<p>Cu–Ni–Al ternary alloys are typical coherent precipitation-strengthened systems, whose mechanical properties are strongly influenced by the morphology, size and volume fraction of the L1₂-γ′ phase. This study focused on the effects of various heat treatment processes on its microstructure and mechanical properties, as well as thoroughly analyzing the tensile deformation mechanism. The results show that both aging routes produce the γ matrix and coherent L1₂-γ′ precipitates, but with distinct microstructural characteristics. After low-temperature aging, the L1₂-γ' phase exhibits smaller dimensions and displays spherical or lamellar-like morphologies, accompanied by a high density of annealing twins. In the high-temperature aged alloy, it exhibits increased size and is predominantly cubic in shape. With increasing Cu content, the number of annealing twins and the volume fraction of lamellar-like L1₂-γ′ phases decrease under low-temperature aging, while under high-temperature aging, the precipitate morphology shifts gradually from cubic to spherical alongside reduced precipitation content. The cubic L1₂-γ′ phase provides stronger precipitation strengthening, exhibits a pronounced Bauschinger effect and markedly hinders dislocation motion, leading to the formation of anti-phase domain boundaries and accumulation of edge dislocations upon shearing. Conversely, the spherical or lamellar-like L1₂-γ′ phases contribute less to strength but enhance ductility, with deformed microstructures revealing planar dislocation slip and visible slip traces. Furthermore, serrated grain boundaries from discontinuous precipitation in high-temperature aged alloys intensify local stress concentration, facilitating crack initiation and propagation. These findings provide guidance for tailoring mechanical performance of coherent precipitation-strengthened Cu–Ni–Al alloys through controlled aging and composition design.</p>