电子束扫描横焊薄铌板的熔池动力学行为

在电子束焊接过程中，金属液体蒸发的反冲压力、表面张力、重力等驱动力共同作用于熔池，对焊缝成形有显著影响. 在扫描横焊的情况下，电子束作用范围的扫描摆动和重力方向的旋转使熔池的动力学行为变得更复杂. 采用试验和数值计算方法对电子束扫描横焊薄铌板的熔池形态和凝固后熔合区形貌进行研究，数值模拟得到的熔池形态和熔合区形状与试验结果吻合. 熔池流场分析结果表明，半熔透熔池的驱动力主要为液态金属蒸发引发的反冲压力；全熔透熔池的上表面Marangoni流动占主导，表面张力与反冲压力共同作为熔池流动的驱动力；重力与焊接扫描共同作用使得熔池两侧的质量分布和流场分布不对称，造成了焊缝两侧熔合线的不对称.

Molten pool dynamics of horizontal scanning EBW on thin niobium plate

During the EBW process, the driving force such as recoil pressure induced by evaporation, surface tension and gravity affect the fluid flow and thus influence the bead shape. In the situation of horizontal scanning welding, the scanning oscillation of the heating area of electron beam and the alteration of gravity make the fluid flow in the molten pool more complicated to describe. Experimental and computational methods are used to observe and investigate the shape of the molten pool and the fusion zone after solidification. The penetration depth, melting width and the fusion line profile are predicted accurately by the simulation results compared to the experiments. Analysis of the flow field of molten pool indicates the main driving force of fluid flow in half-penetration weld pool is the recoil pressure. By contrast, the Marangoni flow dominates the fluid flow on the top surface of the full-penetration weld pool, and the surface tension and recoil pressure have a combined action to the molten pool. Gravity and the scanning of electron beam cause the asymmetry of molten pool both in the mass distribution and flow field distribution, and thus the asymmetry of the fusion line profile.