Dynamic recrystallization mechanisms on spot welding of 6008 Aluminium alloy to steel by Friction Stir Welding

摘要

At the prospect of a lightening of the automobile structures, welded spots have been realized on a stacking of two sheets (a 6008 aluminium alloy on steel) by Friction Stir Welding (FSW). Different process parameters have been tested but only the influence of the dwell time will be described in the present paper. The dwell time corresponds to the time during which the probe stays in rotation at its bottom location before extracting. A study of the microstructures and the crystallographic textures associated to mechanical tests (shear and tensile tests) allowed to determine the best set of welding parameters. The recrystallized area around the welding spot has been characterized by Electron BackScattered Diffraction (EBSD). The aim of the present work is to identify the recrystallization mechanisms which occur during welding, and to understand the influence of the dwell time on the recrystallized area. A mechanism of continuous dynamic recrystallization has been identified since misorientation of sub-boundary increases close to the weld and this for all the dwell times tested. Elsewhere, it has been found that the increase of the dwell time induces a larger recrystallized zone.