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Al-Cu alloy has broad application prospects in the field of aerospace due to its excellent performance. In this paper, deposits with different Cu contents were prepared by the wire arc additive manufacturing (WAAM) process, and the effects of Cu content on the microstructure and mechanical properties were investigated. The microstructure of Al-Cu alloy was investigated by metallography, scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), and transmission electron microscope (TEM). The results show that both the number and size of the precipitated θ phases (Al2Cu) in the as-deposited material increase with the increase of Cu content. After the T4 treatment, the solid solution amount of Cu in the matrix showed a trend of first increasing and then remaining stable. When the content of Cu was greater than 5.65%, as the Cu content increased, the number and size of the remaining θ phases both increased. In the peak ageing state, the amount of precipitated θ' phase showed a trend of increasing and then remaining stable. After the T6 treatment, the mechanical properties showed a trend of first increasing and then decreasing with the increase of the content of Cu. When the Cu content was 5.65%, the deposit achieved the best mechanical properties, and the anisotropy of the mechanical properties disappeared. The tensile strength, yield strength, and elongation reached 538 MPa, 478 MPa, and 10.5%, respectively. When the content of Cu was greater than 5.65%, the anisotropy of mechanical properties was obvious, and the fracture mode of the vertical specimen changed from ductile fracture to brittle fracture. [ABSTRACT FROM AUTHOR]