A novel droplet plus arc additive manufacturing for aluminum alloy: Method, microstructure and mechanical properties

In this paper, a novel droplet + arc additive manufacturing (DAAM) has been proposed for building aluminum alloy components with high quality and high efficiency. A special droplet generation system (DGS) was designed to replace the traditional wire feeding system, making the material addition process and the arc heat input process two independent parts. During the DAAM process, the arc heat source with variable polarity is arranged tilted below the DGS, the droplets which generated from DGS drop vertically and sequentially into the molten pool, and the aluminum alloy component can be deposited layer-by-layer by moving substrate. The droplet generation process, droplet + arc deposition process, as well as the heat input strategy, microstructure and mechanical properties of the thin-wall component are discussed in detail. The experimental results show that the small and sequential droplet generation mode is beneficial to improve the continuity of deposition process and significantly reduce the harmful impact of droplets on the molten pool. Meanwhile, the DAAM process shows great inclusiveness of droplet falling deviation. A multi-layer thin-wall component and a ring-shaped structure were fabricated successfully by DAAM with the deposition rate of 140 mm3/s. The microstructure of the thin -wall component is dominated by columnar crystals and it has obvious periodic distribution along the deposi-tion direction. The tilted growth of columnar crystals results in different grain morphology in the cross section and longitudinal section. After T6 heat treatment, the average ultimate tensile strength (UTS) and elongation in the horizontal direction are 435.0 MPa and 10.4%, while the average UTS and elongation in the vertical direction are 406.5 MPa and 16.4%, respectively. The fracture morphology is dominated by ductile fracture, but it exhibits some intergranular fracture characteristic in the horizontal direction. This novel DAAM provides a new choice for additive manufacturing of aluminum alloy, and shows great potential for the simultaneous improvement of the manufacturing quality and efficiency.