Abstract Third-generation advanced high-strength steels (3G AHSS) are widely used in automotive applications due to their exceptional mechanical properties, including high tensile strength and fracture toughness. Resistance spot welding is the dominant joining process for these steels in the body-in-white production due to the high productivity and automation capability. Though exhibiting satisfying welding current ranges, AHSS can have the downside of showing zinc-induced liquid metal embrittlement (Zn-LME), a phenomenon in which the exposure of the susceptible base material to the liquid zinc coating in combination with the induced tensile stresses during resistance spot welding can lead to cracking of varying severity. The presence of zinc-induced LME cracks can result in an unexpected failure of the component due to potential premature crack initiation and propagation under a mechanical load. While extensive research has been conducted on the effects of LME on static mechanical properties such as tensile strength and fracture toughness, its impact on fatigue life—a critical factor in the automotive application—remains less well understood. Fatigue failure can occur earlier as the presence of LME can accelerate the crack growth under cyclic loading. Understanding the interplay between LME-induced cracks formed during resistance spot welding and fatigue behavior is essential for improving the reliability and widening the application field of 3G AHSS. This study, which is the first part of a larger investigation, is aimed at developing a methodology for analyzing the influence of zinc-induced LME on the fatigue life of third-generation advanced high-strength steels (3G AHSS), focusing on the fatigue crack initiation and propagation mechanism under cyclic loading. To achieve this, LME cracks were generated via the usage of a decreasing electrode force profile and the reproducibility was investigated. The LME crack surface was investigated with stereo and scanning electron microscopy. The fatigue test for a specimen with severe LME cracking was monitored via digital image correlation (DIC), which enabled the evaluation of critical areas. The derived methodology serves as a guideline for quantifying the influence on LME cracks on the fatigue life and thereby assisting the development process of new materials and parts. In upcoming investigations, the methodology will be used to evaluate the influence of specific LME crack sizes and types.
Ullrich et al. (Sun,) studied this question.