纵向磁场与活性剂联合下镁合金焊接接头组织性能的研究

发布时间：2018-04-30 08:21

本文选题：镁合金 + 活性焊接　；参考：《沈阳工业大学》2017年硕士论文

【摘要】：在现有的工程用金属中,镁合金的密度最小并且具有强度高、刚性好等一系列优点,在汽车、航空航天和运动器材等领域有着广泛的应用空间。但是镁合金由于自身的物理化学特性,导致其焊接时易产生热裂纹、气孔、夹杂等缺陷,不容易获得高质量的焊接接头。因此,提高镁合金焊接性,获得优质的焊接接头是非常必要的。磁控焊接和活性焊接同传统焊接相比具有成本低、效率高、质量好等优点,因此进行镁合金活性焊接并且施加纵向磁场对改善镁合金的焊接方法有着重要的实际意义。实验采用A-TIG焊焊接AZ91镁合金试板,焊接过程中外加纵向交流变频磁场,并采用正交实验对工艺参数进行优化。焊接时采用高速摄像观测电弧形态的变化,焊后,对不同参数下焊接接头的成形状态、接头力学性能和显微组织进行测试,研究其中的规律和机理,主要研究结果为:(1)正交实验结果表明,在纵向磁场和氯化物活性剂联合作用下,四个因素对焊缝成形系数的影响由大到小分别为:磁场频率磁场电流焊接电流涂覆量。当磁场电流为3.5A、磁场频率为30Hz、焊接电流为85A、涂覆量为1mg/cm2时,AZ91镁合金焊缝的硬度达到最大值73.83HV,此时焊接接头显微组织由α-Mg基体和沿晶界弥散分布的β-Al12Mg17第二相组成,晶粒细化明显,故力学性能得到提高。(2)根据正交实验发现在纵向磁场和氧化物活性剂联合作用下,四个因素对焊缝成形系数的影响由大到小分别为:涂覆量磁场频率磁场电流焊接电流。最佳参数为磁场电流1.5A、磁场频率30Hz、焊接电流80A、涂覆量3mg/cm2,焊缝硬度达到最大值76.3HV。此时焊缝组织细小,力学性能提高明显。(3)基于高速摄影技术可以发现,施加纵向磁场电弧会发生旋转并且收缩明显。磁场对焊接熔池起着电磁搅拌的作用,使焊接接头组织细化。当涂覆氧化物活性剂进行焊接时,氧元素能够使改变熔池的流动方式使焊缝的熔深增加。当涂覆氯化物活性剂进行焊接时,氯化物活性剂作用于电弧从而使试件熔深增加。
[Abstract]:Magnesium alloy has a series of advantages such as low density, high strength, good rigidity and so on, among the existing engineering metals, it has a wide range of applications in the fields of automobile, aerospace, sports equipment and so on. However, due to its physical and chemical characteristics, magnesium alloys are prone to heat cracks, pores, inclusions and other defects during welding, so it is not easy to obtain high quality welded joints. Therefore, it is necessary to improve the weldability of magnesium alloy and obtain high quality welded joints. Compared with conventional welding, magnetically controlled welding and active welding have the advantages of low cost, high efficiency and good quality. Therefore, it is of great practical significance to improve the welding method of magnesium alloy by applying longitudinal magnetic field and active welding. In the experiment, the AZ91 magnesium alloy test plate was welded by A-TIG welding, and the longitudinal AC variable frequency magnetic field was added in the welding process, and the process parameters were optimized by orthogonal experiment. After welding, the forming state, mechanical properties and microstructure of welded joints under different parameters were tested, and the rules and mechanisms were studied. The main results are as follows: (1) orthogonal experiment results show that the influence of four factors on the weld formation coefficient under the combined action of longitudinal magnetic field and chloride active agent is as follows: magnetic field frequency magnetic field current welding current coating amount. When the magnetic field current is 3.5A, the magnetic field frequency is 30Hz, the welding current is 85A, and the coating amount is 1mg/cm2, the hardness of the weld seam of AZ91 magnesium alloy reaches the maximum value of 73.83HV.The microstructure of the welded joint is composed of 伪 -Mg matrix and the second phase of 尾 -Al12Mg17 dispersed along the grain boundary, and the grain refinement is obvious. Therefore, the mechanical properties are improved. (2) according to the orthogonal experiment, it is found that the influence of four factors on the weld formation coefficient under the combined action of longitudinal magnetic field and oxide active agent is as follows: coating magnetic field frequency magnetic field current welding current. The optimum parameters are magnetic current 1.5 A, magnetic frequency 30 Hz, welding current 80 A, coating amount 3 mg / cm 2, and weld hardness reaching the maximum value of 76.3 HV. On the basis of high speed photography, it can be found that the longitudinal magnetic arc will rotate and shrink obviously. Magnetic field plays the role of electromagnetic stirring in weld pool, which makes the microstructure of welded joint fine. When the oxide active agent is applied in welding, oxygen can increase the weld penetration by changing the flow mode of the weld pool. When coated with chlorides for welding, chlorides act on the arc to increase the penetration of the specimens.
【学位授予单位】：沈阳工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG407

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