Research on Vacuum Electron Beam Welding of BT5-1 Titanium Alloy and C-103 Tantalum Alloy

Study of Vacuum Electron Beam Welding Process of BT5-1 Titanium Alloy and (-103铌) Alloy 1 Yang Shanglei 12, Lou Songnian, Xue Xiaohuai, Li Shimin 1 (1. Welding Research Institute, Shanghai Jiao Tong University, Shanghai 200030, China; 2. Qingdao Science and Technology Institute of Polymer Engineering Materials, University of Qingdao, Shandong 266042, China) The experimental results show that the joints of BT5~1 and C-103 connected with the appropriate electron beam welding process specifications are well-formed, and there are no defects such as cracks. Welding quality has an important influence.

C-103 tantalum alloy is a new tantalum alloy developed by TWCA of the United States. It has better welding performance and forming performance than other tantalum alloys. It can meet the needs of rocket engine components with an operating temperature of 1480*C. It is a new aerospace propulsion system. Generation alloy. Communication satellite rocket boosters made of C-103铌 alloys have significantly reduced costs due to reduced weight and improved reliability.

Titanium alloys have low density, high specific strength and good thermal strength. The long working temperature of BT-1 titanium alloy can reach 723K. It is often used in high-temperature structural parts in the aerospace field. The electron beam welding of BT51 titanium alloy and C-103 germanium alloy is of great significance in the aerospace fields such as satellites, rockets and space stations.

1 Test equipment and materials 15 electron beam welding machines, industrial control computers, far infrared thermometers, automatic control tables, cooling devices, etc.

1 Titanium alloy and C-103 tantalum alloy pipe. The chemical composition, mechanical properties and physical properties of BT;1 and C-103 are shown in Table 1, Table 2 and Table 3. Table 1 BT-1 and (-103 chemical composition (mass fraction, %) basis Table 2 BT1 and (-103 Mechanical properties (annealed) 5 (%) (annealed) Table 3 BT-1 and (-103 Pipe physical properties atomic radius Crystal structure Melting point Coefficient of linear expansion/10-6K - Specific heat 2 Vacuum electron beam welding process 2.1 Welding The BT51 titanium alloy and the C-103 alloy can form a solid solution structure without brittle intermetallic compounds.

The melting points of BT51 and C-103 alloys are different, and the thermal conductivity is also different. If the heat input is the same on both sides, the weld geometry will be asymmetric. If the conventional heat input is symmetrical during welding, when the electron beam energy is large, the C-103 side fuses well, but BT; 1 melts seriously; when the electron beam energy is small, although the BT51 fuses well, the C-103 will Poor fusion occurs, resulting in unmelted or incomplete penetration.

Therefore, when welding, the energy input to the titanium alloy side should be reduced, so that the electron beam energy can be biased to the higher melting point niobium alloy, and the effect of the difference in the thermal physical properties of the two alloys can be balanced to prevent the fusion of the two alloys to be insufficient.

1:200 This 1-27 2.2 electron beam welding process is shown. The joints before welding were cleaned with acetone to remove oil stains, and then assembled into an electron beam welder vacuum chamber after assembly.

For: acceleration voltage 60kV, focusing current 0.496A, welding speed 8.72mm / s, vacuum electron beam welding joint type electron beam scanning amplitude of 1.0mm. Welding process according to the beam loading curve () is completed in three steps: First Steps to use a small beam to preheat the weld, preheat the beam 1~4mA; the second step uses a large beam for welding, welding beam 10~20mA; the third step uses a medium beam for post-processing, post-processing beam Flow 5 ~ 10mA. Electron beam welding process is completed, the workpiece in the vacuum chamber with the furnace cooling to the specified temperature 50 * C. 3 results and analysis of D = 0.9 when the BT5> 1 and C-103 electron beam welded joint morphology . It can be seen that the joints are well-formed, the weld geometry is symmetrical, the weld edge fusion is good, the transition is uniform, and there are no defects such as cracks, undercuts, and pores.

For the same electron beam welding process specification C-103 duty cycle D was Q7 and 0.9 when the weld appearance. From (a), it can be seen that when the BT51 electron beam energy accounts for 30% and (-103 electron beam energy accounts for 70%, the j-side width of the titanium side is large, but the penetration is small, and the excessive melting of the titanium alloy liquid metal Under the action of the electron beam impact, the alloy is rapidly cooled to the surface of the niobium alloy to form a weld bead. Although the energy of the niobium alloy side reaches 70%, it is still insufficient to penetrate the niobium alloy so as to form an incomplete penetration at the root.

When the titanium side of the relatively small melting width, but the deep penetration, the weld surface shape is better; C-103's energy reaches 90%, so that the melting of the niobium alloy is sufficient, the interface is well combined.

4 Conclusions The joints of BT5 "1 titanium alloy and C-103 niobium alloy connected with the appropriate electron beam welding process specifications were well formed without defects such as cracks.

-1 titanium alloy side of the melting width is large, but the penetration is small, C-103 tantalum alloy incomplete penetration; when the C-103 tantalum alloy with a large duty cycle, BT51 titanium alloy side of the relatively small melting width, However, the depth of penetration is very large and the surface of the weld seam is well formed. The C-103 niobium alloy melts well and the interface is well bonded.

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