Resistance spot welding (RSW) is the most common joining process in car body manufacturing and is frequently used to join components made of advanced high strength steels (AHSS). These steels are typically applied with a zinc coating to improve their resistance against corrosion. During the RSW-process the liquefied zinc is reported to infiltrate the grain boundaries of the steel substrate causing a phenomenon referred to as liquid metal embrittlement (LME). In cases where LME is egregious, joint performance might be affected; therefore, prevention or mitigation of LME is desirable. To allow a practical implementation of avoidance strategies, it is favorable to interfere with the parametrization of the established spot welding processes as little as possible. This study investigates methods suitable for the practical avoidance of liquid metal embrittlement during the resistance spot welding of AHSS. At first, the effect of various process influences is investigated and major influence factors are identified. Occurring effects are analyzed in detail and correlated with an FE-simulation to generate a better understanding of the mechanisms causing LME in RSW. In this context the impacts of excessive energy input by high weld currents and elongated weld times on LME crack formation are discussed. Successively the avoidance of LME is achieved by a combined adaption of the electrode geometry and hold-time, with respect to the welding boundary conditions. Finally, the robustness of the proposed methods is validated in a more complex welding scenario.
liquid metal embrittlement; crack; advanced high-strength steels; resistance spot welding; electrode geometry; weld time; hold time; heat input; simulation