The liquid metal embrittlement (LME) cracks form in galvanized DH steel during resistance spot welding because of the low melting temperature of Zn layer. Zn penetrates into steel substrate through the liquid Zn infiltration and the rapid solid‐state diffusion. The crack propagation path obtained by electron probe microanalyzer shows that the path is along the distribution of Zn. The preplating technique in this study is supposed to reduce the LME sensitivity of DH galvanized steel. It has been proved by transmission electron microscopy observation that the preplated Ni layer shows columnar‐like grain morphology. The liquid Zn would form high‐melting‐point intermetallic phase Ni 5 Zn 8 together with Ni when diffusing through the channels of columnar Ni layer. The higher current density preplating technique produces more nucleation sites, introducing more tinier and denser columnar Ni crystals. Then, there would be more channels for the Ni–Zn intermetallics to form, preventing Zn from penetrating into the substrate. The mechanical properties of galvanized plates and preplated plates have been evaluated by the Gleeble tests. The preplated ones possess superior elongation. Correspondingly, the higher current density preplating sample performs the longer displacement. Therefore, the preplating technique, especially the higher current density one, can be employed to alleviate the LME phenomenon.

Liquid metal embrittlement (LME) occurs when a normally ductile alloy undergoes brittle fracture in contact with a liquid metal. The mechanisms behind LME remain unclear, and most of the models rely on post mortem analyses. In this work, we overcome this limitation by performing in situ scanning electron microscopy (SEM) notched micro-bending tests on α-brasses exposed to the gallium–indium eutectic (EGaIn) at room temperature, enabling real-time correlation between load–displacement curves and crack evolution during LME. In the Cu-30%Zn alloy, LME was observed only after prior plastic deformation and ductile crack growth, confirming that liquid metal did not influence early plasticity. A two-step experiment further showed that a pre-existing crack in contact with EGaIn, under continued loading, was sufficient to trigger brittle fracture. The Cu-20%Zn alloy displayed alternating ductile and brittle events, with brittle cracks propagating horizontally before arresting in undeformed zones, leading to stepped load–displacement curves. By contrast, pure Cu and Cu-15%Zn showed only ductile fracture despite continuous contact with EGaIn. These results demonstrate that LME in the Cu-Zn/EGaIn system acts during crack propagation rather than initiation. The present in situ SEM methodology provides direct evidence of fracture mechanisms and a framework for future experimental modeling comparisons.

Liquid metal embrittlement poses a challenge in resistance spot welding of zinc-coated advanced high-strength steels. Liquid metal embrittlement often leads to surface cracking, which degrades the mechanical properties of the welded joints. Therefore, understanding the liquid metal embrittlement cracking behaviour and developing mitigation strategies are essential. This study proposes the implementation of an infrared camera for in-situ temperature measurement during welding. Given the substantial variation in surface emissivity during resistance spot welding, a temperature correction model is necessary at critical temperatures associated with liquid metal embrittlement onset. This study proposes a temperature correction model that achieves an 85% improvement in accuracy with a 20 °C error. The model is tailored for quantitative analysis of liquid metal embrittlement cracking, utilising the Boltzmann sigmoidal and BiDoesResp functions.

Liquid metal embrittlement during FAST joining of magnesium and galvanized steel

Liquid metal embrittlement of T91 steel in liquid lead–bismuth eutectic: The role of long-term pre-exposure and threshold stress of crack initiation

Bronze-steel bimetallic structures are structural components finding a growing application in industrial sectors such as aerospace, power generation, and machinery. Recent legislation on green economy and sustainable manufacturing is boosting industry to implement innovative manufacturing processes and new metal alloys capable of lowering environmental footprint by avoiding toxic substances. Laser Metal Deposition is a cost-effective Additive Manufacturing technique for producing bimetallic components by limiting material waste and reducing energy consumption. In this research work, the influence of the main LMD process parameters on the final quality of CuSn11Bi3 coatings on C45 surfaces is analyzed. The Cu-based powder is specifically designed and developed to reduce environmental pollution and increase worker safety by avoiding the use of hazardous chemical elements. The performed observations demonstrate that high-density (99.90%) and crack-free clads are feasible by preventing melt pool dilution zones. Cu diffusion into the C45 substrate deteriorates the structural integrity at the clad-substrate interface by inducing liquid metal embrittlement cracking, whereas steel diffusion into the as-deposited clad promotes crack propagation. High-density (up to 99.97%) and crack-free CuSn11Bi3 coatings are achieved by using low specific energies (from 17 J/mm2 to 40 J/mm2) and reducing the Oxygen content during sample manufacturing up to 0.02%.

