Towards an explanation of liquid metal embrittlement cracking in resistance spot welding of dissimilar steels. (October 2020)

• Record Type: Journal Article
• Authors: Ling, Zhanxiang; Wang, Min; Kong, Liang; Chen, Ke
• Is Part Of: Materials & design. Volume 195(2020)
• Publication Date: 2020-10
• Subjects: Resistance spot welding -- Liquid metal embrittlement -- Q&P980 steel -- Low carbon steel; Materials -- Periodicals; Engineering design -- Periodicals; Matériaux -- Périodiques; Conception technique -- Périodiques; Electronic journals; 620.11
• DOI: 10.1016/j.matdes.2020.109055
• Languages: English
• ISSNs: 0264-1275

Abstract

Abstract: Automotive advanced high-strength steels and ultra-high-strength steels, such as Q&P980 steel with a Zn coating, are prone to liquid metal embrittlement (LME) surface cracking during resistance spot welding, while traditional low carbon steels (LCSs) do not appear to undergo LME. In this work, galvanized Q&P980 steel sheets were welded with LCS sheets. LME cracks were found on both the Q&P980 steel and LCS sides. However, the severity of LME cracking on the Q&P980 side was much higher than that on the LCS side, indicating that Q&P980 steel has a higher LME susceptibility than LCS, which was also proven by a hot tensile test. The higher LME susceptibility of Q&P980 was attributed to its lower reactivity with liquid Zn, higher achievable stress and increased number of LME-susceptible grain boundaries. Micro-analysis revealed that Zn most likely entered the steel matrix via diffusion and not via liquid penetration, and stress-assisted diffusion is the likely mechanism for LME. Graphical abstract: Unlabelled Image Highlights: Liquid metal embrittlement occurred in resistance spot welding of galvanized Q&P980 steel and galvanized low carbon steel. Q&P980 steel is more susceptible to liquid metal embrittlement cracking than low carbon steel. Stress-assisted diffusion is the mechanism of liquid metal embrittlement in resistance spot welding.