Effects of Longitudinal Alternating Magnetic Field on the Microstructure and Properties of CMT-WAAM Al-5%Mg Alloy

Abstract

The major challenges in wire arc additive manufacturing (WAAM) of aluminum alloys include improving the forming quality, reducing pore and crack defects, and optimizing the overall mechanical properties. In this study, an external longitudinal alternating magnetic field (LAMF) was applied to assist cold metal transfer (CMT) WAAM process of Al-5%Mg alloy. This study compared the effects of different LAMF intensity parameters on the electrical behavior, molten droplet transition, macroscopic forming, microstructure and mechanical properties of CMT-WAAM multi-layer thin-walled structures. Compared with the situation without the alternating magnetic field, the application of an external LAMF could cause the arc to expand and rotate, deflect droplets and stir the molten pool periodically. When the alternating magnetic field parameters were set at a current of 3A and frequency of 100Hz with magnetic field intensity of 9mT, the deposited samples achieved macroscopic forming with superior surface quality and geometric accuracy, and the internal defect rate was reduced from 0.742% to 0.168%. Also, the mean grain size of the deposited layer was reduced from 186μm to 154μm, and the average hardness was increased from 68.1HV0.2 to 91.1HV0.2 with an improvement rate of 33.7%. Moreover, the longitudinal tensile strength was increased from 249 MPa to 257 MPa, the transverse tensile strength was increased from 264 MPa to 273 MPa, and the yield strength and elongation at break were both increased. This study demonstrates theoretical guidance for enhancing the component overall performance of aluminum alloy LAMF-WAAM technology.