EFFECT OF TOOL ROTATIONAL SPEED ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF FRICTION STIR WELDED JOINT OF ULTRAFINE-GRAINED AA 5083 ALLOY
Ultrafine-grained (UFG) materials are widely used as a structure material owing to their unique microstructure and mechanical properties. In this study, friction stir welding (FSW) was used to weld UFG AA 5083 alloy. The effect of tool rotational speed on microstructure and mechanical properties of ultrafine-grained AA 5083 alloy was investigated. Different rotational speeds of 410, 600, 865, 1140, and 1500 rpm, a fixed travel speed of 264 mm/min and tool tilt angle of 2° were used as processing parameters. Visual inspection, macroscopic and microscopic analyses, microhardness and tensile properties using camera, optical microscope, Vickers hardness tester and universal testing machine were used to assess the weld quality and strength. The heat generation and material flow during FSW welding was influenced by rotational speed. At low rotational speed, insufficient heat and material flow caused many defects and reduced the mechanical properties of welded joint. In contrast, high rotational speed caused high heat generation and excess material flow. Hence optimum heat generation is obtained at the rotational speed of 865 rpm. The smooth welded surface, defect-free weld, and finest grain within nugget zone (NZ) were obtained at 865 rpm tool rotational speed that result in high microhardness (91.78 HV) and tensile strength (145.14 MPa).