A Phenomenological Model of Resistance Spot Welding on Liquid Metal Embrittlement Severity Using Dynamic Resistance Measurement

Liquid metal embrittlement (LME) is one of the severe problems of Zn-coated steel in resistance spot welding (RSW). Hence, proper welding schedules for Zn-coated steel are of practical interest. RSW involves a complex interaction between electrical, thermal, and mechanical phenomena. Identification and integration of all these governing physics are almost impossible by performing simple experiments. Hence, phenomenological modeling of RSW has gained a significant attention in the recent past. The complexity of the physical process introduced by the dynamic nature of contact resistance brings challenges for the model. A simplified but effective modeling approach of RSW is proposed where attention is focused on the evaluation of the thermal field using the finite element (FE) method. The interaction of the mechanical and electrical field is performed by the dynamic variation of the contact area, stress concentration, and non-uniform current density distribution in a semi-analytical model. These internal variables of the model are incorporated through the scaling of the governing parameters by the dependence of the transient and converged temperature field within a time step. The transient-dynamic contact resistance is detached from the measurement of total resistance and mapped adaptively by the implicit scheme within a time step of the numerical model. The transient development of the nugget is investigated for dual-phase steel (DP980) with an interrupted test of the dynamic resistance curve. The FE model is validated with experimentally measured results at different process conditions. The characterization of the thermal history from the model relatively identifies the LME phenomena and suggests corresponding modification of the welding schedule.