There are mainly the following technologies for aluminum alloy brazing:
Flame fiber welding is generally used in small components, small batch production and aluminum combination of nail welding.Manual flame brazing is sometimes used to connect pipes to seat, heat exchanger elbows, and other similar joint shapes.You can use air gas or oxygen gas torch.Adjust the torch flame to a weak reducing flame.The heat is applied to the local position to be joined until the brazing and solder melt and the base metal surface is wetted.As 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.
Brazing in furnace
When brazing is used, aluminum alloys can be brazed in an air furnace, but a controlled atmosphere is better.With the elimination of moisture in the drying process, brazing without brazing agent can be realized.Dew point in an air or nitrogen atmosphere of 15℃, special non-corrosive flux may be used.In argon and vacuum conditions, brazing agent may not be used.When brazing, the furnace temperature must be kept even, and the temperature of the brazing parts shall not exceed ±15℃.
Third, brazing in air furnace
Brazing furnaces for brazing aluminum alloys have many similarities with heat treatment furnaces for aluminum alloys.These devices are designed to operate at temperatures below 650 ° C with a temperature control accuracy of 3 ° C (e.g. 650 ° C ±3 ° C).The furnace may be heated by gas or oil and by electricity.The air inside the furnace is forced to ventilate, and the temperature inside the furnace is uniform by improving the speed of heat transfer.The recommended process is to adjust the furnace cycle time, heat the components to the brazing temperature, and then hold the heat for 30~120s.Prolonged exposure at this temperature will result in harmful diffusion, corrosion or other undesirable brazing agent reactions.
Four, noble gases brazing
All designed furnaces can be brazed using inert gas. Prior to the use of inert gas flushing systems, a combination of heating and pumping must be used to remove water molecules from the workpiece surface.An inert gas atmosphere is sufficient for brazing with flux.Inert gases must have a dew point below 51℃. In order to reduce the cost, nitrogen, helium and chlorine are usually used. Hydrogen can be used to prevent oxidation, but it is too dangerous.
Brazing in vacuum
Aluminum alloys can be brazed in a vacuum without a brazing agent.Furnaces up to 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 film, and aluminum.Brazing in furnace is mainly used for brazing heat exchangers. The joints of main structural parts are vertical. Vacuum brazing is not recommended.
Brazing of heterogeneous metals
Aluminum can be brazed with other metals.Titanium, nickel, cobalt, and beryllium can be brazed directly with aluminum;The fluidity of other alloys can be improved by pre-plating nickel to protect the surface from oxidation.Copper and brass cannot be brazed directly with aluminum and aluminum alloys and require special measures to weld.