Investigation of transport phenomena and defect formation in pulsed laser keyhole welding of zinc-coated steels
Investigation of transport phenomena and defect formation in pulsed laser keyhole welding of zinc-coated steels
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DOI：
10.1088/0022-3727/39/24/036
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发表时间：
2006-12
期刊：
影响因子：
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通讯作者：
Jia Zhou;H. Tsai;T. F. Lehnhoff
中科院分区：
文献类型：
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作者：
Jia Zhou;H. Tsai;T. F. Lehnhoff
由于激光焊接速度快、纵横比大、热影响区窄等优点，激光焊接镀锌钢板得到了广泛的应用。然而，在焊接过程中，高压锌蒸气的逸出会破坏焊接熔池的连续性，并在最终焊缝中引起大的空隙和严重的咬边。本文建立了镀锌钢脉冲激光小孔焊接过程的数学模型，并利用数值模拟技术研究了镀锌钢脉冲激光小孔焊接过程中的传输现象和缺陷形成机理。流体体积法（VOF）被用来追踪自由表面。采用连续介质模型处理金属的液相、固相和糊状区。采用焓法来计算熔化和凝固过程中的潜热。计算了小孔形成和塌陷过程中熔池内的瞬态传热和熔体流动。研究了锌蒸气通过小孔的逸出以及锌蒸气与熔池的相互作用。焊缝中的空洞被发现是由锌蒸气-熔体相互作用、小孔塌陷和凝固过程的综合作用引起的。通过控制激光脉冲轮廓，发现可以延迟小孔塌陷和凝固过程，允许锌蒸气逸出，这导致空隙的减少或消除。模型预测结果与实验结果吻合较好，表明该模型为今后镀锌钢激光焊接的研究奠定了坚实的基础。
Lasers are being used to weld zinc-coated steels due to high welding speed, high aspect ratio, and narrow heat affected zone. However, escape of high-pressure zinc vapour in the welding process can damage the weld pool continuity and cause large voids and serious undercuts in the final welds. In this paper, a mathematical model and the associated numerical techniques have been developed to study the transport phenomena and defect formation mechanisms in pulsed laser keyhole welding of zinc-coated steels. The volume-of-fluid (VOF) method is employed to track free surfaces. The continuum model is used to handle the liquid phase, the solid phase and the mushy zone of the metal. The enthalpy method is employed to account for the latent heat during melting and solidification. The transient heat transfer and melt flow in the weld pool during the keyhole formation and collapse processes are calculated. The escape of zinc vapour through the keyhole and the interaction between zinc vapour and weld pool are studied. Voids in the welds are found to be caused by the combined effects of zinc vapour–melt interactions, keyhole collapse and solidification process. By controlling the laser pulse profile, it is found that the keyhole collapse and solidification process can be delayed, allowing the zinc vapour to escape, which results in the reduction or elimination of voids. The good agreement between the model predictions and the experimental observations indicates that the proposed model lays a solid foundation for future study of laser welding of zinc-coated steels.