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Aluminum Alloy Brazing in Vacuum Furnace

Aluminum alloy electronic chassis

With the continuous development of science and technology, the requirements for the reliability and appearance quality of electronic equipment are increasing day by day. At present, aluminum alloy plate-fin structure electronic chassis with high heat transfer efficiency, compact structure and good adaptability to environmental conditions (such as electromagnetic compatibility, corrosion, high temperature) are widely used in electronic equipment due to its unique advantages. Aluminum alloy plate-fin electronic chassis is generally welded by components such as panels, side panels, heat exchange plates, cooling fins, and partitions. The structure of a common plate-fin chassis is shown in the figure.

Due to the structural and technological characteristics of the aluminum alloy plate-fin chassis, the dimensional accuracy and shape and position tolerance requirements of the chassis welding are relatively high. At present, there are many researches on welding methods of aluminum alloy electronic chassis, mainly focusing on welding methods such as friction stir welding, laser welding, ultrasonic welding, vacuum electron beam welding and TIG welding. Due to the complexity of the plate-fin enclosure, the above methods have their own limitations in terms of welding accessibility and weld corrosion resistance. Especially in the actual production process, due to the large thickness difference (0.2-8.0 mm) of the aluminum alloy plate-fin chassis, the deformation problem of the chassis after welding is relatively serious, which makes the secondary processing of the internal structure of the chassis after welding difficult. In this case, in recent years, vacuum brazing technology has been widely used in aluminum alloy electronic chassis due to its unique advantages.

Vacuum brazing has the following advantages: 1) The brazing temperature is lower than that of the base metal, which has little effect on the structure of the base metal; 2) Even heating, welding should be

Small force and small deformation; 3) Multiple welds can be formed at one time, high production efficiency; 4) No flux is used, which can eliminate the possibility of flux inclusions and improve the corrosion resistance of welds.

During the vacuum brazing process, due to the influence of various factors such as brazing material, process and environment, brazing defects such as brazing filler metal accumulation, cracks, deformation, oxidation and dissolution often occur in the brazing joint.

Aluminum alloy vacuum brazing process parameters

Vacuum brazing process parameters include heating rate, cooling rate, holding time, holding temperature and vacuum degree, etc. Vacuum brazing of aluminum alloy chassis is generally carried out at a vacuum degree of 3×10-3 Pa. The vacuum brazing process route of an aluminum alloy electronic chassis is shown in the figure.

In the case of using adhesive tape or paste solder and tooling for aluminum alloy plate-fin electronic brazing cabinets, the furnace should be heated to about 200°C and kept for 20 minutes to allow the adhesive and the gas released during the heating process to fully Volatilize (the vacuum degree will drop during this process), and the temperature can continue to rise when the vacuum degree is higher than 3x 10-3 Pa. Before heating to the brazing temperature, in order to fully heat the parts, it is generally held for a period of time below the solid-liquidus line of the solder. The length of the holding time is related to the thickness, size and structure complexity of the parts, which is reflected in the figure 550 C’s insulation platform. In this temperature section, the vacuum degree in the furnace should be observed. If the pressure in the furnace is higher than 3×10-3Pa, the heat preservation state should be maintained. Keep the temperature at 550 C until the pressure in the furnace is less than 3x 10-3 Pa before continuing to heat up to 6109C.

The final vacuum brazing temperature of the parts is determined by the melting point of the solder and the base metal. The ideal vacuum brazing temperature should be 30~1009C higher than the solid-liquidus temperature of the solder, but lower than the solid-liquidus temperature of the base metal. . The holding time should be able to ensure that the solder and the base metal diffuse each other to form a firm joint. If the holding time is too short, the solder is not completely melted. If the holding time is too long, the grains of the base metal will grow and the strength will decrease. Generally, the vacuum brazing time is ~ 5 minutes. If the parts are equipped with tooling, if the parts need to be fully heated, the holding time needs to be extended. For the aluminum alloy plate-fin electronic chassis, since the plate fin exists on the edge of the case, and the thickness of the plate varies greatly (0.2-8.0 mm), the secondary processing after welding is difficult, and the deformation of the plate fin has a significant impact on the heat exchange rate, so Chassis deformation should be minimized. After vacuum brazing stops heating, the parts can be cooled to 450±10 C with the furnace temperature, and then filled with argon gas at 0.02~0.05 MPa, quickly cooled to below 100 C and released from the furnace.

Vacuum brazing furnace selection: The vacuum furnace control system produced by SIMUWU company adopts PLC control; the temperature is controlled by intelligent temperature controller, with accurate control and high degree of automation. User selectable automatic or manual bumpless switching operation. Safe, reliable and easy to use.