Vacuum brazing technology of aluminum and aluminum alloy

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1. Vacuum Brazing Process

1.1 Cleaning of the workpiece before brazing

Before brazing, the oil stains on the surface of the solder and aluminum must be removed. However, caustic sodium water solution cannot be used for degreasing. Because the magnesium in the solder is easy to react with alkali, it affects the vacuum degree, increases the consumption of getter metal, and causes the flowability of the solder to decrease. The process flow of the cleaning process is shown in the figure 1.

Fig1 Cleaning process

1.2 Assembly and positioning of the workpiece

In order to ensure the relative position of the workpiece and the good contact of the joint during the vacuum heating process, a stainless steel clamp is used for positioning, which has a certain degree of high-temperature flexibility. It can also ensure the close contact of the joint at the brazing temperature. In order to prevent the brazing phenomenon between the solder and the fixture, ceramic paper (ceramic sheet) is often used to separate the solder and the fixture. When assembling the positioning fixture, pay attention to the control of the joint The size of the gap between the assembly and the gap will directly affect the capillary effect of the filling process, which is an important factor that must be considered. When brazing aluminum-based alloys with aluminum alloys, the assembly gap is generally 0.025-0.635 mm.

1. 3 Heating specification during vacuum brazing

Brazing temperature: 20-50C higher than the melting point of the solder.

Brazing holding time: generally 2 to 5 minutes.

Vacuum degree during brazing: generally 10-6 Torr.

When using magnesium activator: 5x 10-4 Torr.

1.4 Vacuum brazing process technology

(1) The workpiece is loaded into the furnace and the getter magnesium is placed.

(2) Evacuate to 10-4 Torr and start heating.

(3) When the furnace reaches 400C, fill with nitrogen, argon, and helium to make the pressure reach a vacuum of 2x 10-1- 3x 10-1 Torr.

(4) The workpiece is raised to 540C, and then evacuated to 10-4 Torr.

(5) When the temperature reaches 600-620 quickly, keep it warm for 2 to 5 minutes, and then perform brazing.

(6) Fill nitrogen, argon, etc. to cool the workpiece to 540. the following.

(7) Take out the workpiece and remove the welding fixture.

A typical brazing process cycle is shown in Figure 2. This process equipment is simple and easy to operate, but it has a long cycle and low productivity.

Fig 2 Brazing cycle

2. Vacuum Brazing Equipment

At present, the new vacuum brazing furnace is mainly of cold wall type, the heating element is arranged in the vacuum chamber, the heating element and the furnace wall are separated by a radiation screen, and the furnace wall is cooled by circulating water. According to the process requirements, the vacuum pipeline system is equipped Valve filled with shielding gas and separate source of metal getter evaporation. To prevent magnesium vapor from entering the vacuum piping system,

Sometimes an oil jet containing high boiling point oil is installed in front of the vacuum pump, and the extracted gas passes through the oil jet first to protect the vacuum.

The pump is not contaminated by magnesium vapor.

The cold fireplace heats the workpiece faster, the working temperature is higher, the power consumption is small, and the structure is more advanced. The radiant plate is generally made of stainless iron plate, tantalum plate or molybdenum plate. In order to improve the heat insulation effect, the surface finish is required to be high. The heating element is mostly chromium 20-nickel 80 resistance wire or resistance tape, sometimes tantalum tape or silicon carbide rod.

In order to meet the needs of large quantities, the United Kingdom, the United States, Japan and other countries all use continuous vacuum brazing furnaces with multiple studios.

Shanghai Geheng Vacuum Technology Co., Ltd. is a vacuum heat treatment furnace manufacturer with many years of experience in design, manufacturing and production. It mainly produces true air quenching furnaces, double chamber vacuum oil quenching furnaces, vacuum annealing furnaces, vacuum tempering furnaces, and other vacuum furnaces.

Learn more:

Aluminum Vacuum Brazing Furnace

Three Chambers Vacuum Continuous Brazing Furnace

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