Aluminum Alloy Vacuum Brazing Process and Key Points

---

Aluminum alloy vacuum brazing process

Aluminum alloys are widely used in aerospace, construction, electrical appliances, automobiles, ships and other sectors due to their light weight, good corrosion resistance, and excellent thermal conductivity, the amount of use is increasing. It has long been considered a structural material for making heat exchangers, waveguides, and many other complex components. The processing technology of aluminum alloy plays a very important role in the manufacture of its products, and one of the important methods is the vacuum brazing process.

Flux selection:

Aluminum has strong chemical activity and usually has a very dense oxide film on the surface. The properties of the oxide film are very stable. When the old film is destroyed , a new film can be formed quickly. During brazing, flux is required to destroy this film , otherwise the molten brazing filler metal cannot be wetted with the base metal. Aluminum vacuum brazing uses an appropriate amount of magnesium powder as flux, and uses magnesium vapor to replace and destroy the aluminum oxide film to improve the wettability of the solder. The infiltration of magnesium vapor also reduces the interfacial tension between the solder and the base metal , thereby enhancing the wetting ability of the solder.

Solder selection:

Most brazing alloys are based on Aluminum – Silicon systems, where (w) Si is typically 7% – 12% . This series of solders are excellent in brazing、strength and color consistency of base metal、platability and corrosion resistance, which are rare and excellent solders. Especially these solders can be modified Greatly increases the toughness and flexural strength of brazed joints.

Adding manganese and other elements to the Aluminum – Silicon brazing filler metal can prepare new brazing alloys, but low boiling point elements such as zinc cannot be added to the aluminum brazing filler metal, otherwise it will cause great pollution to the vacuum brazing furnace.

Process flow and key points:

Process : Solder cutting – Removal of the oxide film on the base metal of the brazing part and the surface of the solder – Solder fixation – Assembly – Vacuum brazing – Inspection.

The surface of vacuum brazed aluminum alloy parts should be thoroughly cleaned, the temperature should be strictly controlled, and the brazing holding time should be as short as possible while ensuring the penetration.

Selection of vacuum furnace:

In order to ensure the high efficiency, no pollution and excellent performance of the finished product, the vacuum furnace should meet the following performance indicators: working pressure ≤1×10 ^-3 Pa, pressure rise rate <0.67Pa/h, temperature control accuracy ±1℃ , The furnace temperature uniformity is ±5℃, and it has the function of air cooling.