Effect of TIG welding active agent on weld formation
Abstract: Activated welding (A-TIG welding) has been highly valued abroad in the late 1990s. Compared with traditional TIG welding (tungsten inert gas shielded arc welding), activated welding can be greatly improved under the same specifications. Increase productivity and reduce production costs. In this paper, the effects of single component active agent and coating amount on weld formation in A-TIG welding were studied for stainless steel and titanium alloy materials. The test results show that the active agents CaF2, SiO2, NaF, Cr2O3 and TiO2 can effectively increase the penetration depth of stainless steel and titanium alloy welds compared with the weld without active agent. The weld penetration is also increased correspondingly, and the melt width is reduced. However, stainless steel welds coated with CaF2 active agent were not well formed, and there was no significant change in the front melt width of the titanium alloy weld coated with Cr2O3. In the stainless steel welding, the active agent SiO2 has the best effect; while the titanium alloy has the best effect in the welding of CaF2. Arc shrinkage and changes in the surface tension of the bath are the main reasons for the increase in penetration of the active agent. Basin faucet is a common bathroom device, used to control the flow of water switch and temperature regulation. It is made of high quality copper material that is durable and corrosion resistant. The appearance of the faucet design is simple and generous, the surface after fine polishing treatment, smooth and bright. It uses advanced ceramic spool technology to ensure the stability and smoothness of water flow and avoid water leakage and dripping. The faucet is also equipped with a temperature control knob to adjust the water temperature as needed, making the user more comfortable when using. Easy to install, suitable for all kinds of basin and wash basin. In short, the basin faucet is a practical and aesthetically pleasing option that provides users with a comfortable and convenient washing experience. Wall Concealed Basin Mixer,Bathroom Wall Concealed Mixer Tap,Wash Basin Faucet Mixer,Modern Brass Faucet Mixer Tap Kaiping City Kaipu Sanitary Ware Co.,Ltd. , https://www.china-kpo.com
Key words: activated TIG welding; active agent; weld formation; penetration;
0 Preface
TIG welding has been widely used in production, it can obtain high quality welds, commonly used to weld non-ferrous metals, stainless steel, ultra-high strength steel and other materials. However, TIG welding has the disadvantages of shallow penetration (≤3mm) and low welding efficiency. For thick plates, it is necessary to perform multi-pass welding on the opening. Increasing the welding current can increase the penetration depth, but the width of the melt and the volume of the molten pool increase much more than the increase of the penetration depth.
The activated TIG welding method has attracted worldwide attention in recent years. The method was first developed by the Ukrainian Barton Welding Institute (PWI) in the 1960s, but it was not until the end of the 1990s that research institutions in Europe and the United States (such as the Edison Welding Institute (EWI) and the British Welding Institute (TWI)) The research, in which the flux developed by EWI has been used in the naval shipbuilding industry. This technique is to apply a layer of active flux (referred to as active agent) to the surface of the weld before welding. Under the same welding specification, the penetration can be greatly improved compared with conventional TIG welding. 300%). For 8mm thick plate welding, a larger penetration or a single penetration can be obtained without opening the groove, and the welding heat input can be reduced for the thin plate without changing the welding speed. At present, A-TIG welding can be used to weld materials such as stainless steel, carbon steel, nickel-based alloys and titanium alloys. Compared with traditional TIG welding, A-TIG welding can greatly improve productivity, reduce production costs, and also reduce welding distortion, which has very important application prospects.
The key factor in A-TIG welding is the choice of active ingredients. At present, the active ingredients used are mainly oxides, chlorides and fluorides, and different materials have different active ingredients. However, due to the importance of this technology, the composition and formulation of active agents are subject to patent restrictions in PWI and EWI, and are rarely reported in public publications. At present, the research on A-TIG welding mainly focuses on the research of the action mechanism of active agents and the research of application technology of activated welding.
