MICROSTRUCTURE EVOLUTION IN FRICTION STIR WELDED ALUMINIUM ALLOYS

Friction stir welding (FSW) is a relatively new technique which was invented by The Welding Institute in the early nineties. It is a very promising method of welding aluminum alloys on a large scale. FSW is a novel solid-state joining process that is gaining popularity in the manufacturing sector and, in particular, the aerospace industry. During the FSW process the material is mixed and undergoes intense plastic deformation accompanied by a temperature increase. This results in significant microstructural evolution, including change in grain size, grain boundary character, coarsening and dissolution of precipitates and their further re-precipitation. The objective of this study was to evaluate the microstructural changes produced by friction stir welding of age-hardenable aluminum alloys from the 6xxx and 7xxx series. This research also addresses microstructure correlation with basic mechanical properties. The microstructure of the weld was examined by light and electron microscopy. The particular regions, i.e. thermomechanically affected zone, heat affected zone and unaffected base material, were studied in detail to better understand the microstructural evolution during FSW in various aluminum alloys.