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Welding methods and research status of titanium and titanium alloy

As an important metal processing technology, welding plays an important role in industrial production and national defense construction. With the change of industrial structure and the development of science and technology, advanced welding structure is an effective way to reduce material consumption and structural quality. Various welding technologies have broad application prospects. With the development of titanium industry, people pay more and more attention to its welding technology.

Titanium has the advantages of high specific strength, corrosion resistance to seawater and other media, low temperature resistance, high fatigue strength at high temperature, low coefficient of expansion and good processability. The structure constructed with titanium can give full play to its role in any natural environment. In ship application, in addition to its seawater corrosion resistance and high specific strength, there are non-magnetic, sound transmission and shock resistance.

Titanium has the advantages of high specific strength, corrosion resistance to seawater and other media, low temperature resistance, high fatigue strength at high temperature, low coefficient of expansion and good processability. The structure constructed with titanium can give full play to its role in any natural environment. In ship application, in addition to its seawater corrosion resistance and high specific strength, it also has the advantages of non magnetism, sound transmission and shock resistance. The use of titanium and titanium alloy in ship greatly extends the service life of the equipment, reduces the weight, and improves the technical and tactical performance of the equipment and the whole ship. Therefore, titanium is an excellent ship structural material [1-3].
As an important metal processing technology, welding plays an important role in industrial production and national defense construction. With the change of industrial structure and the development of science and technology, advanced welding structure is an effective way to reduce material consumption and structural quality. Various welding technologies have broad application prospects. With the development of titanium industry, people pay more and more attention to its welding technology. Titanium has high melting point and poor thermal conductivity, so it is easy to form a large molten pool due to improper selection of parameters during welding, and the molten pool temperature is high, which makes the weld metal and heat affected zone metal stay at high temperature for a long time, and the grain growth tendency is obvious, which reduces the plasticity and toughness of the joint and leads to cracks. Therefore, the welding process of titanium and titanium alloy is a problem that needs to be solved continuously.

Welding characteristics of titanium and its alloys

Physical and chemical properties of titanium and its alloys

Titanium has two kinds of allotropic bodies, one is allotropic and the other is allotropic α and β The transition temperature is 882.5 ℃ α It is a close packed hexagonal lattice and stable above 882.5 ℃ β The crystal is a body centered cubic lattice.
The thermal conductivity of titanium is lower than that of stainless steel. When there are impurities in titanium, its thermal conductivity decreases. Table 1 lists the comparison of the main physical properties between industrial pure titanium and other metal materials.

Table 1 Comparison of main physical properties between titanium and other metal materials

Titanium   Aluminium   Magnesium   Iron   Nickel   Copper   Zirconium   Stainless Steel
Specific gravity / (g · cm-3) 4.5 2.7 1.7 7.8 8.8 8.9 6.5 7.9
Melting point / ℃ 1668 660 650 1535 1455 1083 1830 1400
Coefficient of linear expansion / (10-6m ·℃ – 1) 8.5 22.4 26 11.7 12.8 16.6 2.5 16.66
Thermal conductivity / (w · M-1 ·℃ – 1) 17.04 217.71 159.1 75.36 92.11 393.56 20.93 16.36
Specific heat capacity / (J · kg-1 ·℃ – 1) 523.35 9295 1046.7 460.55 628 385.19 276.33 502.32
Modulus of elasticity / MPa 110250 69580 42140 196000 195020 127400 77518 198940
Resistivity / (μ Ω· m) 0.195 0.026 0.039 0.097 0.068 0.017 0.446 0.072

Welding structure of titanium alloy

Industrial pure titanium and titanium α The welding structure of titanium alloy is single phase at room temperature, and serrated or acicular structure is formed according to different cooling rate. Compared with the base metal, all kinds of mechanical properties have no big change, and the welding performance is good. α+β Titanium alloy from β Martensite is formed during phase cooling( α’ Phase), α’ The number and properties of phases vary according to alloy composition and cooling rate. In general, with α’  With the increase of phase, the ductility and toughness of the alloy decrease, even for Ti-6Al-4V with good weldability β When the content of stable element vanadium is more than 5%, the weldability decreases. β The martensite formation temperature of titanium alloy is lower than room temperature, and the weld is metastable β So the weldability is not deteriorated. However, due to the excessive addition of alloy elements, it often lacks ductility. In addition, aging and cold working can improve the strength of the alloy, while welding will cause a loss of strength, so welding is not widely used [4].

