Effect of Weld Zone Shape on Microstructure and Tensile Properties in Friction Stir Welding Process

This article presents the effect of weld zone shapes on microstructure and tensile properties of weld joints in friction stir welding. Experiments are conducted using four different tool pin profiles that are cylindrical, conical, cylindrical-conical and stepped-conical for analysing the weld zone shape. The weld zone shape properties are defined by characteristic length. Grain size and mode of fracture surface behavior are analysed by optical microscope and scanning microscope respectively and tensile strength is measured by universal testing machine. It is also observed that the weld zone shape of all pin profile tool is vase shape. In which, cylindrical, conical and cylindrical-conical pin profile tools produce basin dominant vase shape and stepped-conical pin profile tool produces cylinder dominant vase shape. The experimental result shows that the weld joint fabricated by stepped-conical pin profile tool produces the smallest grain, good ductile fracture mode and highest tensile properties as compared to other pin profile tool. This analysis shows that cylinder dominant vase shape produces high tensile properties and enhance ductile fracture mode in the weld joint.