In this work, selective laser melting (SLM) technology was applied to directly realize the in situ synthesis of
medium manganese Mn–xCu (x = 30–40 wt.%) alloys based on the blended elemental powders. The effects of
heat treatment on the microstructural evolution and damping properties of the SLMed Mn–xCu alloys were
investigated. The metastable miscibility gap was studied by thermodynamic modeling and microhardness
measurement. The results showed that c-(Mn, Cu) phase with dendritic arm spacing (DAS) of 0.9–1.2 lm was
the main constituent phase in the as-SLMed alloys, which was one to two orders of magnitude finer than those
of the as-cast samples. Aging at 400–480C for the Mn–30%Cu or 430C for Mn–40%Cu alloys can induce
spinodal decomposition, martensitic transformation, and a-phase precipitation, whose direct evidence was
provided for the first time by transmission electron microscopy and 3D atom probe tomography in the work.
The miscibility gap obtained from thermodynamics calculation was basically consistent with the microhardness
results for the SLMed Mn–xCu alloys. Solution and aging (SA) treatment can improve the microstructure,
tensile and damping properties of the SLMed Mn–xCu alloys more obviously than aging treatment. A 2.3–2.8
and 4.3–4.5 times increase was produced in damping capacity in the aged SLMed and SLMed+SAed Mn–xCu
samples, respectively.