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Analysis of Vacuum Brazing Technology for Aluminum Plate Fin Radiator

In the process of producing high-quality aluminum plate fin heat sink products, it is necessary to conduct in-depth research on vacuum brazing technology to ensure that the maximum economic benefits are created at the lowest cost, while meeting the needs of market development and product users. Technicians must fully grasp and understand the basic theoretical knowledge of vacuum brazing technology, clarify its standard process, and reasonably set various process parameters in order to effectively ensure the quality and cost of production of aluminum plate fin type radiators.

Working Principle of Vacuum Brazing for Aluminum Alloy Plate Fin Radiator

In the practical processing and production process of aluminum alloy plate fin heat sinks, the application and working principle of vacuum brazing technology is based on the vacuum environment. By reasonably controlling the temperature in the vacuum furnace within the range below the melting point of the base material and above the melting point of the brazing material, the brazing material in the vacuum furnace can be effectively melted into the required liquid. Then, capillary force is used to force the liquid state brazing material to fill the space between the solid base metal, and they will interact with each other until the temperature cools and solidifies. The current working mechanism of vacuum brazing technology mainly includes three process flows, namely the process of eliminating oxide film under vacuum environmental conditions, the process of filling the gaps of solid base metal with solder in liquid state, and the process of interaction between liquid solder and solid base metal.

Vacuum brazing process personnel must understand that when producing aluminum alloy plate fin type radiators, a stable and dense oxide film is easily formed on the surface of the aluminum alloy material, which can to some extent affect the bonding operation between the brazing material and the base material during the brazing process, leading to vacuum joint cracking at the sealing point of the radiator seal. Therefore, process personnel must attach great importance to the removal of the oxide film on aluminum alloy materials. The mechanism of removing the oxide film mainly includes the following aspects: (1) The effective evaporation of metal Mg into Mg vapor through heating treatment, thereby destroying and eliminating the oxide film on the surface of aluminum alloy materials; (2) The thermal expansion coefficient of metal Mg is much smaller than that of aluminum alloy. Through heating treatment, the oxide film with low expansion rate will crack at the first time; (3) Mg steam will react chemically with the water vapor left behind in the vacuum furnace. When Si diffuses to the surface of the base material, Mg steam will also penetrate the oxide film and penetrate to the base material. This will effectively form an Al Si Mg low melting point alloy on the surface of the membrane material, and the oxide film will automatically float and remove after the melting reaction; (4) After melting the brazing material, the adsorption effect generated can maximize the strength of the oxide film on the surface of the aluminum alloy material, promote the dissolution of the oxide film and penetrate into the brazing material, so that the liquid brazing material can successfully wet the base material.

Analysis of Vacuum Brazing Process for 2 Aluminum Alloy Plate Fin Radiator

2.1 Characteristics of vacuum brazing equipment

In order to produce high-quality aluminum alloy plate fin radiators, processing enterprises must use vacuum brazing furnace equipment. According to the different heating methods in the furnace, we usually divide vacuum brazing furnace equipment into two types, one is hot wall vacuum brazing furnace, the other is cold wall vacuum brazing furnace. Among them, the hot wall vacuum brazing furnace was a commonly used vacuum brazing equipment in the early days. Its most significant characteristics are high efficiency, low cost, and simple production, which are suitable for manufacturing various small and medium-sized components. The disadvantage is that the temperature distribution in the furnace is not uniform enough to effectively meet the production of large parts with complex structure. The cold wall vacuum brazing furnace, as the most advanced modern vacuum brazing furnace equipment, is characterized by the use of a double-layer circulating water cooling structure, which effectively combines the vacuum chamber with the heater, can maximize the heat Radiance in the vacuum environment, avoid a large amount of heat consumption in the furnace, and thus ensure a more uniform temperature distribution in the furnace. With the passage of time and the continuous improvement of vacuum brazing technology, the cold wall vacuum brazing furnace equipment has changed from a bell shaped structure to a multifunctional structure, and the size of the furnace space is also increasing, which can meet the market demand for manufacturing large components.

