5B70铝合金板材疲劳裂纹萌生与扩展机制

Fatigue crack initiation and propagation mechanism of 5B70 aluminum alloy plate

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 microscopic characteristics of high-cycle fatigue fracture and microstructure of 5B70 aluminum alloy plate were studied by means of optical microscope,scanning electron microscopy and energy dispersive spectrometer. The results show that the fatigue cracks are predominantly initiated at the impurity particles in the sub-surface under low loading stress,while also being initiated due to the selfcracking of impurity particles under high loading stress with a multi-source trend. The second phase particles that affect the crack propagation are mainly containing Fe and Mn particles. With the increase of the loading stress level,the interval between the fatigue striation in the fatigue crack propagation zone increases,and the number of secondary cracks and holes increases.