A study on the metallurgical characterisation of the longitudinally sampled friction stir processed TIG welded dissimilar aluminum joints

Abstract

In this work, one-pass and two-pass friction stir processing (FSP) were applied to the tungsten inert gas (TIG) weldments of AA6082-T651 and AA8011-H14 to analyse the microstructure and tensile characteristics of the weldments. The tests included macrostructure, microstructure, microhardness, tensile testing and fractography. When the one-pass and two-pass FSP were applied to the TIG weldments, the coarse grain structure (grain size 24.63 µm) was transformed into a refined grain structure (grain size 2.632 µm for second pass), thereby eradicating the defects that had been seen before FSP. The tensile strengths of the TIG + FSP passes were more significant than that of the TIG welded joints. The ultimate tensile strength of TIG welding, TIG + FSP 1-pass and TIG + FSP 2-pass were 86.86 MPa, 133.833 MPa and 135.75 MPa, respectively. The tensile strain of the TIG + FSPed joints was found to have a minimal difference from that of the TIG welded joints, with the TIG joint with a higher percentage. The joints’ microhardness post-FSP was more significant than the TIG weldment. The maximum hardness (73.84 HV) at the Nugget zone (NZ) was observed in the TIG + FSP 2-pass welded joint. The results obtained corresponded with the grain sizes of the welded joints; the TIG results displayed a coarse-grained structure, while the TIG + FSP results, regardless of the passes, showed a fine sandwich-arranged grain structure.