Microstructural Characteristics and Mechanical Properties of Friction Stir Welded Thick 5083 Aluminum Alloy

Joining thick sections of aluminum alloys by friction stir welding (FSW) in a single pass needs to overcome many challenges before it comes to full-scale industrial use. Important parameters controlling the structure-properties relationships both across weld cross-section and through thickness direction were investigated through mechanical testing, electron backscatter diffraction technique, transmission electron microscopy, and occurrence of serrated plastic flow. The evolution of the properties in the weld cross-section shows that the presence of undissolved and fragmented Al\(_6\)MnFe particles cause discrepancies in establishing the Hall-Petch relationship, and derive the strengthening from the Orowan strengthening mechanism. A ‘stop action’ friction stir weld has been prepared to understand the role of geometrical features of the tool probe in the development of the final microstructure after complete weld. Sectioning through the ‘stop action’ weld with the probe in situ displays the individual effect of thread and flat on the grain structure formation. The material at the thread surface experiences more severe deformation than the material at flat surface. Both the high-angle boundaries and mean grain size are found to be higher at the thread surface. The strain hardening capacity, stress serration amplitude, and frequency are observed to be higher in the stir zone than other weld regions.