Abstract: Friction stir welding was performed on 5 mm thick 2A12 aluminum alloy plates and 2017 aluminum alloy plates under different welding speeds (80,100,120 mm · min⁻¹) and spindle speeds (750, 1 000,1 250 r · min⁻¹), and the microstructure and mechanical properties of the joints under different process parameters were studied. The results show that the 2017 aluminum alloy/2A12 aluminum alloy friction stir welded joints had no obvious macroscopic defects under different welding speeds and spindle speeds, and all joints were composed of nugget zone, thermo-mechanically affected zone, heat affected zone and base metal. The microstructures of 2017 aluminum alloy and 2A12 aluminum alloy in the nugget zone were alternately distributed, and the grains were fine equiaxed grains. The thermo-mechanically affected zone on 2A12 aluminum alloy side (retreating side) consisted of a large number of coarse and irregular deformed grains and a small number of recrystallized grains, and the heat affected zone was composed of larger and more regular deformed grains. The grain size of 2017 aluminum alloy in the nugget zone was smaller than that of 2A12 aluminum alloy, and with the increase of welding speed or spindle speed, the grain size of both aluminum alloys increased. Under different process parameters, the section hardness of the joint presented a "W" shape distribution. The lowest hardness zone and tensile fracture location of the joint were in the heat affected zone on the side of the 2017 aluminum alloy. When the spindle speed was 750,1 250 r · min⁻¹, the tensile strength of the joint at different welding speeds was about 390,350 MPa, respectively; when the spindle speed was 1 000 r · min⁻¹, the tensile strength was greater than 390 MPa. When the spindle speed was 1 000 r · min⁻¹ and the welding speed was 100 mm · min⁻¹, the tensile strength of the joint was the highest, which was 80% that of the 2017 aluminum alloy base metal, the percentage elongation after fracture was the largest, and the fracture type of the joint was ductile fracture.