【作者】 杨涛；

【导师】 吴林；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2013， 博士

【摘要】 2219铝合金为Al-Cu系高强铝合金，由于其具有良好的力学性能，是制造火箭贮箱的理想材料之一。针对常规熔化极惰性气体保护焊（MIG）焊接2219铝合金气孔多、焊接接头质量差、焊接效率低等问题，本文以Plasma-MIG复合热源耦合机制及对应的焊接工艺为研究对象，采用实验研究及理论计算的方法，系统的研究复合热源焊接条件下，外层等离子弧与内层MIG弧的相互耦合机理、复合电弧特性、复合电弧光谱诊断、熔滴的受力模型。通过研究揭示了复合电弧空间温度分布规律，复合电弧耦合机理及各参数对于焊缝质量的影响。本研究丰富了复合热源焊接电弧理论，为2219铝合金进行稳定的高效高质量化Plasma-MIG复合焊接提供了实验基础与理论依据。本文根据Plasma-MIG复合电弧焊要求，对焊枪进行了改进。依靠于PLC及人机工程搭建了Plasma-MIG复合电弧焊接控制系统，实现了复合电弧焊接及焊接过程控制。设计了Plasma-MIG复合电弧焊起弧过程控制程序，解决了复合电弧难起弧的问题。本文利用光谱仪、高速摄像CCD、窄带滤光片、中性减光片和透镜建立了电弧光谱图谱同步采集系统，该系统能够准确的获得电弧信息。系统结构简单，具有较高的精度和采集效率。基于Bockasten三次多项式插值方法设计了离散Abel变换算法，通过将水平方向辐射强度信息恢复为径向发射系数信息，从而来获得Plasma-MIG复合电弧全信息，得到了Plasma-MIG复合电弧等温线分布。实验表明：Plasma-MIG复合电弧外层等离子弧由于受到内层MIG弧的影响，中心最高温度发生了偏移,复合电弧温度的最高区域在外层等离子弧区域。外层等离子弧与内层MIG电弧之间存在着一个明显的最低温度，该最低温度为内层MIG弧与外层等离子弧的分界区；Plasma-MIG复合电弧等温线分布趋势为先升高再降低再升高，整个电弧等温线呈中心对称分布；Plasma-MIG复合电弧，外层等离子弧由于受到喷嘴的压缩对于内层MIG弧具有一定的压缩作用。MIG电弧由于电流流入等离子弧，使得MIG弧的热作用减弱，从而降低了内部MIG电弧温度。结合传统MIG焊接熔滴过渡力学理论，进一步分析了外层等离子弧介入所产生的熔滴受力情况的变化，建立了复合热源焊接熔滴过渡的力学物理模型。计算了不同参数下的熔滴受力，结合电弧热作用机理揭示了焊接参数与熔滴受力的内在联系。对熔滴及电弧图像、电参数的进行同步采集，对Plasma-MIG复合电弧焊接过程中的电弧特性、熔滴过渡形式，熔滴受力，复合电弧特性的影响因素，电弧熔池行为进行了系统的分析。与常规MIG焊相比，复合电弧焊接过程更稳定，可实现不同熔滴过渡形式下的无飞溅焊接。本文设计了二次五元回归模型，系统的研究了单一焊接参数及多参数交互作用对接头抗拉强度的影响。分析结果表明：单因素的影响作用均呈现抛物线规律，焊接速度对抗拉强度影响最大，其次为熔化极电压和等离子弧电流，送丝速度对接头抗拉强度的影响最小。焊接参数范围内存在最佳工艺参数之间相互匹配，其中焊接速度和送丝速度的交互作用最强，MIG电压和焊接速度交互作用影响最小，两者为近似独立。通过对二次五元回归模型进行数学处理，优化了2219铝合金Plasma-MIG焊接工艺参数，优化后焊接接头抗拉强度为285MPa(未去除正反面余高)，强度系数达到了70.3%。本文系统的研究了2219铝合金在Plasma-MIG焊接下的热循环曲线。分析了五种参数下的高温时间、温度梯度、高温停留时间、过冷度等方面的变化规律。研究了等离子电弧对熔池运动的影响规律：等离子电弧的加入一方面抑制了电弧气氛中氢质子向液态金属溶解，另一方面改变了熔池运动形式，加快了过饱和气体的析出。当焊接参数匹配合理，焊缝中气孔缺陷明显减少，甚至消失。与常规MIG相比， Plasma-MIG复合电弧焊接改善了2219铝合金接头力学性能及焊缝组织。更多还原

