【作者】 苗玉刚；

【导师】 吴林； 陈彦宾；

【作者基本信息】 哈尔滨工业大学 ， 材料加工工程， 2008， 博士

【摘要】 为解决铝合金激光焊接存在的焊接过程稳定性差、能量利用率低、焊接缺陷多等关键问题,本文探索了一种新的铝合金焊接工艺—“激光-电弧双面焊”。一方面,通过电弧的加热作用,提高激光匙孔的稳定性,改善焊缝成形,减少焊接气孔;另一方面,通过激光匙孔的加热作用,提高电弧稳定性,改变电弧焊接特性,在双热源耦合加热作用下,提高激光和电弧的能量利用率、改善焊接质量、降低焊接成本,实现铝合金的稳定、高效、优质连接。本文主要以4mm厚5A06铝合金为试验材料,采用CO2激光和TIG电弧进行激光-TIG双面焊试验。从激光-TIG双面焊的焊接特性角度出发,对铝合金激光-TIG双面焊的工艺特性、焊缝成形、内部缺陷等进行研究,分析了典型激光与电弧能量匹配条件下,双面焊接头的组织及力学性能,提出了控制激光-TIG双面焊接头形状的主要方法,给出了工艺优化范围。同时,针对单激光焊接存在的焊接适应性差、装配条件要求高等问题,研究了激光-TIG双面焊工艺在对接间隙、对中偏移以及不等厚板的焊接适应性,并探讨了该工艺在厚板和薄板铝合金上的应用前景。为掌握激光-TIG双面焊过程中电弧与激光等离子体的物理特征及影响规律,借助于图像采集、电信号传感及图像处理手段,研究激光匙孔加热与等离子体穿透作用下的电弧形态及电弧电压、电流特性,着重分析了激光深熔焊特殊的匙孔传热方式对激光-TIG双面焊电弧特性的影响规律及作用机制,确定了激光匙孔加热在电弧作用区产生的“局部高温度梯度区”是导致电弧收缩、弧压下降、稳定性改善的内在原因,揭示了激光-TIG双面焊接过程中电弧能量效应发生转变的物理机制。同时,分析了电弧热作用下光致等离子体特性发生转变的规律及原因,为激光-TIG双面焊过程热传输机理研究提供试验依据。基于激光匙孔形成的临界能量密度与临界温度条件,建立匙孔穿透与匙孔未穿透两种焊接模式下的激光-TIG双面焊动态热源模型,采用有限元方法计算分析了激光-TIG双面焊接过程中热传输途径与影响作用、焊接熔池与匙孔的建立过程,对激光-TIG双面焊的热传输原理进行阐述。利用建立的动态热源模型预测不同焊接速度和板厚条件下激光-TIG双面焊的焊缝成形规律、熔池熔透与匙孔穿透的临界条件。最后,从理论分析、实验及数值分析等角度对铝合金激光-TIG双面焊的熔深增加、熔化效率提高的机理进行探讨,证明影响激光-TIG双面焊热效率提高的主要因素依次为:热集聚区效应、匙孔深度增大和电弧收缩效应。研究不同焊接条件下焊缝金属熔化效率的变化规律,提出激光-TIG双面焊热源最佳的能量匹配原则和位置条件。更多还原

【Abstract】 Laser welding of aluminum alloys faces the problems of high reflectivity, high thermal conductivity and high thermal diffusivity, and heavy porosity formation in the weld metal. To solve these problems, a novel technology of laser-arc double-side welding was developed. On the one hand, it attempts to improve the characteristics of laser welding by the arc heating, such as the stability of keyhole, improvement of welding quality, decrease of porosity. On the other hand, it tries to reform the stability of the arc by the laser heating. Due to the combination heating of laser beam and TIG arc on the opposites of workpiece, the joining of high efficiency and good quality for aluminum alloy can be realized, such as the increase of energy utilizing efficiency for the laser and the arc, the improvement of welding quality and the decrease of cost.In the experiments, the plates of 4mm thick 5A06 aluminum alloy were used as the workpiece material. The experiments were carried out by combining a CO2 laser equipment and an inverter argon arc welding machine. The characteristics of laser-TIG double-side welding (LTDSW) for aluminum alloys were investigated, including welding technology, appearance of the welds and the decrease of defects. The microstructure and mechanical properties of the welds was analyzed under the typical energy matching of the laser and the arc. The control method of cross-sectional profile was put forward, and the welding parameters were optimized. At the same time, aiming at the adaptability of the LTDSW process, the experiments of aluminum alloy butt joint, dissimilar thickness butt joint were pursued, and the application foreground of this method was explored on the thick and thin plates for aluminum alloys.To understand the physics property and interaction of the arc and the laser in the LTDSW process, the arc shapes and its current-voltage characteristics were investigated systemically by signal picking system and image processing technology. The influence of the specific heat transfer for laser keyhole welding on the characteristics of the arc was investigated, and its mechanism was analyzed in the LTDSW process. The local high temperature zone of laser keyhole heating was validated as the reason of arc constriction, the decrease in the voltage, the improvement of process stability. The transformation rule of arc energy effect was explored under various experimental conditions. The transformation rule and cause of laser-induced plasma behavior were analyzed. All the investigations can provide for the experimental data and theory base to analyse the heat transfer of the process.According to the conditions of threshold power density and temperature on the formation of laser keyhole, an adaptive numerical model for examining and simulating the heat transfer process is developed, including the mode of close keyhole penetration and the mode of open keyhole penetration. The temperature fields of the process were calculated with finite element method. The characteristics of heat transfer, the forming process of keyhole and molten pool were investigated by FEM analysis. Utilizing the adaptive heat source model, the transformation rule of the welding formation, the conditions of critical penetration and the open keyhole full penetration were calculated under different welding velocity and plate thickness.At last, from the theory, experiment and numerical simulation point of view, the mechanisms of enhancing penetration and increasing heat efficiency were explored in the LTDSW process. The main causes of increasing heat efficiency were proved as in turn: the formation of heat-congregated region, the increase of keyhole depth and the convergence of the arc. The transformation rules of the melting efficiency were investigated under different experimental conditions. The optimal energy matching and position conditions of the laser and the arc were put forward.更多还原