Similar and dissimilar friction stir welding and characterization of aluminium alloys AA2024 T6 and AA5083 H321

Abstract

The conventional fusion welding of aluminium and its alloys is a great challenge for designers and technologists. The difficulties associated with A1 welding are mainly du to its high thermal conductivity, high coefficient of thermal expansion, solidification shrinkage and above all high solubility of hydrogen and other gases in molten state. The problems identified with conventional fusion welding of A1 alloys which call for the attention of this research. The 2xxx (Al-Cu alloy) series aluminium alloy AA2024-T6 is extensively used in the aircraft industry for applications such as fuselage skins, fuselage frames, and wings. Dissimilar welding of A1 alloys AA2024-T6 and AA5083-H321 has wide range of applications in the fabrication of aircraft structures and other structural applications. Fusion welding processes are not suitable for dissimilar welding of these A1 alloys, because they are not metallurgical compatible and have poor weldability. To address the above problems, systematic investigations were carried out having the objectives of the research to design and fabricate different FS welding tools, to explore operating range of process parameters for defect free weld, and to develop regression models to predict the mechanical properties of similar dissimilar FS welded joints. FS welding tools with five different pin profiles were designed and fabricated. They were viz. tapered Cylinder with Grooves (CG), Tapered Square (TS), Tapered Hexagon (TH), Paddle Shape (PS), and Straight Cylinder (SC). Using these five different tools, trial experiments were conducted to find the feasible limits of the process prarameters for the dissimilar FS welding of A1 alloys AA2024-T6 and AA5083-H321. The SEM fractrograph indicated that the FS welded specimens were fractured by ductile fracture mechanism. Optical photomicrograph at the WN of dissimilar FS weldment showed the good mechanical bonding between the base metals of A1 alloys AA2024-T6 and AA5083-H321 with FS welding tool having tapered hexagon tool pin profile.