Four advantages of copper vacuum annealing process

What are the advantages of vacuum annealing of pure copper?

(1) Effectively prevent hydrogen embrittlement
Vacuum annealing of copper can effectively prevent hydrogen embrittlement. Oxygen-containing copper will become brittle and crack when heated or used in a reducing atmosphere (H, CO, CH). This is because the Cu₂O impurities in the oxygen-containing copper react with the reducing gas to generate water vapor or CO₂.
These gases are insoluble in copper and have no diffusion ability. They form a large pressure in the copper, causing the copper to crack and break during subsequent pressure processing or use. This brittleness may not occur instantaneously and has a certain incubation period. Oxygen-free copper and deoxidized copper (phosphor copper and manganese copper) will also suffer from hydrogen embrittlement when heated in an oxidizing atmosphere and then heated in a reducing atmosphere.

(2) Effectively prevent oxidation
Vacuum annealing of copper can effectively prevent oxidation of copper and improve plasticity. Mirror copper tubes are essential materials in the production of air conditioners and refrigerators. This copper tube has a small diameter (outer diameter 10~20mm), thin wall (0.2~1.8mm), and long body. The copper tube needs to be bent into 90°~180° in the mold at room temperature. The outer edge surface of the bent tube should not be torn. The wrinkles on the inner edge of the tube should be as light as possible. The wall thickness deviation should be less than 20%. At the same time, it must be guaranteed not to break or leak under a pressure of 7MPa. Under 13.3Pa vacuum conditions, T2 copper tubes are heated to 340℃, soft copper tubes are heated to 350~400℃, semi-hard copper tubes are heated to 300~320℃, and soft TUP copper tubes are heated to 420℃. After keeping warm for 60min, the furnace is cooled to below 80℃ and then taken out of the furnace for vacuum annealing. The copper foil used for processing printed circuit boards is a cold-rolled strip with a thickness of 0.02mm. It must be annealed and softened, and there must be no slight oxidation. Heat to 650℃ in a vacuum furnace at 13.3Pa, keep warm for 1h, cool to below 80℃ and take out of the furnace. The surface is bright and the softening effect is good.

(3) Good degassing effect
Vacuum annealing has a good degassing effect on copper. The rotor copper bars are important components of the traction motor of a high-speed EMU with a speed of 250km/h. The quality of the brazing between the rotor copper bars and the rotor end ring has a vital impact on the safe and stable operation of the EMU. When a company brazed the copper bars with the rotor end ring, some of the copper bars always produced bubbles. After vacuum annealing the copper bars before brazing, the gas in the copper bars was removed.

(4) Good degreasing effect
Low vacuum annealing has a good degreasing effect on copper wire and thin tubes. Vacuum annealing of the wire between the wire drawing process can save the degreasing and pickling processes and can be directly painted. Vacuum annealing of gasoline pipes and refrigeration pipes not only removes grease and dirt on the outer surface, but also purifies the inner wall of the copper pipe, thereby eliminating many troublesome cleaning operations. For example, a φ0.6mm capillary can be coiled into a circle and then annealed in a furnace, and the inner wall of the entire 500m long pipe can be degreased at one time. It should be noted that if thin copper wires and thin-walled copper pipes are pressed against each other, the contact surfaces will be welded due to the diffusion of copper atoms. Materials with the same expansion coefficient need to be used as molds to wind them into wire coils and wire rolls, and they should be carried out under low vacuum (13.3Pa) and low temperature (350~600℃). The vacuum annealing process of pure copper materials is shown in the following table.
Vacuum annealing process of pure copper materials

Vacuum Annealing Furnace