Critical LME elongation: a criterion measured with Gleeble correlated to LME sensitivity during spot welding

\nLiquid metal embrittlement may appear on multiphase high strength galvanized steels during the spot-welding process. The aim of this paper is to describe a high temperature tensile test, performed with a Gleeble machine, to evaluate the LME sensitivity of a given coated steel in conditions similar to spot welding (time cycle). The critical LME elongation, corresponding to minimum of stress derivative during force decrease, has been found as being the most relevant parameter to measure the LME phenomenon. Relevant test parameters such as temperature, strain rate, applied thermal cycle, and effect of thermocouple welding have been studied on two steels. The first, TRIP 800 steel, presents a high sensitivity to LME between 750 °C and 900 °C while the second, DP600 steel, is not sensitive. Strain rate effect reveals a competition between LME crack propagation and ductile fracture. The study also shows the need to avoid welding thermocouple on Zn-coated side. Overall, the critical LME elongation from Gleeble test is well correlated to LME cracks number and depth in spot welding.\n