Metallurgical and Mechanical Characterization of High-Speed Friction Stir Welded AA 6082-T6 Aluminum Alloy

Anton Naumov; Iuliia Morozova; Evgenii Rylkov; Aleksei Obrosov; Fedor Isupov; Vesselin Michailov; Andrey Rudskoy

doi:10.3390/ma12244211

Metallurgical and Mechanical Characterization of High-Speed Friction Stir Welded AA 6082-T6 Aluminum Alloy

Materials (Basel). 2019 Dec 14;12(24):4211. doi: 10.3390/ma12244211.

Authors

Anton Naumov¹, Iuliia Morozova², Evgenii Rylkov¹, Aleksei Obrosov³, Fedor Isupov¹, Vesselin Michailov², Andrey Rudskoy¹

Affiliations

¹ Peter the Great St. Petersburg Polytechnic University, 195251 St. Petersburg, Russian.
² Department of Joining and Welding Technologies, Brandenburg University of Technology Cottbus-Senftenberg, 03046 Cottbus, Germany.
³ Department of Metallurgy and Materials Technology, Brandenburg University of Technology Cottbus-Senftenberg, 03046 Cottbus, Germany.

Abstract

The objective of this study was to investigate the effect of the high welding speed on the mechanical properties and their relations to microstructural characteristics of butt friction stir welded joints with the use of 6082-T6 aluminum alloy. The aluminum sheets of 2.0 mm thick were friction stir welded at low (conventional FSW) and high welding speeds (HSFSW) of 200 and 2500 mm/min, respectively. The grain size in the nugget zone (NZ) was decreased; the width of the softened region was narrowed down as well as the lowest microhardness value located in the heat-affected zone (HAZ) was enhanced by HSFSW. The increasing welding speed resulted in the higher ultimate tensile strength and lower elongation, but it had a slight influence on the yield strength. The differences in mechanical properties were explained by analysis of microstructural changes and tensile fracture surfaces of the welded joints, supported by the results of the numerical simulation of the temperature distribution and material flow. The fracture of the conventional FSW joint occurred in the HAZ, the weakest weld region, while all HSFSW joints raptured in the NZ. This demonstrated that both structural characteristics and microhardness distribution influenced the actual fracture locations.

Keywords: FEM; aluminum alloy; fracture behavior; high-speed friction stir welding (HSFSW); mechanical properties; microstructural characteristics; remnant oxide line (ROL).