[China Aluminum Network] Welding methods that can connect high silica and alumina include: fusion welding, brazing, and solid phase welding. The performance of fusion-welded joints is poor, and generally high-energy density welding with rapid thermal cycling and low heat input, including electron beam welding and laser welding, is helpful to reduce the defects caused by fusion welding. Therefore, the research conducted in this area in recent years many. The brazing method is a metal welding method in which the metal is melted after the base metal is melted, and the space is filled with the molten metal after dissolution and diffusion. Solid-state welding technology refers to the welding method that applies static or dynamic pressure to the surface of the weldment after heating, with or without heating, and solidifies the two materials when the base material does not melt. Friction welding, diffusion welding, explosion welding, ultrasonic welding and so on are all examples. High pressure silicon aluminum alloy available pressure welding methods are: friction welding, vacuum diffusion welding and so on.
Laser welding studies have shown that high-silicon-aluminum materials need to be connected using low-power fusion welding methods. Due to the high content of Si in the alloy, needle-like eutectic silicon and thick plate-like polygons are formed in the metal structure of the weld. The primary silicon, severely fractured the matrix; the metal in the near-seam region is prone to overheating and grain growth, resulting in a significant decrease in the mechanical properties of the weld and loss of use value. Laser welding has the advantages of large power density, large ratio of depth to width of weld, small heat affected zone, small workpiece shrinkage and deformation, and fast welding speed. This welding method is suitable for high-silicon-aluminum welding. Zhang Weihua et al. studied the microstructure and properties of ZL109 silicon aluminum alloy CO2 laser welded joints and obtained dense and fine grained joints. The heat input of the welding has a significant effect on the mechanical properties of joints, and the heat input increases, and the joint resistance increases. Tensile strength and elongation after breaking both increased first and then decreased. When the heat input was 44 J/mm, the tensile strength and elongation after breaking reached a large value, which were 121.2 MPa and 4.3%, respectively.
Electron beam welding Electron beam welding uses high-speed electrons generated by a high electric field to form a stream of electrons after focusing, hitting the welded part of the metal to be welded, transforming its power into heat, and welding the welded metal. The electron beam has high energy density, strong penetration ability, large depth-to-width ratio of the weld, fast welding speed, and low input energy, so the heat affected zone is small and welding distortion is small. Therefore, the electron beam welding quality is good, and the mechanical properties of the weld seam are high. Shi Lei et al. performed vacuum electron beam welding on piston crowns and forged piston skirts of AlSi12CuMgNi aluminum alloy extrusion castings, and studied the microstructure and mechanical properties of welded joints under optimized process conditions. The results show that the joints are well-formed, there is no obvious heat affected zone, and the weld seam is narrow; the weld zone is mainly composed of fine α-Al phase, α+Si eutectic, primary crystal silicon and Mg2Si and other strengthening phases; the center of the weld is formed. It is a fine equiaxed crystal and a dendrite; the fused zone mainly consists of columnar crystals. The joint strength is not lower than that of the squeeze casting parent metal. The hardness of the weld is higher than that of the parent metal. A large number of torn and dissociated surfaces are distributed on the tensile fracture surface of the welded joint, showing brittle fracture.
Different from brazing and welding methods, conventional brazing is the use of (or automatically generated in the process) brazing material with a lower melting temperature than the base metal. The operating temperature is lower than the solidus of the base metal and higher than the liquidus of the brazing material. A welding technique. During brazing, the workpiece is usually heated by the entire body or evenly around the brazing seam. Therefore, the relative deformation of the workpiece and the residual stress of the welded joint are much smaller than those of the welding. In today's manufacturing industry, high-silicon-aluminum materials are generally used in high-precision devices in aerospace machinery manufacturing. For these devices brazed welding, the impact on the workpiece is also small. Since the high-silicon aluminum alloy contains a hard silicon phase, the solder has poor wetting properties to the series of materials, and it is difficult to achieve an effective connection by an ordinary soldering method. Hou Ling et al. are conducting high-silicon-aluminum brazing tests. The Ni-Cu-P, Au and Cu layers were pre-plated on the 65Si35Al alloy substrate first, and then the Ni-Cu-P, Au and Cu layers were separately plated, which effectively improved its soldering performance. Using Sn-Pb, Sn-Ag-Cu, Sn-In, and Sn-Bi solders to perform soldering analysis on 65Si35Al alloy samples with different coatings in the furnace, including the use of metallurgical microscopy and spectroscopy. The analytical (EDS) function of scanning electron microscopy and other testing methods were used to examine the microstructure, morphology and phase composition of the welded joints. The influence of brazing process parameters on the quality of the brazed joints of the 65Si35Al alloy was analyzed. The causes of macro defects and micro defects in joints and the differences in the wetting properties of brazing materials for different coatings.
