The Al-Cu alloy walls (ZL205A) produced by wire + arc additive manufacturing (WAAM) have good mechanical properties, but toxic cadmium oxide is generated during production. Therefore, to prevent the generation of cadmium oxide, we replaced the Cd in the Al-Cu alloy (ZL205A) with Sn. The microstructural and mechanical properties of the newly developed alloy with Sn and the ZL205A alloy before and after T6 heat treatment were investigated and compared by conducting metallographic, scanning electron microscopy, energy dispersive spectroscopy, transmission electron microscopy, and tensile tests. The surface of the Al-Cu-Sn alloy wall was smooth and exhibited a silver-white luster, and the burning loss rate of Sn was 5.9%. The wall of the WAAM Al-Cu-Sn alloy was fine and contained grains with a size of approximately 30 μm, which is smaller than that of the ZL205A alloy wall. The main precipitated phase was uniformly distributed among the grains or on the grain boundaries. Following T6 heat treatment, the θ phase was completely dissolved in the Al matrix, and the re-melted T phase and small co-phases of Sn and Al2Cu were uniformly distributed on the grain boundaries. The TEM results show that a large number of θ" phases were dispersed among the grains. The mechanical properties of the Al-Cu-Sn alloy after heat treatment were as follows: tensile strength – 493 MPa; yield strength – 434 MPa; elongation rate – 9.5%. The alloy shows excellent performance in WAAM process and has broad application prospects.