Research on the Shear Forces and Fracture Behavior of Self-Riveting Friction Stir Lap Welding Joints with Medium-Thick Aluminum/Steel Plates

The self-riveting friction stir lap welding (SRFSLW) method was utilized to improve the bonding strength of lap welding joints with medium-thick aluminum/steel plates and to realize structural lightweighting. The effect of plunge depth on the shear force and the microstructure of the joint was studied, and the influence of groove structure (rectangular groove and dovetail groove) on the failure behavior of the joint under shear load was obtained, simultaneously. The EBSD results indicate that the aluminum alloy grains in the stir zone (SZ) of groove joints have been refined compared to the non-groove joint. Meanwhile, due to the presence of grooves, the proportion of high-angle grain boundaries of the SZ is increased, and more dynamic recrystallization has emerged; thus, the KAM value of the SZ is reduced to a certain extent. The non-groove joint exhibits {111}//ND fiber texture, while the groove joint shows F-plate texture. In self-riveting joints, due to the increased metallurgical bonding area and the weakened effect of external loads, the failure of metallurgical bonding in the joint requires higher external load, and the separation of the self-riveted structure from the groove requires greater bending moment, thereby improving the strength of the joint.