Effect of Si concentration on the liquid metal embrittlement susceptibility of advanced high strength steels

Resistance spot welding (RSW) trials were performed on electrogalvanized steel sheets with 0.6 and 1.5 wt% Si. It was shown that LME cracks were longer in the 1.5Si alloy. Moreover, Atom Probe Tomography (APT) in the vicinity of the crack tips revealed (i) an accumulation of Si at the solid/liquid interface due to the low solubility of Si in the Zn-based liquid and (ii) greater Zn diffusion from the liquid into the bulk steel substrate on either side of the crack for the 0.6Si alloy. Diffusion simulations indicated that a longer time is needed for the solidification of the Zn-based liquid in the 1.5Si alloy compared with the 0.6Si alloy, further suggesting a prolonged period of contact between the aggressive Zn-based liquid and substrate grain boundaries in the case of the 1.5Si alloy.