For the welding process of thick-walled structural components in liquid rocket engines, the activated-flux TIG method can effectively address issues such as the formation of intermetallic phases in the weld seams, thereby enhancing mechanical performance. The present study investigates the activated-flux TIG welding technique on 10mm thick 1Cr21Ni5Ti duplex stainless steel plates. Various activated-flux, including -SiO₂, TiO₂, V₂O₅, NiO, MnO₂, CaO, AlCl₃, CaF₂, B₂O₃ Cr₂O₃, and Al₂O₃, were examined to understand their impact on the weld-bead geometry. The aim was to determine the optimal activator ratio for the effective welding of 1Cr21Ni5Ti duplex stainless steel. The weld-shift experiment confirmed that the deep penetration observed in flux-assisted welding is attributed to Marangoni convection in the molten pool. Comprehensive evaluations and analyses were performed on the microstructure and mechanical properties of the normal welded joint and the A-TIG welded joint. Finally, the study delves into a discussion on the factors influencing changes in the weld penetration, microstructure, and mechanical properties of the weld.

As a highly effective welding method, PPCA-TIG (Powder Pool Coupled Activating Flux–Tungsten Inert Gas) welding aims to achieve automated activation of TIG welding through the use of suitable activating fluxes. However, due to the unique transitional behavior of activating elements, the mechanism of PPCA-TIG is a little bit different from common activating TIG welding. In this research, a two-dimensional model is established to investigate the effect of four activating fluxes (TiO₂, SiO₂, MnO₂, CaF₂) on arc morphology and force. A series of welding experiments is performed to study the impact of the different activating elements on the molten pool. The results show that the increase in the penetration of TiO₂ is related to the high arc temperature and great arc force and electromagnetic force in the molten pool. The problem of the softening of 3003 aluminum alloy welded joints is solved. Other activating fluxes are less effective than TiO₂. The addition of calcium fluoride significantly affects penetration. The use of TiO₂, SiO₂ and MnO₂ changes the molten pool viscosity and affects the molten pool oscillation, thus affecting the weld quality.

In the Gas Pool Coupled Activating TIG (GPCA-TIG) welding, double shielding gases are employed to dramatically enhance the weld penetration, the inner inert gas to protect tungsten electrode and molten pool metal and the outer active gas to introduce activating element oxygen. In order to examine the effects of V-groove on the arc characteristics of GPCA-TIG welding in different groove angles and welding currents, probe method, static hole method and thermocouple method were used to obtain the distributions of current density, arc pressure and temperature on the arc anode, respectively. The experimental results indicate that, in the process of groove welding, the peak current density is on both side surfaces of the groove when the groove angle is 90, while the peak of 120° groove is just below the electrode. The maximum arc pressure is located just below the electrode no matter what angle and welding current are. The temperature distribution in groove welding is similar to the current density distribution. The peak temperature is on the side surface in 90° groove, and just beneath the electrode in 120° groove. Besides, all the current density, arc pressure and temperature distribution present different dependence on arc current for different groove angles. The weakened deep weld penetration compared to that without groove results from the change of arc characteristics in the grooved GPCA-TIG welding.