Influencing mechanism of an external magnetic field on fluid flow, heat transfer and microstructure in aluminum resistance spot welding

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.

Effects of Magnetic Fields in Arc Welding, Laser Welding, and Resistance Spot Welding: A Review

“…To understand the change of nugget size in the RSW with magnetic field, the numerical simulation method was used to analyze the fluid flow mode in magnetic‐assisted RSW (MA‐RSW). [ 107,108 ] Under the action of magnetic field, the direction of the induced Lorentz force changes from the radial direction to the tangent direction around the welding joint. The simulation results of fluid flow modes of MA‐RSW and RSW are shown in Figure .…”

“…Under the circumstances, more heat is used for diameter expansion and less for penetration because of the constant Joule heat. [ 108 ] Besides, the simulation results indicated that the nugget shape is influenced by the local fluid flow mode, but the local fluid flow mode is dominated by the magnetic field distribution. Therefore, the nugget in MA‐RSW can grow toward the edge with increasing magnetic flux density.…”

“…Except the studies of Xu et al [ 106 ] and Ao et al, [ 107 ] Qi and Li et al [ 74,77,108–112 ] explored the effect of magnetic field on RSW in a more comprehensive and detailed way. In these studies, the single‐side magnet, [ 109,111 ] bilateral magnet, [ 111 ] and double‐side axial magnet [ 74,77,108,112 ] were used.…”

“…Except the studies of Xu et al [ 106 ] and Ao et al, [ 107 ] Qi and Li et al [ 74,77,108–112 ] explored the effect of magnetic field on RSW in a more comprehensive and detailed way. In these studies, the single‐side magnet, [ 109,111 ] bilateral magnet, [ 111 ] and double‐side axial magnet [ 74,77,108,112 ] were used. Qi and Li et al [ 74,108,109,112 ] found that the internal shrinkage cavities and even the residual solidification line in nugget center of austenitic stainless steels can be effectively eliminated during the MA‐RSW.…”

“…a) RSW nugget and b) MA-RSW nugget. Reproduced with permission [108]. Copyright 2021, The Authors, published by Taylor & Francis.…”