【Abstract】 2219aluminum alloy, a kind of high strength Al-Cu alloys, is an ideal materialfor the fabrication of the rocket fuel storage box. Aiming at solving the problems ofhigh porosities and low welding efficiencies in the conventional MIG weldingmethod of2219aluminum alloy welding process, plasma-MIG hybrid arc weldingis introduced, and the coupling mechanism of the hybrid arcs and the weldingprocedure are investigated. During the plasma-MIG hybrid arc welding process, thecoupling mechanism of outer plasma arc and inner MIG arc, hybrid arccharacteristics, spectral diagnostics information of hybrid arcs and the force modelof droplets are systematically studied by experimental and theoretical methods. Thetemperature distributions in the arc zones, the coupling mechanism of hybrid arcsand the effects of various welding parameters on the weld properties are disclosed,which enrich the theory of the plasma-MIG hybrid arc welding and provide theexperiment and theory basis for high quality welds of2219alloy with stableplasma-MIG hybrid arc welding procedure.The special welding torch is developed to meet the requirement of plasma-MIGhybrid arc welding, and the control system for the plasma-MIG hybrid arc weldingis also constructed to control the welding parameters by the use of PLC andhuman-machine engineering. Furthermore, a well designed arc starting system isrealized to solve the difficulty at arc starting during plasma-MIG hybrid arcwelding.The spectrum and image acquisition system for hybrid arcs, which is made upof the spectrometer, high-speed CCD digital cameras, narrow bandpass filters,Neutral filters and optical lens, can get the accurate full-field information of thearcs, and this system is simple in constructions with high accuracy and dataacquisition efficiency. Discrete Abel transfer algorithm is designed based onBockasten cubic polynomial interpolation method. The plasma-MIG hybrid arcfull-field information is available by converting the horizontal radiation strength toradial emitting coefficiency, and base on which the isothermal lines can be got inplasma-MIG hybrid welding process. The experimental results show that the highesttemperature zone in the arc center shifts due to the influence of inner MIG arc on outer plasma arc, and thus the highest temperature zone locate at the outer plasmaarc in plasma-MIG hybrid arc welding. There is a lowest temperature zone betweenthe outer plasma arc and the inner MIG arc, which locates at the interface of the twoarcs. The distributions of isothermal lines increase firstly, and then decrease, finallyincrease again, and they are centrosymmetrically distributed. The inner MIG arc iscompressed by the outer plasma arc for the constrict effect of the nozzle. The heateffect of MIG arc is weakened because of the bypass flow of the MIG current intothe plasma arc, and thus the temperature of MIG arc is lowered.With referencing to the mechanical theory of droplet transfer in conventionalMIG welding, the influence of outer plasma arc on the changing of droplet transferbehavior is further analyzed and a mechanical physical model is developed in thePlasma-MIG welding process. According to the theory of arc heating effect and thestatic force balance, the force actions on the droplets are calculated and the relationsbetween welding parameters and force are also revealed. The Plasma-MIG hybridarc characteristic, droplet transfer behavior, the influencing factors of arccharacteristic are studied systematically by adopting droplet photos andsynchronous acquisition of electrical parameters. Compared with conventional MIGwelding, the hybrid arc welding process is further stability, and thus non-spatterwelding process with difference of droplet transfer modes can be achieved.The quadratic regression mode with five factors is used to study the effects ofsingle factor and interactions multi-factor on tensile strength. The results show thatthe effect of single factor on tensile strength display parabola rules, welding speedis the greatest impact on the tensile strength, MIG voltage and Plasma current issubsequent effect, and the wire feed plays minimal role to tensile strength. The bestof interaction weld parameter is existed; the interactions between welding speed andwire feed are the greatest impact on the tensile strength, and meanwhile theinteractions between MIG voltage and welding speed which are mutuallyindependent play minimal role to tensile strength. The welding process parametersof2219aluminum are optimized by the mathematical treatment of the quadraticregression mode with five factors, the tensile strength of weld joint is285Mpawhich is the70.3%of base metal.The thermal cycling curve of Plasma-MIG welding for2219aluminum alloy isinvestigated. In the condition of five different kinds of parameters, the temperature gradient, residence time of high temperature and super cooling are analysised. Theinfluence of plasma arc on the motion of weld pool has been researched. It wasfound that the process of proton in arc atmosphere dissolving into liquid metal hasbeen controlled, the motion form of weld poor behavior is changed and theevolution of saturated gas has been accelerated due to introduction of outer plasmaarc. Compared with conventional MIG welding, the joint properties and weldmicrostructure of2219aluminum alloy are improved by Plasma-MIG hybrid arcwelding.更多还原