Improving interface morphology and shear failure load of friction stir lap welding by changing material concentrated zone location

The morphology of lap interface is the key factor to affect the tensile properties of friction stir lap welding (FSLW) joint. Choosing the pin length as research object, effects of material concentrated zone (MCZ) location on interface morphology and shear failure load of FSLW joint were mainly investigated. Based on 2024-T4 aluminum alloy with 3 mm thickness, four tools were discussed, whose pin lengths are respectively 2, 3, 4, and 5 mm. Material flow models of four different tools are established to explain how MCZ locations over, on, and below lap interfaces influence the formation of hook and cold lap morphology. For both configurations A and B of FSLW joint, lap shear failure load curves changing with pin length exhibit a “N” shape under the special rotating speed varying from 850 to 1000 rpm. The highest lap shear load of 25,665.34 N is attained under the pin length of 3 mm and the rotating speed of 850 rpm. The typical shear and tensile fracture modes are found and the fracture morphologies present ductile fracture.