ABSTRACT

The magnetically assisted resistance spot welding (MA-RSW) method provides a promising approach for improving weld performance. However, the MA-RSW process involves complex multiphysics fields that make numerical modeling very challenging. Thus, most resistance spot welding (RSW) models adopt electrothermal-mechanical coupling and ignore the influence of fluid flows caused by electromagnetic forces on nugget growth. In this paper, a magnetohydrodynamic (MHD) model, which couples the electric, thermal, magnetic and flow fields, is developed to explore the influencing mechanism of an external magnetic field (EMF) on the flow patterns and microstructures of aluminum resistance spot welds. Numerical results show that the application of an EMF can lead to the formation of Lorentz force in the liquid nugget, which transforms the flow pattern from an in-plane flow to a combined in-plane and out-of-plane flow. The flow velocity of molten metal in the MA-RSW process is 5 times higher than that of the RSW process, and the maximum temperature of the MA-RSW model is reduced from 774°C in the MHD RSW model to 725°C. Therefore, the MA-RSW joint exhibits a 25.5% larger nugget diameter, a more than 20% finer grain structure, and fewer defects than the RSW joint in the experimental results.

摘要

磁辅助电阻点焊 (MA-RSW) 方法为提高焊接性能提供了一种有前景的方法。然而，MA-RSW 过程涉及复杂的多物理场，这使得数值建模非常具有挑战性。因此，大多数电阻点焊 (RSW) 模型采用电热-机械耦合，忽略了电磁力引起的流体流动对熔核生长的影响。在本文中，建立了耦合电场、热、磁和流场的磁流体动力学 (MHD) 模型，以探索外部磁场 (EMF) 对铝电阻点焊流型和微观结构的影响机制。数值结果表明，施加 EMF 会导致在液核中形成洛伦兹力，它将流型从平面内流转换为平面内和平面外流的组合。MA-RSW工艺中熔融金属的流速比RSW工艺高5倍，MA-RSW模型的最高温度从MHD RSW模型中的774℃降低到725℃。因此，在实验结果中，MA-RSW 接头的熔核直径比 RSW 接头大 25.5%，晶粒结构细化 20% 以上，缺陷更少。