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- Flame brazing
Flame brazing is generally used for pin welding of small parts, low volume production and aluminum assemblies. Manual flame brazing is sometimes used to connect piping to headers, heat exchanger elbows and other similar joint shapes. Air-gas or oxy-fuel torches can be used. Adjust the flame of the torch to a weak reducing flame. Heat is applied to the localized locations to be joined until the flux and solder melt and wet the surface of the base metal. Since the melting point of the solder is close to that of the base metal, special care must be taken to avoid overheating the base metal.
- Furnace brazing
When flux is used, aluminum alloys can be brazed in a furnace in an air atmosphere, but it is better to use a controlled atmosphere. Flux-free brazing can be achieved as the wet components are eliminated during the drying process. In air or nitrogen atmosphere with dew point of -15℃, special non-corrosive flux can be used. Under the conditions of argon and vacuum, flux can not be used. During brazing, the temperature of the furnace must be kept uniform, and the temperature of the brazed workpiece does not exceed ±15 °C.
- Brazing in an air furnace
Brazing furnaces for brazing aluminum alloys have a lot in common with heat treatment furnaces for aluminum alloys. These devices are designed to operate in the temperature range below 650°C with a temperature control accuracy of ±3°C (eg 650°C ± 3°C). The stove can be heated by gas or oil as well as by electricity. The air in the furnace is forcedly ventilated to achieve uniform temperature in the furnace by improving the speed of heat conduction. The recommended process is to adjust the furnace cycle time, heating the assembly to the brazing temperature, and then holding it for 30~120s. Excessive exposure to this temperature will result in detrimental diffusion, corrosion or other undesired flux reactions.
- Inert gas brazing
Various designed furnaces can be brazed with inert gas. Before flushing the system with inert gas, a combination of heating and evacuation must be used to remove water molecules from the workpiece surface. For brazing with flux, an inert gas atmosphere is sufficient. The inert gas must have a dew point lower than -51°C. In order to reduce the cost, nitrogen gas is usually used, but also helium and chlorine gas can be used. From the perspective of preventing oxidation, hydrogen gas can be used, but its danger is too great. The main heating exchange method.
- Brazing in vacuum
Aluminum alloys can be brazed in vacuum without flux. Furnaces with a vacuum of 10-6 to 10-5 are often used in conjunction with magnesium, which acts as a denaturant for absorbing gaseous oxygen, oxide films and aluminum. Furnace brazing is mainly used for brazing heat exchangers, the joints of main structural parts are vertical, and vacuum brazing is not recommended.
- Brazing of dissimilar metals
Aluminum can be brazed with other metals. Titanium, nickel, cobalt and beryllium can be directly brazed with aluminum; other alloys can be pre-plated with nickel to improve the fluidity of the alloy and protect the surface from oxidation; copper and brass cannot be directly brazed with aluminum and aluminum alloys, requiring special measures to weld.
