Effect of Heat Input on Microstructure and Mechanical Properties of Automated Tungsten Inert Gas-Welded Dissimilar AA6061-T6 and AA7075-T6 Joints

Abstract

This study explored the heat input effects on automated TIG welded dissimilar AA6061-T6 and AA7075-T6 joints using filler ER5356. Three heat input welded samples, namely HI1 (0.73 kJ/mm), HI2 (1.69 kJ/mm), and HI3 (2.27 kJ/mm), were utilized and their corresponding microstructure and grain boundary features were investigated and correlated with the joint’s mechanical properties. Electron backscattered diffraction (EBSD) results showed that the low-angle grain boundaries (LAGBs) in the base alloys transformed into high-angle grain boundaries (HAGBs) in the fusion zone (FZ) after welding. However, the grain boundary transformations were more pronounced in the high heat input welded sample HI3. Pole figures revealed strong dominance of ${\mathrm{A}}_{1}^{*}$/${\mathrm{A}}_{2}^{*}$ and A/$\stackrel{\mathrm{-}}{\mathrm{A}}$ textures with a small amount of C and B/$\stackrel{\mathrm{-}}{\mathrm{B}}$ textures at the FZ for all the heat input joints. Orientation distribution functions also exhibited the recrystallization textures P {011} <112> and Goss {110} <001> , plane strain texture S {123} <634> with some deformation texture H {001} <110> at the FZ center. The medium heat input sample HI2 had the highest tensile strength of 182 MPa, elongation of 14.4%, and flexural strength of 202 MPa; while, the welded sample HI1 had the highest microhardness of 81 HV when compared to other welded samples. The HI2 joint fracture surface exhibits fine dimples devoid of porosities, suggesting ductile fracture manner. However, the fracture surface of the HI3 joint displayed both smooth and rough cleavage facets with coarser dimples, resulting in a combination of ductile and brittle fracture modes.