Liquid metal embrittlement susceptibility of two Zn-Coated advanced high strength steels of similar strengths

Abstract

Advanced high strength steels (AHSS) exhibit an increased susceptibility to Zn-assisted liquid metal embrittlement (LME). The strength of an AHSS is believed to be one important factor controlling LME sensitivity; this study investigated the LME behavior of two AHSS having different chemical compositions, while maintaining similar tensile strength at elevated temperatures. Hot tension tests were performed using simulated spot-weld thermal cycles to determine the critical ranges of temperatures and strain rates capable of triggering LME in these AHSS. Despite the fact that the two investigated AHSS had similar strengths, distinct differences were observed in their LME-associated ductility trough characteristics and LME cracking severity. This comparison helps isolate the contributions of chemical composition on the Zn-LME susceptibility. Specifically, the AHSS grade with higher-LME sensitivity had a Si content of 1 wt%, while the AHSS grade with lower-LME sensitivity had a Si content of 0.06 wt%. Three-dimensional elemental characterization using time-of-flight secondary ion-mass-spectroscopy indicated Si-enrichment in the coating-substrate interface layers of galvanized samples during thermal cycling at elevated temperatures. The difference in the LME sensitivity of the two AHSS is discussed in the context of this Si-enrichment behavior, which potentially suppresses Fe–Zn alloying reactions and increases the likelihood of direct contact between liquid Zn and the steel substrate.