Vacuum Brazing and Vacuum Heat Treatment of Aluminum Alloy Radiators

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Aluminum alloys are light in weight, corrosion-resistant, and have excellent thermal properties. They are commonly used in aerospace, car bombs, etc. to build heat exchangers and complex structures. For aluminum and aluminum welds, the fabrication and removal of aluminum foil can interfere with the smooth operation of the weld and cause errors such as condensation, air holes, etc. The use of vacuum vacuum brazing aluminum alloy does not require inhibitors, thereby greatly reducing the oxygen concentration of the vacuum welding process and improving the production efficiency.

Aluminum alloy case radiators are an aluminum alloy cooling solution for everyday use. It is characterized by high durability, light weight, high thermal conductivity and compact construction.

1 The principle and mechanism of vacuum brazing of aluminum alloys

The brazed connection is under vacuum, and the temperature inside the vacuum chamber is set to a specific area. At this temperature, the material is in a fixed state and the spoon is in a liquid state. The liquid is on the surface, it is easy to flow, fill, expand, interact, and finally cool and solidify, realizing the metal connection method. The aluminum alloy has strong strength to hydrogen and oxygen, and a dense oxide film is formed on the surface during welding, which hinders the connection between the brazed joint and the nut. This is one of the main obstacles to aluminum welds. Under vacuum conditions, most gases can be cleaned with very little oxygen, effectively eliminating the harmful effects of air on welds and removing oxide layers under vacuum conditions. In addition, metallic Mg plays an important role in eliminating the oxide layer. Heating converts the Mg vapor into Mg vapor, removing the oxide film from the polymer surface. The thermal expansion coefficient of Mg is lower than that of aluminum, aluminum expands rapidly by heating, and the relatively low expansion rate of oxide film continues. The Mg vapor forms a chemical reaction with the remaining water vapor in the vacuum. Smelting cemented carbide reduces the oxygen concentration, which splits and dissolves the oxide film, thereby increasing moisture through other liquid substances.

2 Advantages of vacuum brazing technology

Vacuum brazing technology uses potassium nitrate to prevent product contamination, create good and safe production conditions, and make products with good anti-corrosion effect. In addition, this provides significant savings in the cost of additional potassium chloride, which bypasses the complex flux cleaning process. At the same time, the metal material has strong fluidity, which can weld complex parts and improve the success rate of product manufacturing. Vacuum brazing technology is designed for long life, low maintenance costs, and is suitable for a variety of materials most commonly used in aluminum alloys.

3 Influencing factors of vacuum brazing of aluminum alloy radiator

In the process of practical operation, vacuum brazing has defects such as loss of solder, incomplete welding, incomplete welding feet, corrosion of raw materials, structural deformation of radiator, and surface erosion of base metal. The reasons for the above problems are explored, and the main influencing factors are raw materials, vacuum brazing temperature, cleaning before welding, brazing environment, holding time, vacuum degree, etc.

4 Practical analysis of vacuum brazing process of aluminum alloy radiator

4.1 Process flow

The heat exchanger is mainly composed of baffles (composite plates), side walls, wings and seals. In vacuum brazing, the composite plate of the heat sink plays a key role. All components of the water heater are dimensioned, profiled, and then surface treated. These include processes such as rinsing, rinsing, pickling and drying, and finally vacuum cleaning, post-heating, temperature, etc. The heat exchanger after vacuum brazing can be mechanically corrected for deformation problems. The pressure test checks the back pressure of the AC unit by air penetration, leaks. To improve the packaging of the heat exchanger, the appearance of the heat exchanger can be cleaned, dried and painted.

4.2 Temperature setting

Since aluminum alloys become more active during heating, rapid heating can lead to uneven mold temperatures, deformation due to thermal stress or zone relief, which can affect the dimensional stability of the part. As the brazing temperature is approached, if the increase rate is too slow, the solid-liquid temperature of the polymer, the residence time between the low brazing group and the vapor pressure will increase, and the remaining brazing group will remain in an infusible state, brazing The connection won’t dissolve either. Therefore, the heating rate should usually be increased accordingly to 50oC between 600°C. In this study, a graded heating method was used to adjust the furnace temperature at different time periods of 300°C, 400°C, 520°C, and 570°C. The advantage of incremental heating is that it is kept at the set furnace temperature for a certain time, so that the temperature of the workpiece is as close to the set temperature as possible, the heating speed of the workpiece is controlled, the workpiece is heated evenly, it is convenient to melt the cemented carbide, fill the gap, and at the same time Avoid deformation due to overheating of the workpiece. The shock heat was set at a workpiece temperature of 600°C, between the highest melting point of the polymer and the lowest melting point of the base metal.

4.3 Cleaning

Cleaning welding parts before vacuum brazing joints is an important measure to ensure the quality of aluminum and aluminum alloys. Aluminum alloys are cleaned to remove surface oxide films and oil contamination to prepare brazed joints with nuts. The cleaning method is chemical cleaning with an organic solvent to remove the oil pollution of the aluminum alloy. The purification process is organic and is used for oily river water acid drying. After cleaning, place parts in clean, dry containers to prevent contamination, such as gasoline. In addition to chemical cleaning, mechanical cleaning can also be performed to remove aluminum surfaces. For example, polishing grinding, sandpaper grinding, etc., this method is inefficient and not suitable for mass production.

4.4 Scientific selection of radiator vacuum brazing brazing materials

The aluminum alloy radiator material is made of 6 series aluminum alloy plate. It has the advantages of good processing performance, high toughness and corrosion resistance, and is widely used in industrial production. In the process of vacuum brazing of 6061 aluminum alloy products, AISi11.5Mg1.5 solder has enhanced applicability and can meet the requirements of vacuum brazing and heat treatment of products.

Vacuum brazing is a brazing process with good application prospects in the current production process of aluminum alloy radiators. In the practice process, in order to meet the production needs of aluminum alloy radiators, the raw materials, vacuum brazing temperature, surface treatment process, brazing environment, vacuum degree, holding time, etc. should be strictly controlled to reduce the loss of brazing material, discontinuous welds, The occurrence of defects such as dissolution ensures the welding quality of the aluminum alloy radiator. At the same time, while clearly understanding the scientific application value of heat treatment process, we can explore the most suitable heat treatment scheme according to the specific situation and production requirements of aluminum alloy radiators, so as to meet the design requirements of aluminum alloy radiators and subsequent processing requirements, and improve the quality of radiators. .

Equipment selection: The RVB series vacuum brazing furnace produced by SIMUWU is a high-quality product for the vacuum heat treatment of tooling and molds. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum brazing process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.