Influence of welding parameters and preheating temperature on abnormal grain growth after post-weld heat treatment in friction stir welding of 5083 Al alloys

摘要

The abnormal grain growth (AGG) during heat treatment in friction stir welds of aluminium alloys has been observed by several authors and some associated mechanisms have been identified. In spite of this understanding, only a few papers describe methods to limit or eliminate this AGG during heat treatment of friction stir welds in aluminium alloys. This study focuses on the influence of welding parameters and preheating temperature on AGG after heat treatment in 5083 aluminum alloys. Friction stir welding (FSW) parameters, as rotational and travel speed, have been varied in order to investigate a wide envelope of heat inputs during welding. It is shown that the extent of AGG depends strongly on the welding temperature and can be avoided with a good combination of welding and preheating parameters. However, care must be taken to avoid local melting in high heat input welds. Electron back-scattered diffraction (EBSD) was used to analyze the grain size and grain boundary orientation in samples prone or not to AGG. It was observed that the use of preheating narrowed the grain size distribution and reduced the mean misorientation of the low angle grain boundaries. This is in agreement with the explanation that AGG origins from a difference of mobility between subgrain boundaries.