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Extreme High-Speed Laser Metal Deposition (EHLMD) is an efficient additive manufacturing technology that can quickly form difficult-to-machine materials. However, the rapid melting and solidification of EHLMD has the characteristic of forming a metastable microstructure. This study examines the effect of different aging temperatures on the microstructure and properties of EHLMD K648 superalloy. It is found that the formation of long needle-like α-Cr phase and γ' phase at lower aging temperatures (750 °C and 800 °C) is more beneficial for improving the strength of EHLMD K648 superalloy. The tensile strength was highest at 750 °C (1236 MPa) but its elongation was low (9.4 %). As the aging temperature increased (850–900 °C), the α-Cr phase transformed into rods and small particles, resulting in a decrease in tensile strength and an increase in elongation. At 900 °C, the tensile strength was 918 MPa and the elongation was 21.0 %. With further increase in aging temperature (>900 °C), coarse carbide and α-Cr phase precipitated in EHLMD K648 superalloy, causing its tensile strength and elongation to decrease. When the aging temperature reached 1000 °C, the tensile strength and elongation decreased to 790 MPa and 13.3 %, respectively. • The microstructure and mechanical properties of EHLMD K648 superalloy were investigated by different aging temperature. • The α-Cr phase evolves from long needle-like to rod-like and coarse particles with increase of aging temperature. • As the aging temperature increases, the tensile strength gradually decreases. [ABSTRACT FROM AUTHOR]