( 1． College of Material Science and Engineering，Liaoning Technical University，Fuxin 123000，China; 2． Liaoning Institute of Science and Technology，Benxi 117300，China; 3． College of Engineering，Yantai Nanshan University，Longkou 265713，China)
Key words: aluminum alloy; A-TIG; oxide; halide
1 Lead word
Aluminum alloy has become the most widely used non-ferrous metal material due to its large reserves, low density, excellent conductivity and thermal conductivity, and has been widely used in shipbuilding, construction, electronic power, aerospace and other fields [1, 2]. At present, the commonly used aluminum alloy welding methods include oxyacetylene gas welding, electrode arc welding, tungsten inert gas welding, etc., but due to the shallow welding penetration, poor weld quality, low production efficiency and other reasons, the further promotion and application of aluminum alloy is seriously hindered [3, 4]. In order to solve the problems encountered in aluminum alloy welding technology, a new welding technology - A-TIG (active flux tungsten insert gas) welding technology came into being [5, 6]. A-TIG welding refers to a welding technology in which a layer of active flux is coated on the surface of the weldment before welding. During welding, the active flux causes the welding arc to shrink or the metal flow state in the molten pool to change, so as to significantly increase the welding penetration . Oxides are ubiquitous in the earth and the universe and are widely used in metal thermal processing [8, 9]. Oxide can significantly increase the penetration and width of the weld, especially silicon dioxide . Halides are compounds in which cations of metal elements interact with anions of halogen elements (F, Cl, Br, I, at) . There are about 120 kinds of halide minerals, mainly fluorides and chlorides, while bromide and iodides are very rare. Fluorides and chlorides are most used in A-TIG and have a great impact on arc .
Development of 2a-tig welding technology
In the mid-1960s, the baton Welding Institute of Ukraine found that the existence of halides can produce arc contraction and increase welding penetration, which was used in titanium alloy welding technology . In the 1970s, active flux based on oxides and fluorides was developed and mainly used in stainless steel welding. By the 1990s, the former Soviet Union had applied active flux to the welding of low carbon steel and low alloy steel, as well as in aerospace, pressure vessels and nuclear power facilities
About the author: Ma Zhuang (1963-), Ph.D., professor. Mainly engaged in the research on the strengthening and toughening of surface modifier materials
Issue 11 Ma Zhuang et al: Research Progress of oxide / halide activator for argon arc welding of aluminum alloys three thousand two hundred and thirty-three
And other aspects have made great progress and entered the practical stage . At the end of the 20th century, well-known welding institutions such as the United States, Britain and Japan also began to systematically study the development and application of active flux for argon arc welding, and explored the mechanism of surfactant flux increasing welding penetration. In recent years, great progress has been made in the research and application of active flux for nickel based alloys, aluminum alloys and magnesium alloys. Liu et al.  used A-TIG welding to weld AZ31B deformed magnesium alloy. It was found that the addition of oxides cr2o5, TiO2 and chlorides CdCl2 and ZnCl2 can increase the penetration of magnesium alloy welded joints, among which the effect of chloride to increase the penetration is more obvious. The coarse-grained area in the heat affected zone is the thinnest and weakest area of the welded joint. A-TIG welding can improve the joint quality by reducing the width and grain size of the coarse-grained area in the heat affected zone.
A-TIG welding technology started late in China. Lanzhou University of technology was the first to develop active flux for low carbon steel and stainless steel
The depth is increased by 2 ~ 3 times [16, 17]. Luoyang Institute of shipbuilding materials, Dalian University of technology, Shandong University, Harbin Institute of technology, Nanjing University of Aeronautics and Astronautics, Tianjin University, etc. not only have they carried out detailed studies on the welding parameters and coating amount of active flux for stainless steel, carbon steel, titanium alloy and magnesium alloy, but also on the numerical simulation of the influence of oxygen content on the flow mode of molten pool , the influence of laser welding active flux on plasma  The corrosion resistance of stainless steel A-TIG welded joints  and the influence of surface active elements on the flow field in the molten pool  were analyzed in detail.
3 oxide type activator
The oxygen element in oxide activator affects the flow mode of liquid in the molten pool, which is the main reason for the increase of penetration and depth width ratio . At present, the oxides used in aluminum alloy A-TIG welding activator include SiO2, TiO2, V2 O5, Al2O3, MnO2, cr2o5, etc.
Zhang Yong et al.  studied the effect of SiO and TiO activators on the properties of LD10 aluminum alloy A-TIG welded joints and found that two kinds of activators were used
The weld surface of flux welding is uneven, and the weld has undercut locally; The weld with SiO2 activator has a penetration of 4.36 mm and a fusion width of 7.26 mm; Compared with conventional weldments, the grain structure of weld is coarse, and the hardness of weld and welding heat affected zone is low; The penetration depth and width of the weld with TiO2 activator are 1.58 mm and 6.29 mm. Compared with the conventional parts, the grain structure of the weld is fine and the hardness of the weld is low, but the hardness of the heat affected zone of the weld is higher than that of the conventional parts. Zhang Yong believes that the arc contraction is not the overall arc contraction, but only the plasma contraction, which is consistent with the plasma contraction viewpoint of Yang Chunli et al. 
