6061-T6铝合金及其与紫铜搅拌摩擦焊模拟和实验研究

发布时间：2018-06-25 20:40

本文选题：搅拌摩擦焊 + 数值模拟　；参考：《南京航空航天大学》2017年硕士论文

【摘要】：本文通过数值模拟与实验研究相结合的方法,研究了6061-T6铝合金对接搅拌摩擦焊的温度场与流场,对6061-T6铝合金与T2紫铜异种材料进行搅拌摩擦焊对接,探索了温度场对焊接接头组织及性能的影响。研究过程首先是建立了搅拌摩擦焊的二维模型,其中除了包含最基本的质量和动量连续方程模型,还有热量方程模型,能够对焊接的摩擦产热和塑形变形产热、焊接过程中的热传导、板材与空气间的热交换进行求解。模型对搅拌针周围网格进行非结构性划分,采用了自适应网格(动网格),能够通过不断地消除和生成网格,使搅拌针壁面实现像实验中一样的水平运动。模型耦合了欧拉多相流模型,将实验中的铝定义为第一相,锌和铜分别定义为第二相进行双相求解。通过设置边界条件和编译用户自定义功能,将材料的包括粘度、散热系数在内的各种物理参数均耦合到了模型中,以获得更加精确的实验结果。在6061-T6铝合金的焊接过程中,在焊缝前进侧中间高度上加入小的锌块,以求获得实验的示踪效果,并在模型中也有所体现。通过热电偶的温度记录与模型的计算可知,在焊接过程中锌发生了熔化,并对温度场造成一定的影响,但这有限的温度影响并不影响焊缝流动行为的观察研究。通过结合分析焊缝搅拌针附近的节点运动矢量图和迹线图,可以得出搅拌针附近材料的三条基本运动轨迹,分别是搅拌针周围顺时针涡流、焊缝后退侧右前方逆时针涡流和搅拌针后端顺时针涡流。这些涡流的存在,使得焊缝中的材料混合更加充分,焊缝力学性能更加均匀。在6061-T6铝合金与T2紫铜的对接实验过程中,实验记录了焊接过程中的温度变化,但用模拟得到的温度云图更能反映搅拌针周围的温度场变化。铜一侧产热较少,热传导快,热容也相对较低,使得远离焊缝处铜相对铝一侧的温度较高,而在焊缝中心能量无法聚集,使得铜一侧流动性降低。通过给铜一侧设置外加热源,增加该侧的焊缝中心温度,提升了焊缝材料的流动性。当焊缝流动性较差时,焊接的热加工过程易生成铝铜的中间相化合物,并堆积在铜一侧的热机影响区附近,使得该区域硬度值上升,而抗拉强度急剧降低。流动性较好时,只生成少量的中间相,并且大部分中间相流动到焊缝中去,减少了铜一侧中间相的堆积,提升抗拉强度。
[Abstract]:In this paper, the temperature field and flow field of 6061-T6 aluminum alloy butt friction stir welding are studied by means of numerical simulation and experimental study. Friction stir welding of 6061-T6 aluminum alloy and T2 copper dissimilar material is carried out. The effect of temperature field on the microstructure and properties of welded joints was investigated. First of all, the two-dimensional model of friction stir welding is established, which includes not only the most basic mass and momentum continuum model, but also the heat equation model, which can generate heat for friction and plastic deformation of welding. Heat conduction during welding, heat exchange between plate and air is solved. The model uses adaptive mesh (moving mesh) to divide the meshes around the needle into non-structural ones. It can eliminate and generate the mesh continuously and make the wall of the agitated needle achieve the same horizontal motion as in the experiment. The Euler multiphase flow model is coupled. Aluminum is defined as the first phase in the experiment, and zinc and copper are defined as the second phase for two-phase solution. By setting boundary conditions and compiling user-defined functions, various physical parameters, including viscosity and heat dissipation coefficient, are coupled to the model to obtain more accurate experimental results. In the welding process of 6061-T6 aluminum alloy, a small zinc block was added to the middle height of the forward side of the weld in order to obtain the experimental tracer effect, which was also reflected in the model. Through the temperature record of the thermocouple and the calculation of the model, it can be seen that zinc melts in the welding process and has a certain effect on the temperature field, but this limited temperature effect does not affect the observation and study of the flow behavior of the weld. By analyzing the joint motion vector diagram and trace chart, three basic motion trajectories of the material near the needle can be obtained, one is clockwise swirl around the needle, and the other is the clockwise eddy current around the needle. Weld receding side right front counterclockwise eddy current and mixing needle back end clockwise eddy current. Due to the existence of these eddies, the materials in the weld are more fully mixed and the mechanical properties of the weld are more uniform. During the docking experiment between 6061-T6 aluminum alloy and T2 copper, the temperature change in welding process was recorded, but the temperature cloud diagram obtained by simulation could reflect the temperature field around the stirring needle more effectively. The heat production on the copper side is less, the heat conduction is fast, and the heat capacity is relatively low, which makes the temperature of copper far away from the weld seam higher than that of the aluminum side, while the energy in the center of the weld cannot be accumulated, which makes the fluidity of the copper side decrease. By setting the additional heat source on the copper side, the center temperature of the weld seam is increased and the fluidity of the weld material is enhanced. When the fluidity of weld is poor, the mesophase compound of aluminum and copper is easily formed in the hot working process of welding, and it accumulates near the influence zone of heat engine on the side of copper, which makes the hardness value of this area increase and the tensile strength decrease sharply. When the fluidity is good, only a small amount of mesophase is generated, and most of the mesophase flows into the weld, which reduces the accumulation of mesophase on the copper side and enhances the tensile strength.
【学位授予单位】：南京航空航天大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG453.9

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