Refractory high-entropy alloys（RHEAs） are widely used in the aerospace field due to their excellent high-temperature performance. This study employs multi-wire arc additive manufacturing（M-WAAM） technology to fabricate Ta_1.5Mo_1.5Nb_0.5Zr₂Ti refractory high-entropy alloy. Using equipment such as optical microscopy（OM） and high-speed cameras, the influence rules of base current, peak current, and peak time ratio on forming quality are investigated. The optimal process parameters for preparing the Ta_1.5Mo_1.5Nb_0.5Zr₂Ti alloy are determined（base current 100 A, peak current 300 A, and peak time ratio 35%）. Metallographic characterization demonstrates that the fabricated components exhibit excellent forming quality, with unmelted area ratio below 10% and porosity less than 0.5%. To address the melting point differences among various wires, hot-wire technology is employed to facilitate the melting of high-melting-point Ta/Mo wires. For the first time, we propose a“single droplet pre-alloyed transfer”mechanism, elucidating the thermodynamic process of discontinuous liquid bridge transition and subsequent formation of a unified molten droplet from four simultaneously fed wires. Based on the thermodynamic mechanism of synchronous four-wire discontinuous liquid bridge transition forming a unified molten droplet, a“single droplet pre-alloyed transfer”mode is established. Parts deposited under this droplet transfer mode demonstrate good macroscopic morphology and fewer internal defects. Through force analysis of molten droplets, we establish a mechanical model incorporating key factors including gravity, electromagnetic force, and plasma flow force, demonstrating that synchronous non-continuous liquid bridge transition of four wires constitutes a sufficient condition for the formation of a unified molten droplet. Additionally, the developed bead width prediction model provides quantitative guidance for process optimization. This work establishes an important theoretical foundation for M-WAAM of RHEAs.

Wire-arc additive manufacturing (WAMM) is an emerging manufacturing technology that employs metal wire as the raw material and arc as the heat source. It offers advantages in fabricating large and complex parts. Nevertheless, it still faces challenges, including prolonged fabrication cycles, intricate path planning, and substantial residual stress. In this study, we explore the optimization of the manufacturing path for wire-arc additive manufacturing when fabricating complex structural components, aiming to mitigate the significant residual stress and strain induced by suboptimal manufacturing paths. Finite element software is utilized to optimize the manufacturing path, and a unit body of a grid component with excellent forming quality has been successfully produced using the optimized path. Through finite element analysis, it can be revealed that for the unoptimized path, the equivalent residual stress at the thin-wall after cooling reaches 361 MPa, while that at the nodes after cooling is 666 MPa. In contrast, for the optimized path, the equivalent residual stress at the thin-wall after cooling is 206 MPa, and the equivalent residual stresses at two nodes after cooling are 260 MPa and 427 MPa, respectively. Compared to the unoptimized path, the optimized path leads to a 61% reduction in residual stress at the nodes and a 43% decrease in stress at the thin-wall. Moreover, the difference in residual stress between the nodes and the thin-wall is smaller than that of the unoptimized path, resulting in less deformation and fewer defects caused by residual stress. The grid component unit body fabricated using the optimized path exhibits well-combined melt tracks and superior forming quality, with no discernible residual stress deformation. This effectively validates the feasibility of the optimized path in controlling residual stress during the wire-arc additive manufacturing of grid components.

Here we propose to employ wire-arc directed energy deposition (WA-DED) to tune the microstructure and the mechanical property of Mg-Al-Si alloys, on the basis of its sub-rapid solidification effect. According to finite element analysis, WA-DED shows higher cooling rate than conventional casting, reaching 598.3 K/s for Mg-Al-Si alloy, and the lower heat input, the larger cooling rate of WA-DED. Significant microstructure refinement is thus achieved, with reduced grain size and Mg₂Si particle diameter. The transition from hypereutectic to fully eutectic microstructure is triggered by reducing the heat input. Compared with the as-cast alloy, WA-DED alloys demonstrate higher ultimate tensile strengths (UTS) at both room- and high-temperature (150 ℃) properties, increasing by 50.1% and 30.3%, respectively. The superior strength-ductility synergy for Mg-Al-Si alloys results from the microstructure tuning via sub-rapid solidification of WA-DED.