铝合金磁控MIG焊接电弧特性及焊缝组织性能的研究

发布时间：2018-01-01 14:01

本文关键词：铝合金磁控MIG焊接电弧特性及焊缝组织性能的研究　出处：《沈阳工业大学》2017年硕士论文　论文类型：学位论文

【摘要】：Al-Mg系铝合金在现代制造业追求轻量化发展过程中应用越来越广泛,但铝合金MIG焊接时存在焊缝成形性差、结晶组织粗大、焊缝气孔率高等问题,限制了Al-Mg系铝合金大范围使用。文章以5083铝合金作为实验对象,通过施加交变纵向磁场方法来探究磁场参数中励磁电流及励磁频率对焊接电弧、熔滴过渡及焊接熔池的影响。进而通过高速摄像机、金相观察、力学性能测试、X射线无损探伤等方法来分析磁场参数对焊接电弧、熔滴过渡、结晶组织、力学性能、气孔率的影响规律,并探究作用机理。通过高速摄像与电信号动态分析系统观察电弧运动及熔滴过渡过程,并建立电弧空间内粒子受力模型来分析焊接电弧运动机理。实验得出:无磁场下,电弧形态形似锥形。当施加交变纵向磁场时,随励磁电流及励磁频率增大,电弧产生旋转,且电弧旋转程度随励磁电流变大而加强,表现为先扩散后缩紧形态。尤其当励磁电流2A、励磁频率45Hz时,焊接电弧表现为以焊丝为轴线的中心对称分布,由无磁场时的锥形变为钟罩形。随磁场参数加大,熔滴由无磁场时的圆球状逐步转变成椭球状,熔滴过渡频率先增大后变小,在励磁电流2A下达到最大,每滴约5.8ms。当磁场参数在一定范围内增加,在宏观形貌上,焊缝表面鱼鳞纹变得更加致密,焊缝熔宽先增加后减小,焊缝熔深主要受励磁电流影响先减小后增大,但在焊接电弧稳定燃烧时受励磁频率影响较小。在微观组织上,引入磁场促进了结晶组织由柱状晶转变成等轴晶,焊缝晶粒变得细小。尤其当励磁电流2A、励磁频率45Hz时,焊缝组织细小,此时与无外加磁场时相比焊接接头抗拉强度提高了34.7MPa、伸长率提高了5.86%、接头最大硬度值提高11HV。随外加磁场引入,一定长度焊缝上气孔数目明显下降,说明磁场参数对焊缝气孔率有着显著的影响。在励磁电流2A、励磁频率45Hz时,焊缝中气孔数目由无磁场时8个变为2个,有效降低了焊缝气孔率。
[Abstract]:More and more widely used Aluminum Alloy seeking light with the development of modern manufacturing process in Al-Mg system, but Aluminum Alloy MIG welding weld are poor, coarse grains, high weld porosity, limiting the use of a wide range of Al-Mg Aluminum Alloy. Taking 5083 Aluminum Alloy as experimental object, by applying an alternating longitudinal the magnetic field method to explore the welding arc excitation current and excitation frequency of the magnetic field parameters, droplet transfer and influence of welding pool. Then through metallographic observations of high speed camera, mechanical properties test, to analyze the magnetic field parameters of arc welding nondestructive testing methods such as X ray, droplet transfer, microstructure, mechanical properties, impact law of porosity, and explore the mechanism. By observing the motion of arc and droplet transfer process and dynamic signal analysis system of high speed camera, and the establishment of the arc space particle force model To analyze welding arc motion mechanism. Experiment results: no magnetic field, the arc shape resembling a cone. When applying an alternating longitudinal magnetic field, with excitation current and excitation frequency increases, caused by the rotation, and rotation arc degree with excitation current becomes larger and the strengthening performance of the first diffusion after tightening form. Especially when the excitation current of 2A. The excitation frequency of 45Hz, the welding arc performance of the wire as the center symmetry axis, by cone without magnetic field into a bell shape. With the increase of magnetic field parameters, droplet by magnetic field in the spherical gradually transformed into ellipsoidal and the droplet transfer frequency increases first and then decreases, reaches the maximum at the excitation the current 2A, every drop of about 5.8ms. when the magnetic field parameters are increased to a certain extent, in the macro morphology on the weld surface ripple becomes more dense, the weld width increased first and then decreased, the weld penetration is mainly affected by the excitation current decreased Increased, but in the welding arc burns stably when the excitation frequency is less affected. The microstructure, magnetic field promotes the crystal structure changed from columnar grains to equiaxed grain. The weld grain becomes small. Especially when the excitation current is 2A, the excitation frequency is 45Hz, the weld microstructure is small, when compared with no external magnetic field the tensile strength of welded joints increased 34.7MPa, elongation increased by 5.86%, the joint maximum hardness value increased 11HV. with the applied magnetic field, a certain length of weld stomata decreased significantly, indicating the magnetic field parameters have significant effects on weld porosity. In the excitation current of 2A, the excitation frequency of 45Hz, the number of stomata in the weld by magnetic field 8 to 2, effectively reducing the weld porosity.

【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】：TG457.14

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