Mechanical and Microstructural Investigation on AZ91B Mg Alloys with Tool Tilt Variation by Friction Stir Welding

Abstract

By modifying the angle of tilt of 2 distinct tool pin shapes, both tapered with and without threaded structures, TPT tool pin with threads and TPNT tool pin with no threads, the mechanical behaviour and microstructural attributes were examined for the joints of AZ91B alloy formed by friction stir welding. Spindle torque and unique forces operating laterally and axially (referred to as Y-force and X-force, respectively) were created at the junction of the tool and plate, which were monitored and assessed in order to know the influence of degrees of tilt. When the tool’s angle of tilt advances, torque and forces of the spindle also show an increasing trend that is important to friction stir welding. The spindle torque and Y-force produced by the TPT tool are higher than those of the TPNT tool, whereas the X-force associated with the TPT tool is less. Discrepancies in forces grow along the concurrent increase in the angle of tilt for the TPNT as well as TPT tools, exhibiting opposite behaviour. The onion ring-type structure was visualized in the threaded tool pin structure TPT due to the high flow of plasticized metal compared to TPNT tool joints, for which the onion ring shape is not visible. With the TPT tool, the joint made at a 0° angle of tilt had a peak tensile strength of 232 MPa.