It has been shown that high silicon aluminum materials need to be connected by a lower power welding method. Due to the high content of Si in the alloy, the acicular eutectic silicon and the coarse plate-shaped polygons are formed in the weld metal structure. Silicon, severely cracking the matrix; the metal in the near-slit area 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 high power density, large ratio of weld width to width, small heat affected zone, small shrinkage and deformation of the workpiece, 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 joints with fine microstructures. The heat input of the weld has a significant effect on the mechanical properties of the joints, the heat input is increased, and the joints are resistant. Both tensile strength and elongation after fracture increased first and then decreased. When the heat input was 44J/mm, the tensile strength and elongation after fracture reached the maximum, which were 121.2MPa and 4.3%, respectively.
Electron beam welding
In the electron beam welding, a high-speed electron generated by a high electric field is used to form a welding method by focusing a metal stream, striking a welded portion of the metal to be welded, and converting the power into heat to fuse the metal to be welded. The electron beam has high energy density, strong penetrating ability, large weld width-to-width ratio, fast welding speed and small input energy, so the heat affected zone is small and the welding deformation is small. Therefore, the quality of electron beam welding is good and the mechanical properties of the weld are high. Shi Lei et al. carried out vacuum electron beam welding on the piston top ring and forged piston skirt of AlSi12CuMgNi aluminum alloy extrusion casting, and studied the microstructure and mechanical properties of the welded joint under optimized process conditions. The results show that the joint is well formed, there is no obvious heat affected zone, and the weld is narrow; the weld zone is mainly composed of fine α-Al phase, α+Si eutectic, primary silicon and Mg2Si strengthening phase; weld center structure It is a small equiaxed crystal and dendrites; the fusion zone structure is mainly columnar crystal. The strength of the joint is not lower than that of the extruded cast base metal, and the weld hardness is higher than that of the base metal; the tensile fracture section of the welded joint is distributed with a large number of tearing edges and dissociation surfaces, which is brittle fracture.
Different brazing and welding methods, conventional brazing is the use of (or automatically generated in the process) lower than the melting temperature of the base material, the operating temperature is lower than the solid phase of the parent metal and higher than the liquidus of the solder Kind of welding technology. During brazing, the workpiece is often heated by the whole or uniformly heated over a large area around the brazing joint, so the relative deformation of the workpiece and the residual stress of the welded joint are much smaller than the fusion welding. In the current manufacturing industry, high silicon aluminum materials are generally used in high-precision devices in the aerospace machinery manufacturing industry. For these devices, soldering is used to minimize the effect on the workpiece. Since the high silicon aluminum alloy contains a hard silicon phase, the solder has poor wettability to the series of materials, and it is difficult to achieve effective connection by ordinary soldering methods. Hou Ling et al. conducted a high silicon aluminum brazing test. The method of pre-chemically pre-plating Ni on the 65Si35A1 alloy substrate and then plating the Ni-Cu-P, Au and Cu layers respectively is used to effectively improve its solderability. The soldering test of 65Si35Al alloy samples with different coatings was carried out by using Sn-Pb, Sn-Ag-Cu, Sn-In and Sn-Bi solders, including the use of metallographic microscope with energy spectrum. Analytical (EDS) function scanning electron microscope and other testing methods were used to detect the microstructure, morphology and phase composition of the welded joints. The influence of brazing process parameters on the quality of the brazed joint of 65Si35Al alloy was discussed. The joint produces macroscopic and microscopic defects and the difference in solder wetting properties of the different coatings.
Friction welding is a method in which the end faces are brought into a thermoplastic state by utilizing the heat generated by the mutual movement of the workpiece end faces, and the ends are brought into a thermoplastic state, and then rapidly forged. This welding method has not been studied for a long time. It was a process proposed in 1991, but it has also been developed very quickly. N.ARODRIRIGUEZ et al. studied the friction welding of A319 and A413 aluminum-silicon cast aluminum alloys. The experimental results show that the particle spacing is reduced in the weld zone and the corresponding hardness is also improved. Ji Yajuan et al. studied the hardness, microstructure and mechanical properties of the friction stir welded joint of ZL114A aluminum alloy under different parameters. Experimental results: The tissue in the center of the weld is a small equiaxed crystal. The silicon particles were refined during the welding process, and evenly covered in the entire weld zone. The weld beads were fine, uniform and dense, and no defects such as pore cracks were observed.
Diffusion welding is the combination of metal bonds between the materials in contact with each other at high temperatures, the adhesion between the surfaces and the interdiffusion between the surfaces to obtain a combination of metal bonds, thereby obtaining a certain form of integral joint. Interdiffusion between atoms is the basis for diffusion bonding. Diffusion welding requires large pressures, high precision of mating surface, difficult to uniformly pressurize complex components, and even expensive and complicated fixtures. Therefore, diffusion welding Requires a higher end. Diffusion welding can be divided into dissimilar material diffusion welding, same material diffusion welding, intermediate layer diffusion welding, superplastic forming diffusion welding, isostatic pressure diffusion welding, transition liquid phase diffusion welding (TLP), etc., among which transition liquid phase diffusion welding (TLP) combines the advantages of both 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 joint surface. Domestic and foreign scholars have begun to deepen this method. Research. The domestic research on TLP is still in its infancy, mainly for the welding process of some different kinds of difficult-to-weld metals. Compared with the domestic research, the research direction of foreign countries is broader, not only involves the research of the process, but also the simulation of TLP welding. The key factors of the TLP process are studied. At present, the research on TLP at home and abroad mainly has the following aspects: Wang Xuegang, an engineer of Shandong Electric Power Research Institute, etc., uses self-developed Fe-Ni-Si-B-based amorphous metal foil tape as intermediate layer material and TLP process in open gas The steel pipe used in the welding power station under the protection environment can obtain continuous and uniform weld structure and better mechanical properties than manual fusion welding. The process parameters include the intermediate layer material, heating temperature, holding time, pressure and requirements for the welding end face. Liu Liming, Niu Jitai and others used vacuum diffusion welding to weld aluminum-based composite material SiCw/606Al. Through a series of experimental studies, the results show that the welding temperature is the main process parameter affecting the joint strength during the diffusion welding of the material. When the welding temperature is between the matrix When the liquid-solid two-phase temperature range of the aluminum alloy occurs, a liquid base metal appears on the bonding surface, and a high joint strength can be obtained. Many researchers at home and abroad are engaged in the research of diffusion welding, but there are not many researches on diffusion welding of silicon-aluminum alloy. In this respect, the research prospects and exploration space are relatively long-term.
High-silicon aluminum alloy plays an important role in aerospace, aviation, automotive, space technology and other fields. The research on high-silicon aluminum alloy is getting deeper and deeper. In the development and application of high-silicon aluminum alloy, the welding method is related. More research into welding technology is also a major trend. The application of these fields is very high on the performance of high silicon aluminum solder joints. In addition, the high silicon aluminum material contains high silicon and easy oxidation. This requires high silicon aluminum welding technology and welding methods. Welded and brazed joints do not meet the welding requirements of weldments in some applications, and more advanced welding methods—diffusion welding is the trend of silicon-aluminum alloy welding research.