外加横向磁场作用电弧增材成形过程中的传热传质仿真

Simulation of Heat and Mass Transfer in Arc Welding based Additive Forming Process with External Transverse Magnetic Field

为了揭示外加横向磁场对电弧增材成形过程中电弧和熔池传热传质以及成形件微观组织影响的内在机理,建立基于GMAW电弧增材成形过程中电弧和熔池的弱耦合数值模型,通过数值模拟对比分析了有/无外加横向磁场作用下熔池电磁力分布、电弧和熔池传热传质的差异,发现横向磁场作用使电弧向熔池后方偏转,使熔池发生单向强制对流并驱动熔融金属和热量向熔池后方运动,从而更加直接地冲刷熔池结晶面。由此预测横向磁场作用能降低熔池凝固过程中枝晶前沿温度梯度和溶质浓度,提高枝晶前沿的成分过冷,使得靠近熔池中心的枝晶前端生长加速并细化晶粒。相同工艺条件的对比试验表明:相比无外加磁场的普通熔积,横向磁场作用下熔池底部等轴晶区域减小,整个结晶面上细密的胞状枝晶区域面积增大,验证了数值模拟的预测。研究结果可为外加磁场在电弧增材成形微观组织控制中的应用提供依据和参考。

In order to reveal the inherent mechanism of the influence of transverse magnetic field on heat and mass transfer of the arc and molten pool in arc welding based additive forming(AWAF) process, and the microstructure of the AWAF parts, a three-dimensional weak coupling numerical model of arc and metal transport is developed to simulate the arc, molten pool dynamic in GMAW baesd AWAF process. The studies of with and without external transverse magnetic field treatment in AWAF process are applied to analyze the electromagnetic force distribution in molten pool, the differences of heat and mass transfer of arc and molten pool by numerical simulation. The analytical results show that the external transverse magnetic field can deflect the arc toward the rear of molten pool, induce forced convection in one direction, drive the molten metal and heat to the rear of molten pool, and wash against the dendrite frontier more directly in molten pool. Therefore, it can predict that external transverse magnetic field enables the capacity of decreasing the temperature gradient and solute concentration at the front of dendritic during the solidification of the molten pool, which is able to increase the concentration undercooling of this area, increase the growth rate of dendritic that near the center of the molten pool and refine grains. The comparative experiments show that the external transverse magnetic field treatment can reduce the area of equiaxed zone at the bottom of molten pool as well as increase the area of refined cellular dendrite zone. The experimental results verify the predictions of numerical simulation. The conclusions of the above study provide the basis and reference for the application of the external magnetic field in the control of microstructure of AWAF parts.