EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Advanced High Strength Steels have been developed within the last decades to meet the growing demands for weight reduction and improved crashworthiness properties in the automotive industry. They present an effective combination of formability and weldability, which is of interest for the production of three-dimensional automotive body parts by laser welding. The aim of this work is to investigate the interaction between the chemical heterogeneity and the microstructural characteristics of a similar joining of Advanced High Strength Steels. With the purpose of understanding the mechanisms that occur during a laser welding process, this study carries on a multitechnical, micro-scale characterisation to relate , mechanical properties and microstructure of these assemblies. The tests are conducted by an experimental protocol based on the coupling of different techniques: microindentation, Scanning Electron Microscopy (SEM), Electron BackScatter Diffraction (EBSD) and Energy-Dispersive X-ray Spectroscopy (EDX). The present work will show the characterisation of the microstructural evolution from the fusion zone to the base metal, allowing the identification of the gradients in the heat affected zone. Some expected results include the observation of the highest microhardness values in the fusion zone, which are explained by the presence of a full martensitic microstructure. Furthermore, this work is interested in the use of EDX analyses for identification of potential chemical segregations, coupled with the EBSD data concerning the misorientation between adjacent grains. Thereby, if segregation occurs, this interaction of techniques makes it possible to distinguish whether they take place rather in joints with low or high misorientation. This study will help the understanding and optimisation of the welding process.

Keywords: Laser Welding, Advanced High Strength Steels, Microstructural Characterisation, Gradients of properties.