【作者】 车小平；

【导师】 常云龙；

【作者基本信息】 沈阳工业大学 ， 材料加工工程， 2007， 硕士

【摘要】 防锈铝合金5A05含镁为主要的合金元素,并含有少量的铜、锰、铁、硅和锌。这种合金锻造退火后是单相固溶体,抗腐蚀性能好,塑性好。但是铝镁合金焊接接头力学性能比较差,如果细化焊缝晶粒组织的方法来提高接头力学性能,铝镁合金将在较大的载荷下得到广泛的应用。电磁搅拌作用下MIG焊中,熔滴过渡在焊接过程中起着非常重要的作用。观察不同激磁电弧和频率下熔滴过渡的形态具有主要意义。但是在强烈的焊接弧光下,很难观察的熔滴过渡的过程。为了获得不同外加磁场与熔滴过渡之间的关系,利用高速摄像机拍摄了熔滴过渡过程和熔滴形态的变化。研究了不同外加磁场作用下的不同熔滴的过渡形式。结果表明在相同的焊接条件下,外加纵向磁场不仅影响熔滴过渡的形式,而且改变熔滴的形状。在对不同频率及强度的磁场作用下的5A05铝合金的微观组织研究中发现,并非任何的磁场处理都可细化晶粒,若所加磁场条件不合适,晶粒反而会比未经磁场处理的更粗大,提出这是由于磁场作用下,一方面强化对流,细化晶粒:另一方面,减小过冷度,粗化晶粒,所得到的凝固组织是这两种作用相互制约的结果。此外还有形核和长大两方面的共同作用。此外还有形核和长大两方面的共同作用。当磁场频率过高,或者磁场强度过高,晶粒尺寸有不同程度的增大的趋势。实践表明,利用外加磁场对焊接中电弧旋转、熔滴的过渡、熔池金属的流动、熔池的结晶形核及结晶生长等过程有显著作用,使MIG焊焊缝的一次结晶组织细化,减小化学不均匀性。激磁电流和磁场频率需要恰当匹配,而且还必须与焊接规范参数相适应,才能细化晶粒,从而提高焊缝的抗拉强度和延伸率。分析了电弧中带电粒子的运动,研究了电弧旋转的机理。在外加纵向交变磁场的作用下,电弧的形态和旋转的方向有关,当电弧顺时针旋转时,电弧呈现“钟罩形”。当电弧逆时针旋转时,电弧呈现“锥形”。与不加磁场的电弧形态相比较,不加磁场的电弧形态总是呈“锥形”。利用ANSYS有限元分析软件对外加磁场作用下,铝合金焊缝温度场等进行了数值模拟。模拟结果吻合双峰热源分布模型。更多还原

【Abstract】 The aluminum alloy 5A05 contains magnesium as major alloying element and small amounts of copper, manganese, iron, silicon and zinc. This alloy is commonly used for welding parts working in liquid condition due to its good resistance to corrosion. However, the mechanical properties of joints are low. If the yield strength of the weld metal can be improved by some means it will be useful in increasing load.Metal transfer is an important phenomenon in Metal Inert Gas arc welding (MIG) with longitudinal alternating magnetic field. It is of great significance to observe the metal transfer modes under different excitatory currents and frequencies. However, it is very difficult to view the metal transfer process directly during welding, for the strong interference from the arc light. To obtain the relationship between the metal transfer modes and the different magnetic fields, a high-speed video camera was used to acquire the images of globules. Different metal transfer modes in the condition of different magnetic fields and welding parameters were studied. The experiment shows clear images of droplet transfer and how the longitudinal magnetic fields influence the metal transfer and the globule shape.The influence of different magnetic fields during MIG arc welding in 5A05 Al-alloy was studied. It was found that the structures of alloy could not be refined under any magnetic fields, the proper magnetic field conditions could largely reduce the grain size, and however, the improper magnetic field conditions would make the grain bigger than that without magnetic field. With application of magnetic field, on the hand, the convection becomes large and the grains were refined; on the other hand, the under cooling was decreased and the grain was coarsened. The solidification structure was the result of the restriction by these two actions. At the same time, the macrostructures was also determined by the other two actions, which were nucleation and growth. It was also found that the grain size was tended to enlarge when the frequency or the magnetic density was too big.Experience shows that the introduced magnetic field can give an effective intervention to the transition of droplet, flowing of molten bath metal, crystalline and nucleation of molten bath and the process of crystalline growth. The magnetic field promotes the refining degree of primary crystallization structure, decreases the chemistry non-homogeneity. The technique resulted in fine equaixed grains in weld metal and optimum parameters of electromagnetic stirring were suggested based on the extent of refinement. Fine-grained weld metal exhibited better yield strength and significant improvement in percent elongation.The paper compared different arc forms under pulsed and steady MIG arc welding and studied how the external magnetic field affected the shape of arc. In addition, the movement of charged particles in longitudinal magnetic field was analyzed, and the mechanism of arc rotation was studied. In reversed longitudinal magnetic field, the profile of arc forms bell shape when the direct of rotation is clockwise in helix while the arc shape is cone shape when it rotates in counter clockwise. Compared with the arc shape with external field, the arc without longitudinal field forms cone shape.By using the large-scale finite element analysis software-ANSYS based on equivalent thermal enthalpy finite element theory, the temperature field in the influence of magnetic stirring was simulated. The result of simulation in accordance with double-peak heat source.更多还原