The effects of preheating temperature and the addition of alloying elements (specifically, Scandium and Zirconium) on the microstructure and defects of Al-Zn-Mg-Cu alloys during laser-directed energy deposition (LDED) are investigated. The result shows that preheating (280 °C) effectively suppressed crack formation, and 7b55-Sc alloy was successfully obtained under the following parameters: laser power of 2000 W, powder feed rate of 0.2 L/min, and scanning speed of 500 mm/min. Microstructural analysis demonstrated that the addition of Sc and Zr facilitated the formation of Al3Sc and Al3(Sc, Zr) precipitates in the matrix. The resulting average equiaxed grain sizes measured 7.64 μm in the YOZ direction and 8.43 μm in the XOZ direction. In addition, a large number of continuous eutectic structures precipitate along the grain boundaries, and the second phase precipitated within the grains mainly consists of η phase and η′ phase. Mechanical testing indicated a longitudinal tensile strength of 330.2 MPa with 3.89% elongation, and a transverse tensile strength of 325.6 MPa with 4.76% elongation. The high-quality production of LDED 7b55-Sc alloy will provide strong support for the processing and manufacturing of lightweight, high-strength components in the aerospace industry.
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