Microstructure of the T4 heat-treated WAAM Al-Cu alloy with different contents of Cu: (a) is the microstructure of the accumulated body with 5.0% Cu content under T4 heat treatment, the grain size is 40–50 μm, and no large size precipitated phase is found at the grain boundary; (b) is the microstructure of the accumulated body with 5.65% Cu content under T4 heat treatment, the grain size is 40–50 μm, and no large size precipitated phase is found at the grain boundary; (c) is the microstructure of the accumulated body with 6.3% Cu content under T4 heat treatment, the grain size is 40–50 μm, and large size precipitated phase is found at the grain boundary (C1).