Welding defects of titanium alloy

Embrittlement of welded joint zone

The welding zone of titanium and titanium alloy is easy to be embrittled due to the contamination of gas and other impurities. The main elements causing embrittlement are o, N, h, C, etc. At room temperature, titanium and titanium alloys are relatively stable, but with the increase of temperature, the ability of titanium and titanium alloys to absorb o, N and h also increases significantly. Ti began to absorb hydrogen at 250 ℃, oxygen at 400 ℃ and nitrogen at 600 ℃. Nitrogen and oxygen have great influence on the strength and bending plasticity of the joint. With the increase of nitrogen and oxygen content in the weld, the strength of the joint increases and the bending plasticity decreases, and the influence of nitrogen is greater than that of oxygen. Hydrogen mainly affects the impact toughness of the joint.

Weld zone crack tendency

Hot cracks.

Because there are few impurities such as s, P and C in titanium and titanium alloy, few eutectic with low melting point is formed at the grain boundary, and the range of crystallization temperature is very narrow, and the shrinkage of weld is small during solidification, so the hot crack sensitivity is low.

Cold crack and delayed crack.

When the content of oxygen and nitrogen in the weld is high, the performance of the weld becomes brittle. Under the action of larger welding stress, cracks will appear, which are formed at lower temperature.
In the welding of titanium alloy, delayed cracks sometimes appear in the heat affected zone, and hydrogen is the main reason for the formation of delayed cracks. The main way to prevent the delayed crack is to reduce the source of hydrogen in the welded joint. If necessary, vacuum annealing can be carried out to reduce the hydrogen content in the welded joint.

Weld porosity

Porosity is a common defect in titanium and titanium alloy welding. O2, N2, H2, CO2 and H2O may cause porosity. Most of the pores in titanium and titanium alloy weld are distributed near the fusion zone, which is a characteristic of pores in titanium and titanium alloy. The pores in the weld not only cause stress concentration, but also reduce the plasticity of the metal around the pores, and even lead to the fracture of the whole welded joint. Therefore, the generation of pores must be strictly controlled [5].

Welding methods and research status of titanium and its alloys

TIG welding

Argon tungsten arc welding is the most commonly used method for titanium and its alloys. It is an excellent method for connecting thin plates and backing welding. Better welding can be achieved by selecting appropriate process parameters. The disadvantages are slow welding speed, large deformation of weldment and coarse weld microstructure [6]; It is easy to produce gas hole and tungsten inclusion in the weld; The welding process is easy to appear poor gas protection and affect the weld quality. The results show that the pulse frequency of TIG welding has an effect on the grain size and morphology of titanium alloy. When the pulse frequency is too high or too low, the weld zone is columnar crystal with low strength. When the pulse frequency is moderate, it is equiaxed crystal with higher strength. In recent years, the research on TIG welding of titanium alloy in India is relatively comprehensive [7].
M. Balasubramaniana et al. Studied the pulsed arc welding of titanium alloy (Ti-6Al-4V) and found that the grain size, hardness and welding parameters have the following relationships

  • Grain size: GS = 81.43- 18.33P -14.17B – 10.83F + 15T + 25.68P2 +18.18B2 + 61.93F2 + 25.68T2 ;
  • Hardness H = 472.15 + 8.54P – 6.87B + 4.38F- 5.62T -17.57P2 -12.57B2 -36.32F2 -15.07T2 + 1.56PF.

Where p is the peak current, a; B is the base current, a; F is the frequency, Hz; T is the time. The accuracy of the model to predict the grain size and hardness can reach 99% level [8].
Balasubramanian et al. [9] found that with the increase of pulse peak current and pulse frequency, the corrosion resistance of the joint increased. After reaching the optimal value, the corrosion resistance decreased with the increase of pulse peak current and pulse frequency, At the same time, with the increase of grain purity, the corrosion resistance will also increase. However, whether other properties can be kept at a good level with the minimum corrosion can be predicted by calculating the grain size and hardness through the above formula. A-TIG welding method is a new technology developed in recent 10 years, which can increase welding penetration, improve weld forming and welding quality, and improve welding production efficiency. For the penetration of A-TIG welding, Liu et al. [10] found that the penetration of A-TIG welding was significantly higher than that of traditional TIG welding under the same process parameters. Further test results show that the flurochloride activator can increase the weld penetration, that is, flurochloride is the main factor to increase the weld penetration of titanium alloy [11].
Li Xiaohong et al. [12] determined through experiments that the influence of active flux on the weld formation of titanium alloy is very obvious: under the same conditions, it not only increases the weld penetration, reduces the weld width, reduces the heat input during welding, but also significantly reduces the weld grain size; When A-TIG welding is carried out on titanium alloy with different thickness, the crystal morphology of the weld is the same, which grows from the base metal on both sides to the weld centerline in opposite direction; The cross-section shape of A-TIG welding seam is very different from that of TIG welding. The shape of A-TIG welding seam presents the cup-shaped feature of one-sided welding and two-sided forming, which can improve the mechanical properties of the weld seam. As the core of the technology, the formulation of active agent is the bottleneck restricting the development of the technology. Due to the complexity of the research on the formula, the introduction, orthogonal test and uniform test method are used to find the suitable materials in China. Due to the different action mechanism, the effect of better single acting materials may decrease after mixing. Therefore, the research on the surfactant needs further experimental research.

