Abstract: 7075-T6 aluminum alloy and galvanized DP590 steel are friction stir lap welded. Combining with the numerical simulation results of temperature field and material flow during welding, the effects of intermetallic compound (IMC) thickness and hook structure on the mechanical properties of the joint are studied. The results show that when the thickness of IMC is large, the microcracks are easy to initiate and expand at the IMC layer, which reduces the joint metallurgical bond strength. As the IMC thickness increasing from 0.8 μm to 4.3 μm, the joint strength decreases by 17.8%. The width difference between the upper and lower ends of the higher hook structure is larger. Under the tensile shear load, the hook structure is unevenly stressed. The weak part is prone to stress concentration and fracture, which reduces the mechanical bond strength of the joint. As the height of the hook structure increases, the strength of the joint gradually decreases.

Key words: friction stir welding, hook structure, intermetallic compound thickness, mechanical properties