【作者】 蒋健博；

【导师】 刘黎明；

【作者基本信息】 大连理工大学 ， 材料加工工程， 2011， 博士

【摘要】 胶焊技术是一种把焊接和胶接工艺相结合的复合连接方法,它充分发挥了焊接和胶接工艺的优点,其接头具有承载能力高、抗剥离性能好等特点。但是,目前采用的焊接热源仅有电阻焊和激光焊两种,焊接热源比较单一。同时,关于胶粘剂的加入对焊接热源的影响及其机制的研究也鲜有报道,大大限制了胶焊技术的发展和应用。因此,本文提出了将等离子弧焊和激光-钨极氩弧(Tungsten Inert Gas, TIG)复合热源焊技术与胶接技术相复合的新型胶焊方法,即等离子弧胶焊和激光-TIG复合热源胶焊技术,以镁/铝异种合金为研究对象,重点讨论了胶粘剂的加入对不同类型焊接热源和镁/铝异种合金接头组织结构的影响及其机制。本文主要研究内容与结论：1.采用等离子弧胶焊技术,以镁/镁同种合金为对象进行搭接连接。在确定等离子弧胶焊技术焊接性的同时,初步分析胶粘剂的加入对焊接过程的影响,并建立其观测分析系统,包括焊接等离子体形态、焊接电流、电压和焊接工件表面温度场的采集分析以及接头组织和力学性能的观察检测。结果发现,通过工艺参数的调节可以去除由于胶粘剂的加入而产生的接头不易成形和易出现气孔缺陷的负面影响,获得了良好成形的等离子弧胶焊接头。此外,研究发现,由于胶粘剂的加入,等离子弧形态在电流负半波区间发生拘束、收缩,焊接电流不变,焊接电压升高。接头熔池组织的晶粒细化,熔池金属的冷却速度提高。与等离子弧焊和胶接接头相比,等离子弧胶焊接头的拉伸剪切失效载荷增大。2.采用等离子弧胶焊技术,以镁/铝异种合金为对象进行搭接连接,系统分析胶粘剂的加入对等离子弧热源和镁/铝异种合金接头组织结构及力学性能的影响。结果表明,在镁/铝异种合金等离子弧胶焊过程中,由于胶粘剂的加入,其焊接等离子体形态发生拘束、收缩,大量镁原子进入到等离子弧的电离气氛中,改变了电离气氛的粒子组成,使等离子弧中镁原子和镁离子的谱线强度提高,电子温度降低,电子密度提高,焊接电流不变,但焊接电压升高。同时,使接头中熔池组织不均匀,熔池底部过渡区由连续、平滑转变为起伏、无序结构,增大了Al3Mg2层与a-Al之间的连接面积,并降低了接头的裂纹倾向性。此外,等离子弧胶焊接头的拉伸剪切失效载荷虽高于等离子弧焊接头但低于胶接接头。分析得出,提高焊缝拉伸剪切失效载荷的同时,降低胶粘剂的失效面积是提高镁/铝异种合金胶焊接头拉伸剪切失效载荷的根本方法。3.采用激光-TIG复合热源胶焊技术,以镁/铝异种合金为对象进行搭接连接,研究分析胶粘剂的加入对激光-TIG复合热源和镁/铝异种合金接头组织结构及力学性能的影响。结果发现,在镁/铝异种合金激光-TIG复合热源胶焊过程中,由于胶粘剂的加入,焊接等离子体形态发生膨胀,亮度增强。镁原子分布体积增大,氩原子分布体积缩小。对应其光谱谱线,镁原子和镁离子的谱线强度提高,氩原子和氩离子的谱线强度降低,TIG电弧的电子温度降低,电子密度提高。焊接电流几乎不变,但焊接电压增大。同时,焊接熔深增大,熔池金属的流动性增强,熔池底部过渡区由连续、平滑结构转变为起伏不平、无序结构,增大了A13Mg2层与a-Al层之间的连接面积,并降低了接头的裂纹倾向性。与激光-TIG复合热源焊接头相比,激光-TIG复合热源胶焊接头的拉伸剪切和剥离失效载荷均增大。4.通过对镁/铝异种合金等离子弧胶焊和激光-TIG复合热源胶焊过程中,焊接等离子体信息和接头组织结构及力学性能的采集、观测和检测,研究分析胶粘剂的加入对等离子弧热源和激光-TIG复合热源以及镁/铝异种合金接头组织结构的影响及其机制。研究表明,在等离子弧胶焊过程中,胶粘剂的加入促进了镁蒸气的蒸发,改变了等离子弧电离气氛的粒子组成,使之发生“热收缩”效应,导电通道收缩,等离子弧能量密度提高,获得了更大的焊接熔深。在激光-TIG复合热源胶焊过程中,胶粘剂的分解、气化增大了“匙孔”内压强,促进了“匙孔”内金属等离子体的逸出,降低了“匙孔”周围液态金属层的厚度。从而降低了“匙孔”内金属等离子体对激光束的弱化作用(吸收和散焦),增大了“匙孔”底部固态金属对激光能量的吸收速率,使激光束的穿透能力增强。同时,改变TIG电弧的电离气氛,引起电弧的“热收缩”,提高了电弧的能量密度。此外,胶粘剂的分解、气化和逸出,对熔池金属产生强烈的搅拌作用,破坏了接头组织的均匀性,使熔池底部过渡区由连续、均匀、平滑结构转变为凹凸起伏、无序结构,提高了A13Mg2层与a-Al层之间的连接面积,有助于增大焊缝的承载能力。更多还原

