Comparative investigation of wire arc additive manufacturing of Al-5%Mg alloy with and without external alternating magnetic field

In order to optimize the fabrication quality, an external longitudinal alternating magnetic field is introduced into the wire arc additive manufacturing (WAAM) system of aluminum alloy in this investigation. The arc behavior, metal transfer, deposit morphology, microstructure, and mechanical properties of WAAM of Al-5%Mg alloy with and without external magnetic field (EMF) are investigated comprehensively and comparatively. Results indicate that the increase of excitation current promotes the dilatation of arc plasma to reduce the heat flux density, broadens the bead width, and decreases the bead height and penetration depth, while the increase of excitation frequency has the opposite effect on those. Furtherly, the spray transfer process which occurs at the beginning of each welding wire motion cycle can be restricted under appropriate excitation current and excitation frequency. Compared with that without EMF, the surface accuracy of thin-wall parts deposited with the EMF of excitation current 2 A and excitation frequency 70 Hz is remarkably improved, whose surface waviness is decreased by 34%. Simultaneously, the secondary phase of Al3Mg2 is distributed more uniformly, and the number and dimension of pores of deposit are greatly reduced. The microstructures in the bottom layer and top layer of deposit with EMF get furtherly refined by the electromagnetic stirring, but those in the middle layers and final tensile properties of the deposit are not obviously optimized, which are mainly caused by severe heat accumulation and repeated heating from subsequent deposition, and the nature of non-heat treatment strengthening of Al-Mg alloy.