Effect of Sn Content on the Microstructure and Properties of Wire and Arc Additive Manufactured Al-Cu Alloy Deposits

Al-Cu-Sn alloy deposits with different Sn contents were prepared by the wire and arc additive manufacturing process. The microstructure and mechanical properties of the deposits were examined by metallography, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and tensile tests. The results indicated that the addition of Sn significantly refined the microstructure of the deposits in their as-deposited state, and the grains were transformed from dendrites to equiaxed crystals with a uniform grain size of ∼30 μm. For the deposits with Sn ≥0.15%, the continuous and elongated θ phase on the grain boundary became block-shaped, and the size of the precipitated phase increased. After T6 heat treatment, the θ phase completely dissolved in the substrate in the deposits with Sn ≤0.1%, whereas the θ-phase solid dissolution was incomplete in the deposits with Sn ≥0.15%; the higher the Sn content, the greater the amount of θ phase remaining. After the T6 treatment, the deposits with an Sn content of 0.25% exhibited cracks distributed along the grain boundaries. The addition of Sn significantly increased the density of the θ' phase, which was diffused and uniform in size; with an increase in the Sn content, the distribution density of the θ' phase in the deposits first increased and then decreased as the peak-aging condition was reached. The addition of Sn could effectively improve the mechanical properties of the deposits, which first increased and then decreased with an increase in the Sn content. The mechanical properties of the deposits were optimal at an Sn content of 0.1%, with a tensile strength of 493 MPa, yield strength of 434 MPa, and elongation of 9.5%.