Effect of Zr Content on Microstructure, Texture and Mechanical Properties of Friction Stir-Welded Aluminum Alloy Joints

Optical microscopy, scanning electron microscopy, XRD diffraction analysis and tensile testing were employed to investigate the effects of varying Zr content on the microstructure, texture and mechanical properties of aluminum alloy friction stir-welded joints. The results indicate that the addition of Zr significantly refines the grain size of the base material. Concurrently, the nugget zone undergoes continuous dynamic recrystallization and geometric dynamic recrystallization, forming fine recrystallized grains. As Zr content increases, the grain size in the nugget zone slightly decreases, and the proportion of large-angle grain boundaries increases. The texture types in different joint areas vary significantly; recrystallized textures form in both the base metal and the heat-affected zone, while \(A/\overline{A}\) and C shear textures develop in the nugget zone. The advancing-side thermo-mechanically affected zone exhibits S, brass and A textures, whereas the receding-side thermo-mechanically affected zone shows \(A/\overline{A}\) and R-Cube textures. The hardness distributions in joints with different Zr contents were all "W" shaped, and the hardness values were lowest in the heat-affected zone. The addition of Zr was able to improve the performance of the joints, in which the tensile strength and elongation of the joints were 221 MPa and 14.3%, respectively, at a Zr content of 0.7%.