Influence of Welding Current on Nugget Formation and Mechanical Performance of Dissimilar Steel Joints: A Multiphysics Approach

Abstract

The current requirement of lightweight and crash-resistant automotive construction methods and the application of multi-material groupings have promoted the extensive application of this material groupings making solid joining of different grades of steel desired. The proposed research investigates the Resistance Spot Welding (RSW) of three dissimilar mixtures: Mild Steel (MS) to Stainless Steel (SS), SS to HSLA 355 Steel (HSLA 355 metal), MS to HSLA 355 metal. The following sequential electro-thermal-mechanical numerical model was established using ANSYS 19.2 to predict nugget assembly and stress distribution. A wide-field experiment which was evaluated was conducted in the welding range 8–12 kA with a constant sheet thickness of 3 mm. Results illustrate an interplay of performance, where the SS-HSS joint displayed the best maximum Tensile Shear Strength at 11 kA of 9.85 kN with the highest TSS: 18.6% enhancement over MS-SS from a baseline standard. The numerical model presented was shown very closely, with nugget diameter and TSS predictions also in accordance with the experimental data by only 6%, being close to experimental results. Analysis of stress showed that maximum concentrations occurred at the nugget periphery to 1350 MPa in high-strength concomitant welds, which eased the evolution from interfacial to nugget pull-out failure modes. Final word: A good welding current of 11 kA was defined to allow joint strength without any expulsion of metal. With this knowledge, a validated framework for predictive prediction of mechanical integrity of dissimilar automotive welds could emerge that will mitigate the need to rely on experimentation.