Study On Activating TIG Welding And Mechanism Of Fluxes Increasing Weld Penetration For Aluminum Alloys

Activating welding is a new welding process with high production efficiency, high quality, low energy consume and low cost. It has broad application prospects, has attracted widespread concern. In this paper, a new type activating Tungsten Inert Gas welding process (TIG welding) for aluminum alloys is proposed by altering activating flux coating method. This new type welding process and the mechanism of activating fluxes increasing weld penetration were studied. This study has important significance for improving weld penetration and increasing production efficiency of TIG welding for aluminum alloys. Especially, the study of mechanism of activating flux increasing weld penetration has direct significance to develop flux and develop welding process, and has important theoretical significance to enhance understanding on the effects of activating flux on the welding arc and weld pool coupling system.For aluminum alloys, a new type activating welding process called FZ-TIG welding (Flux Zoned TIG welding) is proposed by altering activating flux coating method. A thin activating flux coat with low melting temperature, low boiling temperature and low current resistivity and a thin activating flux coat with high melting temperature, high boiling temperature and high current resistivity are coated on the central region and the side regions of weld surface before conventional TIG welding, respectively. For A-TIG welding and FB-TIG welding (Flux bounded TIG welding) for aluminum alloys, it is difficulty to simultaneously increase weld penetration dramatically and improve weld surface forming. Using FZ-TIG welding, this problem can be solved.Activating flux FZ108 for AC FZ-TIG welding for aluminum alloys was developed for the central region coat material using uniform design method. When AC FZ-TIG welding with SiO₂ for the side region material and FZ108 for the central region coat material is made, the weld penetration reaches 3.3 times of that of conventional AC TIG welding. All of weld shape, weld organization and weld mechanical properties are fine.A welding process called DCEN activating TIG welding is proposed, which combines activating TIG welding process with DCEN TIG welding. Using this process can remove the weld surface oxide film and increase weld penetration. The activating flux FZ109 for the central region coat for DCEN activating welding aluminum alloy was developed. When FZ109 + SiO₂ are used as activating fluxes for aluminum alloy, the weld penetration is dramatically increased to 2.7 times of that of conventional DCEN TIG welding. Both the weld forming and the weld organization are fine.SiO₂ and AF305 are the mono-component flux and multi-component flux most increasing weld penetration of AC A-TIG welding, respectively. The mechanisms of activating fluxes increasing weld penetration were studied, including SiO₂ and AF305 for AC A-TIG welding for aluminum alloys, FZ108+SiO₂ for AC FZ-TIG welding for aluminum alloys, respectively. It is proposed that the arc constriction but liquid metal flow type change due to weld pool surface tension temperature gradient is the main mechanism. The low surface tension and low viscosity of aluminum alloys are the reason that the change of surface tension temperature gradient is not the main mechanism of activating flux increasing weld penetration of activating TIG welding. For different activating fluxes and flux coating methods, there are three kinds of arc constriction mode. They are arc boot wholly constriction while arc column expands, arc boot and column both constriction, arc spot separate constriction while arc column expands. The reason is the different effects of activating fluxes on the physical process in the arc due to the different flux physical and chemical properties mainly including melting temperature, boiling temperature, current resistivity, work function, dissociation energy of the flux, ionization potential, electron affinity of the flux element, and so on.For the arc spot separate constriction when flux AF305 is used to make AC A-TIG welding for aluminum alloy, a 3-D mathematical model to describe the weld pool of AC A-TIG welding with a moving heat source is developed. The software PHOENICS is employed to perform the numerical simulation to the mechanism of the activating flux increasing weld penetration. The simulation results accord with the welding experimental results. When the arc spots are separately constricted, dramatically decreasing spot area will enhance both the outward convection and the inward convection driven by the negative surface tension temperature gradient and the Lorentz force, respectively. Due to the arc spot separate distribution, the inward convection affected regions expand obviously. The arc heat is effectively transferred to the weld pool bottom and the weld penetration is improved dramatically.