超过 400 MPa 的超高拉伸屈服强度是一项具有挑战性的任务。在这项研究中，我们通过传统的热挤压技术成功生产了具有优异强度的 Mg–7Zn–2Gd–0.5Zr (wt.%) 合金。该合金的拉伸屈服强度为 440 MPa，可接受的延展性为 4.5%，超过了大多数先前报道的 Mg-Zn-RE 基合金。我们的研究结果表明，在 Mg-Zn 基合金中添加 Gd 可以有效地延缓挤压过程中的动态再结晶 (DRX)，从而形成独特的双峰结构，其中包含约 13.8% 的粗未再结晶 (unDRXed) 晶粒和约 86.2% 的粗大未再结晶 (unDRXed) 晶粒。细 DRX 颗粒。此外，Gd 的合金化作用提高了颗粒密度，包括微米级颗粒和动态纳米沉淀物。这些动态析出物在阻碍挤压过程中位错运动方面发挥着至关重要的作用，从而有助于双峰结构的形成。此外，纳米沉淀物以及 Zn 和 Gd 原子向晶界的偏析都有助于通过钉扎效应形成细 DRX 晶粒。因此，在我们的 Gd 改性合金中观察到的显着增加的拉伸屈服强度可归因于多种强化机制：细 DRX 晶粒、未 DRX 晶粒表现出的强织构、大量动态析出物、高密度残余位错和溶质共偏析。然而，由于其强的基础织构，双峰结构的形成加剧了Gd变质合金的屈服不对称性。这些结果为旨在实现超高强度镁锌稀土基合金的进一步开发工作提供了宝贵的见解。