5A06铝合金及其焊接接头的疲劳断裂行为Fatigue fracture behavior of 5A06 aluminum alloy and its welded joint

对5A06防锈铝合金及其焊接接头疲劳性能断裂行为进行研究，采用疲劳试验、光学显微镜、扫描电子显微镜等手段对 5A06 铝合金的疲劳性能、金相组织、裂纹扩展特征和疲劳断口进行分析。结果表明：在循环次数为2×10 6 时，铝合金母材、对接接头、横向十字、侧面连接和纵向十字接头的疲劳性能分别为99.97、70.96、57.48、48.20 和 41.80 MPa；铝合金母材疲劳裂纹起裂于截面最小部位，对接接头和横向十字接头裂纹起裂于焊趾等应力集中部位，裂纹沿着热影响区扩展；侧面连接接头裂纹起裂于两板连接处应力集中部位，纵向十字接头裂纹起裂于热影响区；微 观裂纹为沿晶和穿晶混合的扩展特征。对 母材及其焊接接头的宏观断口呈暗灰色纤维状，具有一定的塑性；接头的微观断口具有准解理特征，断口中存在球状孔洞、疲劳条纹和韧窝，并存在二次裂纹。

Fatigue testing fracture behavior was researched on 5A06 antirust aluminum alloy and its welded joints. The
fatigue properties, microstructure, fatigue crack propagation character and fatigue fracture were investigated by fatigue test, optical microscopy (OM) and scanning electronic microscopy (SEM). Under cycle times of 2×10 6, the fatigue strengths of base metal (BM), butt joint (BJ), transverse cross joint (TJ), lateral connection joint (LJ) and longitudinal cross joint(LCJ) are 99.97, 70.96, 57.48, 48.20 and 41.80 MPa, respectively. The fatigue crack initiation site is in the smallest section for base metal, the crack initiation is in the weld toe and the crack propagates along the HAZ for the BJ and TJ, the crack initiation is in the fillet weld leg for the LJ, the crack initiation is in HAZ for the LCJ, the microcrack propagates for transgranular and intergranular. The fatigue macrofracture shows a dark gray fibrous fracture patterns and has some plasticity, the microfracture surface consists of quasicleavage patterns, spherical hole, fatigue striation and dimple, and numerous secondary cracks are observed.

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