Investigation on the effect of tool pin profile on the joint quality of Friction Stir Welded aerospace grade Aluminium Alloy

Abstract

Abstract Present paper explores the effect of the various tool pin profiles viz. cylindrical, threaded cylindrical, threaded cam and threaded triflute on the joint quality of Friction stir welded aerospace grade aluminium alloy (AA7475). 2.5 mm thick plates of AA7475-T761 are welded using Friction stir welding (FSW) and subsequently, the welds are characterized using optical microscopy (OM) and mechanical testing. Microstructural examinations reveal that the tools with threaded cylindrical, threaded cam, and threaded triflute pin profile lead to the formation of tunneling defect and joint line remnant (JLR) in the welds probably due to imbalance in material movement caused by insufficient plunge and sticking of base material around and on the bottom of the pin. Further, it is also found that cylindrical pin profile results in the maximum tensile strength (291.8 MPa) and threaded cam pin profile gives minimum tensile strength (247.5 MPa). Low tensile strength is observed due to sticking of 0.1 mm thick layer of aluminium on the bottom of the pin leading to reduction in the active plunge causing defects formation and deteriorating the joint quality.