Influence of tool pin profiles on the mechanical and microstructural properties of a single-pass friction stir-welded AA7075-T6 aluminium alloy

Abstract

ABSTRACT This research explores the influence of distinct tool-pin geometries on the mechanical and microstructural characteristics of single-pass friction stir-welded (SP-FSW) joints in 6 mm-thick Al-alloy (AA7075-T6) plates. The study involves three distinctive tool pin profiles: a cylindrical tool pin (M1), a square tool-pin (M2), and a conical tool-pin (M3), all featuring a scrolled shoulder, which was utilised to create the welded joints, ensuring that fully penetrated and defect-free welds were achieved by maintaining a constant tool rotation speed of 800 rev/min and a travel speed of 50 mm/min. Notably, the average grain size within the stir zone (SZ) of the M2 joint was smaller than the M1 and M3 joints. Furthermore, the microhardness of the M2 joint exhibited higher values in the thermo-mechanically affected zoneand SZ in contrast to the M1 and M3 welded joints. Additionally, the results of the tensile tests revealed joint efficiencies of 46.2%, 60.5%, and 51.1% for the M1, M2, and M3 joints, respectively. The ductility of M1, M2, and M3 welded joints was 8.68%, 11.3%, and 11.9%, respectively. The fractured tensile sample was characterised by SEM and micro-cracks and large dimples with brittle fractures were observed in all M1, M2, and M3 welded joints.