With the development of the aerospace industry, the welding of titanium alloys and aluminum alloys has attracted the attention of various countries and many researchers. However, due to the large differences in the crystal structure, thermal expansion coefficient, melting point, and thermal conductivity of titanium alloys and aluminum alloys, it is difficult for conventional welding methods to obtain welded joints that can meet the requirements of use. In order to solve the problems existing in the welding process of titanium alloys and aluminum alloys, researchers have conducted methods such as diffusion welding, friction stir welding, electron beam fusion brazing, laser welding, vacuum brazing, and liquid phase diffusion welding on titanium alloy / aluminum alloy. A lot of experiments and research have been carried out.
Diffusion welding technology was used to conduct experiments on TA2 / LF6 dissimilar metals. It was found that when the welding temperature exceeds 525 ° C, the three elements of Ti / Al / Mg will undergo diffusion reaction to form Al18Ti2Mg3 mesophase. In the new phase zone and the solid solution metallurgical bonding zone produced by the diffusion reaction, the bonding strength decreases with the increase of the new phase zone of the diffusion reaction, and increases with the increase of the solid solution metallurgy bonding zone. Figure 1 shows the effect of welding temperature on the shear strength of TA2 / LF6 diffusion welded joints. It can be seen that when the welding temperature is 500 ℃, the shear strength of the welded joint increases with the extension of the holding time, and the maximum value is 74 MPa when the holding time is 600 min; when the welding temperature is 525 ℃, the resistance of the welded joint The shear strength reached a maximum value of 83 MPa at 240 minutes of heat preservation, and then decreased sharply; when the welding temperature was 550 ℃ and 565 ℃, respectively, the maximum shear strength of the welded joints decreased, respectively, 61 MPa and 55 MPa.
Friction stir welding experiments were carried out on TC4 titanium alloy and 5A06 aluminum alloy, and it was pointed out that the best process conditions (n = 1500 r / min, ν = 60 mm / min, T = 0.1 mm) were used for Ti / Al butt welding. The tensile strength of the weld seam can reach about 88% of the tensile strength of 5A06 aluminum alloy, and its fracture mainly occurs in the aluminum side welding zone. It is a scan of the fracture surface of the titanium alloy corresponding to the TC4 / 5A06 friction stir welding joint under the best process conditions. It can be seen that the round marked area is a flat and smooth brittle cleavage surface, indicating that the interface is a brittle connection and the interface bonding strength is low. A partially enlarged view of the rectangular marked area. The large number of closely arranged dimples in this area indicate that the interface is a ductile connection, and the interface bonding strength is high. Electron beam fusion brazing was used to metallurgically combine the TC4 titanium alloy and the 5A06 aluminum alloy. The study found that the Ti / Al element produced interdiffusion at the interface during the welding process, and formed a middle with a width of about 1.0 to 1.6 mm In the layer, a diffusion layer with a width of about 20-40 μm is formed on the titanium alloy side, and a large number of intermetallic compounds are distributed on the aluminum alloy side. The interface formed by this method can improve the mechanical properties of titanium alloy / aluminum alloy welded joints.
Magnesium alloys are widely used in aerospace, automotive industry, electronic products and other fields due to their advantages such as high specific strength and specific rigidity, good geomagnetic shielding performance and good damping performance. Welding dissimilar metals of titanium alloy and magnesium alloy can effectively improve the shortcomings of poor high temperature mechanical properties and corrosion resistance of magnesium alloy, solve the shortcomings of magnesium alloy performance, combine the performance advantages of titanium alloy and magnesium alloy, and increase its application range. At present, there are mainly welding methods such as diffusion welding, explosion welding, resistance welding and friction stir welding between titanium alloy and magnesium alloy.
The friction stir welding of ZK60 magnesium alloy and titanium alloy plates is focused on the microstructure of the interface diffusion zone and the mechanical properties of the joint, and compared with the pure magnesium-titanium friction stir welding joint. Research shows that the metallurgical connection between ZK60 magnesium alloy and titanium alloy sheet can be achieved by friction stir welding. The tensile test found that the fracture surface mainly occurred between the ZK60 magnesium alloy at the interface of the joint and the stirring zone. In addition, zinc, zirconium and other alloy elements in the ZK60 magnesium alloy react with titanium at the joint interface during friction stir welding to form a very thin reaction layer. Since no reaction layer is formed at the interface between the pure magnesium and the titanium alloy joint, The tensile strength of ZK60 magnesium alloy and titanium alloy joints is higher than that of pure magnesium and titanium alloy joints.
Diffusion welding experiments were conducted between AZ31B magnesium alloy / Ti-6A1-4V dissimilar metals with pure Al as the transition metal. The study found that if the holding time is controlled at 3h, the welding temperature is a key influencing factor to change the microstructure of the joint, the new phase of the interface and the connection strength. If the welding temperature is lower than 450 ℃, no eutectic structure is formed in the Mg / Al contact layer, and the effective bonding between the magnesium alloy and the titanium alloy cannot be completed; if the welding temperature is between 450 ℃ and 480 ℃, the welding temperature becomes Mg / Al The main control factor of the / Ti contact layer mainly produces fluctuations in the structure and morphology of the reaction products at the connection interface. If the welding temperature reaches 470 ℃ and the holding time reaches 3h, the shear strength of the connection interface is the highest, which is 72.4MPa, which is 84.2% of the AZ31B base material (86MPa).