This paper mainly focuses on stainless steel materials and titanium alloy materials, and tests the effects of different active agents and active agents on weld formation, laying the foundation for the subsequent determination of the best active agents for these materials.
1 Test method
1.1 Selection of active agent types
There are three main types of active agents developed and used at home and abroad: oxides, fluorides and chlorides. The active agents for titanium alloy welding developed by PWI in the early days were mainly oxides and chlorides, but the toxicity of chlorides was large, which was not conducive to popularization and application. At present, the active agents used in welding stainless steel and carbon steel abroad are mainly oxides, and for the welding of titanium alloy materials, the active agent contains a certain fluoride component. Therefore, the single component oxides (SiO2, Cr2O3 and TiO2) and fluorides (CaF2 and NaF) were selected as active agents to study the effect of the amount of active agent applied on the weld formation.
1.2 Test methods
150mm × 50mm × 6mm plate surfacing, material 0Cr18Ni9 stainless steel and TC4 (Ti6Al4V) titanium alloy, titanium alloy specimens have a thickness of 2mm. The specification parameters of welded stainless steel are shown in Table 1, and the specification parameters of titanium alloy welding are shown in Table 2. In order to ensure the accuracy of the test results and the comparability of TIG and A-TIG, before each weld is welded, the electrode is reground to a standard shape, and the arc is adjusted to the standard length to ensure that each weld is under the same specification. welding.
During the test, five kinds of activator powders such as ASiO2, BNaF, CCr2O3, D TiO2 and ECaF2 were mixed with acetone to form a solution, and then evenly coated with five flats in five kinds. The block has a total of 31 test panels, but the coating thickness varies. After the acetone is completely volatilized, the test plates of 150 mm in length are divided into two zones of 90 mm and 60 mm, wherein the activator on the 60 mm zone is wiped onto the filter paper, and each test is measured and calculated by an electronic analytical balance (accuracy of 0.01 mg). The amount of activator applied per unit area of ​​the plate is shown in Tables 3 and 4.
2.1 Effect of single component active agent on stainless steel weld formation
Figure 1 shows a photograph of the effect of five single component active agent coatings on weld formation. The welding direction in the figure is from left to right, the active agent is not applied to the left side of the white line, and the active agent is applied to the right side of the white line. When different amounts of the active agent and the amount of the active agent applied are different, the formed weld bead can be seen as follows.
(2) The effect of the active agents NaF and Cr2O3 on the bead formation is not obvious. As the amount of coating increases, the weld width does not change much, and the crater does not change significantly. There is no significant change in the width of the weld bead compared to the weld without the active agent, but the crater is larger than the active agent.
(3) With the increase of the amount of TiO2 applied, the appearance of the weld bead does not change much, and the crater does not change significantly, similar to the case of no active agent. However, the surface of the weld formed is relatively flat, and there is no undercut phenomenon, which is better than the bead formation without active agent.
(4) The active agent CaF2 has a great influence on the bead formation. As the amount of CaF2 applied increases, the weld bead formation deteriorates, the crater does not change much, and the weld width does not change much. However, defects such as undercuts occur as the amount of CaF2 increases.
(5) For the influence of the penetration depth, the above five active agents can increase the penetration depth of the weld bead compared with the inactive agent, and the penetration depth increases correspondingly as the coating amount increases. However, when the coating amount reaches a certain value, the penetration depth increases to saturation, and the coating amount is increased, and the penetration depth is decreased. as shown in picture 2.
Figure 3 shows the effect of using an active agent on the surface surfacing of a 2 mm thick TC4 titanium alloy. In order to facilitate the comparison, the application amount of each active agent was selected in the test, and the weld seam was completely penetrated. It can be seen from Fig. 3 that the effects of the active agents CaF2, NaF, SiO2 and TiO2 on the penetration depth and the melt width are relatively large when the titanium plate is welded. The weld bead in the area where the active agent is not applied has only a wide melting on the front side and no obvious melting on the back side. The weld seam coated with the active agent has a suitable melt width on the front side and the back side is also completely melted. Through, the front and back are in good condition. The width of the weld bead is narrower than that of the inactive agent. Although the surface coated with the surfactant Cr2O3 has an increased penetration compared with the weld without the active agent, the front width is almost unchanged, and the central portion of the weld is concave, which is prone to undercut.
