Liquid Metal Embrittlement Elimination in RSW of Galvannealed AHSS DP980

Liquid metal embrittlement (LME) is a longstanding problem for resistance spot welding (RSW) of Zn-coated automotive sheet steels, especially third generation advanced high-strength steels (AHSSs). This work designed a multi-principal element alloy (MPEA), considered a high entropy alloy (HEA), that preferentially absorbs Zn during RSW and forms a single solid solution phase. The MPEA composition was designed using a highthroughput multi-physics-based analysis, which down-selected the FeMnNiCoZn system as favorable to present a single face-centered cubic (FCC) phase over a broad dilution composition space with the substrate. Comparing the welds made with MPEA foils to control welds without the MPEA, optical microscopy revealed no visible LME cracks in MPEA welds, whereas Zn-lined cracks with a length of 5–100 μm populated the control welds. Energydispersive spectroscopy demonstrated the MPEAlimited Zn penetration distance into the AHSS grain boundaries to less than 10 μm. Kinetic simulations also predicted the MPEA would retain Zn as a solid solution and limit its penetration into the AHSS substrate. Site-specific synchrotron diffraction confirmed a single FCC phase in the MPEA and an unaffected ferrite/martensite microstructure in the adjacent DP980 AHSS substrate. Furthermore, tensile-shear tests showed average improvements of 21% in peak load and 80% in fracture energy in welds employing MPEA foils when welded with the same current and schedule.