2198铝锂合金激光填丝焊接接头腐蚀行为

Corrosion Behavior of Laser Beam Welded Joint of 2198 AluminiumLithium Alloy with Filler Wire

2198铝锂合金具有密度低、力学性能好、比强度高、耐高温、可塑性强等优点,是航空航天领域理想的结构材料。针对2198铝锂合金填充ER4047 Al-Si焊丝激光焊接接头的显微组织及在质量分数为3.5%的Na Cl溶液中的腐蚀行为进行研究。利用光学显微镜、扫描电镜及透射电镜对焊接接头微观组织形貌、析出相的种类及分布研究的基础上,室温下采用浸泡实验法和电化学腐蚀法对母材和焊缝腐蚀行为进行了系统的研究。结果表明,2198铝锂合金母材组织较粗大,晶粒沿轧制方向生长,在粗大的组织中随机分布着尺寸在几百纳米左右的颗粒状和针状的T1相,而填充ER4047 Al-Si焊丝激光焊接后,热影响区极窄、焊缝组织细小、成分均匀、析出相的种类多样,呈等轴细晶状组织,靠近熔合线处组织呈垂直于熔合线生长的柱状晶。室温下在质量分数为3.5%的Na Cl溶液中,焊缝和热影响区为均匀腐蚀,腐蚀斑点面积小、蚀点浅。母材为点蚀,随着浸泡时间增加,腐蚀斑点面积变大、蚀点加深。焊缝的开路电位、自腐蚀电位和极化电阻均高于母材,腐蚀电流密度则小于母材。

2198 aluminium-lithium alloy is extensively used in the field of aerospace due to the favorable properties,such as low density, good mechanical property, high specific strength, good thermostability and plasticity. 2198aluminium-lithium alloy is welded by fiber laser using the filler of ER4047 Al-Si. The microstructure and corrosion behavior of joint in Na Cl solution with 3.5% mass fraction is studied. The micromorphologies, precipitate species and their distribution have been examined using the optical micrograph, scanning electron microscope and transmission electron microscope. The corrosion behavior of weld and base metal has been compared by the methods of immersion test and electrochemical corrosion test at room temperature. The results indicate that the microstructure of 2198 aluminium-lithium alloy base metal, compared to the weld, is coarser and grows along to the rolling direction. Plenty of T1 precipitates with the diameter of hundreds of nanometers distributed randomly in the base metal. After laser welded with the filler ER4047 Al- Si, the heat affected zone is narrow, the microstructure is tiny, the component is uniform, the kind of precipitate is various, and the fine grain is equiaxed,the columnar crystal is vertical growth close to fusion line. At room temperature in Na Cl solution with 3.5% mass fraction, the weld and heat affected zone show the uniform corrosion behavior, the small corrosion spot area, the shallow corrosion spot. By comparison, the parent metal shows the pitting corrosion. With the immersion time increasing, the pitting area is enlarged and the depth is deeper. The open circuit potential, self-corrosion potential and polarization resistance of weld are all higher than those of the parent metal, but the corrosion current density is less than that of the parent metal.