So far, it has been considered that "arc shrinkage" and "melt surface tension change" are the two main causes of increased penetration in A-TIG welding.
3.1 Arc shrinkage mechanism
The theory of "arc shrinkage" for increasing the penetration depth suggests that the active agent is surrounded by the atomic form in the peripheral region of the arc after evaporation at the high temperature of the arc. Due to the lower temperature of the peripheral region of the arc, the active agent evaporates the atoms to capture electrons in the region to form negative ions. Dissipated into the surrounding space, the number of electrons in the arc is reduced, and the arc conductivity is weakened. The final result is that the arc automatically shrinks, the heat is concentrated, and the arc force is concentrated, thereby increasing the weld penetration. However, so far, there is no exact measurement of the problem of negative ions in the arc.  A test observation found that after adding sulfides, chlorides and oxides to the molten pool, the anode spots on the molten pool showed obvious shrinkage, as shown in Fig. 4, and a large penetration was produced at the same time. According to the comprehensive test phenomenon and analysis results, the metal vapor generated by the molten pool is suppressed after the addition of the active element, and the metal vapor is more easily ionized, and in the case of less metal vapor, only a small range of anode spots and arcs can be formed. The conductive channel is tightened, and while the electromagnetic convection inside the molten pool is activated, the plasma convection on the surface of the molten pool is weakened, thereby forming a large weld penetration. In the case where the presence of negative ions in the arc has not been confirmed, since the change in the anode spot has been more confirmed and is in line with the actual effect of the welding, it is correct to explain the increase in penetration from the angle of "arc shrinkage".
The welding workers have carried out extensive and in-depth research on the surface tension of the molten pool. In the active welding, the basic point of view is that the flow state of the molten pool metal plays a considerable role in the formation of the penetration depth, and the common welding metal melts. The surface tension has a negative temperature coefficient. In this case, the surface of the molten pool forms a surface tension flow from the central region of the molten pool to the periphery of the molten pool, and the obtained penetration depth is shallow; when there is some kind in the molten pool metal When the trace elements (contents above a certain value) or when exposed to the active atmosphere, the surface tension value of the molten metal of the molten pool decreases and becomes a positive temperature coefficient, so that the molten pool metal forms a surface from the periphery of the molten pool toward the central portion of the molten pool. During the tension flow, the arc heat in the central portion of the molten pool is directly transmitted to the bottom of the molten pool through the flow of the liquid metal, so that the heating efficiency at the bottom of the molten pool is increased, thereby forming a greater penetration. The effect of the above two cases on the weld penetration is shown in Fig. 5.
4 Conclusion
(1) In the 0Cr18Ni9 stainless steel surfacing test, the active agents CaF2, SiO2, NaF, Cr2O3 and TiO2 were used to increase the penetration of the weld. Compared with the weld of the inactive agent, as the amount of the active agent applied increases, the penetration depth increases correspondingly, and the melt width decreases. However, the weld bead of the active agent CaF2 is poorly formed.
(2) When welding titanium alloy, the welds with active agents CaF2, NaF, SiO2 and TiO2 are formed on the front and back surfaces, and the penetration depth is more obvious than that of the weld without active agent. Although the weld depth to which the active agent Cr2O3 is applied is increased, the front width does not change, and the undercut phenomenon is likely to occur.
(3) The arc shrinkage and the change in the surface tension of the molten pool are the main reasons for the increase in penetration of the active agent.
Heilongjiang Provincial Study Abroad Funding Project LCO1C14;
State Key Laboratory of Modern Welding Technology Open Fund Project