In this work, interlayers with different thickness were used to weld A6061 aluminum alloy and SUS 821L1 duplex stainless steel. The results indicated that the interlayer thickness had a significant effect on the welding. The influence of the air shock wave between the plates on the welding results was examined. The fluid-Solid coupling finite element method was used to simulate the movement of the interlayer under the action of the air shock wave. The smoothed particle hydrodynamics method was used to simulate the oblique impact process of the plates, and the unwelded samples were analyzed using the simulation results. In the analysis of weldability window, the influence of the interlayer on the upper and lower limits was examined.