We fabricated Al–Cu alloys by powder metallurgy technology with high-purity Al powder, Cu powder, Si powder, and Mn as raw materials. The impact of Si doping on the microstructure and material properties of the Al–7.5Cu alloy was investigated. Subsequently, the impacts of the Mn content on the microstructure evolution and properties of the Al–7.5Cu–xSi alloy were also analyzed. Experimental data demonstrate that the Si incorporation effectively enhanced both relative density and hardness in the Al–7.5Cu alloy system. When the content of Si is 1 wt. %, the Al2Cu phase in the alloy is coarsened, the Si phase is precipitated and distributed at the grain boundaries, and the pores are reduced. However, some pores are larger. The addition of Mn leads to the formation of Al6Mn in the alloy, thereby strengthening the alloy, and the addition of Mn has a solid solution strengthening effect on the alloy. With the increase in Mn content, the alloy exhibits an enhanced relative density coupled with an increased hardness; the α phase and Al2Cu phase are refined; the Al6Mn phase content is increased; and the tensile strength exhibits an initial enhancement, followed by a gradual reduction. When the Si addition content is 1 wt. % and the Mn addition content is 8 wt. %, the alloy has the best comprehensive mechanical properties, with a hardness of 81.5 HB and tensile strength of 145.2 MPa. Further addition of Si (>1 wt. %) or Mn (>10 wt. %) leads to deformation of the sample, brittle phase aggregation, damage to the toughness of the material, and weakened material properties.