Results of our latest study on Liquid Metal Embrittlement confirm that LME is predictable and preventable.
In the automotive industry, ensuring the strength and safety of vehicle welds is critical. With the growing adoption of Advanced High-Strength Steels (AHSS), concerns have emerged around a phenomenon known as Liquid Metal Embrittlement (LME) which can result in small surface cracks in welded joints.
As manufacturers increasingly use AHSS to improve vehicle performance and safety, understanding and mitigating LME has become a top priority. In response, WorldAutoSteel has published a new component study – a follow-on to their first LME study in 2017 – shedding new light on this issue for real-world applications.
What is Liquid Metal Embrittlement?
Liquid Metal Embrittlement (LME) occurs during resistance spot welding when heat causes the zinc coating on AHSS to liquefy and interact with the steel, resulting in potential small cracks. For vehicle manufacturers, these cracks can raise concerns about the long-term integrity of welds, particularly under crash conditions.
Phase 1: Liquid Metal Embrittlement Study (2020)
In 2017, WorldAutoSteel embarked on a three-year technical research project to address LME, working in collaboration with three leading engineering institutions: Laboratory of Materials and Joining Technology (LWF) Paderborn University in Paderborn, Germany; The Institute de Soudure, Yutz, France; and Fraunhofer Institute for Production Systems and Design Technology (IPK), Berlin, Germany.
The objective was to understand the root causes of LME and develop strategies to mitigate its effects. The results revealed that when using standard welding techniques and equipment, the occurrence of LME was shown to be both highly unlikely and extremely low risk in the AHSS materials tested.
The study also indicated that LME could be effectively prevented with proper techniques including avoidance of excessive heat input (e.g. excess welding time, current), employing extended hold times to allow for sufficient heat dissipation and lower surface temperatures, and avoidance of improper welding equipment (e.g. misalignments of the welding gun, highly worn electrodes, insufficient electrode cooling).
However, an important question remained – would these findings hold true in real-world manufacturing applications?
Phase 2: Liquid Metal Embrittlement Component Study (2024)
WorldAutoSteel’s newest study, conducted in partnership with LWF and Fraunhofer addresses these unanswered questions, focusing on Liquid Metal Embrittlement in industrial-scale applications. The study would investigate whether solutions developed on academic samples can also be used in real parts and whether there are any additional characteristic features of LME when looking at a complete part versus isolated tests.
The findings were significant: advancements in metallurgy, production and welding techniques have significantly reduced AHSS’s sensitivity to LME.
In order to create LME in various material combinations, researchers had to impose extreme, highly unusual weld conditions. Even in those cases, the cracks that formed were typically minor and had no meaningful impact on the part’s strength during crash testing – aligning with what experts currently understand.
The study also confirmed that manufacturers can use optimised welding processes (such as electrode alignment and timing adjustments) to further reduce LME risk in large-scale production. In addition, the use of advanced simulations allowed researchers to predict the formation of cracks with remarkable accuracy. This information enabled development of a criterion that allows comparisons of different welding and material parameters, helping to pinpoint and pre-empt potential LME risks.
A criterion was developed and tested that allows comparisons of welding parameters and different stack-ups with the same AHSS. With this criterion, potential at-risk resistance spot welds can already be optimized during the planning phase of a new automotive car body, giving another tool to reduce and even altogether avoid Liquid Metal Embrittlement formation.
What These Findings Mean for Automotive Manufacturing
Redefined risk parameters: Recent advancements in steel manufacturing and welding techniques make AHSS less prone to LME, reducing the risk of brittle fractures.
Confidence in material selection: Manufacturers can use any grade in the AHSS portfolio with confidence and enable greater design flexibility without the threat of LME by using latest generation AHSS.
New tools to enhance vehicle design: The use of predictive simulations provides a powerful tool for designers to foresee and mitigate LME risk, enabling the development of safer and more robust vehicle designs.
Optimised manufacturing processes: Manufacturers can adopt identified mitigation strategies, such as addressing welding process imperfections, to further minimise LME risk and enhance production quality.
The findings from this component study provide a new level of confidence for automotive manufacturers who utilize AHSS in vehicle design. As the automotive industry continues to push the design envelope, these insights provide a critical foundation for building the next generation of vehicles with AHSS vehicles that are safer, stronger, and more resilient than ever before.