Same. Mao Lizhen et al.  studied the effect of SiO activator on 6061 aluminum alloy weld by using fb-tig welding, and found that SiO did not pass through
Changing the temperature gradient of the surface tension of the welding pool can increase the weld penetration, but by affecting the behavior of the welding arc. They believe that the main mechanism of SiO2 increasing AC A-TIG penetration of aluminum alloy is the contraction of arc polarity zone. Huang Yong et al.  studied the effect of activator on the penetration of TIG welding during DC reverse connection. When TiO2 and V2O5 activators are used, the arc voltage is lower than that without activator (22 V), which may be due to the low electronic escape work of oxide when there is oxide at the cathode, which is easy to form cathode spots on the oxide. When aluminum alloy is used as cathode, the cathode is cold cathode, and electron emission mainly depends on the strong electric field in the cathode voltage drop area. Therefore, when there is oxide in the cathode, the voltage required for electron emission decreases, and the cathode voltage drop decreases.
When SiO2 activator is used, the arc voltage increases, which may be due to the high melting point and high resistivity of SiO2, which leads to the increase of conductive channel resistance. Zheng Qin et al
The effect of SiO2 activator on the properties of aluminum alloy TIG welded joints was studied. It was found that the impact toughness of SiO2 coated weldments was 22.7 J / cm,
Higher than that of non active flux weldment. This is because of the existence of active agent, the welding arc will shrink obviously, which will reduce the conductive area and increase the current density, and then increase the Lorentz force in the arc and molten pool, resulting in the increase of weld penetration. At the same time, the addition of SiO2 activator makes the weld grain refined and improves the mechanical properties of the welded joint.
4 halide activator
Halide type activator is the first activator used in A-TIG. The influence of active agent on arc morphology is mainly in the following two aspects: the dissociation temperature of active agent vapor; The affinity between active agent evaporated particles and electrons. The contraction of arc and cathode spots increases with the enhancement of the affinity between ions and electrons evaporated from the active agent and the increase of dissociation temperature. The electron affinity of halides is higher than that of metal oxides.
Zhou Zejie et al.  studied the effect of single component activator on the welding penetration of 3003 aluminum alloy. The results showed that the halide CAF and MnCl were coated
The weld penetration of and NaCl single component activator is 2.0216 cm, 1.9427 cm and 1.9597 cm respectively, which is 0.2 ~ 0.3 mm higher than that of the weld without activator, and the weld penetration width changes little; There are large weld reinforcement and pores on the surface of CaF2 coated weld, which are mostly distributed near the
Near weld fusion zone. Shen et al.  found that with the increase of CAF addition, the weld surface morphology deteriorated, but the weld depth width ratio increased and the tensile strength increased
Degree and elongation increased first and then decreased. Huang Yong et al.  used halide CaF2 and NaF as the activator of aluminum alloy, using DC reverse connection
three thousand two hundred and thirty-four Comprehensive review Silicate Bulletin Volume 34
During TIG welding, it was found that CaF2 and NaF did not cause the change of arc voltage, which proved that the increase of heat input could not cause the increase of penetration. Light red arc light appeared around the arc during welding, indicating that when halides affect the welding arc, but the arc voltage did not rise, so they recognized that
Arc shrinkage is not the reason for the increase of weld penetration. Yang Keng et al.  used activators CAF and BaCl to carry out A-TIG welding on aluminum alloy
When the current is 140 A, the weld penetration is 0.2 mm and 0.44 mm respectively, which is lower than that when there is no active agent. However, with the increase of welding current from 150 a to 160 a, the penetration increase ratio of BaCl2 activator is 2.07 and 2.04 respectively, while CaF2 penetration increase ratio does not change significantly, which is 1.15 and 1.02. They also believe that arc shrinkage is not the main reason for increasing penetration. He Lijun et al.  studied single component active agents NaF, MGF, CAF
The effect of AlF3 on 2A14-T6 aluminum alloy is that the penetration increases by 68.05%, 173.4%, 107.0% and 139% compared with the matrix respectively. Because fluoride decomposes into metal atoms and fluorine atoms under the high temperature of the arc, the fluorine atoms combine with hydrogen to produce hydrogen fluoride, which greatly reduces the existence of hydrogen and reduces the pores in the weld, so there are very few pores in the weld coated with AlF3 activator; However, a large number of pores are found in the weld coated with MgF2 activator, which is due to the addition of MgF2. Although the generation of hydrogen fluoride is conducive to reducing the content of hydrogen, because the arc is extremely unstable during the welding process, the gas protection effect becomes worse and the water from the arc atmosphere increases; After adding MgF2, CaF2 and AlF3 activators, the microstructure of the weld becomes finer and the NaF activity
The flux has little effect on the microstructure of weld. Zhang Zhaodong et al.  used three metal chlorides MnCl, KCl and ZnCl as activators on the surface of aluminum alloy
AC A-TIG welding is carried out. It is found that during A-TIG welding, the metal elements in chloride enter the conductive space of the arc and affect the state of the arc. The welding penetration is related to the first ionization energy of the metal elements in the active agent. With the increase of the first ionization energy of the metal elements in the active agent, the weld penetration increases first and then decreases.
