Mitigating the influence of industrially relevant disturbances on LME severity of dissimilar resistance spot welded advanced high-strength steels

Abstract

The third generation of advanced high-strength steels (3G-AHSS) has been developed to provide high strength and high ductility, which attract automakers. To protect these materials from corrosion during service, these materials are typically coated with zinc. During resistance spot welding (RSW), the zinc coating can melt, allowing it to penetrate into the grain boundaries (GBs), and lead to liquid metal embrittlement (LME) phenomena. Concerns regarding LME susceptibility have impacted the industrial application of 3G-AHSS; therefore, its mitigation has become a top focus for automakers. Several possible strategies for lowering LME severity by altering welding parameters have been proposed to mitigate LME in similar spot weld joints. However, these strategies were not tested on a dissimilar spot weld joint. Therefore, in this work, 1.4 mm gauge thickness galvanized (GI-coated) 3G-980 AHSS was joined with 0.6 mm thick Interstitial Free (IF) steel. In this work, current pulsation and ultra-short hold time were proposed to minimize LME severity. The robustness of the developed welding schedule was then tested on welds made with industrial disturbance factors such as pre-strained sheets (between 0 to 80% of 3G-980 material yield strength) and electrode misalignment (between 0° to 10° misalignment) compared to baseline parameters. In severe circumstances of disturbance factors, the resulting optimized welding schedule decreased LME cracking and showed improved resistance to LME, lowering LME severity by 41% for the extreme pre-strain condition and 27% for the extreme misalignment angle.

Keywords

• Liquid metal embrittlement (LME)
• Resistance spot welding (RSW)
• Third generation advanced high strength steel (3G-AHSS)
• Dissimilar welding
• Electrode misalignment
• Industrial disturbance factors