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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

Vacuum Brazing Furnace

Metallurgical Studies of the Vacuum Brazing of Aluminum

1.Brazing materials

When vacuum brazing aluminum and aluminum alloys, most aluminum-based solder materials used for vacuum brazing are based on aluminum-silicon eutectic and add a small amount of magnesium, an element that can improve wetting properties. Because magnesium is a very strong activator, during the brazing process, magnesium vapor can combine with the remaining oxygen in the brazing atmosphere or the oxygen in the water vapor to protect the parts from re-oxidation, and may also penetrate into the oxide film on the surface of the parts that has not been cleaned. and remove it. In addition, in order to improve the soaking and gap-filling capabilities of the solder, the “process cover” formed by the speaker itself after assembly is used to place an appropriate amount of magnesium chips on the bottom plate of the inner cavity to obtain a good soldered joint.

2.Vacuum brazing process

(1) Cleaning the material before welding The vacuum fiber welding process does not allow oil stains on the surface of the parts. If oil stains exist, they will remain on the metal surface after heating, which will hinder the flux and destroy the wetting and spreading of the liquid flux on the base metal. and good brazing seam formation.

The cleaning steps are as follows:

Parts: alkali washing (oil removal) → cold water washing → pickling (photochemical) → cold water washing → hot water washing → drying

Solder: sandpaper polishing

(2) Assembly and positioning of parts

Assembly is carried out on the bench, and is operated by a dedicated person wearing gloves to prevent sweat on the hands from contaminating the parts to be welded. The parts are assembled using self-clamping methods, relying on positioning pins and the self-weight of the parts to fix them. In order to facilitate assembly, the ring-shaped solder material is pre-cut according to the size of the part. The angularly ground positioning blocks are evenly placed between the oval plates, which can reduce deformation and improve the accuracy of the inner cavity.

(3) Process parameters and processes

In order to obtain a good brazing seam and control the deformation of the workpiece, the brazing process parameters must be reasonably selected. The main parameters are as follows:

Vacuum degree: 1.0×10^-2~1.0×10^-3Pa

Brazing temperature:580-604C

Cooling method: air cooling in the furnace

Out of oven temperature:<100C

The equipment uses a vacuum brazing furnace with grid vacuum for operation, which is safe and reliable.

After the workpiece is assembled, it is removed from the bench and placed flat between the stainless steel plates on the guide rails in the vacuum furnace. The five temperature measuring thermocouples in the furnace are inserted into the small holes at different positions around the workpiece. Due to the large volume of the workpiece, the gas output of the workpiece increases significantly at 520C, resulting in a decrease in vacuum in the furnace and affecting the overflow of solder. In order to improve the brazing seam formation, we extended the holding time at 400C and reduced the holding time at 500C, and achieved obvious results. Vacuum cooling to 450C, fill the furnace with high-purity nitrogen, and start the fan circulation system to rapidly cool to below 100C and discharge.

3.Post-weld inspection

The obtained workpiece brazing seam has a uniform, full and bright appearance. After electrical performance testing and mechanical dimensional accuracy measurement, it meets the design requirements.