Study on the Flow Behavior and Mechanism of Molten Nuggets in Aluminum/Steel Dissimilar Resistance Spot Welding

The adoption of lightweight materials, especially Al/steel hybrids, is a key trend in automotive lightweighting for energy efficiency and emissions reduction. For the manufacturing of Al-steel hybrid automobile bodies, a three-dimensional magnetohydrodynamic(MHD) simulation model is developed to simulate the resistance spot welding(RSW) process of heterogeneous materials by coupling electrical, thermal, magnetic, and fluid fields. The flow behavior of aluminum nuggets and their influence on temperature evolution during welding are investigated. The results indicate that the Al nugget exhibits an outer counterclockwise flow driving and an inner clockwise flow-dominated pattern. The nuggets’ flow behavior promotes the concentration of high-temperature zones in the middle of the Al nugget, enhancing the clockwise flow on the inner side and the heat transfer from the steel sheet through the interface to the aluminum sheet, resulting in the unique bell-shaped morphology of the Al nugget closely adhered to the Al/steel interface. © 2024 Chinese Mechanical Engineering Society. All rights reserved.