Wetting mechanisms in the mass transfer process of CuSi3 droplets on the TC4 and 304SS multi-metal system controlled by the hybrid shielding gas atmosphere

To explore the synergistic wettability of the Ti-Cu-Fe multi-metal system, the wetting behaviors of CuSi3 droplets on the TC4 and 304SS plates during the cold metal transfer welding process in various gas atmospheres were studied in this work. The effects of Ti, Fe, Si, C, and O on the spreading dynamics of liquid Cu were analyzed in detail. The results reveal that the CO₂ + Ar hybrid gas shielding atmosphere significantly affects the interfacial mass transfer. The sufficient interfacial reaction and increased element diffusion promoted the formation of Ti₂Cu/TiCu multiphase microstructure at the Cu/Ti interface instead of a continuous Ti₂Cu layer, and a thicker and loose Fe (s, s) layer was formed at the Cu/Fe interface. The variations of surface phase composition and the generation of inward flow weakened the wettability of CuSi3/TC4 and CuSi3/304SS systems. The dissolution of Si and surface adsorption of O decreased the σ_lv of liquid Cu, whereas Ti and Fe had the opposite effect. When the shielding gas changed from pure Ar to CO₂ + Ar hybrid gas, the potential spreading model of the CuSi3/TC4 system changed from reaction-limited to diffusion-limited, and the wetting activation energy increased from 46 kJ/mol to 57 kJ/mol. Removing oxide film, forming Ti₂Cu and diffusion of Ti controlled the wetting. Whereas for the CuSi3/304SS system, the potential spreading model changed from diffusion-limited to a molecular dynamics model. Removing oxide film, diffusion of Fe and interfacial adsorption were the dominant factors for wetting.