超声焊接纯铜过程塑性变形与微观组织演变
Plastic deformation and microstructures evolution in pure copper ultrasonic welding
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摘要: 焊接界面塑性变形及晶粒组织演变决定了超声波焊接纯铜接头形成过程，但目前对纯铜超声波焊接机理认识有限.首先建立了一个纯铜超声波焊接的有限元模型探究了焊接温度场和塑性应变分布规律，其次将模拟的温度及塑性应变结果与动态再结晶理论结合，分别采用有限元法、元胞自动机法模拟了焊接过程的动态再结晶及晶体长大过程. 结果表明，材料晶粒的不规则分布，导致材料在焊头下方、焊接界面及底座上方处的材料塑性变形有明显差异. 工件与焊头及底座接触的区域产生了超细的动态再结晶晶粒. 在焊接时间0.19 s之后整个焊接区域发生了动态再结晶，且上工件的动态再结晶时间长于下工件. 粗的晶粒分布于焊头接触面的铜侧，而焊接界面处为细小的晶粒. 模拟的塑性变形分布规律与试验的维氏硬度的分布存在近似性，此外模拟的晶粒长大过程与试验也基本一致，较好地模拟了超声作用下的纯铜塑性变形与晶粒组织演变过程.Abstract: The formation process of ultrasonic welding of pure copper joints was determined by Interfacial plastic deformation and grain evolution. However, the understanding of the welding mechanism is still unclear. In this work, a three-dimensional finite element model of pure copper ultrasonic welding is established to investigate the welding temperature field and plastic strain distribution. Secondly, the predicted temperature and plastic strain results are used as the initial condition, and combined with the theory of dynamic recrystallization. Finally, the dynamic recrystallization process and the growth of the grain in the welding were simulated by the finite element method and the cellular automata method, respecitively. The results show that the irregular distribution of grain leads to the obvious difference between the plastic strain of the material under the welding interface and the materials beneathe the sonotrode and above the anvil. The materials near the sonotrode and anvil tips have generated a utra-fine grain that suffers dynamic recrystallization. After welding time of 0.19 s, the dynamic recrystallization is generated in the entire welding area, and the process of dynamic recrystallization of the upper specimen should be longer than of the lower specimen. The corse grains are distributed at the copper side of the sonotrode/Cu interface, while the finer grains are distributed at the welding interface. The distribution of simulated plastic deformation is basically the consistance with the distribution of experimental vicker's hardness. In addition, the simulated grains is basically in line with the test. These demonstrate that plastic deformation and grain evolution in pure copper ultrasonic welding were successful simulated.
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