5 compound activator
Although a single activator can increase the weld penetration, there are still some shortcomings, such as the weld depth width ratio is not ideal, the weld structure is coarse, and the mechanical properties are poor. The compound activator can better integrate the advantages of various activators to obtain an ideal weld.
Zhou Zejie et al.  found that the composite activator composed of NaCl, MnO, SiO, TiO and ZNF was coated on the surface of 3003 aluminum alloy to obtain
The penetration depth of the weld is increased by 3.1 times, and the weld width is increased by 0.4 times; The weld is well formed, without cracks, pores, slag inclusions and other defects, and has little effect on the average grain size of the welding heat affected zone. When using A-TIG welding to weld aluminum alloy, it is difficult to ensure that the penetration is significantly increased and the weld surface is well formed, so the French scholar Sir et al. Studied a new welding method fb-tig (flux bounded TIG). Although this welding method can ensure that the weld surface is well formed, the penetration increase is less [33, 34]. Mao Lizhen et al.  applied a 3 mm wide composite activator Al-5Ti-B to the center of the aluminum alloy sample, and the rest was coated with SiO2 activator for fb-tig welding. The results showed that the microstructure of the central area of the weld was significantly refined compared with that without activator. This was due to the existence of TiAl3, TiB2 and other intermetallic compounds in Al-5Ti-B, which played the role of heterogeneous nucleation in the molten pool, making the heat affected zone narrow and the weld microstructure fine. Huang Yong et al.  used fz-tig welding (flux zoned TIG welding). Before traditional TIG welding, the central area of the surface of the weld bead to be welded was coated with 4 mm low melting boiling point and high resistivity activator fz108, whose components were te, CdCl2, MnCl2, ZnF2, and the areas on both sides were coated with high melting boiling point and high resistivity activator SiO2, and then welded. The results show that fz108 + SiO2 aluminum alloy fz-tig welding has the endothermic reaction between the active agent fz108 in the middle area and the molten pool metal, which plays the role of shrinking the arc and increasing the penetration. Zhang Yong et al.  in order to improve the efficiency of AC TIG welding of aluminum alloy, LD10 aluminum alloy was used as the matrix, and 0.1 ~ 0.2 mm thick fly ash was coated on the surface of the specimen. The main components of fly ash used in the test: 50.8% SiO2, 28.1% Al2O3, 6.2% Fe2O3, 3.7% Cao, 1.2% MgO, 0.8% SO3. The obtained weld penetration is 2.31 mm and the fusion width is 7.07 mm. However, the oxide in the fly ash activator reduces the cathodic crushing effect of AC arc on the welding pool, so the surface of the weldment is uneven. When fly ash is used as the activator, the multi-component oxide reacts with the aluminum matrix, which can increase the precipitation of aluminum alloy. At the same time, because fly ash increases the welding voltage, the welding heat input increases, so the weld grain is coarse. Due to the precipitation strengthening effect and arc concentration effect in the weld area of the weld coated with Fly Ash Activator, the heat input in the heat affected zone is reduced, resulting in the hardness of the heat affected zone and weld coated with fly ash activator is higher than that of conventional weldments. Zhang Yong et al.  also added SiO2 to fly ash for TIG welding on the basis of fly ash active flux. The ratio of the two is 1:1. The weld penetration is 4.26 mm and the weld width is 7.46 mm. However, the microstructure of weld precipitates is larger than that of conventional weldments, and the hardness of weld and weld heat affected zone is higher than that of conventional weldments.
6 knot language
Compared with conventional TIG welding, A-TIG welding can effectively increase weld penetration and reduce weld defects. A-TIG welding of aluminum alloy can increase
Issue 11 Ma Zhuang et al: Research Progress of oxide / halide activator for argon arc welding of aluminum alloys three thousand two hundred and thirty-five
Weld penetration, improve weld formation and improve welding production efficiency. The active agents of aluminum alloy A-TIG welding mainly include oxide type, halide type, simple active agent type and composite active agent type. Each active agent increases the weld penetration to varying degrees. Among them, composite active agent type active agent has more advantages than other types of active agents and has great development potential. It is expected that more oxides and halide activators will be used in A-TIG welding.