Dissimilar modified friction stir clinching of AA2024-AA6061 aluminum alloys: Effects of materials positioning

Abstract

Modified friction stir clinching (MFSC) process was employed to joint dissimilar AA2024-T3 and AA6061-T6 Al sheets by interchanging the upper and the lower sheets during the joining process. The material flow, microstructure, tensile strength and fracture behaviors of the MFSC joints were studied. The results reveal that material positioning significantly affects the material flow behavior of the MFSC joint due to the disparity in the properties (flow stress) of the AA2024-T3 and AA6061-T6 Al alloys. The flow-induced hook path and proximity of hook tip to the geometric differential flow-induced defect (at the refilled end of the keyhole) are undesirable in the welded AA6061-T6/AA2024-T3 joint as compared to the AA2024-T3/AA6061-T6 joint. The microstructure (precipitate dispersion, dislocation density, and tangles), hardness distribution, and fracture morphology of the joints are altered by the material positioning-induced flow behavior. Improved tensile strength (97.88 MPa) is obtained in the AA2024-T3/AA6061-T6 joint as compared to the AA6061-T6/AA2024-T3 joint (86.65 MPa).