A7N01铝合金激光—变极性TIG复合填丝焊接工艺及组织性能研究

发布时间：2018-04-24 03:33

本文选题：激光技术 + 变极性TIG　；参考：《北京工业大学》2016年硕士论文

【摘要】：采用铝合金代替传统钢铁材料是实现轨道列车轻量化的有效途径。A7N01铝合金是一种专门为高速列车研发的新型铝合金,大量应用于高速列车铝合金车体生产制造。当前,A7N01铝合金车体的焊接主要采用传统的电弧焊,但焊后容易产生焊接变形及接头软化的问题。激光焊接具有能量密度高、焊接速度快、焊后热影响区窄等优点,能有效克服焊接变形及接头软化的问题。但激光焊接A7N01铝合金存在焊缝表面成形差及气孔等问题。光纤激光-变极性TIG复合焊接综合利用了激光和电弧两种热源的优势,同时变极性TIG电弧既能满足阴极清理,又能最大限度降低钨极烧损,可有效改善铝合金焊接表面成形差及气孔等缺陷,具有明显的技术优势。针对高速列车用4mm厚A7N01-T4铝合金,采用光纤激光-变极性TIG复合填丝焊接方法,主要研究了复合焊接工艺参数对焊缝成形及焊缝气孔的影响规律,探讨了焊缝气孔的种类、形成机理及得到抑制的方法。通过工艺参数优化,获得了成形良好内部无缺陷的焊接接头,同时分析了优化工艺参数条件下焊接接头的显微组织和力学性能。工艺试验研究结果表明,采用激光在前电弧在后的焊接方向焊缝成形较好,且热源间距为2mm时焊接过程稳定,焊缝成形较好;随着焊接电流的增加,焊缝正面熔宽增加,背面熔宽基本不变;而焊接速度降低,焊缝正面和背面熔宽均增加;同时发现气孔是焊缝中存在的主要缺陷,其气孔类型主要是氢气孔和工艺气孔,氢气孔可以通过去除母材表面一定厚度包铝层得到抑制,而工艺气孔与焊接工艺参数密切相关。随着焊接速度降低,焊缝中工艺气孔减少;而送丝速度增加,焊缝工艺气孔增加;光丝间距为1mm时焊缝气孔减少。在激光功率为6kW,焊接电流为180A,焊接速度为4m/min,送丝速度为4m/min时,获得了成形良好内部无缺陷的焊接接头。接头组织分析表明,焊缝主要由熔合线附近细小等轴晶、柱状晶和焊缝中心的树枝晶构成,从上至下熔合线附近等轴细晶区逐渐减少,且焊缝中心线附近树枝晶晶粒尺寸逐渐减小,二次枝晶逐渐弱化;接头硬度测试显示焊缝区存在一定程度的接头软化。拉伸试验表明,焊态下接头抗拉强度为325.25MPa,达到母材的73.5%,延伸率为3.1%。而自然时效一个月后接头力学性能显著增强,接头抗拉强度为363.78MPa,达到母材的82.2%,延伸率为4.65%。拉伸试验接头均断裂于焊缝位置,焊缝区为接头薄弱位置,焊缝断口存在大量等轴韧窝,表现出明显的韧性断裂特性。
[Abstract]:Aluminum alloy replacing traditional steel material is an effective way to realize the lightweight of rail train. A7N01 aluminum alloy is a new type of aluminum alloy specially developed for high-speed train, which is widely used in the manufacture of aluminum alloy body of high-speed train. At present, traditional arc welding is mainly used in welding of A7N01 aluminum alloy body, but welding deformation and joint softening are easy to occur after welding. Laser welding has the advantages of high energy density, fast welding speed and narrow heat affected zone after welding, which can effectively overcome the problems of welding deformation and joint softening. However, laser welding of A7N01 aluminum alloy has some problems such as poor weld surface forming and porosity. Fiber laser-variable-polarity TIG composite welding makes full use of the advantages of laser and arc heat sources. At the same time, variable polarity TIG arc can not only satisfy cathode cleaning, but also minimize tungsten burn loss. It can effectively improve the defects of aluminum alloy welding surface, such as poor forming and porosity, and has obvious technical advantages. Aiming at the thick A7N01-T4 aluminum alloy of 4mm used in high-speed train, the influence of welding process parameters on weld formation and weld porosity was studied by fiber laser and variable polarity TIG composite filling wire welding method, and the types of weld porosity were discussed. Formation mechanism and method of inhibition. By optimizing the process parameters, the welded joints with good internal defects were obtained, and the microstructure and mechanical properties of the welded joints were analyzed under the optimized process parameters. The experimental results show that the welding process is stable and the weld forming is better when the laser is used in the welding direction of the front arc and the distance of the heat source is 2mm, and the weld width increases with the increase of welding current. The width of the back weld is almost unchanged, while the welding speed decreases, the width of the front and the back of the weld increases. At the same time, it is found that the porosity is the main defect in the weld, and the main types of porosity are the hydrogen pores and the technological pores. The hydrogen pore can be restrained by removing a certain thickness of aluminum coating on the surface of the base metal, and the process porosity is closely related to the welding process parameters. With the decrease of welding speed, the process porosity decreases, while the wire feeding speed increases, and the weld porosity decreases when the distance between light wire and wire is 1mm. When the laser power is 6kW, the welding current is 180A, the welding speed is 4m / min, and the wire feeding speed is 4m/min, the welded joints with good internal defects are obtained. The microstructure analysis shows that the weld is mainly composed of fine equiaxed crystals near the fusion line, columnar crystals and dendrite in the center of the weld, and the equiaxed fine grain area decreases gradually from the top to the bottom near the fusion line. Moreover, the size of dendritic grain and secondary dendrite were gradually decreased, and the hardness test showed that there was a certain degree of joint softening in the weld zone. The tensile test shows that the tensile strength of the welded joint is 325.25 MPA, which reaches 73.5% of the base metal, and the elongation is 3.1%. The mechanical properties of the joints increased significantly after one month of natural aging, and the tensile strength of the joints was 363.78 MPa, which reached 82.2 of the base metal and the elongation of the joints was 4.65. The tensile test joints are all broken in the weld position, the weld zone is the weak position of the joint, and there are a large number of equiaxed dimples on the fracture surface of the weld, which shows obvious ductile fracture characteristics.
【学位授予单位】：北京工业大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG457.14

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