A novel electrode tip geometry to mitigate liquid metal embrittlement during resistance spot welding

Third-generation AHSS (advanced high-strength steels) have been developed for carmaking industry, their increased strength at a given ductility allowing a replacement of lower grades with a lower thickness and weight, at a given resistance. However, for some 3rd-generation AHSS, LME (liquid metal embrittlement) during resistance spot welding appears as a roadblock. During the welding process, molten zinc may diffuse into the grain boundaries of the heat-affected zone, and open cracks which may later impact the spot weld performance. In order to limit this phenomenon, a novel electrode tip geometry has been designed and tested on a 1180-MPa 3rd-generation AHSS. First, specific LME testing has been carried out, showing the reduced amount of cracking generated under different welding conditions, including sheet/electrode misalignment, by the new electrode tip geometry. Then, welding current range and electrode life tests have been performed to check the industrial applicability of such an electrode geometry. It appears that the LME mitigation property is robust against electrode wear for at least 1000 welds. On the other hand, it turns out that a sufficient welding range can only be obtained for sufficient total thickness of the stack-up. Finally, the numerical simulation approach has been used to better understand the mechanisms of LME limitation, although the full mechanism is not yet established.