Microstructural evolution and the effect of electron beam melting on the fatigue characteristics of 7075 Al alloy deposited by MIG arc additively manufacturing

The current investigation was carried out to study the microstructural and mechanical characteristics of the AA7075 fabricated part by MIG arc additive manufacturing. It was observed that primary columnar grains and fine secondary phases form along the grain boundaries to generate the solidification structures. Grain refining and particle uniform distribution were discovered to be responsible for the increased mechanical characteristics. The porosity of the samples was found to be less than 2%. The microhardness of the samples was found to increase with layer depth in the fabricated part. Comparatively, the average fatigue strength of the bottom region samples increases by 16% compared with the other samples. The marginal increase in fatigue strength is mainly caused by the formation of strengthening mechanisms due to the lower temperature gradient. The fatigue fracture propagation behavior of fabricated parts was primarily influenced by dented plastic zones and stress concentrations produced by impact-induced geometric changes. The reduced life of the fabricated part close to the middle region was primarily due to tensile residual stress, leading to early fatigue crack initiation. The fatigue performance of the fabricated part near the bottom region is attributed to the increase in surface hardness and beneficial compressive residual stresses. Electron beam melted fatigue tested samples sustained a greater number of cycles due to the refinement of fine to coarse precipitates, with crack initiation from the surface and crack propagation occurring with fatigue striations.