Thermodynamics of grain boundary segregation transition and their relevance for liquid metal embrittlement in Fe-Zn system

The role of intermetallic compounds in mitigating liquid metal embrittlement in Al-Zn-Si coated steels

Decoupling early-stage cracking and propagation mechanisms in liquid metal embrittlement of Zn-galvanised TWIP steel

The role of microstructure in crack growth during liquid metal embrittlement of Zn-galvanised TWIP steel

Abstract Zn-induced liquid metal embrittlement (LME) cracks tend to be formed in hot-dip galvanizing (GI) medium-Mn advanced high-strength steel (AHSS) in the process of resistance spot welding (RSW). In the present study, the LME susceptibility of the medium-Mn AHSS with GI coating was systematically evaluated in accordance with the criterion of “Auto/Steel Partnership (A/SP)”. The samples were welded at 16 groups of distinct welding current levels from 7.0 kA to 14.5 kA in 0.5 kA increments. Some severe LME cracks were evident in the cross sections of the RSW joints even below expulsion, and more pronounced and serious LME cracks appeared at or above expulsion. It was discovered that the tendency for LME crack formation tended to worsen as the welding current increased. The maximum LME crack lengths of Type A, B, C, and D among all groups were approximately 1,285.0 μm, 980.5 μm, 1,397.0 μm, and 131.9 μm, respectively. Results revealed that the medium-Mn AHSS with GI coating displayed high LME susceptibility, which consequently failed to satisfy the necessary criterion for RSW application in the automotive industry. Moreover, the elevated Mn content was deemed as a critical factor leading to the high LME susceptibility of medium-Mn AHSS with GI coating.

Abstract Thermal and mechanical loading, combined with zinc coating, are the primary factors influencing liquid metal embrittlement (LME) in the investigated advanced high-strength dual-phase steel, with a yield strength of 1200 MPa and high ductility during resistance spot welding. LME results in a ductility loss of up to 95% and is driven by an intergranular decohesion mechanism, leading to brittle failure in otherwise ductile steel. Validated numerical models provide deeper insights into the critical conditions during welding. The presented multi-physical model enables the optimisation of welding parameters, reducing experimental efforts and enhancing manufacturing efficiency. This study introduces new methods to reduce LME while improving overall weld quality. Surface-coated refractory electrodes significantly reduce embrittlement compared to standard copper electrodes. For copper electrodes, a newly developed shape minimises stresses and misalignment-induced stresses, further reducing embrittlement and enhancing weldability. Additionally, a mandatory holding time after welding effectively lowers embrittlement, while interrupted cooling creates critical conditions. Downward ramped current improves surface conditions, rendering the weld spot less susceptible to embrittlement.

Zn segregation in BCC Fe grain boundaries and its role in liquid metal embrittlement revealed by atomistic simulations

On the preference of liquid-metal embrittlement along high-angle grain-boundaries in galvanized steels

Abstract Advanced high-strength steels (AHSS) are increasingly used in the automotive industry for lightweight components due to their superior mechanical properties. Quench and partitioning (QP) steels provide an optimal balance between strength and formability, but their susceptibility to liquid metal embrittlement (LME) during resistance spot welding presents challenges. Laser welding, with its low heat input and high efficiency, offers a promising solution for reducing LME risks while ensuring strong, reliable joints for automotive applications. This study investigates the microstructural changes and mechanical performance of laser-welded joints between QP and dual phase (DP) steels. The fusion zone (FZ) and supercritical heat-affected zone (HAZ) primarily exhibited martensitic microstructures, while the midcritical and subcritical HAZ contained tempered martensite and ferrite on the DP side and a combination of tempered martensite, ferrite, and retained austenite on the QP side. These microstructural transformations contributed to enhanced FZ and HAZ regions, resulting in defect-free welds. Fractures occurred within the softer base metal (BM) regions, exhibiting ductile fracture characteristics without significant strength loss. However, joint ductility was slightly reduced compared to BMs due to strain localization caused by microstructure and thickness variations. The results demonstrate that laser welding is an effective method for joining QP steels in automotive manufacturing.

