Aluminum vacuum brazing technology
Analysis of vacuum brazing
Lt-3 aluminum composite plate is manufactured by cold rolling process. First roll the core metal 3003 into shape and then roll the epithelial metal 4004 over the top of the core metal. The core metal 3003 belongs to al-mn alloy, with good corrosion resistance and pressure processing.
Cortical metal 4004 is based on eutectic al-si alloy. It has good wettability and fluidity, containing 1.0%-2.0% Mg, which helps to remove the oxide film. Vacuum brazing cladding plate is more convenient to use than wire, tape or powder. When the cladding metal on the brazed sheet melts, it wets the bonding base metal directly and immediately fills the gap.
Joints may be formed only by slight diffusion. The chemical composition and melting temperature of lt-3 aluminum composite plate are shown in the table below.
Chemical composition table of lt-3 aluminum alloy core and core layer
The melting temperature of the material/C Si Fe Cu Mn Mg Zn Al
Core layer (3003 aluminum alloy) 0.60.70.05-0.21.0-1.5/0.1 edge 643-654
Leather (4004 aluminum alloy) 9.0-10.50.80.25 0.1 1.0-2.0.2 residual 559-591
Welding process of vacuum brazing
Cleaning before vacuum brazing
High cleanliness of workpiece surface is required for brazing of aluminum and aluminum alloys. In order to obtain good quality, the oil and oxide film on the surface must be removed before brazing. By washing with Na2CO3 solution under 60-70 ℃ for 5-10 minutes, then rinse with water, can remove surface oil; By using NaOH solution under 20-40 ℃ for 2-4 minutes to remove surface oxidation film, and then rinse with hot water; After removing the surface grease, the workpiece and oxide film can be cleaned in tap water and finally dried with air. After treatment, brazing and brazing as soon as possible within 6-8 hours.
Due to the activity of aluminum, if the metal surface is kept too long, it is easy to regenerate oxide film on the metal surface. The surface of the workpiece should not be over-polished before welding to avoid damage to the metal skin. It is also easy to break the smoothness of the workpiece surface during grinding, which makes brazing difficult.
Vacuum brazing technology
In general, vacuum brazing adopts the stage heating mode to ensure the uniform heating of the workpiece. Vacuum brazing technology parameters is as follows: in the brazing temperature control instrument set temperature 620 ℃, keep 15 minutes to 30 minutes, 3 x 10-3 pa, vacuum heating rate at 10 ℃ / min. In the initial cooling stage, the brazing temperature control at 10 ℃ / min, ends at 450 ℃, and then use the furnace cooling to room temperature.
Using six different brazing holding time and temperature for 15 min - 90 min and 595-620 ℃ vacuum brazing aluminium radiator experiment was carried out. The effect of holding time and temperature on weld structure of vacuum brazing was determined by scanning electron microscopy. Microscope, X-ray energy dispersive spectrometer and hardness test. Relationship.
The results show that with the extension of vacuum brazing heat preservation time and the appropriate increase of heat preservation temperature, the element diffusion between welds becomes more and more sufficient, and the shape of Si segregation changes from dendritic to point-like. When the vacuum brazing process stay 75 minutes under 615 ℃, the welding structure exists only in a small dot Si segregation structure, most of them dotted Si segregation structure. Solid solution, the solder has a little corrosion to the base material, the bonding is stronger, the vacuum brazing process is better.