本文選題：激光技術(shù) + 變極性TIG��； 參考：《北京工業(yè)大學》2016年碩士論文

【摘要】：采用鋁合金代替?zhèn)鹘y(tǒng)鋼鐵材料是實現(xiàn)軌道列車輕量化的有效途徑。A7N01鋁合金是一種專門為高速列車研發(fā)的新型鋁合金,大量應用于高速列車鋁合金車體生產(chǎn)制造。當前,A7N01鋁合金車體的焊接主要采用傳統(tǒng)的電弧焊,但焊后容易產(chǎn)生焊接變形及接頭軟化的問題。激光焊接具有能量密度高、焊接速度快、焊后熱影響區(qū)窄等優(yōu)點,能有效克服焊接變形及接頭軟化的問題。但激光焊接A7N01鋁合金存在焊縫表面成形差及氣孔等問題。光纖激光-變極性TIG復合焊接綜合利用了激光和電弧兩種熱源的優(yōu)勢,同時變極性TIG電弧既能滿足陰極清理,又能最大限度降低鎢極燒損,可有效改善鋁合金焊接表面成形差及氣孔等缺陷,具有明顯的技術(shù)優(yōu)勢。針對高速列車用4mm厚A7N01-T4鋁合金,采用光纖激光-變極性TIG復合填絲焊接方法,主要研究了復合焊接工藝參數(shù)對焊縫成形及焊縫氣孔的影響規(guī)律,探討了焊縫氣孔的種類、形成機理及得到抑制的方法。通過工藝參數(shù)優(yōu)化,獲得了成形良好內(nèi)部無缺陷的焊接接頭,同時分析了優(yōu)化工藝參數(shù)條件下焊接接頭的顯微組織和力學性能。工藝試驗研究結(jié)果表明,采用激光在前電弧在后的焊接方向焊縫成形較好,且熱源間距為2mm時焊接過程穩(wěn)定,焊縫成形較好;隨著焊接電流的增加,焊縫正面熔寬增加,背面熔寬基本不變;而焊接速度降低,焊縫正面和背面熔寬均增加;同時發(fā)現(xiàn)氣孔是焊縫中存在的主要缺陷,其氣孔類型主要是氫氣孔和工藝氣孔,氫氣孔可以通過去除母材表面一定厚度包鋁層得到抑制,而工藝氣孔與焊接工藝參數(shù)密切相關。隨著焊接速度降低,焊縫中工藝氣孔減少;而送絲速度增加,焊縫工藝氣孔增加;光絲間距為1mm時焊縫氣孔減少。在激光功率為6kW,焊接電流為180A,焊接速度為4m/min,送絲速度為4m/min時,獲得了成形良好內(nèi)部無缺陷的焊接接頭。接頭組織分析表明,焊縫主要由熔合線附近細小等軸晶、柱狀晶和焊縫中心的樹枝晶構(gòu)成,從上至下熔合線附近等軸細晶區(qū)逐漸減少,且焊縫中心線附近樹枝晶晶粒尺寸逐漸減小,二次枝晶逐漸弱化;接頭硬度測試顯示焊縫區(qū)存在一定程度的接頭軟化。拉伸試驗表明,焊態(tài)下接頭抗拉強度為325.25MPa,達到母材的73.5%,延伸率為3.1%。而自然時效一個月后接頭力學性能顯著增強,接頭抗拉強度為363.78MPa,達到母材的82.2%,延伸率為4.65%。拉伸試驗接頭均斷裂于焊縫位置,焊縫區(qū)為接頭薄弱位置,焊縫斷口存在大量等軸韌窩,表現(xiàn)出明顯的韌性斷裂特性。
[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.
【學位授予單位】：北京工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2016
【分類號】：TG457.14

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