Laser-beam welding as a method to characterise in-situ local thermo-mechanical conditions leading to liquid zinc embrittlement of Dual-Phase steel
Huub Rombouts (TU Delft - Mechanical Engineering)
M.J.M. Hermans – Mentor (TU Delft - Mechanical Engineering)
G. Agarwal – Graduation committee member (TU Delft - Mechanical Engineering)
V. Popovich – Graduation committee member (TU Delft - Mechanical Engineering)
He Gao – Graduation committee member (Tata Steel Europe Limited)
A. Sood – Graduation committee member (TU Delft - Mechanical Engineering)
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Abstract
Liquid metal embrittlement (LME) is a problem encountered in the resistance spot welding joining process of advanced high-strength steels in the automotive industry. Its occurrence reduces the mechanical performance of welds. The nature of resistance spot welding prevents in-situ characterisation of thermo-mechanical conditions causing LME. Laser-beam welding (LBW) under tension is proposed as an alternative method to analyse LME cracks growing during the welding process of a DP1000 dual-phase steel grade. The influence of global thermo-mechanical parameters on the degree of embrittlement is investigated through Gleeble hot tensile tests. LBW schedules are explored, and material characterisation used to find and prove LME crack occurrence. Finite element analysis with COMSOL is used to connect results from Gleeble hot tensile tests with results from LBW and relevance to RSW is outlined. Results show that a temperature dependent ductility trough is present between 750 and 900°C. The Fe-Zn system is further found to require specific mechanical conditions (stress and strain rate) to become susceptible to LME. The proposed LBW setup is found to be susceptible to LME, but not in a high enough severity to be detectable through SEM and EDS. Changes should be made to the loading setup of the LBW setup to induce LME crack growth to a sufficient degree to allow for in-situ monitoring of local thermo-mechanical conditions surrounding the crack.