A review of current LME test methods and suggestions for developing a standardized test procedure

To improve automotive fuel economy, automobile manufacturers are minimizing the weight of the body-in-white. To do this, they are adopting new 3rd generation advanced high strength steels that have excellent strength and ductility. However, these steels are also prone to liquid metal embrittlement (LME) cracking; intergranular cracks caused by molten zinc, from the galvanized coating, penetrating the steel substrate during the resistance spot welding (RSW) process. These cracks are not acceptable to automobile manufacturers as it is unknown how LME cracks affect joint strength during weld service. To decrease LME cracking, extensive research into understanding its governing metallurgy, optimizing welding parameters, and comparing the LME sensitivity of multiple grades has been done. Most of this work was done using hot-tension testing or RSW testing. However, as there is no standard methodology for these tests, producing results that were difficult to compare. This review examined test methodologies for hot-tension and RSW testing LME severity. It was determined that the usefulness of LME testing could be improved if test methods reflected the temperature and stress-state of the welding process, facilitated comparisons between tests, and quantified results were reported. Recommendations are provided to improve hot-tension and RSW tests to meet these goals.