To improve the surface quality of Ti6Al4V parts formed by selective laser melting (SLM), this paper systematically studies the effects of laser power, scanning speed and inclination angle on the different surface morphology and roughness of parts. On this basis, the effect of surface remelting and multi-layer profile scanning process strategies on improving the surface quality of parts is explored. The upper surface roughness varies parabolically with increasing line energy density, the line energy density value that minimizes the upper surface roughness is around 0.22 J/mm, and the minimum Ra value is 4.41 μm. The roughness of upper and lower sides increases significantly with the increase in scanning speed. As the inclination angle increases, the roughness of the upper and lower sides gradually decreases, which is caused by the combined influence of powder adhesion and step effect. The surface remelting process strategy can reduce the upper surface roughness by 35.68% and reduce its Ra value to 2.65 μm. The multi-layer profile scanning process strategy can reduce the upper side and vertical side roughness by more than 50%, down to Ra 5.10 μm and Ra 4.61 μm, respectively.
Due to the high reflectivity of Ag to infrared lasers, there is little research focused on the manufacturing of Ag and Ag alloys by selective laser melting (SLM) technique. In this paper, the manufacturing characteristics, microstructure, and thermal conductivity of SLMed Ag, 925Ag, and their heat-treated parts were studied. With the suitable processing parameters, Ag and 925Ag samples with relative densities of 91.06% and 96.56%, respectively, were obtained. Due to the existence of non-molten particles inside the samples and local high energy density of the laser during the processing, a large number of irregular pores and micropores were formed in the microstructures. XRD analysis shows that no phase transition occurred in the annealed Ag and solution-treated 925Ag parts, as compared to their as-built conditions. The SLMed Ag exhibited fine equiaxed grains, while both columnar grains and elongated lath grains existed in the SLMed 925Ag parts. The annealed Ag and solution-treated 925Ag exhibited large equiaxed grains. Due to the grain growth that occurred in the microstructure, the thermal conductivity of Ag increased by 11.35% after completing the annealing treatment. However, that of 925Ag decreased by 17.14% after completing the solid solution treatment, due to the precipitation of the strengthening phase at grain boundaries. A comparison of the thermal conductivities of Ag and 925Ag shows that the influence of the materials on the obtained thermal conductivities was more pronounced than that of the porosity.
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