An experimental method for choosing the tool pin profile and shoulder size to join dissimilar aluminum alloys AA7075-T651 and AA6061-T6 joints

Many military and light weight aircraft designs call for joints between two different grades of aluminium alloy. This present study looked at the effect of tool shoulder diameter and tool pin profile on the tensile strength properties of dissimilar aluminium alloy AA6061-T6 and AA7075-T651 joints created by friction stir welding. The joints were fabricated utilizing three distinct tool shoulder diameters 15 mm, 20 mm and 25 mm along with two distinct tool pin profiles namely taper and square. The microstructure and microhardness of weld stir zone (WSZ) were examined and linked with the strength parameters of the joints. Adequate frictional heat generation from 20 mm shoulder diameter and pulsating stirring action of square pin revealed the formation of very fine grains in the weld nugget zone (WNZ). Due to enhanced material flow and the production of a defect-free stir zone, the joint created using a tool with a 20 mm shoulder diameter and square pin profile had the maximum hardness of 117 HV and the highest tensile strength of 284 MPa. The ductile mechanism of fracture is revealed by the presence of fine dimples accumulating in the tensile fractured surface of the joint fabricated by 20 mm tool shoulder diameter and square pin.