This study conducts low-cycle fatigue tests on an extruded magnesium alloy cabin. The relationship between the microstructure and macroscopic cyclic-deformation behavior was established by regulating the microstructure of the different precipitated phases. The results show that only the β’ phase is precipitated in the 200AT sample, and lamellar Long-Period Stacking Ordered (LPSO) phase and β’ phase overlapping structures are precipitated in the 250AT sample. Different microstructural states lead to the intersection of the fatigue-life curves of the two samples. Under a low strain amplitude, the 200AT sample is more likely to produce short-range reversible basal slip, which easily releases stress and has a high fatigue life. The 250AT sample has a low fatigue life because the stress concentration in the grain caused by the irreversible < c + a > slip of the medium growth process leads to higher intragranular strength, and the crack initiates along the grain boundary with weaker strength. At high strain amplitudes, cracks in the 200AT sample mainly propagate along the basal and prismatic planes with faster crack-propagation speeds and lower fatigue resistance. In contrast, cracks in the 250AT sample mainly propagate along the pyramidal < a > and pyramidal < c + a > directions with slower crack-propagation speeds and higher fatigue resistance.

中文翻译：

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不同析出相组织对 Mg-Gd-Y-Zn-Zr 合金低周疲劳性能的影响

本研究对挤压镁合金舱进行了低周疲劳试验。通过调节不同沉淀相的微观结构，建立了微观结构和宏观循环变形行为之间的关系。结果表明，200AT 样品中仅沉淀了 β' 相，而 250AT 样品中沉淀了层状长周期堆叠有序 （LPSO） 相和 β' 相重叠结构。不同的微观结构状态导致两个样品的疲劳寿命曲线相交。在低应变幅值下，200AT 样品更容易产生短距离可逆基底滑移，容易释放应力，疲劳寿命长。250AT 试样的疲劳寿命较短，因为介质生长过程中不可逆的<c+a>滑移导致晶内强度较高，裂纹沿晶界萌生，强度较弱。在高应变幅值下，200AT 样品中的裂纹主要沿基面和棱柱面扩展，裂纹扩展速度更快，抗疲劳性较低。相比之下，250AT 试样中的裂纹主要沿金字塔形< a >和锥体< c + a >方向扩展，裂纹扩展速度较慢，抗疲劳性较高。