Abstract: Combining the advantages of titanium alloys, such as high strength, corrosion resistance, and lightweight properties, with those of aluminum alloys, including low density, excellent plasticity, and low cost, the preparation of titanium/aluminum composite shells was considered to have broad application prospects in aerospace, underwater equipment, and other fields. This study fabricated a titanium/aluminum composite shells with a three-dimensional mechanically interlocking interface by pre-machining threaded grooves on the inner surface of the outer titanium alloy shell and employing internal spinning forming. The forming performance, microstructure, and mechanical properties of the composite shell were investigated using ABAQUS numerical simulation combined with experimental methods. The results indicate that during the internal spinning process, the outer TA2 shell does not undergo plastic deformation and instead serves as a supporting structure, while plastic deformation occurs on the inner 5A06 tube. Under the spinning load, the aluminum alloy flows into the threaded grooves. The reduction rate is selected in the range of 15-30%, when the reduction rate reaches 30%, excessive plastic strain occurs on the inner surface of the 5A06 tube, resulting in severe material accumulation and leading to spinning failure. As the reduction rate increases, equivalent plastic strain and threaded groove fill rate of 5A06 tube increase with it. After spin forming, the grain size of the 5A06 tube becomes finer and the grain distribution more uniform along the radial direction from the outer layer to the inner layer. The hardness of the 5A06 tube gradually increases along the radial direction from the outer layer to the inner layer, with the hardness of the inner surface increasing by 11.8% compared to the base material. The ultimate tensile strength and yield strength are enhanced by 15.5% and 19.3%, respectively, relative to the base material.