6061-T6 铝合金激光焊接接头腐蚀疲劳裂纹扩展

目的研究6061-T6铝合金激光焊接接头的腐蚀疲劳裂纹扩展特性,并分析裂纹扩展的影响因素。方法利用光纤激光器,焊接尺寸为150 mm×100 mm×4 mm(焊接方向、横向、熔深方向)的6061-T6铝合金,采用SE(B)三点弯曲疲劳裂纹扩展试验并利用连续降K法,分别在空气和人工海水中进行疲劳裂纹扩展试验,通过使用金相显微镜(OE)和扫描电子显微镜(SEM),对金相结构进行观测分析。结果同样工艺参数的焊接接头,在海水中疲劳裂纹门槛值(4.063 016 MPa·m~(0.5))大于空气中的门槛值(3.479 166 MPa·m~(0.5));在疲劳裂纹扩展中速区(da/dN10~(-5) mm/cycle)时,海水焊接接头疲劳裂纹扩展速率大于空气中的,低速区(da/d N10~(-5) mm/cycle)则小于在空气中的。结论成形良好的焊缝、晶粒细小的焊缝组织有助于接头疲劳裂纹扩展性能的提高;中速区,海水中疲劳裂纹扩展速率偏大,主要是由腐蚀条件下焊缝裂纹尖端阳极溶解和交变载荷共同作用导致;低速区,海水中疲劳裂纹扩展速率偏小,主要原因是腐蚀产物堆积于疲劳裂纹扩展尖端,产生较强裂纹闭合效应。

Corrosion Fatigue Crack Growth in Laser Welded 6061-T6 Aluminum Alloy

The paper aims to study corrosion fatigue propagation characteristics of 6061-T6 aluminum alloy welding joint under different welding process conditions by laser welding and analyze influence factors of crack growth. A fiber laser was used to weld 6061-T6 aluminum alloy by the size of 150 mm×100 mm×4 mm (welding direction, transverse and penetration direction). The three point bending crack propagation test of SE (B) sample and the method of continuous decrease of K were used for fatigue crack propagation test in air and artificial seawater. Metallographic microscope (OE) and scanning electron microscope (SEM) were adopted to observe the metallographic structure. The threshold value (4.063 016 MPa·m0.5) of the welded joint in the seawater was greater than that (3.479 166 MPa·m0.5) in the air. The corrosion fatigue crack propagation rate in the intermediate speed area (da/dN>10-5 mm/cycle) of welding joint was greater than that in the air, as the rate was smaller in the low speed area (da/dN<10-5 mm/cycle). Good welding forming and fine grain of the welding microstructure could improve the fatigue crack growth performance. The fatigue crack growth rate of welded joint in seawater at intermediate speed is greater. This is mainly caused by combined action anodic dissolution of crack tip and alternating load of weld crack of corrosion. The fatigue crack growth rate of welded joint in seawater at low speed is smaller. The main reason for the result is the strong crack closure effect caused by accumulation of corrosion products on fatigue crack growth tips.