EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Driven by the demands for energy efficiency and weight savings, the improvement of Advanced High Strength Steels (AHSS) is of high industrial interest. Despite the high strength and ductility of AHSS, the Zinc (Zn) coating typically applied to increase its corrosion resistance can be the origin of significant mechanical property degradation if, for example, joined with spot welding. This property degradation is a manifestation of the well-known Liquid Metal Embrittlement (LME) phenomena, during which liquified Zn infiltrates into the steel substrate along grain boundaries (GBs). In response to the infiltration, the GB-network weakens, thereby promoting microcracking and eventual failure. Much work has focused on evaluating cracked and Zn infiltrated GBs, with a focus on the phases being present inside the infiltrated cracks. Based on such efforts, a sequence of mechanistic events for the LME phenomena in galvanized steels has been proposed, but the early stages of this damage process continue to remain poorly understood. In order to shed more light on the early stages of LME in AHSS, we pursue here the approach to study infiltrated but uncracked GBs. We use scanning transmission electron microscopy (STEM) to investigate these boundaries and conclude that prior to cracking nucleation and growth of intermetallic phases occurs inside the uncracked GBs. We discuss these findings in the context of resulting local strain heterogeneities that may eventually trigger microcracking in LME.