Effect of ultrasonic power on microstructure and mechanical properties of WAAM 4043 aluminum alloys under ultrasonic-magnetic composite field

Due to severe component deformation, susceptibility to porosity, coarse grain size, and uneven mechanical properties in wire arc additive manufacturing (WAAM) of aluminum alloys, the industrial application of this process is severely restricted. Multi-field coupling auxiliary technologies can significantly enhance defect control and mechanical properties by homogenizing the molten pool. This study proposes an ultrasonic-longitudinal alternating magnetic composite field to assist cold metal transfer wire arc additive manufacturing (CMT-WAAM) of 4043 aluminum alloy. The effects of different ultrasonic vibration powers (ultrasonic power range: 0-2000 W) on molten pool behavior, forming quality, microstructure, and mechanical properties are investigated. Results indicate that ultrasonic vibration reduces molten droplet surface tension, facilitating smoother droplet transfer, shortening the transfer cycle, and increasing deposition height and width. Simultaneously, rapid molten pool rotation induced by the ultrasonic-magnetic composite field enhances thermal convection and accelerates solidification, resulting in grain refinement and optimized mechanical properties. Compared to deposits with only magnetic field assistance, the ultrasonic-magnetic coupled specimens exhibit significantly refined microstructures and substantially enhanced mechanical properties. At an ultrasonic power of 1400 W, specimens with optimal forming quality and mechanical properties are achieved. The average deposition width increases by 4.8% and height by 4.3%. Grain size decreases from 166.9 μm to 98.2 μm (41.6% reduction). The percentage of porosity defects decreased from 0.73% to 0.56%. Transverse tensile strength reaches 166 MPa (24.8% increase), while longitudinal strength attains 158 MPa (29.5% increase). This study elucidates the mechanism through which ultrasonic-magnetic field coupled CMT-WAAM enhances forming quality and mechanical properties in 4043 aluminum alloy, proposing a novel approach for multi-field assisted fabrication of high-performance additively manufactured aluminum components.