2.2 Vacuum brazing workflow of aluminum alloy plate fin radiator

When processing enterprises use vacuum brazing technology to manufacture aluminum plate fin type radiators, relevant operators must follow strict and standardized workflow to carry out operations, rather than relying solely on their own experience. Currently, the workflow of vacuum brazing technology in the manufacturing of aluminum alloy plate fin radiators is as follows: (1) prepare qualified manufacturing materials; (2) Clean and assemble the vacuum brazing furnace equipment; (3) Conduct brazing processing operations; (4) Conduct quality inspection on the manufactured products; (5) Dry and clean the qualified products after inspection. When selecting the vacuum furnace equipment, the relevant personnel of the processing plant must select and apply the vacuum brazing furnace equipment according to the actual size and complexity of the radiator welding. The operations involved in the whole brazing process mainly include vacuum pumping, furnace Negage, heat preservation and cooling.

2.3 Vacuum brazing process parameters

In the application process of vacuum brazing technology for aluminum plate fin type radiators, process personnel should correctly recognize the importance of setting process parameters. Among them, vacuum degree is the core process parameter of vacuum brazing technology, and the setting of vacuum degree directly determines the final welding quality. Therefore, when the processing plant is put into long-term use of vacuum brazing furnace equipment, it is necessary to operate the equipment in advance and let it run idle for a period of time before using it to process and produce aluminum alloy plate fin heat sinks. At the same time, the heating rate parameter setting of the vacuum brazing furnace equipment can also affect the welding quality of the product. If the heating rate is too fast, it will cause the surface of the part to lose color, affecting the cleanliness and smoothness of the part surface; If the heating rate in the furnace is too fast, it will cause uneven heating of the processed parts, leading to deformation of the parts; If the heating rate is too slow, it will cause volatilization of components with lower melting points in the brazing material, while the parts with higher melting points will remain solid, making it difficult to effectively wet the base material, and ultimately the parts cannot be accurately brazed. Therefore, operators of vacuum brazing furnace equipment should scientifically control the brazing insulation time and furnace temperature. Among them, the brazing insulation time should be reasonably controlled within 3 minutes after the processed parts reach the liquidus temperature of the brazing material. If the insulation time is too short or too long, it will affect the welding quality of the parts to a certain extent, which is not conducive to the high-quality processing and production of parts in large quantities. The temperature inside the vacuum brazing furnace should be strictly controlled between the liquidus temperature of the brazing material and the solidus temperature of the base material. If the temperature inside the furnace is too low, it will cause the brazing material to not completely melt, thereby promoting the strength of the parts' brazing joints to be too low. If the temperature inside the furnace is too high, it can lead to problems such as corrosion defects inside the furnace.

When the temperature inside the vacuum brazing furnace is less than 365 ℃, the operator can quickly increase the temperature inside the furnace. At this time, it is only necessary to ensure that the temperature difference between the vacuum brazing furnace and the actual temperature of the production parts is controlled within 25 ℃. When the temperature inside the furnace exceeds 365 ℃, the operator must strictly control the insulation time inside the furnace during this stage to ensure the continuous diffusion of Si. When the temperature inside the furnace reaches 525 ℃, metal Mg will undergo sublimation reaction. At this stage, the temperature control requirement in the furnace is the highest, and the operator must ensure that the temperature difference between the furnace and the processed parts is controlled within 20 ℃. When the temperature in the furnace has reached 597 ℃ as shown in the figure, almost all of the metal Mg sublimates, and the oxide film on the surface of the aluminum alloy will be eliminated. The brazing material can effectively wet the base metal parts in the furnace, thus achieving the best brazing operation for the parts.

3 Conclusion

In summary, in order for the processing plant to manufacture high-quality aluminum alloy plate fin radiator products and meet the needs of the vast market users, it is necessary to scientifically apply vacuum brazing technology, complete relevant equipment, arrange professional personnel to operate the vacuum brazing furnace, reasonably set various parameters of the vacuum brazing process, and operate according to the standardized process.

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