Friction welding Friction welding is the use of the heat generated by the end faces of the workpieces moving against each other and friction, so that the ends reach the thermoplastic state, and then quickly forged to complete the welding method. This welding method has not been studied for a long time. It was a process proposed in 1991, but it has also been rapidly developed. N. ARODRIRIGUEZ et al. studied the friction welding of A319 and A413 aluminum-silicon cast alloys. The experimental results show that the distance between the particles in the weld zone decreases and the corresponding hardness increases. Ji Yajuan et al. studied the hardness, microstructure and mechanical properties of friction stir welding joints of ZL114A aluminum alloy under different parameters. Experimental results: The microstructure of the welding center area is a fine equiaxed crystal. The silicon particles were refined in the welding process and evenly covered the entire weld zone. The grain of the weld was small, uniform and dense, and no defects such as blowhole cracks were observed.
Diffusion welding diffusion welding is the use of localized plastic deformation between the materials in contact with each other at high temperatures, the close adhesion between the surfaces and the interdiffusion between the surfaces to generate metal bonds, thereby obtaining a certain form of integral joints. Interdiffusion between atoms is the basis for achieving diffusion connections. Diffusion welding requires the use of relatively large pressures, requires high precision in the mating surface, makes it difficult to uniformly pressurize complex components, and even requires expensive and complicated fixtures. Therefore, diffusion welding Requirements more high-end. Diffusion welding can be divided into dissimilar material diffusion welding, diffusion welding of the same kind of material, adding intermediate layer diffusion welding, superplastic forming diffusion welding, isostatic pressure diffusion welding, transitional liquid phase diffusion welding (TLP), among which transitional liquid phase diffusion welding. (TLP) combines the advantages of brazing and solid-phase diffusion welding to form a new joining method. The principle is to place the intermediate layer alloy matching the matrix material on the connecting surface. Domestic and foreign scholars have begun to deepen the method. Research. Research on TLPs in China is still in its infancy. It is mainly aimed at welding processes for some dissimilar hard-to-weld metals. Compared with domestic research, the research direction of foreign countries is broader. It involves not only the research of the process, but also the simulation of TLP welding, and focuses on the key factors of the TLP process. At present, the research on TLP at home and abroad mainly includes the following aspects: Engineer Wang Xuegang of Shandong Electric Power Research Institute adopts self-developed Fe-Ni-Si-B amorphous metal foil tape as intermediate layer material and TLP process in open gas. In the protected environment, the steel pipe used in the welding power station can obtain continuous and uniform weld microstructure and better mechanical properties than manual fusion welding. The process parameters include intermediate layer material, heating temperature, holding time, pressure, and requirements for welding end surfaces. Liu Liming and Niu Jitai et al. used vacuum diffusion welding to weld aluminum matrix composite SiCw/606Al. Through series of experiments, the results showed that when the material is used for diffusion welding, the welding temperature is the main process parameter that affects the strength of the joint. When the welding temperature is between the matrix In the liquid-solid two-phase temperature range of the aluminum alloy, a liquid matrix metal appears on the bonding surface, and a higher joint strength can be obtained. Many researchers at home and abroad are engaged in diffusion welding research, but there are not many researches on diffusion welding of silicon aluminum alloys. The research prospects and exploration space in this area are relatively long-term.
High-silicon aluminum alloys play an important role in aerospace, aviation, automotive, and space technology. Research on high-silicon aluminum alloys is becoming more and more in-depth. In the development and application of high-silicon aluminum alloys, related welding methods, It is also a big trend to invest more in welding technology. The application of these fields to the high-silicon-aluminum welding joints requires very high performance, coupled with the high silicon-aluminum material containing silicon, which is easy to oxidize, which has high requirements for high-silicon-aluminum welding technology and welding methods. Welding and soldered joints can not meet the welding requirements of the weldment in some applications, and use more advanced welding methods - diffusion welding is the trend of silicon aluminum alloy welding research.
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