Plasma arc welding

Due to the narrow welding specification, poor welding stability and repeatability of plasma arc welding, it has become a prominent obstacle restricting the application process of plasma arc welding industry and the development of its own technology. Since the 1990s, the stability of plasma arc welding has been improved to a great extent due to the continuous improvement of manufacturing level and control technology of plasma arc welding equipment. Therefore, in the process of perforating plasma arc welding, mastering the factors affecting the welding stability and the law of action, using advanced control technology to further improve the degree of welding automation and control accuracy, is bound to be the focus of future research. The research results of Liao Zhiqian et al. [13] show that the tensile property of plasma welded joint is good, which is equivalent to that of base metal, the impact toughness of weld is lower than that of base metal, and the weld microstructure is residual β Phase and martensite acicular α Corresponding to the tensile properties, impact properties and hardness distribution of the joint, these microstructures have higher hardness and strength than the base metal, but lower plasticity. There are some problems in perforation welding, such as arc starting instability and line energy can not be kept at the minimum after perforation, which are the problems to be solved to realize stable perforation welding. Peilicheng [14] mainly studied the effect of arcing parameters on the heating process and excavation process of perforation, and realized the stable forming of arcing by controlling the temperature field distribution at the time of perforation. Through the experimental analysis, it is found that the welding current is the decisive factor affecting the heating process and temperature field distribution, and the ion gas flow rate mainly affects the perforation time in the welding heating process. The influence of welding current and ion gas flow rate on weld pool depth and keyhole shape is equally important. By adjusting the arc starting procedure, the temperature field distribution around the small hole at the time of perforation is close to the steady temperature field distribution of the excellent weld, and the wire feeding time is 1 ~ 2S ahead of the time of perforation, which can realize the stable transition and forming control of the arc starting section. Chen et al. [15] found that dynamic control of plasma welding can make plasma arc welding switch between perforation welding and penetration welding by controlling the peak current and ground state current under the condition of ensuring penetration, so as to meet the service conditions of weld under the condition of minimum heat input. Compared with conventional plasma welding, due to the decrease of heat input, the fusion zone and grain size of the joint decrease. Although the microstructure changes little, the first precipitates in the weld β The results show that the phase grains are greatly reduced, so the formation of martensite is restrained, and the welded joint has better toughness and higher hardness [15].

Vacuum electron beam welding

Vacuum electron beam welding is very suitable for the welding of titanium and titanium alloy. This is mainly because it has a series of advantages: good welding metallurgical quality, narrow weld, large depth width ratio, small welding angular deformation, fine grains in weld and heat affected zone, good joint performance, no air pollution in weld and heat affected zone, high efficiency in welding thick parts. The disadvantage is that pores are easy to appear in the weld, and the structure size is easily limited by the vacuum chamber, so it is not suitable for mass production, but it has absolute advantage for the quality of small size workpieces. Considerable residual stress will be produced in the welded joint, and it will increase with the increase of the thickness of the weldment. Therefore, researchers explore the possibility of reducing residual stress by electron beam local heat treatment. It is found that electron beam local heat treatment can improve the microstructure and properties of titanium alloy weld, refine the grain structure of weld zone, not only make the peak value of longitudinal tensile stress in weld center move outward, but also make the transverse residual stress in weld center become compressive stress, which greatly improves the distribution of welding residual stress and improves the welding quality. A similar phenomenon is also found for 14.5mm thick plate [17], which further proves that electron beam local heat treatment has a significant effect on improving welding residual stress and welding quality for thick plate titanium alloy. Due to the large residual stress of heavy plate, vacuum electron beam welding is widely used in thin plate. The electron beam welding (EBW) of heavy plate titanium alloy was studied by Lu et al. [18]. It was found that the microstructure was typical α Phase and lamellar( α+β) TC4-DT with two-phase structure can obtain high quality welded joint without deposition defects by electron beam welding. Among them, the fusion zone forms the rebound structure of martensite, and the layer by layer accumulation is the precursor β The phase boundary is clearly visible in the upper and middle parts of the weld metal, but not so obvious at the bottom. The microstructure of the HAZ is uneven. The HAZ near the fusion zone is composed of acicular martensite and a small amount of primary martensite α The heat affected zone near the base metal is composed of primary phase α Phase and contain acicular α The transformation of β Phase composition. The boundary of these two parts of HAZ depends on the cooling process β Phase transition temperature. With the increase of the depth along the plate thickness direction, the grain size of the fusion zone decreases and the microhardness increases. This test provides a good experimental basis for further research, theoretical analysis and application of titanium alloy for heavy plate in the future.

