Four Types of LME Cracks in RSW of Zn-Coated AHSS
American Welding Society, Siva Prasad Murugan, Y. D. Park, Vijeesh Vijayan, Changwook Ji
Abstract
Zinc-coated advanced high-strength steels are known to be susceptible to liquid metal embrittlement (LME) cracking during resistance spot welding (RSW). Despite numerous reports with regard to LME during RSW, a systematic approach has not been proposed for the classification of cracks based on the cracking mechanism. The objective of this study was to characterize the LME cracks at various RSW locations, and thereby propose a classification method to identify the mechanism of the LME cracks at each location. The experimental results revealed the LME cracks were concentrated at certain weld locations and exhibited different features in terms of length, number, and orientation, owing to the synergetic effect of temperature, stress, microstructure, time of exposure to liquid zinc, and time of exposure to tensile stress at the corresponding lo-cations. Thus, the LME cracks were classified into four categories, namely type A, type B, type C, and type D, based on the formation location. The effect of time of exposure to liquid zinc and tensile stress on LME cracking revealed the time dependency of LME in RSW. The nature of contact be-tween the electrode and the sheet, and the heat input during welding, were found to be the main reasons for the difference in the thermal, mechanical, and metallurgical characteristics of various crack locations, which caused the formation of various LME crack types.