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In this paper,a high strength Al-4.82Mg-0.75Sc-0.49Mn-0.28Zr (Al–Mg-Sc-Mn) alloy was prepared by selective laser melting (SLM). The effects of laser power on microstructures, relative density, and mechanical properties of SLM-fabricated Al–Mg-Sc-Mn alloy were studied. The results shown that the bimodal structure with an ultra-equiaxed grain and columnar crystal is formed in Slammed-fabricated Al–Mg-Sc-Mn alloy. The columnar crystal is surrounded by ultra-fine equiaxed crystal, and the columnar crystal shows (001) preferred orientation, the ultra-fine equiaxed structure shows no anisotropy in SLM-fabricated alloy. With increase of laser power, the molten pool size increases during SLM process, and the samples relative density and hardness decrease as laser power increase. The relative density of SLM-fabricated Al–Mg-Sc-Mn alloy is 99.74% under the process parameters of laser power 310W and scanning speed 1200 mm/s, and the hardness of alloy is as high as 107.73 ± 1.27 HV. The tensile strength of SLM-fabricated Al–Mg-Sc-Mn alloy samples are all higher than 400 MPa, and elongations are more than 19%. The fracture morphology of SLM-fabricated Al–Mg-Sc-Mn alloy is a typical ductile fracture feature, which shows a high comprehensive mechanical property. Supersaturated solid solution is formed in Al–Mg-Sc-Mn alloy because of rapid cooling during SLM process, resulting in grain refinement and improvement of mechanical properties. Fine-grain strengthening and second phase strengthening are the main reasons for the improvement of mechanical properties of SLM-fabricated Al–Mg-Sc-Mn alloy.

A TiB2/AlMgScZr composite was fabricated by selective laser melting (SLM) with direct powder mixing. The microstructure and mechanical properties of SLM-fabricated TiB2/AlMgScZr composites were investigated. Nearly fully dense and crack-free SLM-fabricated TiB2/AlMgScZr parts were obtained. The results showed that TiB2 formed a coherent relationship with the matrix and was swallowed by the solid–liquid interface as a nucleation point to refine grains during the SLM process. In addition, some TiB2 particles did not form a coherent relationship with the matrix, moving the solid–liquid interface at the grain boundary, which reduced the recrystallization fraction and refined the grains significantly. TiB2 also promoted the precipitation of Al3Sc and Al3Zr phases and increased the volume fraction of the Al3Sc and Al3Zr phases during the SLM process. The SLM-fabricated TiB2/AlMgScZr composites showed a very high ultimate tensile strength of ∼483 MPa and excellent ductility of ∼15.8%, which are higher than those of wrought Al alloys. The solid solubility of the Mg element slightly increased in the SLM-fabricated TiB2/AlMgScZr composites because of the high heating and cooling rate during the SLM process. The high heating and cooling rate caused discontinuous strain and Portevin–Le Chatelier effect and weakened the strengthening effect of TiB2 in SLM-fabricated TiB2/AlMgSc composites.