In the aerospace industry, the additive manufacturing of aluminum alloys has encountered significant challenges owing to fusion defects. In this work, the B2O3–NaF–SiO2 fluxes are employed for the first time to improve the fusion defects and mechanical properties of butt-welded A7N01 alloy with unequal thickness under natural ageing. The finite element analysis (FEA) approach is used to account for the evolution mechanism of residual stresses. The simulated results indicate that the distribution and values of residual compressive stresses are improved, which contribute to the microhardness. After applying a coating-position optimization of the B2O3–NaF–SiO2 fluxes, the fluxes plays a role in enhancing the welding current density and increasing the concentration of oxygen elements. The melt pool morphology and the fusion defect of the thicker side are ameliorated, resulting in a considerable increase in the yield strength and the tensile strength. Therefore, this paper establishes the viability of applying B2O3–NaF–SiO2 fluxes for additive manufacturing of A7N01 aluminum alloys and provides new ideas for exploring the optimal active fluxes of other 7xxx series aluminum alloys.
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