Three-dimension characterization of the liquid metal embrittlement crack in the resistance spot welded joint of the advanced high strength steel

The characterization of the liquid metal embrittlement (LME) cracks is significant to illustrate their formation and propagation, however, the overall morphology of the cracks produced in the spot weld cannot be fully reflected by the two-dimension (2D) section. The present results showed that the LME cracks distributed throughout the specimen, and the details of the crack length and crack tip position could be better revealed based on their three-dimension (3D) morphology. Moreover, it was deemed that Zn could not continuously distribute in the whole crack owing to the curve feature of the grain boundaries and the different directions for the Zn penetration. In particular, the Zn penetration could erode and embrittle the grain boundaries, and resultantly the cohesion of the grain boundaries at the tip of the Zn penetration could be weakened due to the change of the grain boundary and its thermal expansion, causing further propagation of the LME cracks.