Abstract:The microstructures and mechanical properties were systematically studied for the high-strength Al-5Mg₂Si-1.5Ni alloy fabricated by laser powder bed fusion (L-PBF). It is found that the introduction of Ni (1.5 wt.%) into an Al-5Mg₂Si alloy can significantly improve the L-PBF processibility and provide remarkable improvement in mechanical properties. The solidification range of just 85.5 K and the typical Al-Al₃Ni eutectics could be obtained in the Ni-modified Al-5Mg₂Si samples with a high relative density of 99.8% at the volumetric energy density of 107.4 J/mm³. Additionally, the refined hierarchical microstructure was mainly characterized by heterogeneous α-Al matrix grains (14.6 μm) that contain the interaction between dislocations and Al-Al₃Ni eutectics as well as Mg₂Si particles. Through synergetic effects of grain refinement, dislocation strengthening and precipitation strengthening induced by Ni addition, the L-PBFed Al-5Mg₂Si-1.5Ni alloy achieved superior mechanical properties, which included the yield strength of (425±15) MPa, the ultimate tensile strength of (541±11) MPa and the elongation of (6.2±0.2)%.

Key words: laser powder bed fusion; Al-Mg-Si alloy; microstructural evolution; mechanical properties; strengthening mechanism