基于三维重构技术的K-TIG熔池流动表征
Morphology Characterization of Molten Pool Flow Behavior During K-TIG Welding Based on 3D Reconstruction Techniques

采用钛元素示踪方法表征K-TIG焊接430不锈钢熔池流动行为，在完全熔透焊缝中观察到熔池沿板厚方向分为3个区域，包括马兰格尼对流圈、洛伦兹力推动的对流圈及中间过渡区域; 未熔透时熔池中只有马兰格尼对流圈及对流圈与熔池边缘之间的区域．基于连续金相切片的三维重构技术建立了熔池小孔附近流动未稳定区的三维模型与未熔透情况下气孔处焊缝的三维模型．观察了K-TIG熔池流动由未稳定过渡至稳定的过程，小孔前壁只有很薄的一层液态金属流动层，液态金属沿小孔侧壁流动至后方熔池中，熔池在小孔后部开始形成马兰格尼对流圈，在小孔形成后一段距离之后，开始形成洛伦兹力推动的对流圈．未熔透时熔池流动行为明显弱于熔透时熔池流动行为，对流流动减弱易于造成气孔的产生．
Titanium tracer was introduced to characterize the K-TIG molten pool flow behavior of 430 stainless steel. When fully penetrated，the molten pool consisted of three parts along the thickness direction，which were Marangoni convection，a convection driven by Lorentz force，and a transition layer. When incompletely penetrated，the molten pool consisted of two parts along the thickness direction，which were Marangoni convection and a transition layer between the convection and molten pool edge. 3D models of the flow behavior in the unsteady region around the key-hole and the porosity in the incompletely penetrated weld were established based on serial sectioning reconstruction techniques. The stabilization process of K-TIG molten pool was observed. There was a thin layer of molten metal on the anterior wall of the key-hole. Molten metal flowed along the side wall to the rear of the molten pool，and the Marangoni convection came into being at the end of the key-hole. The convection driven by Lorentz force appeared in a short distance after the key-hole formed. The flow of molten pool was obviously weak when incompletely penetrated. The loss of convection flow tended to cause porosity