【Abstract】 Weld bonding technology was a hybrid join method, combining the welding and adhesive bonding process. It took the advantages of the welding and adhesive bonding technique. The combined connections ensured better the carrying power and the peel performance. However, the welding source used in weld bonding process was few, which only contained resistance spot welding and laser welding at present. At the same time, the effect of adhesive on the welding source was almost not investigated. It limited the development of the weld bonding technology greatly. Therefore, "plasma arc weld bonding" (PAWB) and "laser-Tungsten Inert Gas (TIG) weld bonding" (LTWB) technology, two new weld bonding method, were presented in this paper. Through PAWB and LTWB process of Mg to Al alloy, the effect of adhesive on different welding source and structure of Mg/Al joint was investigated. The main research contents and results were as follow:1. PAWB process of Mg/Mg alloy was conducted, and the welding characteristic and weldability were investigated. The variety of welding process due to the addition of adhesive was observed and tested, including the welding plasma, welding current, welding voltage, temperature distribution on the surface of weldment, macrostructure, microstructure and mechanical property of joints. The results showed that the the welding problem, such as non-shape and pores, could be avoided by the adjustment of technics parameters, as a result a better PAWB joint was obtained. Besides, it was found that in PAWB process of Mg alloy, because of the addition of adhesive, the welding plasma contracted in alternating current electrode positive stage. The welding current was not changed, and the welding voltage was increased. The melton pool grain was refined. The heat-transfer rate between sheets was enhanced, leading to increment of cooling velocity of melton pool. PAWB joint showed higher tensile shear failure load comparing with plasma arc weld joint and adhesive bonding joint.2. PAWB process of Mg/Al alloy was conducted. The effect of adhesive on the plasma behaviors and structure and mechanical property of Mg/Al joint was investigated. The results showed that due to the addition of adhesive, the welding plasma contracted in PAWB process of Mg to Al alloy. More Mg atom entered the ionization atmosphere of plasma arc, and then ionized. The spectrum intensity of Mg and Mg+ increased. The electron temperature of the plasma arc reduced, and the electron density of the plasma arc increased. The welding current was not changed, and the welding voltage increased. At the same time, because the addition of adhesive, the joint structure was changed to non-uniform, the transitional zone between fusion zone and lower base metal was changed from smooth to wavily, as a result the connect area between Al3Mg2 layer and a-Al increased. Besides, the tensile shear failure load of PAWB joint was higher than plasma arc welding joint, and was lower than adhesive bonding joint. Based on investigation, it was concluded that increasing the carrying power of joint and dereasing the failure area of adhesive at the same time was the ultimate method to improve the carrying power of Mg/Al weld bonding joint.3. LTWB process of Mg/Al alloy was conducted. The welding weldability and the effect of adhesive on the welding source and structure and mechanical property of Mg/Al joint were investigated. The results showed that because of the addition of adhesive, the welding plasma expanded, and the brightness of which enhanced during the LTWB process of Mg to Al alloy. The spectrum intensity of Mg and Mg+increased, and the spectrum intensity of Ar and Ar+ dereased. The distribution of Mg atom increased, and the distribution of Ar atom dereased. The electron temperature of the arc plasma reduced, and the electron density of the arc plasma increased. The welding current was not changed, and the welding voltage increased. At the same time, the joint structure was changed to non-uniform. Transitional zone between fusion zone and lower base metal was changed to wavily and disordered. The connect area between Al3Mg2 layer and a-Al layer increased. Besides, LTWB joint showed higher tensile shear and peel failure load than laser-TIG welding joint.4. Through the investigation of PAWB and LTWB process of Mg to Al alloy, the effect mechanism of adhesive on the different welding source and Mg/Al joint structure was investigated. The results indicated that during PAWB process, the addition of adhesive casued more Mg atom to enter the ionization atmosphere of plasma arc, leading to the thermal contraction effect. The electric path contracted and the energy density of plasma arc increased, which was helpful to get a deeper penetration depth. During LTWB process, the adhesive decomposed and producted a lot of gases by the welding source, which increased the pressure inside the laser keyhole. It not only accelerated the escape of the metal plasma inside laser keyhole, but also reduce the the thickness of liquid metal layer around the laser keyhole. It casued that the absorption and the defocus effect of metal plasma on laser inside the laser keyhole decreased, and the absorb speed of solid metal for laser energy increased. The penetration power of laser beam was enhanced, thus the deeper penetration depth was obtained. Besides, more Mg atom entered the arc plasma and ionized instead of Ar atom. By the thermal contraction effect, the energy density of arc was also increased. For Mg/Al joint structure, because of the decomposition and gasitication of adhesive, the flow of molten pool metal was accelerated. The transitional zone between fusion zone and lower base metal was changed from smooth to wavily. The connect area between Al3Mg2 layer and a-Al layer was increased, which was helpful to increase the carry power of the joint.更多还原