Laser welding

The quality and efficiency of laser welding are better than other welding methods. It is easy to change the light path with mirrors or prisms, and can be welded at any position of the workpiece. Laser welding may be widely used in the welding of titanium and titanium alloy sheet and precision parts. But laser welding also has its shortcomings: the penetration is not as strong as electron beam. Research on the properties of laser welded titanium alloy sheet shows that the mechanical properties of laser welded joint are affected by weld formation and weld microstructure [19-20]. When the welding heat input is large, there is dense and scattered acicular martensite in the weld, which makes the tensile strength increase. When the coarse columnar structure appears in the weld, the yield strength and relative displacement of the welded joint decrease, and the plastic toughness of the joint decreases. Through reasonable parameter selection, the tensile strength and shear strength of the joint can be equivalent to that of the base metal, and the fatigue performance of the joint can be significantly improved after vacuum heat treatment. Although the bending angle is improved after vacuum heat treatment, it can only reach 1 / 2 of the base metal. Therefore, the weld should not be placed at the maximum bending moment in titanium alloy structure design. The advantages of laser welding are very obvious, but at present, laser welding involves some technological problems, such as gas protection, Specimen cleaning and photoinduced plasma control, which affect the welding quality of titanium alloy. Due to the problems of laser welding, the laser hybrid welding technology can reduce or even eliminate the defects in laser welding, so as to improve the welding quality.
The results of Li et al. [21] test on the quality of laser hybrid welding show that the excellent weld without surface oxidation, porosity, crack and incomplete penetration can be formed under suitable welding conditions. Compared with LBW, the ductility of laser MIG welding joint is better. TA10 welding wire with low strength can improve the weld forming quality and reduce the micro hardness, but the hardness of heat affected zone may increase greatly due to large heat input. J. Zhou et al. [22] think that laser MIG welding technology can eliminate micro cracks, hinder the formation of pores and improve the composition of weld. By adding some anti crack elements into the welding wire, the defects such as high sensitivity of weld hot crack and low strength can be reduced and eliminated. The mixing and diffusion degree of welding wire droplets into the base metal is greatly affected by the liquid flow dynamics in the molten pool [22]. This requires that in the future research, attention should be paid to find more suitable welding wire and reasonable combination of process parameters, so as to ensure good welding quality. How to reasonably combine laser with MIG or TIG and other methods to ensure the optimal performance of hybrid welding is a constant exploration of scientific researchers
It’s a matter of time. Chen et al. [23-24] found that laser energy density determines the formation and disappearance of keyhole. Therefore, they calculated and quantitatively measured the propagation characteristics and absorption characteristics of the laser when passing through the arc, thus confirming the viewpoint that the laser TIG hybrid welding has limited enhanced penetration and welding mechanism transformation, thus providing the basis for optimizing the composite welding effect. In addition to reducing defects, the microstructure of composite welding is different from that of laser welding. There are many defects in laser welding and hybrid welding α There are rough columnar phases in laser welding α Phase and a small amount of fine needle like α The microstructure of the composite welded joint contains acicular phase α、 Flaky α And the twin phase, which makes the composite welded joint have good joint strength and ductility [25]. EDX analysis shows that the density fraction of oxygen in the fusion zone is higher than that of the base metal, but it can not be considered that the oxygen content is the only factor affecting the hardness of the weld at a given welding speed. The final hardness should be related to the interaction of cooling rate and oxygen and nitrogen content.
Other parameters such as shielding gas, gas flow and the distance between laser and electrode need to be studied, which can optimize the hybrid welding and produce the most desirable weld. The establishment of relevant knowledge base is helpful to realize automation.

