Influences of welding parameters on axial force and deformations of micro pinless friction stir welding

Abstract

0.5-mm-thick 7075-T6 aluminum alloy sheets were butt joined successfully by high-speed micro friction stir welding (μFSW) as well as conventional μFSW using a pinless tool. The influences of welding parameters on the axial force, residual stresses, and deformations were studied through experiments. Good surface morphology and defect-free joints were obtained by high-speed μFSW as well as conventional μFSW in a fixed rotational speed/welding speed of 6.67 rad/mm. The axial force during μFSW increased with the increment in welding speed and decreased with the increment in rotational speed. When the ratio of rotational speed/welding speed was 6.67 rad/mm, compared with conventional μFSW (2000/300), the lower axial force of 1460 N was obtained by using high-speed μFSW (10,000/1500). Longitudinal tensile residual stress and transverse compressive residual stress occurred around the weld zone for all μFSW joints. The residual stresses of joint fabricated by a parameter of 10,000/1500 were slightly less than that fabricated by 2000/300. Both longitudinal maximum bending deformation Zmax and transverse angular deformation α increased with the increment in rotational speed and decreased with the increment in welding speed. As a comparison to 2000/300, the welded sheet with a parameter of 10,000/1500 exhibited slightly lower Zmax and α.