Liquid metal embrittlement (LME) is a critical challenge in the resistance spot welding (RSW) of zinc-coated advanced high-strength steels (AHSS), where molten zinc penetrates grain boundaries and induces intergranular cracking. This study investigates the suppression of LME through the application of electroplated nickel (Ni) interlayers between the steel sheet and the welding electrode. Comparative RSW trials were performed on GI-coated DP 780 steel with and without Ni interlayers. Dynamic contact resistance (DCR) curves revealed suppressed Zn melting behaviour by using Ni-coated interlayers. SEM-EDS analysis confirmed the formation of Ni-Zn intermetallic phases (NiZn, NiZn4, Ni5Zn2), which act as diffusion barriers preventing molten Zn intrusion. Quantitative crack length analysis showed a significant reduction in LME-induced cracks with Ni interlayers, corroborated by improved mechanical properties. Simulations further demonstrated reduced LME risk and thermal stress concentrations when the Ni interlayer was used.

The effect of current intensity on liquid metal embrittlement in resistance spot welding of QP1180 steel

This study investigates the occurrence and mitigation of liquid metal embrittlement occurring during resistance spot welding in deep-drawn automotive components, specifically focusing on an S-Rail made from advanced high-strength steel. A simulation-based liquid metal embrittlement risk criterion based on local major component stresses was established and used to quantify and compare liquid metal embrittlement risks between different tests. Experimental and numerical analyses were conducted, revealing that springback significantly impacts liquid metal embrittlement formation. Adjustments in electrode geometry and hold time post-welding were found to mitigate liquid metal embrittlement risks. The effects of stack-up configuration and related parameter settings on liquid metal embrittlement occurrence were identified and liquid metal embrittlement was effectively prevented across both stack-up configurations. These findings advance the understanding of liquid metal embrittlement mechanisms and provide practical approaches to enhance the spot weld quality in AHSS-based body-in-whites.

This study focuses on the element effects of Al and Si on the liquid metal embrittlement (LME) phenomenon. Four series of chemical compositions have been chosen for this research, which are 20% higher Al DH780, 20% higher Si DH780, 20% higher Al DH980, and 20% higher Si DH980. The total LME crack length of the welding spot of each state sample has been statistically analysed. The high Al DH780 sample shows the lowest total crack length, whereas the high Si DH980 sample shows the highest total crack length. Then the semi-in situ tensile tests have also been employed to evaluate the mechanical properties of these four different chemical composition samples. The high Al sample shows less LME cracks and higher elongation compared with the high Si sample. The shoulder position transmission electron microscopy (TEM) sample has been cut by the focused ion beam. It could be seen from the TEM observation that the distribution of Si element is close to that of Zn. The Si and Al solute atoms would diffuse towards grain boundaries to form solute-rich clusters in the manner of solute-vacancies loops. The stronger Zn-Si adhesion bonding attracts Zn infiltrating deeper into substrate. The Zn-rich intermetallic phase nucleation on grain boundaries would further worsen the LME sensitivity. The enrichment of Al content would repel Zn on grain boundaries and also stabilise the Fe-Zn intermetallic phase. High Al could also reduce the austenite amount in steel. Thus, it mitigates the LME response of steel. The LME phenomenon of Zn would be severe for the higher Si sample.

Abstract The third generation of advanced ultra-high-strength steel PHS1500, is widely used in automobile manufacturing due to its excellent performance. Still, severe liquid metal embrittlement (LME) cracks will occur when joined by resistance spot welding (RSW). This study aims to elucidate the formation mechanism of LME cracks and optimize welding process parameters to mitigate the severity of LME cracks in PHS1500 steel. Conventional double-pulse resistance spot welding was used to join PHS1500 steel, and the welded joints were characterized using optical microscopy and scanning electron microscopy to analyze the crack morphology, elemental distribution, and the LME formation mechanism. The results revealed that LME cracks were caused by the diffusion of liquid Zn into the grain boundaries of the base metal to form the low-melting-point Γ phase and α-Fe(Zn) phase, which fractured under tensile stress. After optimizing welding parameters, the maximum crack length at the heat-affected zone slope (HAZ slope) decreased from 117.59 μm to 32.76 μm (72.14% reduction), while that in the outward region of the HAZ (HAZ outward) decreased from 80.88 μm to 21.65 μm (73.23% reduction), with most cracks exhibiting a single dendritic morphology.