Diffusion welding

At present, diffusion welding is widely used between titanium alloy and stainless steel. It is required that the surface to be welded should be clean and all impurities should be removed. The titanium alloy and stainless steel were welded by constant temperature and pressure diffusion welding, phase transformation superplastic diffusion welding and pulse pressure diffusion welding. The phase analysis showed that there were Fe2Ti and Fe in the titanium alloy stainless steel joint σ-( FeCr) are two brittle intermetallic compounds [26]. Because pulse pressure diffusion welding can promote the diffusion process, reduce the generation of brittle intermetallic compounds and improve their distribution, it is a promising diffusion welding method. In order to avoid and reduce the generation of brittle intermetallic compounds, diffusion welding is further developed in the form of plating a layer of copper or nickel on the surface of titanium parts, or sandwiching a layer of 0.05 ~ 0.03mm copper or nickel [27]. When titanium alloy and stainless steel dissimilar joints are directly welded by diffusion welding, it is difficult to avoid the occurrence of joint stress and brittle intermetallic phase, which is easy to cause cracks in the welded joints. Therefore, most of the joints adopt intermediate metal [28], and the joints with intermediate transition layer and micro mechanical occlusion have better performance. Through the study of microstructure and tensile properties of joint and base metal under different processes, it is found that [29] when Ni based alloy is used as interlayer material for diffusion welding, the microstructure of diffusion band of joint is good, and there are no welding defects such as holes and voids. With the increase of welding temperature and holding time, the width of diffusion layer increases, but it also causes the grain growth of all structures, which leads to the decrease of joint properties. Therefore, when considering the influence of process parameters on the joint performance and determining the best process, the process with lower welding temperature and shorter holding time should be preferred on the premise of ensuring the welding quality.

Brazing

Brazing is the most simple and reliable way to connect titanium and its alloys with other metals. At 882.5 ℃, pure titanium undergoes isomeric transformation, which changes from a close packed hexagonal structure to a hexagonal structure α Phase transformation to BCC Structure β Phase. The isomerism transformation of titanium alloy determines that the brazing process is limited by temperature and time( α-β) The microstructure and properties will change greatly when the temperature of phase transformation is increased. From the perspective of metallurgy, it is more important that the brittle phase is formed by the reaction between the matrix and solder, which makes the performance of brazed joint deteriorate [30]. To sum up, select the appropriate solder, as far as possible to keep in the low temperature β Brazing of titanium alloy below phase transition temperature is the basic principle. In this way, not only the properties of base metal can be maintained, but also the brazed joint with excellent mechanical properties can be formed. Huaijunfeng et al. [31] took the lead in the research on the joining process of brazing and diffusion treatment for high temperature titanium alloy TA15. By using advanced brazing materials and optimized vacuum brazing and diffusion treatment process, the material was effectively joined. The element distribution of the brazed joint interface and the microstructure of the brazed joint were analyzed by means of electronic microstructure and energy spectrum. The composition design of brazing material is reasonable, and the vacuum brazing process is reasonable and feasible. Cu and Ni elements in solder belong to β The content of phase stable elements is about 30%. The brazed titanium alloy weld can be heat treated at the brazing temperature to make its structure tend to be stable lamellar structure [31].
Chen Shuhai et al. [32] used Al Si eutectic alloy as filler material to weld Al / Ti dissimilar alloy by laser fusion brazing, and obtained welded joint with dual characteristics of fusion welding and brazing. Due to local laser heating and high cooling rate, it is found that a special morphology is formed near the brazing interface of titanium alloy. The intermetallic compound on the upper interface of the weld is thick and mainly zigzag; The thickness of intermetallic compound at the lower interface of weld is less than 1 μ m. In thin layer. The main component of the intermetallic compound is TiAl3, which exists in the form of displacement solid solution with Ti (sixal1-x) 3 structure. The bottom interface is easy to become the source of cracks, and most of the cracks propagate along the eutectic structure in the weld near the interface, and the average tensile strength of the joint is about 85% of the aluminum base metal [32].

