There are many welding methods used in brazing of aluminum and aluminum alloys.

【Summary Description】 Induction brazing, vacuum brazing and protective atmosphere furnace brazing are widely used in the brazing of aluminum and aluminum alloys due to their unique and excellent processes, and their development is relatively fast. Focus on them below. 2.1 induction brazing Compared with flame brazing, induction brazing has obvious advantages, such as small deformation of base metal, environmental protection, easy operation, automation, energy saving and emission reduction, low investment cost, high cost performance, and low requirements for employee operation skills. In recent years, some domestic induction brazing equipment manufacturers (such as Bairui Ship Welding Technology Co., Ltd.) have fully applied induction brazing to the brazing of automotive air-conditioning accessories, such as aluminum pipe joints, aluminum pressure plates, aluminum water cooling belts, and aluminum water Cooling plate, condenser and evaporator inlet and outlet pipes, etc. Here are some aluminum alloy brazing samples using induction brazing: 2.2 vacuum brazing Aluminum is more active, easy to form a dense oxide film on its surface. When brazing, it is difficult to remove oxides only by vacuum conditions, and some metal activators, such as Mg and Bi, must be used at the same time. Generally speaking, the mechanism of activator stripping is: on the one hand, the activator reacts with residual O and HO in vacuum to eliminate their harmful effects on aluminum brazing; on the other hand, magnesium vapor penetrates into the lower surface layer of the film and forms a low melting point aluminum-silicon-magnesium alloy together with the diffused silicon. During brazing, the alloy melts and destroys the combination of the oxide film and the base metal, so that the molten solder wets the base metal and spreads on the base metal under the film, so that the surface film is floated and removed. When vacuum brazing aluminum alloy, the vacuum furnace should be selected according to productivity, cost, weldment size and structure. Before brazing, weldments shall be carefully cleaned. The surface oxides can be washed off with acid or alkali. If there is oil on the surface, it can be wiped with alcohol. Generally, the solder is polished with sandpaper to remove the oxide film on the surface, and then the oil is wiped off with alcohol. For larger workpieces, preheating is performed before welding to ensure that all parts of the weldment are evenly heated before reaching the brazing temperature. As the aluminum alloy vacuum brazing mainly depends on Mg activator stripping, for the complex structure of the weldment, in order to ensure that the base metal is fully affected by the Mg vapor, some domestic units have taken the supplementary process measures of local shielding, and achieved good results. The common method is to put the workpiece into a stainless steel cover, put the Mg chip, and then put it into a vacuum brazing furnace for brazing, which can greatly improve the brazing quality. Vacuum degree is the most important and the most difficult to control process parameters in vacuum brazing. To obtain a high-quality joint, it depends to a large extent on the degree of vacuum. According to the experience of some workers for many years, if the brazing equipment is not used for a long time, the vacuum furnace will run for several hours before it can be used. When using, especially in mass production, the time interval between the two uses should be shortened as much as possible, so that the vacuum degree of the vacuum furnace can meet the requirements easily and quickly. Vacuum brazing is an excellent brazing method, but it also has some shortcomings, such as complex and expensive equipment, difficult maintenance technology of vacuum system, etc. The development of aluminum alloy vacuum brazing in China has begun to take shape. The difficulty and key of future development is to develop low melting point solder with low melting point, high mechanical properties and corrosion resistance. Brazing in 2.3 protective atmosphere Due to the expensive equipment and complicated process, the vacuum brazing application of aluminum is limited. To solve this problem, we can replace the vacuum with a neutral atmosphere. This reduces the requirements on the leakage rate of the system, the equipment is simpler, the equipment maintenance problems caused by the deposition of volatile elements are reduced, and the production cost is lower. The heating method mainly relies on electric current, and the heating speed is fast and uniform, which can not only ensure product quality but also improve productivity. In recent years, neutral gas shielded aluminum brazing has been paid attention to and developed rapidly, which is a promising aluminum brazing method. The stripping mechanism of gas shielded brazing of aluminum alloy is the same as that of vacuum brazing of aluminum alloy, mainly by Mg activator. I won't repeat it here. The quality of brazing can be improved by adding bismuth to the brazing filler metal. The gas shielded brazing of aluminum alloy generally uses argon and pure nitrogen, and the purity of nitrogen must be greater than 99.99%. It is reported that for aluminum/aluminum, aluminum/copper joints, there is a connection method using the principle of diffusion brazing. The mixed powder composed of Si and aluminum potassium fluoride flux was sprayed on the aluminum surface for brazing under nitrogen atmosphere near atmospheric pressure, and the effect was satisfactory. The Si may be replaced by a metal such as Cu, Ge, Zn, etc. It forms a eutectic with the low melting point al.

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Brazing of aluminium and aluminium alloys