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采用光学显微镜、扫描电镜和能谱分析等方法研究了5B70铝合金板材微观组织以及高周疲劳断口的微观特征。研究结果表明:在较低应力水平下合金主要于次表面的杂质粒子处萌生疲劳裂纹,在较高应力水平下疲劳裂纹还可由于杂质相粒子的自身开裂引发,呈现多源化趋势;影响裂纹扩展的第二相粒子主要为含Fe、Mn粒子。随着加载应力水平的提高,合金疲劳裂纹扩展区中的辉纹间距增加,二次裂纹和孔洞的数量增多。
The microstructure of 5B70 aluminum alloy sheet and the microscopic characteristics of high-cycle fatigue fracture were studied by optical microscope, scanning electron microscope and energy spectrum analysis. The results show that the fatigue crack initiation occurs mainly at the impurity particles on the subsurface at the lower stress level, and the fatigue crack can also be induced by self-cracking of the impurity phase particles at higher stress level. The expanded second phase particles are mainly Fe and Mn particles. With the increase of the loading stress level, the spacing of the fringes in the fatigue crack growth zone of the alloy increases, and the number of secondary cracks and holes increases.