Friction stir welding

Under traditional conditions, titanium alloy can be welded by fusion welding. However, due to the harsh welding conditions, complex process, defects and low joint strength, people began to explore the use of new friction stir welding technology (FSW) to solve and improve the welding of titanium alloy. According to the information provided by Welding Research Institute of UK and the published literature abroad, pure tungsten, tungsten rhenium alloy, tungsten iridium alloy or cubic boron nitride (PCBN) are the best materials for friction stir welding of titanium alloy and nickel base superalloy. Luan Guohong et al. [33] carried out an experimental study on friction stir welding of TC4 titanium alloy by using a tungsten rhenium alloy formed by powder metallurgy as a friction stir welding joint of titanium alloy. The results show that the strength of TC4 titanium alloy FSW joint almost reaches the base metal strength (895mpa), but the elongation of the joint is relatively low, the welding process parameters need to be optimized, and the welding process protection needs to be improved. Through careful measurement and observation, it is found that the stirring head is not severely worn, but completely adhered and filled by the titanium alloy material in the weld, and the hole defects are also easy to appear in the weld [33]. This is related to the Superplasticity of materials and the selection of welding process parameters. Further research needs to improve the stirring head, such as surface coating. Further research shows that the friction stir welded joint made of PCBN and W-Re alloy has good weld appearance and no internal defects. The strength of FSW joint is lower than that of base metal. The tensile strength and elongation after fracture of the joint decrease with the increase of welding heat input. In the FSW process of titanium alloy, the temperature gradient near the shoulder in front of the stirring head is the largest, while the temperature gradient near the shoulder in rear of the stirring head is the smallest: the peak temperature of the weld center exceeds the transformation temperature range of titanium alloy, and the peak temperature gradually decreases from the weld center to the outside [34]. These studies provide a basis for finding suitable materials, developing titanium alloy FSW tools and corresponding equipment, and formulating processing technology.
In the follow-up study, a certain amount of hydrogen is added to change the plasticity of titanium alloy, reduce the requirements on the performance of the stirring head, and make it near the phase transformation point, while the hydrogen can be eliminated by post weld dehydrogenation [35]. Research on the microstructure and mechanical properties of titanium alloy friction stir welding joint after hydrogen implantation [36] found that: after hydrogen implantation, TC4 titanium alloy friction stir welding has better surface formability, good microstructure and mechanical properties than traditional titanium alloy friction stir welding, the thermal mechanical properties have been significantly improved, the joint microstructure is relatively small, and the heat affected zone is reduced due to the joint effect of heat and deformation α Xiangyu β However, the amount of hydrogen should be controlled. The plasticity of titanium alloy with 0.1% hydrogen is better than that of titanium alloy with 0.4% hydrogen.

Concluding remarks

Through the development of A-TIG welding, TIG can be efficiently applied in the welding of titanium alloy, which can reduce or eliminate the defects of TIG and other arc welding in the welding of titanium alloy, making it the most convenient and the lowest cost welding method in the welding of titanium alloy. The improved laser welding method adopts compound heat source welding, which not only makes up for the disadvantage of relatively small working thickness of laser welding, but also reduces the possible defects in welding, reduces the cost and improves the efficiency. Plasma welding still has its unique advantages in the welding of thick seam. The monitoring difficulties and heat input of deep penetration welding are large. The poor weld quality is an urgent problem to be solved to improve the welding quality. The stable arc dynamic control method is a reasonable and feasible improvement scheme. Diffusion welding has excellent performance in dissimilar metal welding. Compared with brazing, it has obvious advantages. The service temperature and strength of the joint are not limited by the filler metal. The microstructure and properties of the welded joint are close to or the same as that of the base metal. There are no various fusion welding defects in the weld, and there is no heat affected zone with overheated structure. The process parameters are easy to control, and the deformation of the parts is small, It can be used to weld large cross-section joints and materials that are difficult to be welded by other welding methods. It is especially suitable for the connection of titanium alloy with other dissimilar metals and ceramic materials. Friction stir welding needs to solve the development of mixing tools, and then complete the research of relevant processing technology. It will become a more important method in China in the future. Other methods, such as linear friction welding, are also effective in practical processing.

Other welding methods are also in the further research and development, such as the application of surface self nanocrystallization, phase transformation superplastic diffusion bonding and self propagating technology, so that the welding methods of titanium alloy can be diversified and efficient, so as to meet different welding needs. The future research will focus on the establishment of quantitative influence mechanism of welding parameters on weld formation and penetration of titanium alloy in various methods, formulate corresponding welding processes and operation procedures for different materials to be welded, and finally develop a set of knowledge base of titanium alloy welding technology application, which mainly includes production application, safety, mechanical properties and metallurgical properties, corrosion resistance, corrosion resistance, corrosion resistance, corrosion resistance, etc The re grindability of penetration and the influence of base metal composition change.

Authors: Gao Fuyang, Liao Zhiqian, Li Wenya

SourceChina Titanium Flange Manufacturer: www.titaniuminfogroup.com

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