This work focused on the effects of laser energy density on the relative density, microstructure, and microhardness of Inconel 718 alloy manufactured by selective laser melting (SLM). The microstructural architectures, element segregation behavior in the interdendritic region and the evolution of laves phases of the as-SLMed IN718 samples were analyzed by optical metallography (OM), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and electron probe microanalysis (EPMA). The results show that with an increase in the laser volume energy density, the relative density and the microhardness firstly increased and then decreased slightly. It also facilitates the precipitation of Laves phase. The variation of mechanical properties of the alloy can be related to the densification degree, microstructure uniformity, and precipitation phase content of Inconel 718 alloy.

The effects of the Cu content on the microstructure and strengthening mechanisms of the Al-Mg-Si-xCu alloys were systematically investigated using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), transmission electron microscopy (TEM), and mechanical tensile tests. The results show that, the strengthening mechanisms change with the Cu content. For as-quenched alloys, solution strengthening (σ_SS) is predominant when the Cu content ≥2.5 wt.%, and of equivalent importance as grain size strengthening (σ_H-P) when the Cu content ≤1.0 wt.%. With respect to peak-aged alloys, precipitation strengthening (σ_ppt) is predominant when the Cu content ≥2.5 wt.%, but σ_SS becomes predominant when the Cu content is 4.5 wt.%. As the Cu content increases from 0.5 to 4.5 wt.%, the main type of precipitates in alloy tends to change from a β″ phase to Q′ phase, and then to a θ′ phase. Among the three types of precipitates, θ′-precipitate causes the largest increase in yield strength (σ_0.2) and the largest decrease rate in elongation. β″-precipitate leads to the smallest increase in σ_0.2 and the smallest decrease rate in elongation. The increase of Cu content reduces Si solubility in the Al matrix and thus decreases the nucleation rate of β″ phase during subsequent aging.