Evaluating LME Susceptibility in Third-Generation AHSS: The Role of Testing Methodologies and Silicon Concentration

The automotive industry’s push for lightweight, high-strength materials has led to the advancement of third-generation advanced high-strength steels (AHSS). Known for their blend of ultra-high tensile strength and ductility, these steels are ideal for structural applications. However, their adoption has faced obstacles, notably due to Zinc (Zn)-assisted liquid metal embrittlement (LME), particularly in cases where Zn-based corrosion-resistant coatings are used during resistance spot welding (RSW). This study explores testing methodologies for evaluating LME susceptibility and examines the impact of silicon (Si) concentration, specifically between 0.5 and 1.4 wt.-%, on Zn-LME susceptibility in AHSS. This research introduces two primary testing approaches: spot welding and hot tensile tests, each designed to quantify LME behavior. Both methods show that higher Si levels correlate with increased LME sensibility, evidenced by greater ductility loss and the formation of longer critical cracks during welding. Thermodynamic modeling further demonstrates that Si affects phase stability in the Fe-Zn system, broadening the stability of liquid Zn. The findings highlight Si’s significant role in Zn-LME susceptibility and underscore the importance of robust testing methods to facilitate the safer application of AHSS in automotive manufacturing.