TY - JOUR A1 - Böhne, Chr. A1 - Meschut, G. A1 - Biegler, M. A1 - Rethmeier, Michael T1 - Avoidance of liquid metal embrittlement during resistance spot welding by heat input dependent hold time adaption N2 - Liquid metal embrittlement (LME) cracking can occur during resistance spot welding (RSW) in zinc-coated advanced high-strength steels (AHSS) for automotive production. In this study, a methodological variation of hold time is performed to investigate the process-related crack influence factors. A combination of numerical and experimental investigations confirms, that the extent of heat dissipation and re-heating of the sheet surface can be influenced and thus the degree of crack formation can be controlled in a targeted manner by the parameterisation of the hold time. The temperature and stress history of crack-free and crack-afflicted spot welds are analysed and a conclusion on the borders defining the LME active region is derived. KW - Liquid metal embrittlement KW - Crack KW - Advanced high-strength steels KW - Resistance spot welding KW - Hold time KW - Heat input KW - Simulation PY - 2020 U6 - https://doi.org/10.1080/13621718.2020.1795585 SN - 1362-1718 VL - 25 IS - 7 SP - 617 EP - 624 PB - Taylor Francis Online AN - OPUS4-51096 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Böhne, Chr. A1 - Meschut, G. A1 - Biegler, M. A1 - Frei, J. A1 - Rethmeier, Michael T1 - Prevention of liquid metal embrittlement cracks N2 - Advanced high strength steels are usually coated by a zinc layer for an increased resistance against corrosion. During the resistance spot welding of zinc coated steel grades, liquid metal embrittlement (LME)mayoccur. As a result, cracking inside and around the spot weld indentation is observable. The extent of LME cracks is influenced by a variety of different factors. In this study, the impact of the used electrode geometry is investigated over a stepwise varied weld time. A spot welding finite element simulation is used to analyse and explain the observed effects. Results show significant differences especially for highly increased weld times. Based on identical overall dimensions, electrode geometries with a larger working plane allow for longer weld times, while still preventing LME within the investigated material and maintaining accessibility. KW - Liquid metal embrittlement KW - Crack KW - Advanced high strength steels KW - Resistance spot welding KW - Electrode geometry PY - 2019 U6 - https://doi.org/10.1080/13621718.2019.1693731 VL - 25 IS - 4 SP - 303 EP - 310 PB - Taylor & Francis AN - OPUS4-49833 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frei, J. A1 - Rethmeier, Michael T1 - Susceptibility of electrolytically galvanized dual-phase steel sheets to liquid metal embrittlement during resistance spot welding N2 - Modern advanced high-strength steel sheets for automotive applications are mostly zinc coated for corrosion resistance. However, the presence of zinc can—besides its positive effects—increase the material’s susceptibility to liquid metal embrittlement (LME) during resistance spot welding (RSW). Zinc and its eutectics are, due to their low melting point, present in liquid state during the welding process. This fact can, in combination with other factors like tensile strains or stresses, lead to the formation of brittle, intergranular cracks in the weld, and heat-affected zone. This phenomenon is commonly called liquid metal embrittlement. In order to understand the process from a practical perspective, one must learn what factors facilitate it. In this study, industry-relevant parameters are investigated regarding their influence on the occurrence of LME, embodied by the formation of surface cracks. It was found that electrode wear has less of an influence on the cracking susceptibility than welding current or tensile stresses. Finite element analysis is believed to provide a powerful tool in order to gain insights on the formation process. Modeling of the process shows promising initial results, revealing the underlying local stress and strain fields, unmeasurable with common techniques. KW - Resistance spot welding KW - High-strength steel sheets KW - Surface cracks KW - Liquid metal embrittlement KW - Zinc PY - 2018 U6 - https://doi.org/10.1007/s40194-018-0619-1 SN - 0043-2288 SN - 1878-6669 VL - 62 IS - 5 SP - 1031 EP - 1037 PB - Springer AN - OPUS4-45775 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yang, K. A1 - Meschut, G. A1 - Seitz, G. A1 - Biegler, M. A1 - Rethmeier, Michael T1 - The Identification of a New Liquid Metal Embrittlement (LME) Type in Resistance Spot Welding of Advanced High Strength Steels on Reduced Flange Widths N2 - Liquid metal embrittlement (LME) cracking is a phenomenon observed during resistance spot welding (RSW) of zinc􀀀coated advanced high􀀀strength steels (AHSS) in automotive manufacturing. In this study, severe cracks are observed at the edge of the sheet under reduced flange widths. These cracks, traversing the AHSS sheet, culminate at the edge with a width of approximately 1.2 mm. Through combined numerical and experimental investigations, and material testing, these cracks are identified and validated as a new type of LME crack. The mechanism behind this crack formation is attributed to unique geometric conditions that, when compared to center welding, amplify radial material flow by ninefold to 0.87 mm. The resultant tangential tensile stresses approximate 760 MPa, which exceed the yield strength of the examined advanced high􀀀strength steel (AHSS) under heightened temperature conditions, and when combined with liquid zinc, promote the formation of this new type of LME crack. KW - Liquid metal embrittlement KW - Crack KW - Advanced high strength steels KW - Resistance spot welding KW - Simulation KW - Flange width PY - 2023 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-586940 VL - 13 IS - 10 SP - 1 EP - 13 PB - MDPI AN - OPUS4-58694 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Prabitz, Konstantin Manuel A1 - Antretter, Thomas A1 - Rethmeier, Michael A1 - El-Sari, Bassel A1 - Schubert, Holger A1 - Hilpert, Benjamin A1 - Gruber, Martin A1 - Sierlinger, Robert A1 - Ecker, Werner T1 - Numerical and experimental assessment of liquid metal embrittlement in externally loaded spot welds N2 - Zinc-based surface coatings are widely applied with high-strength steels in automotive industry. Some of these base materials show an increased brittle cracking risk during loading. It is necessary to examine electrogalvanized and uncoated samples of a high strength steel susceptible to liquid metal embrittlement during spot welding with applied external load. Therefore, a newly developed tensile test method with a simultaneously applied spot weld is conducted. A fully coupled 3D electrical, thermal, metallurgical and mechanical finite element model depicting the resistant spot welding process combined with the tensile test conducted is mandatory to correct geometric influences of the sample geometry and provides insights into the sample’s time dependent local loading. With increasing external loads, the morphology of the brittle cracks formed is affected more than the crack depth. The validated finite element model applies newly developed damage indicators to predict and explain the liquid metal embrittlement cracking onset and development as well as even ductile failure. KW - Resistance spot welding KW - Finite element simulation KW - Advanced high-strength steel KW - Liquid metal embrittlement KW - Damage prediction KW - Tensile resistance spot welding experiment PY - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-594848 SN - 0043-2288 SP - 1 EP - 10 PB - Springer Science and Business Media LLC AN - OPUS4-59484 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -