Uncovering the mechanism of the LME susceptibility for the galvanized and electrogalvanized DP 1180 steels

Zn-based coatings generally protect dual-phase (DP) 1180 advanced high-strength steel in automobiles from corrosion. However, liquid metal embrittlement (LME) tends to occur in Zn-coated DP 1180 steel during resistance spot welding. In this study, the LME phenomena of the galvanized (GI) and electrogalvanized (EG) DP 1180 steels were compared based on the LME susceptibility evaluation standard. For DP 1180 steel coated with GI, the maximum length of the LME crack was approximately 121.2 μm at the shoulder of the welding spot. In contrast, for the specimen coated with EG, the maximum length of the LME crack was 792.6 μm at the center of the welding spot. Owing to the different galvanizing processes, the microstructure differed during annealing, thereby influencing the occurrence of the LME. Furthermore, the microstructural observations indicated that the protection of the interfacial oxide layer in the GI specimen could prevent the formation of the LME to some extent. Therefore, the presence of the interfacial oxide layer could account for the different LME susceptibilities of the GI and EG DP 1180 steels.