Microstructures and properties of wire-arc additively manufactured 5356 aluminium alloy protected by different proportions of nitrogen and argon

This study investigated the microstructures and properties of deposits protected by seven different proportions of N₂ and Ar by performing wire-arc additive manufacturing of the 5356 aluminium alloy. The results show that when the proportion of N₂ in the shielding gas was larger than and equal to 50%, flaky nitrides were generated in the deposits. With an increase in the proportion of N₂ in the shielding gas, the number and size of nitrides in the deposits as well as the fluctuation frequency and amplitude of the microhardness of the deposits all increase. The existence of flaky nitrides incurs a low ultimate tensile strength of additively manufactured parts protected by a mixed gas containing N₂. The presence of large-size flaky nitrides between layers in the deposits leads to a large difference in tensile properties in the horizontal and vertical directions of the deposit. Tensile fracture shows that the deposits were fractured in the mixed mode of ductile and brittle fracture.