AbstractThis study focuses on the bonding interface characteristics and mechanical properties of the bobbin tool friction stir welded dissimilar AA6056 and AA2219 aluminum alloy joints using different welding speeds. Voids arise solely in the stir zone at the AA2219 side. A distinct boundary with limited material mixing develops at the middle section of the bonding interface, while excellent material mixing with an irregularly jagged pattern forms at the top and bottom sections of the bonding interface. Increasing the welding speed, the material mixing is rarely changed at the middle section in comparison with the bottom section. Furthermore, a small difference between Guinier–Preston dissolution and Q phase precipitation leads to rare change of hardness in the heat affected zone (HAZ) at the AA6056 side. The increased hardness of the HAZ at the AA2219 side is attributed to avoidance of the dissolution of θ″ phase precipitates. A maximum tensile strength of 181 MPa is obtained at 300 mm min−1. Fractures occur at the AA6056 side near the top and bottom surfaces and at the bonding interface in the middle section of the joints. The regions close to the top and bottom surfaces of the joints show a better ductility.