It has been recognized in practice that niobium is a very poorly welded material. The poor weldability is mainly manifested in two aspects of brazing and fusion welding. Other welding methods such as brazing and diffusion welding are easier than brazing or welding. At present, the laser welding method has become the leading technology of welding boring, and the welding method is brazing welding. During the brazing process, both the base metal and the filler material are melted and condensed to form a weld. Due to the particularity of the material, there are many factors involved in welding. The performance, scale and pretreatment conditions of the coffin and filler materials must be considered. In order to improve the weldability of lanthanum brittle materials, materials with relatively good ductility (such as aluminum-silicon alloy) are used as welding filler materials during welding to complement the advantages of metallurgical reaction.

In the welding method and process, it is necessary to limit the melting amount of the crucible and prevent the weld from being contaminated. The electron beam welding and the laser welding method are all high-energy beam welding, which can limit the excessive melting of the base metal to prevent the joint. The quality is getting worse. The thermal radiation process in which the laser beam interacts with the material is further divided into laser thermal conduction welding and deep fusion welding. If the welding is not preheated, the amount of welding deformation will be difficult to control. Under the influence of other factors, the laser deep-fusion welding will increase the probability of cracking of the base metal and the weld, and the direction of crack propagation is irregular. Regular cracks are difficult to repair. The use of thermal soldering to weld crucibles, because the energy delivered to the workpiece is small, the weld penetration is shallow, the probability of successful welding is greatly increased. According to the characteristics of laser thermal soldering, the samples were welded with low power parameters, and the mechanical properties were tested. The fractures were subjected to electron microscopic analysis. In addition, weld penetration, microstructure, and defects were examined for metallographic samples that were welded in parallel.

In the design of mechanical properties samples, two factors are fully considered: (1) Sampling according to the national standards, the specific size and shape of the tubular specimens are specified in the national standard GB 2651-89 "Test method for tensile joints of welded joints". (2) Considering the brittleness characteristics of the tantalum material, the designed sample is a sample that is easy to clamp and stretch (see Figure 1). The main parameters of welding are: input power is 1.2kW, and welding speed is 700mm/min. The shielding gas flow rate varies between 15 and 20 L/min. The filling material was a 0.4 mm thick Al-Si alloy. The feed amount of the 铍 sample during machining is 0.08~0.12mm. After machining, the parts are vacuum degassed and then welded. The parameters are vacuum degree of 10-2Pa, heating temperature of 200~400 °C, and holding time of 2h.

After metallographic examination, it is found that: (1) the weld is well formed; (2) there is no weld microcrack in the weld and heat affected zone; (3) there are shrinkage holes of different sizes in the root area of ​​the weld, and most of them are welded along the weld. The slits are distributed in a chain shape, forming a through-state along almost the circumferential seam. Individual shrinkage cavities grow toward the surface of the weld, only 0.11 mm thick from the surface of the weld; (4) The crystal structure of the weld is mostly fine dendrites and equiaxed crystals. Composition. According to the area obtained from the metallographic examination results, the tensile strength of the weld is calculated to be 181 to 252 MPa. After the welded sample was broken, the fracture morphology was observed with an electron microscope. The results show that most of the area of ​​the sample is broken in the weld, and very few sections are broken on the base metal. The fracture is a cleavage fracture-brittle fracture. Individual samples have large porosity defects, and the larger pores have a thickness of about 0.47 mm, which traverses the entire weld.