Microstructure Evolution and Properties of Friction Stir Welding Joint for 6082-T6 Aluminum Alloy

Abstract

To investigate the evolution of grain morphologies, grain boundary features, and dislocation structure in upper part of nugget zone during friction stir welding of 6082-T6 aluminum alloys, electron backscattered diffraction and transmission electron microscope techniques were employed. The results showed that the metal on retreating side of the weld zone produced thermoplastic deformation during the welding process. The substructure of the lamellar dislocation wall formed at retreating side. Motivated by the welding thermal cycle, geometric dynamic recrystallization occurred in the substructure of the lamellar grains, leading to the lamellar array of grains. Discontinuous dynamic recrystallization occurred in the lamellar grain, leading the grain to be arranged in a "necklace" form. Simultaneously, the coarse grain of base material was refined. Due to the inhomogenous distribution of stress during the welding process, the alternating presence of large grain and small grain regions on advancing side took place. During the process of welding joint tensile, the fracture results from dislocation piling-up at the Mg 2 Si interface in large grains with a (111)[110] orientation. Thus, the advancing side becomes the weakest part of the mechanical properties in the welding joint,the tensile strength of the joint was 275MPa with a break elongation of 6%.

A Study on the Implication of Modified Joint Configuration in Friction Stir Welding

“…Figure 11b also reveals that the joint efficiency of DBL1 and DBL2 is higher than that of SSB. It can be observed that similar to the microhardness as nugget grain size becomes finer the tensile properties are also increasing (Figure 8 and 9) as a finer grain size obstruct the dislocation movement due to increased grain boundary [22].…”

The Effect of Plug Rotation Speed on Micro-Structure of Nugget Zone of Friction Plug Repair Welding Joint for 6082 Aluminum Alloy

“…The grain size in the weld nugget zone decreased first and then increased when the plug rotating speed increased from 1600 to 2000 rpm, while the high-angle boundary component increased first and then decreased.  At 1600 rpm, recrystallized Cube, recrystallized R and (021) [2][3][4][5][6][7][8][9][10][11][12] deformation texture mainly were found in the nugget zone; at 1800 rpm, Goss, (111)[-101] texture, recrystallized Cube and R texture were found; at 2000 rpm, Copper, Goss, (313)[-312] texture and recrystallized Cube texture were found.  When the speed of the tapper plug increased, the deformation rate and the temperature of the welding nugget zone increased.…”

“…Table 2 shows the texture and components of the weld nugget zone at different plug rotating speeds. At 1600 rpm, recrystallized Cube, recrystallized R and (021) [2][3][4][5][6][7][8][9][10][11][12] deformation texture mainly existed in the weld nucleus; at 1800 rpm, recrystallized Cube, (111)[-101] texture, recrystallized Cube and R texture mainly existed; at 2000 rpm, recrystallized Cube and Copper, Goss and (313) [-312] texture mainly existed. Figure 8 shows the color aberration and distribution of grains corresponding to different textures.…”

“…When the equated grains were refined, the location dislocation density in the weld nugget zone was reduced. Zhang [ 9 ] analyzed the 6082 aluminum alloy FSW joint by adopting electron back scattered diffraction (EBSD) technology; results showed that there were both long strip grains and equated grains in the weld nugget zone, that there were small angle grain boundaries in some equated grains, and that the composition of small angle grain boundaries increased. In some regions, the size of the micro-structure of ultra-fine grains was about 2 µm after complete dynamic re-crystallization.…”

Evaluating The Effect of The Pin’s Length to The Strength of Double Sides Friction Stir Welded Aluminum

“…Keywords: double side friction stir welding, strain hardening, pin length Al-Cu could be obtained from the 800 RPM and 60 mm/min combination. Zhang & Wang [4] investigated the change in microstructure due to the FSW process when applied to 6082-T6 aluminum alloy. At the retreating side they observed an evolution of microstructure characterized by lamellar dislocationformation of subgrainnew recrystallized grain formation and refining of coarse grain.…”